------- AIR POLLUTION ASPECTS OF HYDROCHLORIC ACID Prepared for the National Air Pollution Control Administration Consumer Protection & Environmental Health Service Department of Health, Education, and Welfare (Contract No. PH-22-68-25) Compiled by Quade R. Stahl, Ph.D, Litton Systems, Inc. Environmental Systems Division 7300 Pearl Street Bethesda, Maryland 20014 September 1969 ------- FOREWORD As the concern for air quality grows, so does the con- cern over the less ubiquitous but potentially harmful contami- nants that are in our atmosphere. Thirty such pollutants have been identified, and available information has been summarized in a series of reports describing their sources, distribution, effects, and control technology for their abatement. A total of 27 reports have been prepared covering the 30 pollutants. These reports were developed under contract for the National Air Pollution Control Administration (NAPCA) by Litton Systems, Inc. The complete listing is as follows: Aeroallergens (pollens) Ethylene Aldehydes (includes acrolein Hydrochloric Acid and formaldehyde) Hydrogen Sulfide Ammonia Iron and Its Compounds Arsenic and Its Compounds Manganese and Its Compounds Asbestos Mercury and Its Compounds Barium and Its Compounds Nickel and Its Compounds Beryllium and Its Compounds Odorous Compounds Biological Aerosols Organic Carcinogens (microorganisms) Pesticides Boron and Its Compounds Phosphorus and Its Compounds Cadmium and Its Compounds Radioactive Substances Chlorine Gas Selenium and Its Compounds Chromium and Its Compounds Vanadium and Its Compounds (includes chromic acid) Zinc and Its Compounds These reports represent current state-of-the-art literature reviews supplemented by discussions with selected knowledgeable individuals both within and outside the Federal Government. They do not however presume to be a synthesis of available information but rather a summary without an attempt to interpret or reconcile conflicting data. The reports are ------- necessarily limited in their discussion of health effects for some pollutants to descriptions of occupational health expo- sures and animal laboratory studies since only a few epidemic- logic studies were available. Initially these reports were generally intended as internal documents within NAPCA to provide a basis for sound decision-making on program guidance for future research activities and to allow ranking of future activities relating to the development of criteria and control technology docu- ments. However, it is apparent that these reports may also be of significant value to many others in air pollution control, such as State or local air pollution control officials, as a library of information on which to base informed decisions on pollutants to be controlled in their geographic areas. Addi- tionally, these reports may stimulate scientific investigators to pursue research in needed areas. They also provide for the interested citizen readily available information about a given pollutant. Therefore, they are being given wide distribution with the assumption that they will be used with full knowledge of their value and limitations. This series of reports was compiled and prepared by the Litton personnel listed below: Ralph J. Sullivan Quade R. Stahl, Ph.D. Norman L. Durocher Yanis C. Athanassiadis Sydney Miner Harold Finkelstein, Ph.D. Douglas A. Olsen, Ph0D. James L. Haynes ------- The NAPCA project officer for the contract was Ronald C. Campbell, assisted by Dr. Emanuel Landau and Gerald Chapman. Appreciation is expressed to the many individuals both outside and within NAPCA who provided information and reviewed draft copies of these reports. Appreciation is also expressed to the NAPCA Office of Technical Information and Publications for their support in providing a significant portion of the technical literature. ------- ABSTRACT Hydrochloric acid irritates the membranes of the eye and upper respiratory tract, and prolonged exposure to low concentrations can cause erosion of the teeth. Severe expo- sures can result in pulmonary edema and laryngeal spasm, both of which can be fatal. There are no known chronic or acute systemic effects of hydrochloric acid. Hydrochloric acid is also a phytotoxicant, and its emissions have been responsible for plant damage in several instances. Recent data indicate that it is a stronger phytotoxicant than reported in the earlier literature. The acid is strongly corrosive to most metals. Hydro- gen chloride gas emissions are read.ily converted to hydrochlo- ric acid by the moisture in the air. Hydrogen chloride is a by-product of many organic chlorinating reactions; in some instances the hydrogen chloride is collected for use, but in small operations it may not be economically feasible to recover the gas. Hydrogen chloride emissions result from the burning of coal, chlorinated plastics, and paper. No information has been found on the concentration of hydrochloric acid in the atmosphere. The major uses of hydrogen chloride or hydrochlo- ric acid are in manufacturing chemicals, producing metals, and acidizing oil wells. Effective control of emissions can be ------- accomplished by the use of water scrubbing equipment. No information has been found on costs for obtaining and maintaining the control equipment and economic losses due to hydrochloric acid emissions. Methods of analysis for hydro- chloric acid are based on determining the acidity or the chlo- ride content of samples, and therefore, other strong acids or chloride salts may cause interference. ------- CONTENTS FOREWORD ABSTRACT 1. INTRODUCTION 1 2. EFFECTS 3 2.1 Effects on Humans 3 2.1.1 Toxic ity 3 2.1.2 Sensory Thresholds 5 2.1.3 Synergistic Effects 5 2.2 Effects on Animals 5 2.2.1 Commercial and Domestic Animals .... 6 2.2.2 Animal Experiments 6 2.3 Effects on Plants 7 2.3.1 Phytotoxicity 7 2.3.2 Incidents of Plant Damage 10 2.4 Effects on Materials 11 2.5 Environmental Air Standards 12 3. SOURCES 14 3.1 Natural Occurrence 15 3.2 Production Sources 15 3.2.1 By-Product Process 16 3.2.2 Salt-Acid Process 18 3.2.3 Chlorine-Hydrogen Synthesis 20 3.3 Product Sources 21 3.3.1 Manufacture of Chemicals 21 3.3.2 Metal Production 22 3.3.3 Other Uses 23 3.4 Other Sources . 23 3.4.1 Coal 24 3.4.2 Fuel Oil 26 3.4.3 Automobile Exhaust 26 3.4.4 Burning of Chloride-Containing Plastics 27 3.4.5 Burning of Paper Products 28 3.4.6 DDT Production 29 3.4.7 Lemon Pulp Extraction 29 3.5 Environmental Air Concentrations 30 4. ABATEMENT 31 5. ECONOMICS 34 ------- CONTENTS (Continued) 6. METHODS OF ANALYSIS 35 6.1 Sampling Methods 35 6.2 Qualitative Methods 35 6.3 Quantitative Methods 36 7. SUMMARY AND CONCLUSIONS 39 REFERENCES 43 APPENDIX 52 ------- LIST OF TABLES 1. "Ethyl" Antiknock Compound-Tel Motor 33 Mix .... 27 2. Properties of Hydrogen Chloride and Hydrochloric Acid 52 3. Summary of Reported Effects of Inhalation of Hydrogen Chloride by Humans 54 4. Summary of Reported Effects of Inhalation of Hydrogen Chloride in Animals 56 5. Summary of Reported Toxic Effects of Hydrogen Chloride Exposure on Plants 60 6. Emissions of Hydrochloric Acid in Selected Areas of Niagara County, New York 64 7. Hydrochloric Acid Production in the United States/ 1958-1967 65 8. Production of Hydrochloric Acid by Process and State 66 9. Major Producers of Hydrochloric Acid (Muriatic Acid) in the United States 67 10. Consumption of Hydrochloric Acid by Uses, 1963 ... 69 11. Consumption of Hydrochloric Acid by Selected Industries, 1963 and 1958 70 12. Chlorine Content of Selected United States Coals . . 71 ------- 1. INTRODUCTION Hydrogen chloride (HC1) is a hygroscopic, colorless gas with a strong, pungent, and irritating odor. Because of its high solubility in water, the gas fumes in moist air. An aque- ous solution of hydrogen chloride is called hydrochloric acid. Emissions of hydrogen chloride are readily converted to hydro- chloric acid fumes and droplets in air or when inhaled into the lungs. The strong dehydrating properties of hydrogen chlo- ride can result in serious burns of the skin or mucous mem- branes. Hydrochloric acid is extremely corrosive to most materials. (See Table 2 in the Appendix for the properties of hydrogen chloride and hydrochloric acid.) Inhalation of hydrochloric acid causes coughing and choking, as well as inflammation and ulceration of the upper respiratory tract. Irritation of the eye membranes is another effect, and exposure to high concentrations can cause clouding of the cornea. The teeth can also be affected, and erosion may result. Hydrogen chloride and hydrochloric acid are also phytotoxicants that damage the leaves of a great variety of plants. Several episodes of plant damage from hydrochloric acid emissions have been reported. The possible sources of emissions of hydrogen chloride or hydrochloric acid are not only their commercial production ------- and use, but also the burning of paper products and fossil fuels. Many industries also produce hydrochloric acid as an unwanted by-product in the manufacture of chemicals. The emissions can be effectively controlled with the available methods, which usually involve the use of water scrubbing equipment. ------- 2. EFFECTS 2.1 Effects on Humans Little information is available on the toxicity of hydrogen chloride or hydrochloric acid when inhaled by humans. Most of the information cited in the literature was obtained from studies conducted 30 to 80 years ago pertaining to occu- pational exposure. 2.1.1 Toxicity Hydrochloric acid primarily irritates and attacks the membranes of the eyes and upper respiratory tract. 34,73 i>ne effects increase in severity from irritation to pulmonary edema, and even to death in extreme cases, depending upon the concentration and duration of exposure. No organic damage results from exposure to 7,000 |-ig/m3 (5 ppm*).113 Irritation of mucous membranes occurs at 15,000 ug/m3 (10 ppm),113 although workers accustomed to hydrochloric acid exposure can work undis- turbed, at this concentration.45'72 Work becomes difficult, but not impossible, in the concentration range of 15,000 to 75,000 ug/m3 (10 to 50 ppm), ' and irritation of the throat mem- branes has been reported at exposures of 50,000 (j.g/m3 (35 ppm).87 Work becomes impossible at levels above 75,000 (jg/m3 ,72 and exposure to levels of 75,000 to 150,000 [ig/m3 (50 to 100 ppm) cannot be tolerated, by humans for longer than 60 minutes. 44,45,52 *Conversion factor used in this report: 1 ppm is approxi- mately equal to 1,470 ug/m3. ------- Exposure for only a few minutes at 1,300 to 2,000 ppm may be lethal;52/87 the acid neutralizes the alkali of the tissues and causes inflammation of the upper respiratory tract, pul- monary edema, or laryngeal spasm, with death possibly resulting. Mists of hyd.rochloric acid, are not as dangerous to humans as hydrogen chloride gas because the acid has no strong dehy- d.rating effect on the tissues.^7 However, acid mists from heated metal-pickling solutions may cause bleeding of the nose and gums, ulceration of the nasal and oral mucosae, and tender- ness of the facial skin so that shaving becomes painful.45 A study conducted by Toyama et al..112 of an electrical appliance factory indicated that people not accustomed to hydrochloric acid mists showed a 9 percent decrease in the pulmonary venti- latory peak flow rate when exposed for 1 hour to hydrochloric acid mists (6 |_i in d.iameter), whereas the workers exhibited no change. Prolonged, exposure to low concentrations of hydrochloric acid causes erosion of the teeth. -> However, there are no known systemic effects, either acute or chronic, from inhalation of hyd.rochloric acid or hydrogen chloride.- ' °' The effects of hydrogen chloride on humans are summarized in Table 3 in the Appendix. ------- 2.1.2 Sensory Thresholds The odor perception threshold values for hydrochloric acid given in the literature include 100 to 200 |-ig/m3 (0.067 to 0.134 ppm), 28'29 1,500 to 7,500 iag/m3 (1 to 5 ppm),45 and 14,700 Hg/m3 (10 ppm).105 Elfimova28'29 has studied the threshold reflex of the eyes, respiratory action, and vascular reaction upon exposure to hydrochloric acid aerosols. The results are summarized in Table 3 in the Appendix. 2.1.3 Synergistic Effects Stayzhkin85'102 investigated the effect of chlorine and hydrogen chloride gas mixtures on man. In his study of the odor threshold, the effect on reflex reactions of eye sensitivity to light and of optical chronaxy were examined. His results indicated that the two gases acted in combination in an additive manner to produce a perceivable odor when neither gas could be detected alone. The effect is expressed by the following relationship where X must equal one or greater to have a perceivable odor: x _ Concentration Clp + Concentration HC1 Odor threshold C12 Odor threshold HC1 Furthermore, the physiological and neurological effects of the mixtures were also in the nature of arithmetical summation. 2.2 Effects on Animals ------- 2.2.1 Commercial and Domestic Animals No reports were found in the literature describing injury to domestic, commercial, or wild animals from exposures to hydrogen chloride or hydrochloric acid in rural or urban environments or near factories that produce or use the acid. 2.2.2 Animal Experiments Mackle et_ _a_l_.69 exposed one monkey, three rabbits, and three guinea pigs to 50,000 ug/m3 (33 ppm) of hydrogen chloride for a period of 4 weeks (6 hours per day, 5 days per week). None of these animals exhibited immediate toxic effects or pathological changes. However, the authors commented that inhalation of hydrogen chloride daily for one month at 50,000 l_ig/m3 (33 ppm) may be dangerous. Rabbits and guinea pigs were not killed at a concentration of 100,000 ug/m3 (67 ppm) for 5 days (6 hours per day). However, it was noted that the guinea pigs were more sensitive to irritant properties of hydrogen chloride than the rabbits, but the rabbits exhibited more pul- monary and nasal damage than the guinea pigs. At higher con- centrations, repeated exposures resulted in a weight loss that was proportional to the degree of exposure. A concentration of 1,000,000 ug/1™3 (670 ppm) of hydrogen chloride for 2 to 6 hours was lethal to rabbits and guinea pigs. Furthermore, 30 minutes' exposure at approximately 6,400,000 ug/m3 (4,300 ppm) was lethal to all the animals. At these concentrations, hydrogen chloride causes necrosis of the tracheal and bronchial epithelia and also pulmonary edema, atelectasis, emphysema, and pulmonary blood ------- vessel damage. ' Production of lesions in the liver and other organs by hydrogen chloride is also described. " After Lehmann°4 exposed cats, rabbits, and guinea pigs to 150,000 to 210,000 ug/m3 (100 to 140 ppm) of hydrogen chlo- ride for 6 hours, he found slight corrosion of the cornea and upper respiratory irritation in the animals. Clouding of the cornea occurred after exposure to a concentration of 2,000,000 |_ig/m3 (1,350 ppm) for approximately 90 minutes. After approxi- mately the same exposure time to a concentration of 5,000,000 M.g/m3 (3,400 ppm), death occurred in 2 to 6 days. Leitz -* found that when the respiratory rate is increased by an elevation in environmental temperature, the amount of hydrogen chloride absorption is also increased, thereby height- ening the danger of exposure to low concentrations. Table 4 in the Appendix summarizes the reported effects of hydrogen chloride inhalation by animals. 2.3 Effects on Plants 2.3.1 Phytotoxicity Haselhoff and Lindau studied the effects of hydrogen chloride and hydrochloric acid on plants after an incident in which plant life was damaged near a factory manufacturing alkali (see Section 2.3.2). Their studies demonstrated that damage to plants from hydrogen chloride resulted from the direct action of the gas itself on the above-ground parts of the plants and not from the conversion products produced in the soil. Fumi' gation experiments with viburnum and larch seedlings indicated ------- 8 that approximately 7,500 to 30,000 ug/m3 (5 to 20 ppm) of hydrogen chloride could kill the plants within 2 days. More- over, after 1 day at this concentration, the viburnum leaves remained rolled up at the edges, withered, shrunk, faded, and necrotic, even after they were placed in fresh air. Similar injuries resulted from chlorine gas, but a higher concentration of 750,000 i-ig/m3 (500 ppm) was necessary to produce damage. Hydrochloric acid fumes (approximately 6 percent acid) required only a few hours to damage the plants, primarily producing bleached spots on the tips or margins of the leaves. At low concentrations of hydrochloric acid (approximately 1 to 10 percent acid), the plants remained healthy for several days. Further experiments showed that a 1-hour exposure to 1,500,000 |-ig/m3 (1,000 ppm) hydrogen chloride produced local lesions in fir, beech, and oak leaves. Marginal leaf scorch was found on the leaves of maple, birch, and pear trees exposed to hydrogen chloride. Tipburn of the fir needles resulting from two exposures to 1,500,000 ag/m3 (1,000 ppm) was still visible 3 weeks later. The experiments also indicated that spruce was not visibly affected at daily 1-hour exposures to 3,000,000 ug/m3 (2,000 ppm) hydrogen chloride for 80 days. However, recent studies by Lacasse^l showed that spruce seedlings died from exposure to less than 50 ppm of hydrogen chloride for only 20 minutes. Hydrogen chloride injury in broad-leaf plants is indi- cated by a marginal leaf burn that progresses basipetally with ------- 9 prolonged exposure .^2 In grasses, the tips become brown- colored after exposure to low concentrations. The threshold concentration for plant marking was suggested to be generally 75,000 to 1,500,000 ng/m3 (50 to 100 ppm) hydrogen chloride, but these values were obtained with no air circulation over the plants. Thomas107 found that the marking threshold for sugar beets was a few hours' exposure at 15,000 i-ig/m3 (10 ppm). Lacasse _et_ aJ^.62,74,93 have recently studied the effects of low concentrations of hydrogen chloride on plants. Tomato plants were exposed to 7,500 ng/m3 (5 ppm) hydrogen chloride for 2 hours at 31°C, with a relative humidity between 65 and 75 percent, and a light intensity of 3.9 X 104 ergs/cm2-sec. The leaves developed interveinal bronzing and bleaching, fol- lowed by necrosis, within 72 hours after exposure. The middle- aged leaves were affected more severely than the younger leaves. Furthermore, the hydrogen chloride-exposed plants contained 300 percent more chloride than the unexposed control plants. The immature leaves showed the greatest increase in chloride, while the roots and stems showed little or no significant increase. The increase in chloride was not found beyond 24 hours. In fact, there was a slight decrease in chloride content after the first 24 to 72 hours. Experiments were also conducted to determine the thresh- old for visible damage of 12 species of coniferous and broad- leaf seedlings. "74 ip-^g experimental conditions were as follows: exposure to 4,500 to 64,500 |-ig/m3 (3 to 43 ppm) hydrogen chloride ------- 10 for 4 hours at 27°C, relative humidity between 78 to 85 percent, and light intensity of 1.4 X 104 ergs/cm2-sec. A summary of the threshold values determined by these experiments is given in Table 5 in the Appendix. The results indicate that the coniferous plants were more resistant to incipient injury than the broadleaf plants. Symptoms found in the broadleaf plants included marginal and interveinal necrosis and necrotic flecking. The only symptom observed for the coniferous species was tip necrosis. The period of time for the first appearance of injury varied between 8 and 24 hours. Lacasse^2 found that the relative humidity of the sur- rounding area is a very important factor in the damage to plants exposed to hydrogen chloride. Thus, when the relative humidity was increased from 40 to 65 percent, the rate and severity of damage was observed to suddenly increase. Thomas reported in 1951 that hydrogen chloride is less toxic to plants than sulfur dioxide. Plant responses at high concentrations of hydrogen chloride may resemble acute sulfur dioxide injury. A summary of the reported effects of hydrogen chloride on plants is given in Table 5 in the Appendix. 2.3.2 Incidents of Plant Damage Hindawi ° reported recently that emissions from a glass manufacturing factory injured shrubs, trees, and plants in the surrounding area. Specimens severely injured included maple and cherry trees, rose bushes together with the buds, and begonias, ------- 11 Factory stack emissions analyzed after the incident contained 178,500 to 709,500 |ag/m3 (119 to 473 ppm) hydrochloric acid and 1,560 to 2,760 |Jg/m3 (0.52 to 0.92 ppm) chlorine. Analy- sis of injured silver maples showed a chloride content of 4,700 ppm, compared to 3,800 ppm for uninjured silver maple trees. Although no other incidents in the United States have been reported, several other countries have reported damage to plants from exposures to hydrochloric acid. The best-known case happened in England. °7 Extensive damage to plants occurred near a factory that used the Leblanc soda process to make alkali and emitted hydrogen chloride as an unwanted by-product. Between 1836 and 1863, scrubbers were installed at various alkali factories which removed 95 percent of the hydrogen chloride in the emis- sions so that less than 450 ng/m3 (30 ppm) of hydrogen chloride remained in the stack effluent. This control eliminated the plant damage. Bohne13 reported two examples of damage to plants by emis- sions of hydrogen chloride from incinerators of nearby hospitals. These incinerators were burning 80 to 90 percent paper and card- board packing material. In one case, incineration for only 2 to 3 hours per day, 5 days a week, completely ruined the plants in a nursery located 450 meters from the incinerator. 2.4 Effects on Materials In the literature reviewed, no information was found de- scribing corrosion or damage to materials from exposure to ------- 12 environmental concentrations of hydrochloric acid. However, it is well-known that hydrochloric acid mists and solutions are extremely corrosive to most metals and alloys.49,75 Mellor^S has summarized 24 studies on corrosion of various forms of hard and mild steel and cast iron by hydrochloric acid. He noted that corrosion of cast iron and steel increases regularly as the concentration of the acid increases. 2.5 Environmental Air Standards The American Conference of Governmental Industrial Hygien- ists (ACGIH) has adopted 7,000 ug/m3 (5 ppm) as the threshold concentration for hydrogen chloride for an 8-hour day, 5-day week .HI West Germany has also established 5 ppm as the permis- sible work-station concentration. 5 West Germany has also established an ambient air quality standard of 0.5 ppm (approxi- mately 700 Ug/m3 ) of hydrogen chloride for a 30-minute mean average, with a maximum of 1.0 ppm (1,400 ug/m3) of hydrogen chloride for a 30-minute mean average. 5 Russia has established 15 ug/m3 (0.009 ppm) as a 24- hour maximum average for ambient air concentration of hydrogen chloride and a maximum of 50 Ug/m3 of hydrogen chloride (0.03 ppm) for a single exposure.^5,73. The standard for a 24-hour average is below the concentrations which might cause reflexive reaction of the sensory organs. Czechoslovakia has established a maximum ambient air con- centration which is different from that of Russia. The 24-hour ------- 13 mean was set at 0.02 ppm, with a one-time exposure maximum of 0.07 ppm.84 ------- 14 3. SOURCES Hydrochloric acid may be emitted from a wide variety of sources. Emissions from some sources may go unnoticed because the hydrochloric acid is generated as an unpredicted product. The sources may be classified as follows: (1) Direct manufacturing of hydrochloric acid (e.g., acid-salt and synthesis processes), (2) A predicted by-product of a chlorination process in indirect manufacturing (e.g., by-product process), (3) Unpredicted or undesired product of a manufacturing process (e.g., thermal decomposition of chloride-containing reactants or products), (4) Use of hydrochloric acid in the production or manu- facturing of other products (e.g., pickling of metals), (5) Burning or combustion of chloride-containing materials (e.g., fossil fuels, plastics, paper), (6) Heating of chloride-containing materials (e.g., heating of organic matter). The first two are described in Section 3.2 as production sources. The fourth source is discussed in Section 3.3 as a product source. Those remaining are discussed in Section 3.4 as other sources. In a study' of air contaminant emissions in Niagara County, N.Y., it was found that 4,083 tons of hydrogen chloride were emitted into the atmosphere per year. Of this total, 2,911 tons originated from processing plants and 1,172 tons from the ------- 15 consumption of coal and oil for heating purposes. Table 6 in the Appendix lists the total emissions by urban areas within the county- 3.1 Natural Occurrence Natural occurrences of hydrochloric acid are rare. Almost all of this acid, particularly as an atmospheric pollu- tant, is produced by man, either from manufacturing processes or burning or heating of chloride-containing substances. Minute quantities of hydrochloric acid are present in nature in volcanic fumes and in some rivers. 58 Qf course, it is also present in the gastric juices of the body. 3.2 Production Sources In the United States, hydrochloric acid is produced by three processes:7'50'106 (1) the by-product process from chlorination of organic compounds, (2) reaction of chloride salt with sulfuric acid, and (3) synthesis via reaction between chlorine and hydrogen gas. In 1934, 86 percent of the production of hydrochloric acid was by the salt-acid process, 14 percent by the synthesis process, and none from the by-product process.91 However, in recent years, the by-product process has become the major production source, accounting for over 84 percent of the hydrochloric acid production in 1967.23 This process has also shown a continuing growth pattern (see Table 7 in the Appendix). In contrast, the other two processes have shown very little increase over the past few years. A more detailed description of these processes can be found in other references.7'58'88'106 ------- 16 According to 1962 data,88 60 plants use the by-product process, 22 plants use the synthesis process, and 15 plants use the salt-acid process. However, there are a total of only 88 plants producing hydrochloric acid, since some plants use more than one process. Production by State and process is given in Table 8 in the Appendix. The major producers of hydrochloric acid are listed in Table 9 in the Appendix. 3.2.1 By-Product Process The major commercial source of hydrochloric acid is the chlorination of organic compounds by chlorine gas. Thus, in any manufacturing process in which chlorine gas is used to replace hydrogen with chlorine in a compound, hydrogen chloride is produced as a by-product. Examples of such processes are the preparation of carbon tetrachloride using methane (Equation 1) and of chlorobenzene using benzene (Equation 2). The chlorination process may be used to prepare a desired end product, such as carbon tetrachloride or chlorobenzene, or may be used to pre- pare an intermediate for a non-chloro-containing end product, as in the preparation of phenol from benzene using chlorobenzene (Equations 2 and 3). CH4 + 4C12 > CC14 + 4HC1 , . , (Methane) (Carbon tetrachloride) t^uation j.; CsHs + Cla > CSH5C1 + HC1 (Rmiatinn 7) (Benzene) (Chlorobenzene) liquation 2) CSH5C1 + NaOH > C6H5OH + NaCl (Fnn^inn ^ > (Chlorobenzene) (Phenol) (Equation 3) Therefore, it is not possible to determine from the end products ------- 17 of a company whether by-product hydrochloric acid is being produced if one is not familiar with each of the processes used to obtain the final product. Numerous chlorinated and nonchlorinated organic compounds are made in which hydrogen chloride is evolved as a by-product. In fact, approximately 70 percent of the chlorine produced today is used in the manu- facture or preparation of organic compounds. The ever- increasing use of chlorinated organic compounds is reflected in the production of hydrochloric acid using by-product recovery (see Table 7 in the Appendix). The effluent gas from the chlorination of an organic compound contains not only hydrogen chloride but also various amounts of air, chlorine gas, and organic products, depending on such factors as initial organic reactant and conditions used. Therefore, the recovery system for the hydrogen chlo- ride or hydrochloric acid varies with the nature of the other impurities present in the effluent gas. For example, if the organic contaminants are low-boiling, the hydrogen chloride is removed first by means of a water absorption system (see Section 4). On the other hand, if the organic impurities are high-boiling, they are removed by condensation before the hydro- gen chloride is absorbed. To obtain anhydrous hydrogen chloride, the effluent gas is fed into a condenser or distillation appa- ratus for separation of the different products. Several recovery systems are reported in the literature.16'47'63'77'98 Normally, the hydrochloric acid produced by this method contains organic impurities and may require further purification. ------- 18 Although hydrochloric acid produced as a by-product is collected for use and sale by some companies, in other cases the acid emissions may only be treated to avoid air pollution; and in still others, nothing may be done about the emissions. 3.2.2 Salt-Acid Process In this process, common salt (sodium chloride, NaCl) is reacted with sulfuric acid (60° or 66° Baume). The reac- tion takes place in two steps: first, hydrogen chloride and sodium acid sulfate are formed, and second, sodium acid sul- fate is further reacted with sodium chloride to yield more hydrogen chloride and sodium sulfate (normal sulfate). (See Equations 4 and 5.) In cases in which sodium acid sulfate is available—-e.g., as a by-product in the manufacture of nitric acid—the acid sulfate is used directly as shown in Equation 5. NaCl + HSS04 »NaHSO4 + HC1 (Equation 4) NaHSO4 + NaCl »Na2SO4 + HC1 (Equation 5) Generally, the salt and a slight excess of acid are heated to 1,400 to 1,600°F in a Mannheim oven. The reactants are continuously fed into the center of the furnace, and the salt cake that forms is removed at the periphery, where it is discharged continuously through a chute for transfer to storage, The effluent gas contains 30 to 70 percent (by volume) hydrogen chloride, as well as salt dust, air, and small traces of chlo- rine. This gas is passed through dust removal equipment, such as settling chambers or cyclones, and then cooled to approxi- mately 100°F by means of tube coolers or packed towers.50,58 ------- 19 A further purification system, usually coke filtering, is used to remove sulfuric acid mist and the remaining fine dust particles. After this final step, the hydrogen chloride is collected by absorption methods described in Section 4. One of the major producers of hydrochloric acid in the United States uses the Hargreaves process.58,92 jn this process the salt, sodium chloride, is reacted directly with sulfur dioxide in the presence of steam and air (Equation 6). The sulfur dioxide, obtained by burning sulfur, is passed into a series of vertical chambers which have perforated trays for the salt. The system is designed so that the sulfur diox- ide stream is first passed through a chamber containing nearly spent salt and lastly through a chamber containing the raw salt. The system temperatures vary from 1,000°C initially to 800°C in the final chambers of raw salt. The end gas then is passed through the absorption system to obtain the hydrochloric acid. 4NaCl + 2S02 + O3 + 2H20 >2Na3SO4 + 4HC1 (Equation 6) Hydrogen chloride emissions from the salt-acid process are higher than those from either of the other two processes. In the Mannheim furnace operations, losses of hydrogen chlo- ride can occur through leaks at the furnace, removal of hot salt cake, or from the tail gas emissions. 1' ^2 jn ^he more modern furnaces, emissions are controlled by use of an exhaust fan installed after the absorber system to maintain the pres- sure slightly below atmospheric level at the furnace; the hot ------- 20 salt cake is also precooled in a water-cooled screen conveyor before dumping. However, if large leaks occur in the system, the system becomes blocked, or the exhaust fan fails, the furnace can lose its draft, and emissions into the atmosphere can occur around the furnace, particularly at the doors and at the salt cake discharge. -*0 Short periods of emissions can occur if the furnace door is opened to break up large lumps of salt that interfere with proper operation of the furnace. Emissions resulting from upsets in the hydrogen chlo- ride absorption system, which is common to all three processes, are discussed in Section 4. 3.2.3 Chlorine-Hydrogen Synthesis The advantage of the chlorine-hydrogen synthesis process is that a hydrochloric acid is produced that is very pure, depending on the purity of the reactants. In this process, chlorine is burned in a slight excess of hydrogen in a reac- tor or combustion chamber.50,106 T^Q resulting product is 98 to 99,7 percent pure.106 Since a mixture of hydrogen and chlo- rine is explosive, several safety provisions are incorporated into the system, which is completely enclosed. Thus, there is very little emission of hydrogen chloride in this process. The product gas is passed through a gas-cooling system and then an absorption system similar to that used for the salt-acid process to give hydrochloric acid. If hydrogen chloride is desired, only gas-cooling equipment is necessary- ------- 21 3.3 Product Sources Hydrochloric acid and hydrogen chloride have a wide variety of uses;58'^6 major uses are in the manufacture of organic and inorganic chemicals, production of metals, the cleaning of metal and other materials, food processing, and acidification of oil wells. The consumption of hydrochloric acid for these uses in 1963 is given in Table 10 in the Appen- dix. The consumption by certain industries for 1958 and 1963 is given in Table 11 in the Appendix. As shown by the latter table, the demand for hydrochloric acid is increasing (see also Table 7, Appendix). The use of hydrochloric acid in steel pick- ling, vinyl plastics, oil well acidizing, and industrial cleaning and chemical products is also increasing. However, even with the growing demand, there has been an oversupply of hydrochloric acid in recent years.58'88 This fact, plus the increase in stream pollution by the acid, has made dis- posal of hydrochloric acid an expanding problem. One possible solution for the oversupply problem is the use of hydrochloric acid to manufacture chlorine.58 According to reports by trade sources, the oversupply has shown a gradual decline.20 3.3.1 Manufacture of Chemicals Nearly half of the hydrochloric acid produced is used in the manufacture of organic chemicals, such as chlorinated organic compounds, including the manufacture of alkyl chlorides from olefins and chlorides from alcohols. It is also used in the presence of oxygen (oxyhydrochlorination) to prepare ------- 22 polychlorinated alkyl compounds and chlorinated aromatic compounds. Other uses occur in the production of dyes and dye intermediates and in the preparation of pharmaceutical chemicals, such as various amine hydrochloride salts, aconi- tic acid, adipic acid, and citric acid. In the production of chlorinated polymers, hydrochloric acid is used in the preparation of intermediate monomers, such as chloroprene and vinyl chloride. In addition, it is used as a solvent and a catalyst in organic reactions involving isomerization, polymerization, and alkylation. Only about 5 percent of the hydrochloric acid pro- duced is used for preparing inorganic chemicals, such as metal chlorides, alumina, phosphoric acid, titanium dioxide, silica gel, and paint pigments.58'76'88'96 Recently, hydrochloric acid has been used to manufacture chlorine by electrolysis or oxidation methods. 3.3.2 Metal Production Metal production consumes approximately 17 percent of the hydrochloric acid produced. It is used in many metallur- gical extraction processes for treating various high-grade ores, including those which yield germanium, manganese, radium, tantalum, tin, and vanadium. Hydrochloric acid is also being considered as a substitute for sulfuric acid in treating low- grade ores. The Dron process for obtaining magnesium from seawater uses hydrochloric acid. This acid is also used as an etching medium for chemical milling of metals such as alu- minum, magnesium, steel, and titanium. ------- 23 3.3.3 Other Uses Another major use, accounting for approximately 18 per- cent of the production of hydrochloric acid, is in the Dowell process for activating petroleum wells. Inhibited hydrochlo- ric acid is used to improve oil well porosity and well flow or production by acidizing the formation. Approximately 7 percent of the hydrochloric acid pro- duced is used primarily for pickling and cleaning metal prod- ucts and removing oxides and scale from boilers and heat- exchange equipment. A small amount of hydrochloric acid is used in food processing, including hydrolysis of proteins and starch in the preparation of dextrose and starch syrups, manufacture of monosodium glutamate, and reactivation of bone char and charcoal in sugar refining. It is also used in chlorinating and reclaiming rubber, coagulating latex, fluxing babbitt metals, detanning hides following depilation, and etching airport runways in prepara- tion for resurfacing with bonded concrete. It is also an ingredient in tanning and dye liquors. 3.4 Other Sources Atmospheric emissions of hydrochloric acid result from a large number of sources other than the manufacture and use of this acid. These other sources include heating or burning of chloride-containing materials in the presence of organic compounds or other hydrogen-containing substances. Chlorides ------- 24 are also widespread in nature and in many natural products. Moreover, many manufactured products contain chloride, such as polyvinyl chloride plastics. When these materials are burned, incinerated, or perhaps just heated, hydrochloric acid can be evolved as a predicted or unpredicted product. The examples discussed in this section give an indication of some of the possible emission sources. 3.4.1 Coal Burning coal may be one of the major contributors to hydrochloric acid air pollution. Chlorine is present in coals, mostly in the form of inorganic chloride salts27 that are solu- ble in water.22 when coal burns, most of the chloride salts are converted to hydrogen chloride,^'*^° which is then emitted into the atmosphere. Analysis of United States coals shows that the chlorine content ranges from 0.01 to 0.56 percent.I/51'78»89 Table 12 in the Appendix indicates the chlorine content of some selected coals in the United States. The Central and Appala- chian areas, which have high-chlorine-content coals, are also the areas which consume most of the coal for heat and energy.51 Piper and Van Vliet8^ found that in burning coal con- taining 0.066 percent chlorine, 49 ppm of hydrogen chloride were emitted at the stack, meaning that 60 percent of the chlorine originally in the coal was converted to hydrogen chloride. lapalucci, Demski, and Bienstock^l performed experiments with pulverized coal containing 0.1 to 0.4 percent ------- 25 chlorine at carbon combustion efficiencies of 94 to 98 per- cent. Under these conditions, they found that 93 to 98 percent of the chlorine was emitted as hydrogen chloride and the remainder left in the ash. To verify these results under actual conditions, the stack of a local power plant was sampled after burning a bituminous coal containing 0.087 percent chlorine,, Analysis showed that only 1.5 percent of the chlorine was retained in the ash, and the balance was emitted in the stack gas as hydrogen chloride. Furthermore, the amount of hydrochloric acid pollution by burning coal may be increased when calcium chloride is added to the coal as an antifreeze or dust-proofing agent.53 A potentially large amount of hydrochloric acid pollu- tion may result from coal burning. For example, it is esti- mated that 671 million short tons of bituminous coal will be consumed in 1975.H Assuming that the average chlorine con- tent of the coal is 0.2 percent and that 95 percent of this is converted to hydrochloric acid, then approximately 1.3 million short tons of hydrochloric acid will be produced from coal burning in 1975. For comparison, manufacture of hydrogen chloride and hydrochloric acid was 1.6 million short tons in 1967. 3 lapalucci, Demski, and Bienstock^l estimated on a similar basis (i.e., 0.2 percent chlorine coal) that an 800-MW power plant will emit from the stack 11,300 standard cubic feet of hydrogen chloride each hour, or 4,560 tons each year. ------- 26 3.4.2 Fuel Oil Fuel oils contain small amounts of chlorides and can therefore emit hydrogen chloride when burned. A recent study on fuel oils cited two 1938 reports on chloride emissions. In one report-^-® the chloride content of the ash was given as 0.1 and 4.6 percent by weight for oils found in Kansas and Texas, respectively. The other report-^-^ indicated that the maximum hydrogen chloride content in emissions was approxi- mately 46 ppm in the stack gas, or approximately 1 pound per 1,000 pounds of oil. It has been reported that 500 pounds of hydrogen chloride per day per 100,000 persons is produced by using oil for domestic heating.30 in comparison, the value is four times higher for domestic heating using coal. 3.4.3 Automobile Exhaust Gasolines which contain tetraethyl lead (TEL), tetra- methyl lead (TML), or other lead additives also usually con- tain ethylene chloride or ethylene bromide. These organic halide compounds are used as lead scavengers; that is, these halides will react with the lead to form volatile lead halides which can be emitted with the exhaust gases and, therefore, prevent lead deposits in the automobile engine. An example of an additive mixture for gasoline is given in Table 1. ------- 27 TABLE 1 "ETHYL" ANTIKNOCK COMPOUND-TEL MOTOR 33 MIX101 Weight Compound (percent) Tetraethyl lead 57.5 Methyl cyclopentadieny- manganese tricarbonyl 7.0 Ethylene dibromide 16.7 Ethylene dichloride 17.6 Other (dye, inerts) 1.2 During gasoline combustion, hydrogen chloride or hydro- chloric acid can form and be emitted into the air. Rose ^ feels that hydrochloric acid is present in automobile exhaust but did not know of any quantitative data available. He men- tioned that the exhaust condensates were very acidic, about pH 2. 3.4.4 Burning of Chloride-Containing Plastics Several of the plastics used today contain organically bound chlorine; examples of some of the more common ones are polyvinyl chloride (approximately 57 percent chlorine), poly- vinylidene chloride (approximately 73 percent chlorine), and neoprene (approximately 40 percent chlorine). In addition, organic chlorides are added to other types of plastics and materials as fire-retardants. Chloride-containing plastics are used in making plastic films, containers, seat covers, ------- 28 wire insulation, and many other materials. When these chlo- ride plastics are heated or burned, hydrogen chloride is evolved.12'18'54,71,81 studies have been conducted with poly- vinyl chloride films12'81 to determine the type and quantity of gases evolved. In one investigation,12 a sample was heated at a rate of 3°C per minute; upon reaching 280°C a rapid weight loss started and continued until about 300°C. During this period a 60 percent weight loss was found, and analysis showed that almost all the chloride had been evolved as hydro- gen chloride. In another study,81 it was found that hydrogen chloride evolved at 100°C; moreover, the rate of evolution depended on the length of the heating period. The rate of hydrogen chloride evolution for 1 hour at 100°C was 8,000 |ag/m3 ; after 2 hours, 12,000 |ag/m3 ; and after 3 hours, 20,000 |_ig/m3 • Thus, open burning or incineration of chlorinated plas- tics is a probable source of hydrochloric acid pollution. Without effective control measures, this problem will inten- sify with the increased use of plastics projected for the future. 3.4.5 Burning of Paper Products Analysis of paper products indicates that the chloride content is low,10*'13 approximately 0.03 to 0.16 percent by weight. Nevertheless, two examples cited in the literature demonstrate that the amounts of hydrochloric acid emissions from the incineration of paper can cause injury to plants.13 ------- 29 In both examples (see Section 2.3.2), the plant injury was caused by hydrochloric acid emissions from a hospital incin- erator burning trash consisting of 80 to 90 percent paper products. Additional studies indicated that 53 to 95 percent of the chloride in paper products is lost on heating at 900°C. 3.4.6 DDT Production DDT (dichlorodiphenyltrichloroethane) is a common pesti- cide manufactured from chloral, chlorobenzene, and sulfuric acid2 (see Equation 7). H2SO4 CClgCHO + 2CSH5C1 » CC13CH(C6H4C1)2 + HSO (Chloral) (Equation 7) As seen from the reaction equation, hydrochloric acid is nei- ther a reactant nor a product of the desired reaction. How- ever, the primary contaminate in the emissions is hydrochloric acid from decomposition of chloral. The total amount of ef- fluent gases has been estimated as about 1 percent of the weight of DDT produced. This is an example of a manufacturing process in which hydrochloric acid is considered neither a reactant nor a prod- uct but, nevertheless, is part of the effluent gas stream. In this case, the hydrochloric acid emissions are due to the decomposition of the chloride compounds used in the reaction. 3.4.7 Lemon Pulp Extraction One company has reported on the extraction of lemon pulp with isopropyl alcohol at 120°F. Besides the predictable emissions of the alcohol, the effluent vapor also contained ------- 30 hydrochloric acid droplets. In this case, the company was aware of the content of the emissions and used an appropriate treatment system to control the emissions. Although probably only a very minor source, this repre- sents an example of the heating of organic matter at a low temperature (120°F) with the evolution of small quantities of hydrochloric acid. 3.5 Environmental Air Concentrations No information has been found on environmental air con- centrations of hydrochloric acid. However, Gorham40 observed that in Great Britain, precipitation samples from urban areas exhibited a distinct correlation between chloride content and acidity in samples of pH less than 5.7. ------- 31 4„ ABATEMENT The high solubility of hydrogen chloride in water and the low vapor pressures of even 20 percent hydrochloric acid solutions make collection of hydrogen chloride in water an effective and inexpensive method of control. Thus in the manufacture of hydrochloric acid (or hydro- gen chloride)/ the emission control system, which is also part of the system for obtaining hydrochloric acid from the hydro- gen chloride, consists mainly of water absorption facilities. Different types of absorbers are used, but the systems gen- erally consist of a packed tower or a cooling absorption tower followed by a packed tail tower .->0 ' 58f106 r^e pac;keci tower systems-^-58 normally include a connected set of S- bend tubes, followed by one or more towers in series. Cold water is added at the last or tail tower and flows over into the previous tower. The concentration of hydrochloric acid in this water is thus increased from tower to tower until it reaches the S-bend tubes, where the acid solution attains its final strength. However, the packed tower systems are rapidly being replaced by cooled absorption systems because the latter are more efficient, economical, and compact. The cooled absorption tower designs may consist of either a countercurrent or co-current flow of gas and water. One type uses water-jacketed packed tantalum towers with countercurrent flow. The most common system is the co-current falling film absorbers.49,58,59 jn this system, gas and weak acid solution ------- 32 from the packed tail tower flow downward over vertical, water-cooled, wetted-wall columns. Where anhydrous chloride is the desired product, absorption systems are not used.50 It has been reported that the use of water scrubbing systems can reduce the emissions to less than 0.1 pound of hydrogen chloride per ton of acid produced, although emis- sions can be 30 times that amount with less effective equip- ment.7 According to Faith et _al. ,31 hydrogen chloride emissions can be reduced to a range of 0.1 to 0.3 percent by volume by the use of two or more tail towers in series. The emissions of hydrochloric acid may be high if an upset occurs in the absorption system due to either improper tem- perature control or insufficient feed water.106 Other systems that appear to be effective for the con- trol of hydrochloric acid or hydrogen chloride emissions are the rotary brush scrubber^ anc| the ejector venturi scrubber. With the former system, collection efficiencies of 99.995 per cent have been reported with an initial hydrogen chloride content of 610 g/m3. In the latter system, scrubbing effi- ciency as high as 99 percent has been given for a single- stage unit for fumes containing up to 20 percent hydrogen chloride. The high solubility of hydrogen chloride in water accounts for the high degree of efficiency of these systems. Dry solid adsorbents have also been studied for removal of hydrogen chloride vapors.9'7! Adsorbents investigated include chromium oxinate and basic salts36 such as Beralyme, ------- 33 soda lime, lithium carbonate, and silica-alumina mixtures. Chromium oxinate or tris-(8-hydroxyquinolinato)chromium(III) exhibited physical adsorption with anhydrous hydrogen chlo- ride, but the adsorbing bed showed a tailing effect a long time before the exit gas concentration reached the entering concentration. Studies by lapalucci, Demski, and Bienstock^l indicate that hydrochloric acid emissions from coal burning can be reduced by adding basic salts, such as sodium carbonate, potassium carbonate, calcium carbonate, and dolomite. Chlo- rine retention in the ash when a small amount of basic salt was added was 8.8 to 37.8 percent, compared to 7.9 percent without an additive. ------- 34 5. ECONOMICS No information has been found on the damage costs or economic losses due to the effects of hydrochloric acid air pollution on humans, animals/ plants/ or materials. In addition, no information has been found on the economic costs of abatement (installation and operation costs of control equipment and cost benefits of usable emissions). Data on the production and consumption of hydrochloric acid are presented in Section 3. ------- 35 6. METHODS OF ANALYSIS All of the common methods of analysis for hydrochloric acid in air depend upon (1) measurement of acidity, (2) mea- surement of chloride ions/ or (3) combination of the two measurements. Therefore, other strong acids (e.g., sulfuric acid, nitric acid) or other chloride salts (e.g., sodium chlo- ride) can cause serious interference. 6.1 Sampling Methods In most methods, hydrochloric acid is collected in impingers containing water.4'25'105 The high solubility of hydrochloric acid in water yields excellent absorption effi- ciency. 66 The results of one investigation indicate that certain phosphate salts, particularly silver phosphate, have a high collection efficiency for hydrochloric acid but do not absorb sulfur dioxide.17 However, hydrobromic acid is also absorbed. Preliminary studies indicate that liquid crystals may make effective and selective collection materials for hydro- chloric acid and other gaseous pollutants.33 Acid mists have also been collected on paper,19 gelatinous film,38'68'114 thin metal films,67 and metal-coated glass slides.43,48 6.2 Qualitative Methods The presence of hydrochloric acid or any other strong acid in air can be determined by passing the air over moist pH indicators such as methyl orange, congo red, or blue lit- mus papers. Hydrochloric acid or other chlorides can also ------- 36 tie detected by bubbling the air through water and adding silver nitrate. Depending on the concentration of chloride, the solution may show a slight turbidity, or yield a white to grayish precipitate which will not change on addition of nitric acid but will dissolve or disappear upon addition of ammonia. 6.3 Quantitative Methods In the absence of other strong acids, hydrochloric acid samples which have been collected in water may be determined quantitatively by the usual direct titration methods with oc standard bases. A spectrophotometric method for determination of strong acids has been reported. 9/0 After the air sample is passed through water, methyl red is added to the acidic solution and the optical density at 530 mp. is determined. Normal concen- trations of carbon dioxide and 1,000 Pg of sulfur dioxide per 2 m of air do not interfere. The size and quantity of acid mists have been deter- mined by the use of both gelatinous films 38,68,114 an<^ metal- coated glass slides.43'48 The latter method is not affected by relative humidity. Through use of an electron microscope, it is possible to detect acid droplets with diameters of less than 0.1 p..48 In the absence of soluble chloride salts, hydrochloric acid samples dissolve in water and may be determined by the standard methods for chloride determination," including the ------- 37 Mohr method,99'100 absorption indicator method,32'60 and the modified Volhard method. These methods have a sensi- tivity of approximately 18,000 |jg of chloride per liter. For very small amounts of chloride in air, the determination can be made turbidimetrically or nephelometrically.2^'^9/" The hydrochloric acid solution is treated with silver nitrate and the turbidity determined spectrophotometrically; sensi- tivity is in the microgram range. Recently, a method has been developed for determining chloride colorimetrically. ' This method is based on the yellow color produced by the iron(IH) chloro complex in perchloric acid with a sensitivity of approximately 1,000 ng/m3 of chloride. This method suffers from interference from mercury and sulfate ions and is af- fected by the relative humidity of the air. There is a neutron activation technique for determining chloride in particulates with a sensitivity of approximately 0. 06 |j.g/m3 ,56 An automated analysis method for chloride is used by the National Air Sampling Network.110 This method is based on the reaction of chloride with mercury thiocyanate to yield thiocyanate ions. Thiocyanate ions react with ferric ions to form the stable red complex, hexacyanatoferrate ion, which can be determined spectrophotometrically at 460 m[a. The relative standard deviation for chloride is 1.0 _+ 0.1 |ag/mlo Since air samples usually contain other acids as well as chlorides, these methods are not generally applicable. There are no methods available that are free from interference ------- 38 by all other possible pollutants. However, an air sample containing a mixture of sulfur oxides, hydrochloric acid, and other chlorides can be analyzed by combining the methods reported in two papers.^'105 The air sample is passed through an aqueous solution of hydrogen peroxide. The aqueous solu- tion is then divided into three parts for three separate analyses: sulfate, chloride, and hydrogen ion. From these results the amount of each component can be determined. ------- 39 7. SUMMARY AND CONCLUSIONS Hydrogen chloride reacts rapidly with the moisture in the air and is generally found in the ambient atmosphere as hydrochloric acid. The acid at low concentrations, 15,000 to 75,000 Lig/m3 (10 to 50 ppm) , irritates primarily the mucous membranes of the eyes and upper respiratory tract in both humans and animals. Prolonged exposures to low con- centrations of hydrochloric acid can also erode the teeth. Work is intolerable after more than 60 minutes in atmospheres containing approximately 75,000 to 150,000 M.g/m3 (50 to 100 ppm) of hydrochloric acid. Higher concentrations (approxi- mately 1,500,000 |~ig/m3 or 1,000 ppm) can attack the mucous membranes, causing inflammation of the upper respiratory system and resulting in pulmonary edema or spasm of the lar- ynx, which can be fatal. A wide variety of plant life is susceptible to the toxic effects of hydrogen chloride or hydrochloric acid. Several examples of plant damage due to hydrochloric acid emissions have been reported in the litera- ture. The primary effect on plants is a discoloration or bleaching of the leaves. The threshold for visible damage was originally reported as 75,000 to 150,000 [ag/m3 (50 to 100 ppm) of hydrogen chloride. However, recent studies indi- cate that the threshold for many plants is less than 10 ppm for 4-hour exposures. The strong acidic properties of hydro- chloric acid make it extremely corrosive to most metals. ------- 40 Some countries have established ambient air quality standards for hydrochloric acid, including West Germany (approximately 750 |ag/m3 or 0.5 ppm as a mean 30-minute average) and Russia (approximately 15 \j.g/m3 or 0.009 ppm as a 24-hour average). The production rate since 1961 has shown a general increase of approximately 9 percent. Hydrogen chloride is produced by three main processes in the United States: acid- salt, direct synthesis, and the by-product process from chlorination of organic compounds. The latter process, the major production source, has shown a steady increase. Many organic chlorinating processes and other organic processes involving chlorinated compounds may produce hydrogen chloride as a by-product, but it may not be economically feasible to recover the product for other uses. Hydrochloric acid is produced by absorbing the hydrogen chloride gas into water. Hydrochloric acid (or hydrogen chloride) is primarily used to manufacture inorganic and organic chemicals, the latter accounting for almost 50 percent of the production in 1963. Other major uses include metal production, oil- well acidizing, metal and industrial cleaning, and food pro- cessing. Another potential source of emissions of hydrochloric acid is the heating or burning of chlorinated materials. The burning of coal appears to be a possible major source of hydrochloric acid pollution, since the chloride in coal is ------- 41 converted to over 90 percent hydrogen chloride during the burning process. Similarly, the burning of chlorinated plastics and paper can be an emission source, and possibly the burning of fuel oil and gasoline as well. No information has been found on the concentrations of hydrochloric acid in the atmosphere. Hydrogen chloride emissions from commercial processes can be effectively con- trolled by the equipment that is available today. Systems now in use include packed water scrubbing towers and cooled absorption towers. Emissions from coal burning may be de- creased by the addition of basic salts to the coal before burning. No information has been found on costs for the control of hydrochloric acid pollution or for costs incurred by damage to humans, animals, plants, and materials as a result of hydro- chloric acid emissions. No continuous monitoring methods are available for mea- suring the hydrochloric acid content of environmental air. The common methods used measure either the acidity or chlo- ride content of the air sample, and therefore suffer from interference from other acids and chlorides present in the environmental air. Based on the material presented in this report, further studies are suggested in the following areas: (1) Determination of the amount of hydrochloric acid present in the atmosphere of heavily populated areas, ------- 42 particularly near the source of production and near coal- burning establishments and incinerators. (2) Evaluation of the effects of low concentrations of hydrochloric acid on humans, animals, plants, and materials, (3) Determination of the contribution of automobile exhausts, incinerators, and other combustion sources to hydro- chloric acid air pollution. ------- 43 REFERENCES 1. Abernethy, R. p., and F. H. Gibson, Rare Elements in Coal, U. S. Bur. Mines Inform. Circ. 8163 (1963). 2. Air Pollution Control in Connection with DDT Production, J. Air Pollution Control Assoc. 14 (3) :49 (1964). 3. Air Pollution—Niagara County (Comprehensive Area Survey Report No. 3), New York State Air Pollution Control Board, Albany, N.Y. (1964). 4. Alekseyeva, M. V., and E, V. 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Chem. 28:999 (1936). ------- APPENDIX ------- APPENDIX TABLE 2 PROPERTIES OF HYDROGEN CHLORIDE AND HYDROCHLORIC ACID49'76 Properties Color, odor, normal state Boiling point Melting point Hygroscopicity Density Heat of fusion Heat of vaporization Hydrogen Chloride (HCl)a Colorless gas, pungent, irritating odor, fumes in air -85°C (-121°F) -111°C (-168°F) Very hygroscopic 1.6397 g/1 (0°C, 760 mm) 476-504.5 g-cal/mole 3860_+4 g-cal/mole Hydrochloric Acid (HC1, aqua)b Colorless liquid; sometimes yellowish due to impurities (iron, arsenic, chlorine, and organic matter) ; pungent and irritating odor Aqueous solution containing 20 HC1: 110°C (230°F) .24% 27.92% HC1: -42°C (-43.6°F) 37.14% HC1: -74°C (-101.2 F) Hygroscopic 20.04% HC1: 1.1006 g/1 37.14% HC1: 1.1885 g/1 (continued) Ul ------- TABLE 2 (Continued) PROPERTIES OF HYDROGEN CHLORIDE AND HYDROCHLORIC ACID49'76 Properties Hydrogen Chloride (HCl)a Hydrochloric Acid (HC1, aqua)b Reactivity Non-corrosive when dry. Reacts rapidly with organic materials Highly corrosive to moist metals with evolution of hydrogen gas. Reacts with basic salts (metallic oxides and carbonates) Solubility in H30) (g/lOOg H30) 82 67 63 ,3 ( 0°C) .3 (30°C) ,3 (40°C) 59.6 (50°C) 56.1 (60°C) aAlso called hydrochloric acid, anhydrous. Also called muriatic acid. ------- APPENDIX TABLE 3 SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE BY HUMANS Concentration ( ppm ) * 50-100 10-50 10 1,300-2,000 1,000-1,300 50-100 35 1,000-2,000 10 5 Exposure Time Few min 30-60 min 60 min Effects or Comments Work is impossible Work is difficult but possible Work is undisturbed Lethal Dangerous Intolerable Irritation of throat after short exposure Brief exposures are dangerous Irritation No organic damage Reference 45,72 45,72 45,72 52,103 52 35,44,52,87 87 87 113 113 Ul (continued) ------- APPENDIX TABLE 3 (Continued) SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE BY HUMANS Concentration ( ppm ) * 10 0.067-0.134 0.402 0.134 0.335 0.067-0.134 1-5 Exposure Time Effects or Comments Odor threshold value Odor threshold value Concentration for threshold reflex effect on optical chronaxie Concentration for threshold reflex effect on eye sensitivity to light Concentration for threshold effect on digito-vascular toxicity Threshold concentrations of change in the rhythm and depth of respiratory movement Odor threshold value Reference 105 28,29 28,29 28,29 28,29 28,29 45 *1 ppm = 1,470 at 25°C. Ul ------- APPENDIX TABLE 4 SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE ON ANIMALS Species Rabbits Guinea pigs Cats Rabbits Guinea pigs Cats Rabbits Concentra- tion (ppm)* 4,300 4,300 3,400 3,400 3,400 1,350 1,350 Exposure Time 30 min 30 min 90 min 90 min 90 min 90 min 90 min Effects or Comments Fatal in some cases, due to laryngeal spasm, laryngeal edema, or rapidly developing pulmonary edema Fatal in some cases, due to laryngeal spasm, laryngeal edema, or rapidly developing pulmonary edema Death after 2 to 6 days Death after 2 to 6 days Death after 2 to 6 days Severe irritation, dyspnea, and clouding of the cornea Severe irritation, dyspnea, and clouding of the cornea Reference 45,69 45,69 45,64 45,64 45,64 45,64 45,64 (continued) ------- APPENDIX TABLE 4 (Continued) SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE ON ANIMALS Species Guinea pigs Rabbits Guinea pigs Rabbits Guinea pigs Rabbits Guinea pigs Concentra- tion (ppm)* 1,350 670 670 300 300 100-140 100-140 Exposure Time 90 min 2 hr 2 hr 6 hr 6 hr 6 hr 6 hr Effects or Comments Severe irritation, dyspnea, and clouding of the cornea Fatal in some cases Fatal in some cases Corrosion of the cornea and upper respiratory irritation Corrosion of the cornea and upper respiratory irritation Only slight corrosion of the cornea and upper respiratory irritation Only slight corrosion of the cornea and upper respiratory irritation Reference 45,64 45,69 45,69 45,64 45,64 45,64 45,64 (continued ) Ul -J ------- APPENDIX TABLE 4 (Continued) SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE ON ANIMALS Species Rabbits Guinea pigs Pigeons Monkey Rabbit Guinea pig Concentra- tion (ppm)* 100 100 100 33 33 33 Exposure Time 6 hr/day for 50 days 6 hr/day for 50 days 6 hr/day for 50 days 6 hr/day 5 days/week for 4 weeks 6 hr/day 5 days/week for 4 weeks 6/hr/day 5 days/week for 4 weeks Effects or Comments Slight unrest and irritation of the eyes and nose Slight unrest and irritation of the eyes and nose Slight unrest and irritation of the eyes and nose No immediate toxic effects and no pathological changes No immediate toxic effects and no pathological changes No immediate toxic effects and no pathological changes Reference 45,82 45,82 45,82 69 69 69 (continued) Ul oo ------- APPENDIX TABLE 4 (Continued) SUMMARY OF REPORTED EFFECTS OF INHALATION OF HYDROGEN CHLORIDE ON ANIMALS Species Rabbits Rabbits Concentra- tion (ppm)* 60 30 Exposure Time 5 min 10 min Effects or Comments Cessation of ciliary activity without recovery Cessation of ciliary activity without recovery Reference 21 21 *1 ppm « 1,470 |-tg/m3 at 25°C. ui ------- APPENDIX TABLE 5 SUMMARY OF REPORTED TOXIC EFFECTS OF HYDROGEN CHLORIDE EXPOSURE ON PLANTS Species Plants Plants Sugar beets Viburnum seedlings Beech Oak Maple Birch Pear Concentra- tion (ppm)* 10-50 100-1,000 10 5-20 1,000 1,000 2,000 2,000 2,000 Exposure Time Few hr 24 hr 1 hr 1 hr Effects or Comments No leaf damage Leaf damage Threshold for marking Leaves rolled at the edges, withered, shrunk, faded, and necrotic Local lesions produced Local lesions produced Marginal leaf scorch Marginal leaf scorch Marginal leaf scorch Reference 113 113 107 42 42 42 42 42 42 (continued) ------- APPENDIX TABLE 5 (Continued) SUMMARY OF REPORTED TOXIC EFFECTS OF HYDROGEN CHLORIDE EXPOSURE ON PLANTS Species Viburnum seedlings Larch Fir Spruce Tomato plants Liriodendron tulipifera Alnus fl,lutinosa Prunus serotina Concentra- tion (ppm)* 5-20 5-20 1,000 2,000 5 3 6 6 Exposure Time 48 hr 48 hr 1 hr 1 hr/day for 80 days 2 hr 4 hr 4 hr 4 hr Effects or Comments Plants died Plants died Local lesions formed No apparent injury Developed interveinal bronzing followed by necrosis within 72 hours after exposure Threshold for visible injury Threshold for visible injury Threshold for visible injury Reference 42 42 42 42 93 74 74 74 (continued) ------- APPENDIX TABLE 5 (Continued) SUMMARY OF REPORTED TOXIC EFFECTS OF HYDROGEN CHLORIDE EXPOSURE ON PLANTS Species Acer saccharus Acer platanoides Quercus rubus Pinus strobus Psaudotsuqa mantissii Abies balsamea Pinus abies Pinus niqra Concentra- tion (ppm)* 7 7 13 8 10 10 19 18 Exposure Time 4 hr 4 hr 4 hr 4 hr 4 hr 4 hr 4 hr 4 hr Effects or Comments Threshold for visible injury Threshold for visible injury No visible injury Threshold for visible injury Threshold for visible injury Threshold for visible damage Threshold for visible damage No visible damage Reference 74 74 74 74 74 74 74 74 (continued) tsj ------- APPENDIX .TABLE 5 (Continued) SUMMARY OF REPORTED TOXIC EFFECTS OF HYDROGEN CHLORIDE EXPOSURE ON PLANTS Species Thuja occi- dentalis Spruce seedlings Concentra- tion (ppm)* 43 <50 Exposure Time 4 hr 20 min Effects or Comments No visible damage Plants died Reference 74 61 *1 ppm = 1,470 |ag/m3 at 25°C. U) ------- APPENDIX TABLE 6 EMISSIONS OF HYDROCHLORIC ACID IN SELECTED AREAS OF NIAGARA COUNTY, N.Y.3 HC1 Emitted Community (tons/year) Cities: Lockport 187 Niagara Falls 3,436 North Tonawanda 149 Towns: Cambria 5 Hartland 5 Lewiston 191 Lockport 9 Newfane 16 Niagara 11 Pendleton 4 Porter 10 Royalton 7 Somerset 3 Wheatfield 24 Wilson 6 Villages: Barker 3 Lewiston 3 Middleport 8 Wilson 3 Youngstown 3 Total 4,083 ------- APPENDIX TABLE 7 HYDROCHLORIC ACID PRODUCTION IN THE UNITED STATES, 1958-196723 Hydrochloric Acid* Total HC1 Year (short tons) 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 826, 955, 970, 910, 1,052, 1,053, 1,236, 1,370, 1,519, 1,597, 022 914 167 967 116 502 824 092 372 682 i i (short 107, 100, 90, 87, 105, 128, 136, 138, 139, (preliminary) 137, Process Salt- Ac id tons) (percent) 036 008 461 073 830 652 051 121 778 515 13.0 10.4 9.3 9.5 10.1 12.2 10.0 10.1 9.2 8.6 Synthesis (short tons) (percent) 162, 165, 148, 118, 92, 92, 95, 99, 108, 114, 282 751 304 059 117 276 606 043 028 003 19.6 17.3 15.3 13.0 8.8 8.8 7.7 7.2 7.1 7.1 By-Product and Others (short tons) (percent ) 556, 690, 731, 705, 854, 832, 1,005, 1,132, 1,271, 1,346, 704 155 402 835 169 574 167 928 566 164 67.4 72.3 75.4 77.5 81.8 79.0 82.3 82.7 83.7 84.3 * Includes anhydrous hydrogen chloride. en ------- 66 APPENDIX TABLE 8 PRODUCTION OF HYDROCHLORIC ACID BY PROCESS AND STATE88 State Massachusetts New Hampshire New Jersey New York Pennsylvania Alabama Delaware Georgia Kentucky Louisiana Maryland Tennessee Texas Virginia West Virginia Illinois Indiana Kansas Michigan Missouri Ohio California Nevada New Mexico Washington Total Number Salt- Acid 1 3 1 1 2 1 1 1 1 2 1 15 of Plants Direct Synthesis 1 3 1 3 2 3 1 1 2 1 2 2 22 Using Each By- Product 1 7 5 1 2 2 3 3 1 1 8 6 2 2 6 1 4 3 1 1 60 Process Total 2 1 10 6* 1 2 1 3 5* 5* 1 1 11* 2 6 3 3 1 7* 1 6* 5 1 1 3 88* *Some plants use more than one process, ------- 67 APPENDIX TABLE 9 MAJOR PRODUCERS OF HYDROCHLORIC ACID (MURIATIC ACID) IN THE UNITED STATES 108 Company Location Allen, L. B., Co., Inc. Allied Chemical Corp., Industrial Chemicals Div. American Cyanamid Co., Industrial Chemicals Div. American Oil & Supply Co. Baker, J. T., Chemical Co. Bay Chemical Co. Berg Chemical Co., Inc. Big Ben Chemicals & Solvents, Inc, Calcine Chemical Co. Celanese Corp. of America, Chemical Div. Central Chemical Div. Diamond Alkali Co. Dover Chemical Corp. Dow Chemical Co. Dowell Div. Essex Chemical Corp. General Aniline & Film Corp. Globe Chemical Co., Inc. Haviland Products Co. Hooker Chemical Corp. Industrial Chemicals Div. Hubbard-Hall Chemical Co. International Minerals & Chemical Corp. International Minerals & Chemical Corp. Johnson Mfg. Co. Jones Chemicals, Inc. Knight, Maurice A., Co. Kraft Chemical Co. McKesson & Robbins, Inc., Chemical Dept. Mercury Chemical Corp. Monarch Chemical Works, Inc. Monsanto Inorganic Chemicals Div. National Zinc Co., Inc. Neville Chemical Co. Nitine Inc. Octagon Process Inc. Schiller Park, 111. Morristown, N.J. Wayne, N.J. Newark, N.J. North Phillipsburg, N.J. Chicago, 111. New York, N.Y. Chicago, 111. Jersey City, N.J. New York, N.Y. Calumet City, 111. Cleveland, Ohio Dover, Ohio Midland, Mich. Tulsa, Okla. Clifton, N.J. New York, N.Y. Cincinnati, Ohio Grand Rapids, Mich. Niagara Falls, N.Y. Waterbury, Conn. Skokie, 111. Chicago, 111. Princeton, Iowa Caledonia, N.Y. Akron, Ohio Chicago, 111. New York, N.Y. Metuchen, N.J. Omaha, Nebr. St. Louis, Mo. New York, N.Y. Pittsburgh, Pa. Whippany, N.J. Edgewater, N.J. (continued) ------- 68 APPENDIX TABLE 9 (Continued) MAJOR PRODUCERS OF HYDROCHLORIC ACID (MURIATIC ACID) IN THE UNITED STATES108 Company Location Olin Mathieson Chemical Corp. Pennsalt Chemical Corp. Phillipp Brothers Chemicals Inc. Potash Co. of America PPG Industries Chemical Div. Riverside Chemical Co., Inc. Robinson Bros. Chemicals Inc. Rohm & Haas Co. Seaway Chemical Corp. Siegel Chemical Co., Inc. Solvent Chemical Co. Smith-Douglass Co., Inc. Stauffer Chemical Co. Industrial Chemical Div. Tenneco Chemicals Inc. Triple-X Chemical Laboratories, Inc. United States Rubber Co., Chemical Div. Velsicol Chemical Corp., Tennsyn Div. Vulcan Materials Co., Chemicals Div. Wittichen Chemical Co. New York, N.Y. Tulsa, Okla. New York, N.Y. Carlsbad, N. Mex. Pittsburgh, Pa. North Tonawanda, N.Y, Brooklyn, N.Y. Philadelphia, Pa. Buffalo, N.Y. Brooklyn, N.Y. Maiden, Mass. Norfolk, Va. New York, N.Y. New York, N.Y. Chicago, 111. Naugatuck, Conn. Chattanooga, Tenn. Wichita, Kans. Birmingham, Ala. ------- 69 APPENDIX TABLE 10 CONSUMPTION OF HYDROCHLORIC ACID BY USES, 196358 Uses Approximate % Organic chemicals Inorganic chemicals Metal production Metal and industrial cleaning Food processing Oil well acidizing Total 49 5 17 7 4 18 100 100% HC1 (Short Tons)* 516,500 52,600 179,000 73,700 42,200 189,500 1,053,500 *Approximately calculated on basis of 1963 total pro- duction of 1,053,502 short tons (see Table 7, Appendix). ------- 70 APPENDIX TABLE 11 CONSUMPTION OF HYDROCHLORIC ACID BY SELECTED INDUSTRIES, 1963 and 1958 Industry Organic chemicals3 Intermediate coal tar products Inorganic chemicals9-'*3 Alkalies and chlorine Plastics material and resins Total 100% HC1 1963 438,746 79,505 51,200 44,557 13,993 628,001 (Short Tons) 1958 280,822 18,802 24,400 12,280 36,754 373,058 aNot elsewhere classified. ^Estimated from total money spent in 1958 and 1963 by inorganic chemical industries and prices paid during those periods by other industries. ------- APPENDIX 71 TABLE 12 CHLORINE CONTENT OF SELECTED UNITED STATES COALS95 Source of State Ohio Illinois Indiana West Virginia Pennsylvania Illinois Oklahoma Coal Bed Sharon No. 6 No. 4 Pittsburgh Lower Freeport Central Illinois Henryetta Chlorine Content (percent) 0.01 0.01 0.06 0.07 0.14 0.35 0.46 ------- |