Demetallation of Used Oil to Facilitate Its
Utilization as a Fuel
J. H. Kang and A. R. Tarrer, Chemical Engineering Department,
Auburn University, Auburn, AL 36849
Joe Kaminski, The Office of the Assistant Secretary of Defense
Jim Parrish, Defense Reutilization and Marketing Service (DRMS)
Edward R. Bates, U. S. Environmental Protection Agency
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1
NOTICE
The information in this paper has been funded in part by the United
States Environmental Protection Agency under Cooperative Agreement CR 812090
to Auburn University. It has been subjected to the Agency's peer and admin-
istrative review and has been approved for publication. Mention of trade
names or commercial products does not constitute endorsement or recommendation
for use.
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ABSTRACT: Used oil invariably contains soluble and insoluble metal-bearing
compounds. The presence of these compounds complicates the recycling of used
oil as a fuel, by causing boiler maintenance problems and by making it
difficult to comply with particulate emission standards and RCRA regulations.
Demetallating a used oil prior to its burning minimizes maintenance problems
and facilitates meeting the regulatory requirements controlling its burning.
Different physical and chemical methods can be used to demetallate used oils.
In this work, a chemical demetallation agent was used to convert entrained
non-filterable metals into a form which could be effectively removed by
filtration. Two different types of chemical demetallation agents were used:
metallic borohydrides (NaBH4 and KBH4) and diammonium phosphate (DAP). The
activity and selectivity of these demetallation agents under different
reaction conditions in various types and sizes of reactors (thereby varying
mass transfer rates) were compared. Several types of used oils having
different metal contents were examined.
It was observed in this study that metallic borohydrides were highly
selective with regard to the types of metals they removed. The accompanying
sludge formed also made the separation operation inefficient. On the other
hand, results obtained with DAP were extremely favorable. The presence of
water during the reaction was found to play an important role as a carrier for
the DAP, aiding in its dispersion and reducing the importance of mass
transfer. This study which also evaluated different separation techniques
found the use of both sedimentation and filtration to be practical, with
filtration rates being significantly accelerated by the addition of low
percentages of No. 2 fuel oil.
KEYWORDS: Waste oil, demetallation, ash content, lead content, metallic
borohydrides, diammonium phosphate, lead reduction.
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Introduction
In the United States, automotive and other oil-consuming industries
generate about 1.1 billion gallons of used oil each year [1]. This
voluminuous amount constitutes a serious waste oil disposal problem. Recent
- Environmental Protection Agency (EPA) regulations and growing public concern
over hazardous wastes make development of a viable alternative to land-
filling very desirable. The objective of this work was to develop a practical
and feasible waste oil demetallation process to remove the ash-forming
contaminants, especially organolead compounds, from the oil so that the
demetallated used oil would qualify as a specification-grade fuel oil [2].
Waste oil, although contaminated, has a high energy value. A major
operation in reclaiming waste oil is the removal of water and various ash-
forming impurities that remain dispersed in the used oil. The ash-forming
impurities consists of very fine carbon particles, organometallic particulates
(e.g., organolead compounds), and inorganic materials (e.g., dust).
Reuse of an untreated used oil having a high concentration of lead and
other metallic contaminants may lead to serious air pollution and boiler
maintenance problems. To qualify for minimal regulatory requirements, i.e.,
specification-grade fuel oil requirements under EPA regulations, the lead
content of a waste oil to be recycled as a fuel in a commercial boiler can not
exceed 100 ppm. Since most of the used oil from the automotive industry
contains several times the proposed EPA limit, it is imperative that an
economic process be developed to reduce the lead content of the oil to an
acceptable level so that the reclaimed waste oil can safely be reused as a
fuel oil without endangering public health or the environment.
Waste oils were demetallated using two types of demetallating reagents:
metallic borohydrides and diammonium phosphate (DAP). A detailed parametric
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study was undertaken to map out the process variables so as to identify the
most efficient demetallation conditions. An evaluation of solid-liquid
separation techniques was also done to design an efficient solids removal
operation for future pilot plant studies.
Experimental Procedure
Materials -- All used oil was collected from the Auburn University Waste Oil
Reprocessing Pilot Plant. The demetallating reagents used were sodium
borohydride, potassium borohydride, sodium borohydride aqueous solution, and
diammonium phosphate (DAP). The phase transfer catalyst used was tri-n-butyl-
methyl ammonium chloride.
Equipment -- Three types of reactors were used. They were: an autoclave (3785
ml and 300 ml), a microreactor (45 ml), and a distillation flask (300 ml).
The autoclave was equipped with a turbine agitator, a cooling coil, baffles,
and a thermowell, all made of 316 stainless steel. The autoclave was heated
by an electric furnace and agitation was provided by a magnedrive system. The
tubing bomb microreactor (TBMR).was constructed of 316 stainless steel tubing
(1.9 cm O.D. with 0.165 cm wall thickness and a length of 20.3 cm). Agitation
was provided by a shaker assembly as shown in Figure 1. For a typical run,
the TBMR was immersed in a preheated fluidized sand bath. As for the
distillation flask, the reaction mixture was agitated using a magnetic
stirrer, and the reactor was heated in a constant temperature paraffin oil
bath.
Analysis -- The experimental results were verified in accordance with an EPA
approved quality assurance project plan. The properties of the demetallated
used oil were evaluated to assess its potential as an EPA specification-grade
fuel oil using the following test methods: water content, ASTM D4006-81
(Water in crude oil by distillation); ash content, a modification of ASTM
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D482-80 (Ash from petroleum products); lead content, standard atomic
absorption (AA) analysis.
In each ash analysis, an oil specimen (about 5 g) in a preweighed
crucible was dried first on a hot plate and then heated in a Model F-6000
Thermolyne muffler furnace at a rate of 373K (100°C) per hour. Once the
temperature reached 873K (600°C), the crucible was allowed to stay in the
furnace for an additional 12 hours. Then, the crucible was removed and cooled
in a desiccator. The weight of ash remaining in the crucible was determined,
and its percent concentration in the original oil sample was computed..
In each lead analysis, the ash was dissolved in an acid solution of 10 ml
of HN03 solution (1:1) and 2 ml of concentrated HC1. The lead content was
determined using AA spectroscopy. A lead working standard was prepared by
serial dilution of a lead standard solution (1000 ± 1% ppm) supplied by Fisher
Scientific. A blind-spiked oil sample was occasionally prepared to verify the
results. An organic lead standard (lead cyclohexanebutyric acid,
[C6H11(CH2)3COO]2 Pb) was used for this purpose.
Results and Discussion
Use of Metal Borohydride As A DemeCall ing Reagent
The properties of metal borohydrides, such as NaBH4, KBH4, and SWS
solution (consisting of 12 wt% NaBH4, 40 wt% NaOH, 48 wt% water), are
described in detail in technical literature published by Morton Thiokol, Inc.,
Ventron Division [2,3].
Metallic borohydrides (e.g. sodium borohydride) are strong reducing
agents. The following reaction is typical of the metal reduction that occurs
with sodium borohydride [2].
8MX + NaBH4 + 2 H20 ----> 8M° + NaB02 + 8 HX
where M = the metal (valence 1+)
X = the anion
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In this chemical reaction, stoichiometrically, sodium borohydride
has 8 reducing equivalents per molecule. Based on bench-scale experimental-
results, Morton Thiokol, Inc. reported that a stabilized water solution (i.e.,
SWS solution) was an effective reagent for removing lead from used crankcase
oil [4] . it should be noted that sodium borohydride (NaBH^.) degrades in the
presence of water or acid via hydrolysis to liberate hydrogen and a salt
(NaB02) when the pH of the solution is low. A representative chemical
reaction is as follows:
Water Hydrolysis:
NaBH4 + 2H20 ---> NaB02 + 4 H2
A parametric study was done to investigate the lead reduction efficiency
of two Morton Thiokol products: Venpure powders (NaBH4 and KBH4> and SWS
solution. A tubing bomb microreactor (TBMR) and the reaction conditions
listed in Table 1 were used in this study. A concentrated NaOH aqueous
solution (50 wt%) was usually added to maintain a high pH and thus a low
hydrolysis activity of the metal borohydrides.
In a typical run, the TBMR was charged with 20 g of waste oil, the
specified amounts of 50 wt% NaOH aqueous solution and VenPure product. The
reactor was then sealed. Subsequently, the TBMR was attached to the vertical
shaft of the agitation assembly, as shown in Fig. 1, and agitated at ambient
temperature for 3 minutes at 860 rpm before lowering it into the preheated
fluidized sand bath. The heat-up time was about 60 seconds. At the end of
the chosen reaction time, the TBMR was removed from the sand bath, immediately
quenched in cold tap water, and checked for any leaks. The gases were
released slowly from the bomb under a hood and the liquid product was then
collected and vacuum filtered. The filtrate (or product oil) was collected
for ash and lead analyses.
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With 0.65 wt% SWS and 1.2 wt% NaOH solutions, the lead content of the
Type B oil was markedly reduced from 480 to 70 ppm (Run 1) as shown in Table
2. In other words, an 85.4% lead reduction was achieved. This is well within
the allowable maximum lead content of 100 ppm for specification grade used oil
set by EPA. However, a high sludge production (16 wt%) resulted from this
run.
Since metal borohydrides are expensive, the charge of SWS solution
(containing 12 wt% sodium borohydride) was reduced to 0.43 wt% in Run 2.
Also, the charge of NaOH concentrated solution was reduced from 1.2 wt% to 0.8
wt%. The result was that the lead content of the oil decreased by only about
50%, to 240 ppm. The ash content of the product oil was 0.58 wt%. The amount
of sludge production was about the same as that from Run 1.
In order to reduce the sludge production, in Run 3, only 0.05 wt% NaBH4
powder was used and no NaOH was added. The amount of lead reduction was only
10.4 percent; however, little sludge was produced (2 wt%). To enhance the
demetallation activity, 0.8 wt% of 50 wt% NaOH was added in Run 4 and the
other reactions conditions were kept the same. The lead removal efficiency
increased from 10.4% for Run 3 to 37.5% for Run 4.
To improve the solubility of NaBH4 in the oil phase, 0.10 wt% of phase
transfer catalyst (tri-n-butyl-methyl ammonium chloride) was also added to the
oil (Run 5). Comparing the results of Run 5 with those of Run 3 (in both runs
no NaOH was added), the addition of the phase transfer catalyst did result in
an increase in lead removal efficiency from 10.4 to 27.1%. With 0.8 wt% NaOH
solution added in Run 6, the lead reduction efficiency improved slightly more
to 31.3 wt%. On the whole, there seemed to be a trade-off between using
either SWS or NaBH4 powder as a demetalling reagent; the former performed
better in terms of lead reduction efficiency; whereas the latter produced, less
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sludge.
To determine the reproducibility of the demetallation experiment, Run 1
was duplicated by Run 7, and the results were essentially the same for both
runs, confirming the accuracy of the experiment.
Since waste oil is derived from various sources, it is plausible that the
lead removal efficiency using a demetalling reagent might respond differently
to different types of waste oil. Thus, a different oil, viz., Type A oil
(lead content = 660 ppm, ash content - 0.59%) was used in Runs 8-12.
In Run 8, the reaction conditions were almost the same as those in Run 1
only a different oil was used. The lead content of Type A oil was reduced by
about 24% to 500 ppm; whereas for Type B oil the lead content decreased by 85%
to 70 ppm (Table 3).
When the charge of SWS was doubled (Run 9), the lead content of Type A
oil was reduced by about 58% (from 660 ppm to 280 ppm) as shown in Table 4.
SWS contained 12 wt% sodium borohydride, which implied that the sodium
borohydride concentration in the oil in Run 9 was 1,560 ppm. A sodium
borohydride concentration of this level would not be economically feasible for
reclaiming waste oil.
As mentioned earlier, the runs with caustic and SWS solution were
characterized by high sludge production. A gel-like product was occasionally
observed, which was difficult to filter, making the determination of sludge
content very difficult. The gel formation was probably due to the presence of
sodium hydroxide which acts to saponify fatty acids (e.g. detergents) present
in the used oil. In order to inhibit the gel formation, sodium borohydride
was added in a powder form (Runs 10 and 11) instead of in a solution; NaOH was
still introduced as a 50% aqueous solution to maintain the activity of sodium
borohydride.
, j
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In Run 10, 0.15 wt% (i.e., 1500 ppm) NaBH4 w.s added, vhlch ^
approximately the .„. amount of NaBH* added In Eun 9; the leae reduction
efficiency was slightly lower than that of Run 9. This was probably due to
- the greater solubility of NaBH* In Run 9. In Run 11, a ph.se transfer
~ catalyst (tri-n-butyl methyl ammonium chloride) was added, and the lead
content of Type A oil was reduced by about 73% to 180 ppm.
When potassium borohydride (KBH4) was used in Run 12, the lead reduction
»as 59% (i.e., from 660 to 270 ppm) ^
above the 100 ppm allowable maximum limit.
Examination of the «sh content of the product oil (shown in Tables 2 »d
4, reveals that, for both types of waste oil, the ash content of the product
oil was not markedly decreased by metal borohydride treatment, although the
lead content was selectively reduced in some cases. This »ight be attributed
to the formation of other fine salts which could not be separated by regular
filtration. A major disadvantage of using metal borohydrides as a demetaUing
reagent is that the pH must be tept high for the borohydrides to be stab!.,
and this results in a very viscous (gel) product.
In the previous runs, the reaction temperature used was 110°C. Bhen the
reaction temperature was increased fro. Il0oc Co 150oc, keeplng ^ ^
conditions the same as those used in Run 1, the product was a gel, and as a
result, a poor lead reduction efficiency was obtained (Runs 13 and 14 Table
a cotton seed oil or a non-detergent virgin motor oil was reacted with either
SWS solution or NaBH4 powder to confirm that saponification does occur when
fatty acids are present.
A cotton seed oil (20g) was blended with 1.2 wt% NaOH in 50% aqueous
8
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solution, and then reacted with 0.65 wt% SWS in a TBMR (Run 15). The reaction
was conducted under reaction conditions given in Table 1 (similar to those
used for the TBMR demetallation runs). The reaction product was collected in
a 2.5 cm O.D. x 15 cm length test tube. The sludge produced was about 35
volume % (Table 6). This sludge was probably the salt resulting from the
saponification of fatty acids, in the cotton seed oil, with NaOH. The cotton
seed oil was reacted with 0.05 wt% NaBH4 powder in the absence of sodium
hydroxide (Run 16). In this case no sludge was formed, confirming that the
sludge (gel) was due to the reaction of fatty acids with NaOH. The amount of
NaBH4 was doubled, and still, there was no sludge formed (Run 17). The effect
of NaOH on non-detergent motor oil was observed by reacting an SAE-30 non-
detergent motor oil with SWS (Run 18). After the reaction, two layers of
liquid were formed. The top layer was reddish brown and the bottom layer was
bluish green in color. A trace amount of suspended solids was also observed.
In summary, the gel product formed while treating used oil with borohydrides
with NaOH present was probably due to the saponification of fatty acids.
Effect of Caustic -- In an attempt to reduce the amount of sludge production,
two reactions (Runs 19 and 20, Table 7) were performed in which 1.5 wt% NH4OH
was added instead of NaOH, using the reaction conditions shown in Table 1.
Also, to help stabilize the NH4OH, 25 psig of NH3 was used (Run 19). As
compared to a 0.8 wt% NaOH addition (Run 4), the amounts of. lead reduction and
sludge production were about the same.
Effect of Water — As noted earlier, the reducing ability of metallic
borohydrides can be hampered substantially by water hydrolysis. Since the
waste oils obtained were used as-received (which had a water content of about
5 volume %) , the poor performance for those runs with metallic borohydrides,
in terms of lead reduction efficiency and ash content remaining in the oil,
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may possibly be attributed to the presence of water during the reaction. To
investigate the effect of water on lead removal, a sufficient amount of Type A
oil (containing 5 vol , water) was blended with 0.25 wt, and 0.50 «, NaOH
solutions (50 «, concentrated solution) respectively. Water along with some
light ends were then distilled off via atmospheric distillation. The residual
oils were termed as Type C and Type D, respectively. The properties of Type c
& D oils are given in Table 8.
In Run 21. 20 g of dry Type C oil was reacted with 0.9 wt% of SWS
solution in a TBMR under reaction conditions given in Table 1. As shown in
Table 9, the lead content of the Type C oil was successfully reduced from 700
to 100 PPm; i.e. about 86% lead reduction ^ achieved ftia ^^^^^ ^t ^
much better derailing performance can be achieved with a dry oil (e.g., type
C) than with a wet oil (e.g. Type A).
To further minimize the use of SWS solution, the charge of SWS solution
was reduced to 0.4 wt% in Run 22. As i
obtained.
in Runs 23 and 24, 0.1 wt» of a phase transfer catalyst (tri-n-butyl-
...thyl ammonium chloride, was added to see if the demetsUing performance
could be improved. Compared to run 21 (without catalyst,, catalyst addition
(e.g., Run 23, did not improve the results.
TO study the effect of BaOH charge on lead reduction, Type D oil „„ us«d
in Runs 25 and 26. The difference between Type C and Type D oll was the
amount of HaOH in the oil; the latter had twice the amount of BaOH than the
former (-1250 ppm, . In comparison to Run 22, with th. same charge of SWS
solution, Run 26 gave a lower lead reduction efficiency.
On the whole. Table 9 shows that the presence of water in'the oi! has ,„
adverse effect on demetallation when metallic borohydrides are used. This can
10
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be avoided by distilling off the water before the demetallation reaction.
It should be noted that the results presented so far were obtained for.a
45 ml tubing bomb.microreactor (TBMR). Knowing that these bench-scale
- -demetallation results were to be incorporated in the scale-up and design of
the Auburn University Waste Oil Reprocessing Pilot Plant, experiments were
extended to a larger batch reactor, i.e., a 3785 ml autoclave, to simulate
actual operating conditions as much as possible.
As mentioned above, water can decrease the demetailing activity of
metallic borohydrides. Therefore, the as-received Type A oil, containing
about 5 vol.% of water, was blended with 0.25 wt% NaOH aqueous solution (50
vt%) in the following runs and then distilled to a specified temperature under
atmospheric pressure. The residual oil was assumed to be moisture-free. The
moisture-free oil (or dry oil) was then treated with metallic borohydride
products in the one-gallon autoclave. The results are given in Table 10 and
discussed below:
In Run AS1, 890 g of dry oil (lead content - 700 ppm) was reacted with
0.9 wt% of SWS solution in the 3785 ml autoclave using the reaction conditions
shown in Table 11. For Run AS1, only a 37% lead reduction efficiency was
obtained. The poor demetalling performance was probably due to the low
distillation cut-off temperature (129°C), which resulted in a certain amount
of water being left .behind in the residual oil. In other words, the residual
oil obtained in Run AS1 was not dry enough.
Thus, in Run AS2, the distillation cut-off temperature was further raised
to 175°C. The oil and SWS solution charges to the autoclave were 900 g and
0.91 wt%, respectively, which were about the same as in Run AS1. With the
same reaction conditions, the lead content of the oil was markedly reduced
from 700 ppm to 25 ppm; i.e., a 96% lead reduction was obtained compared to
37% in Run AS1.
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Although a promising result was obtained in Run AS2, the amount of SWS
solution (containing 12 wt% NaBH4) used was considerable, and hence,
uneconomical. Thus Run AS2 was duplicated by Run ASS except that the SWS
solution charge was halved. As a result, only a 40% lead reduction was
obtained; this suggested that more SWS solution was required, if a better
demetailing performance was to be achieved.
To compare the demetalling effectiveness of SWS solution and NaBH4
powder, Run AS4 was performed in which the same amount of NaBH4 was used as in
Run AS1 (i.e. 0.10 wt% NaBH4 power) and 0.20 wt% phase transfer catalyst (tri-
n-butyl-methyl ammonium chloride) were reacted with 545 g of dry oil in the
autoclave. Coincidentally, the same level of lead reduction was obtained.
However, with NaBH4 powder (Run AS4) the product oil had a lower ash content
as compared to Run AS1 with SWS solution; also, less sludge was obtained in
Run AS4.
To study the demetalling ability of KBH4 powder, Run AS4 was duplicated
(Run ASS) except that KBH4 powder was used. As shown in Table 10, the lead
reduction efficiency increased from 37% to 51%, but the ash content of the oil
was not altered significantly.
Since KBH4 powder is more expensive than NaBH4 powder, Run AS4 was
duplicated again in Run AS6, in which the NaBH4 charge was increased from 0.10
to 0.15 wt% while maintaining the rest of conditions the same as in Run AS4 to
determine whether a better lead reduction efficiency could be obtained/ It
was found that the lead reduction efficiency increased from 37 to 71%, but the
ash content of the product oil did not change appreciably, as shown in Table
10. Although the amount of NaBH4 used can be further increased to improve lead
reduction performance, it is uneconomical to do so when the operating costs
for reprocessing waste oil are considered. Therefore, another demetalling
method was explored in an effort to seek the most economical process.
•**""•- 12
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Use of Diammonium Phosphate As a. Demetallation Reagent
As previously described, the major problems in using metallic
borohydrides as deinstalling reagents were: (1) a soap-like sludge was usually
. .formed after the reaction, which was very difficult to filter; (2) a caustic
oil was produced (this could result in corrosion problems); and (3) the
treated oil after filtration usually had a higher ash content than the
original waste oil. Because of these problems, another demetallation process,
which had been proposed by the Phillips Petroleum Company as a pretreatment
step in converting waste oil into a lubricating oil was investigated [1,5].
In this process, waste oil was reacted with a demetalling reagent, diammonium
phosphate (DAP) (both with and without the addition of excess water).
Different types of reactors were used in this investigation to permit dominant
mechanisms over different operational ranges to be identified.
In the bench scale experiments, three types of reactors were used: (1) A
tubing bomb microreactor (TBMR) as described previously; (2) A 500 ml
distillation flask equipped with a magnetic stirrer; and (3) A 3785 ml
autoclave reactor. The TBMR was operated under closed conditions, whereas the
distillation was done under open conditions; i.e. the flask was open to the
atmosphere to distill off water and trace amounts of light components.
TBMR Reaction Studies
Effect of Reaction Time and Temperature -- The variation in lead content
of the DAP-treated oil with reaction time was observed as shown in Figure 2.
The demetallation experiments were done at 150°C. From an initial value of
about 210 ppm, the lead concentration of the product oil decreased with
increasing reaction time to a final value of 16.5 ppm for the 90 minute run at
an 800 cpm agitation rate. From this figure, it can also be deduced that:
agitation has a significant effect on the lead content of the oil. For
example, for a 45 minute reaction time, when the agitation rate was decreased
13
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. SOO to 400
PP.. *
.rea for r«action
the
To
mmutes. The results are shomi ln Fl
2 1SUre3' W"h -»«tion temperature of
o c, lead „ of type B oii _ reduced ^ 4ao M ^^ ^
rd i-> a 52% uad redu"ion- - — - — -
cons_tly, tt can be lnf_d from pi_ 2 and 3 that
. u
demetallation. as seen in Figure 4.
stadies . n _ perf_d
o- « - « ppn, _r „ . 5%) ^ s m DAp
300 ml distillatlon
*llowed to continue
During the re8ctlo|
of, A ^^^ _i£ _ obtsiMd ^ ^
1 ead c°Ment
ords> a g^
ash „ of the
to
0- M se tHe In Run DF1
be
by flltratlon
14
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thus performed in which oil A alone, without adding any DAP, was heated in a
distillation flask for the same period of time as in Run DF1. The result was
that only a 3% lead reduction was obtained, indicating that DAP plays a very
.important role in demetallation. In addition, without DAP, the ash content of
the waste oil was not altered appreciably. In an attempt to reduce the DAP
charge, Run DPI was duplicated by Run DF3 except that the amount of DAP used
was cut from 8 to 2 wt%. Again, a similar lead reduction (97%) was obtained.
Effect of Reactor Configuration on Lead Reduction -- Table 12 shows that
satisfactory demetallation results under mild conditions can be obtained using
a distillation flask as a reactor. It should be noted that the reactor was
open to the atmosphere. To study the effect of the reactor configuration on
the demetallation performance, a tubing bomb microreactor (TBMR) was used as a
closed system reactor. The mass transfer effect for this type of reactor was
also studied. A detailed discussion of the experimental results is given
below.
As shown in Table 12, with 2 wt% DAP, 97% lead reduction could be
obtained (Run DF3). The reaction time for this run was 1 hr. To determine
the effect of the reactor configuration on lead removal, Run Dl was performed
in which 20 g of the same type of oil used in Run DF3 and 2 wt% DAP were
charged to a TBMR and reacted for 1 hr under a closed system. Only a 70% lead
reduction was obtained in Run Dl compared to 97% in Run DF3.
In Run D2, three steel balls (1/4" diameter) were added to the TBMR in
order to increase the mixing effect and interfacial contact area while
maintaining the rest of conditions the same as in Run Dl. The lead reduction
efficiency increased from 70 to 77%. When six steel balls were added in Run
D3, the lead reduction efficiency increased further to 81%.
To study the effect of water presence on lead reduction, Run D3 was
duplicated by D4 in which dry oil (obtained by distilling off water from Type
.-" _• . -- 15
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A oil) was used instead of wet oil (i.e. Type A oil). As shown in Table 13,
the lead reduction efficiency decreased from 81 to 78%. This difference was
attributed to a lower interfacial contact area available for the dry oil. It
-should be noted that this difference was small because of the excellent
dispersion obtained in this type of reactor; a much larger difference was
observed later, using a reactor (autoclave) that did not have as good particle
dispersion properties.
The inconsistent results (Table 12 & 13) obtained from the two types of
reactors (distillation flask and TBMR) may predominantly be due to the
difference in heat-up time; i.e. , for a 150°C demetallation run, the
distillation flask had a much longer heat-up time (75 min) than the TBMR (1
min). In other words, some demetallation may have occurred during the heat-
up.
To study heat-up effects, Run D5 was performed to duplicate Run 1 (see
Table 14). except that the TBMR was preheated in the fluidized sand bath (see
Figure 1) so that the total heat-up time from room temperature to 150°C was
about 75 min., (It should be noted that in a typical TBMR run, the sand bath
alone was preheated to 150°C before the TBMR was immersed; the heat-up time
was then about 1 minute.) Table 14 shows that, with the same heat-up time as
that for distillation (Table 12), a satisfactory result was obtained from Run
D5; i.e. 91% lead reduction could be achieved from a TBMR run. In comparison
with the lead reduction obtained from the distillation run, (91% versus 97%
lead reduction), this result was acceptable for a reactor with a different
configuration and mixing pattern.
As discussed above, with 75 minutes of preheating time and an additional
hour for reaction (i.e. total reaction time, 2 hr), 91% lead reaction could be
obtained in Run D5. It would be interesting to see what the lead reduction
efficiency would be with a 2 hr reaction time, 160°C reaction temperature and
16
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a regular TBMR 1 minute heat-up time. Run D8 was thus performed and the
results given in Table 14 show that about the same level of lead reduction as
Run D5 was obtained.
It was thus concluded that with a total reaction time of 2 hrs at 160°C,
a desirable demetallation result could be achieved for various types of
reactor configurations (distillation flask or tubing bomb microreactor). This
agreement is mostly due to the fact that thermodynamic equilibrium (=
complete lead removable) was achieved under these reaction conditions.
Since the distillation flask was used for the evaporation of water and
light components, so that the hydroxyl phosphate droplets could shrink to
facilitate removal of lead particulates, an open-type reactor such as a
distillation flask (Run DF3) may be more suitable for oil demetallation as
compared to a closed reactor, such as TBMR (Run D5).
To further evaluate the effectiveness of DAP demetallation with respect
to the configuration of the reactor used (i.e., the importance of mass
transfer), a certain amount of Type A oil (lead content - 660 ppm, water
content - 5 vol%) and 1.5-2.0 wt% DAP were reacted in 45 ml, 300 ml, and 3,785
ml (i.e., 1 gallon) autoclaves, at 160°C respectively. The 45 ml
microautoclave, as a matter of fact, was the TBMR (tubing bomb microreactor).
The results are given in Table 15.
One should note the main difference between a TBMR and a regular
autoclave in terms of agitation and heating; the former was vertically
agitated; whereas the latter was horizontally stirred. The mass transfer-
rates in the TBMR are generally better than those in the 300 ml and 3,785 ml
autoclaves [7,8]. Also, the heat-up time varied a great deal; for example,the
heat-up time for a TBMR heated by a preheated fluidized sand bath was about 1
minute, whereas, for a 300 ml or a 3785 ml autoclave (heated by a electrical
furnace from ambient temperature) the heat-up time was approximately 2 hours.
17
-------
Table IS shows that regardless ., the
lead .eduction was obtained uslng DAp as . demetalUng
reaction condition for a reaction ti»e of about 2 hours. The amount of
solid, produced was less than 1 «,, excluding the DAP added. These
observations^plied that DAP is nore suitable for use, oil destination than
sodium borohydride.
d earUer, Bater present at the early stage of .
de..taUation reaction can faciUtate lead removal by Mklng toe surfac.
contact area available for the DAP.
A co^arative study „ carried out using a l-gallon autoclave The
effect of Water on ash and !ead re»ova! TOS i»vestigat.d using the reaction
conditions given in Table 16. Dnlilte the earlier studies .ith a TEME (Table-
13). the dispersion of the DAP vas probably much less in this reactor (a
stirred autoclave) .
in Run AD!, wlth dry oil obtained by distillin, off water fro. Type A
oil, and 4 «. DAP, . 74%
the ash content of the product oil from this run was 0.310 «*
To discern the effect of water on the derailing perforce , Eu» ADI
- duplicated by AD2, except that a wet oil (i.e. , Type A oil, was used As
- "suit, 99.7% !ead reduction was achieved and the ash content of the product
oil was very low (0.020 «.,. ^ observed ^^^ ^ ^ ^^
efficiency that resulted with the addition of water was si.nific.ntly Urger
than that observed b.for. with a TBMH and was felt to be due to the difference
in the MSS transfer characteristics of th« reactors ; na»ely. the desre. to
which the DAP was dispersed.
operating cost and sludge generation and on. part of the top of th. autoclave
»as opened to vent water and the lights to facilitate lead removal In ,o
18
-------
doing, the lead reduction was 98.8% and ash content was 0.030 wt%. It should
be noted that for all the DAP runs, the sludge generation, excluding the DAP
added, was no more than 1 wt%. A duplicate run was done in AD4 and similar
results were obtained as evidenced in Table 17.
Examination of the demetallation results (Runs AD1-AD4) for Type A oil as
shown in Table 17 reveal that: 1) much better lead and ash removal could be
achieved when used oil contained a certain amount of water (apparently, the
water aids in dispersing the DAP during initial period of reaction); 2) total
metal contaminant content (i.e. ash content) was successfully reduced to an
acceptable level (< 0.1 wt%); 3) a good quality of product oil could be
produced with only 1.5 wt% diammonium phosphate (DAP) under mild reaction
conditions; and 4) reproducibility of the DAP demetallation experiment seemed
to be acceptable.
Other types of used oils (Type B & E) were also investigated using the
same operating conditions as Run ADS. The lead contents for Type B and Type E
oils were 480 ppm and 180 ppm, respectively and the ash contents were 0.52 wt%
and 0.65 wt%, respectively.
For Type B oil, a 96% lead reduction was obtained in Run ADS while a 99%
lead reduction was obtained for Type E oil in Run AD6. The ash content of the
product oil from both the runs was very low. Table 17 also shows that with
1.5 wt% DAP treatment, used oil (e.g. Type A, B, or E) seemed to be fairly
well demetallated.
Liquid-Solid Separation Studies -- The objective of these studies was to
evaluate the responses in terms of separation ease to the addition of filter
aid and the use of a diluent (No. 2 fuel oil). As has been done throughout
this work, both gravity sedimentation and filtration were studied for removing
solids.
Two DAP demetallation runs (Runs ADS and AD9) were performed in a 3785 ml
'.. ' .~^ 19
-------
autoclave to study the effects of.filter aid and diluent on the settling time
and filtration rates. The response of ash and lead content of the DAP-treated
oil to the settling time were obtained. The effects of dilution with No. 2
fuel oil on settling time and filtration rate were also studied. In Run ADS,
1 wt% filter aid (diatomaceous earth) was added to the reactor with 700 g of
Type A oil and 2 wt% DAP before the DAP reaction, whereas, in Run AD9, the
same amount of the filter aid was added after the DAP reaction.
Table 18 shows that an oil of better quality was obtained by adding 1 wt%
filter aid before the DAP demetallation (e.g. Run 8) if gravity sedimentation
was adopted; for example, in Run ADS, after 24 hour of settling at 60°C
without any diluents, the lead content of the product oil (i.e., top-layer
oil) was greatly reduced from 660 to 20 ppm (i.e., 97% lead reduction),
whereas, in Run 9, with the addition of 1 wt% filter aid after the DAP
reaction, the lead content of the product oil was reduced from 660 to 46 ppm
.(i.e., 93% lead reduction). A higher ash content for the product oil was also
obtained when the filter aid was added after the reaction (e.g., Run AD9) as
seen in Table 18. When filtration was used, both runs produced a similar oil
quality. In comparison with gravity sedimentation, the solids removal
efficiency with filtration was higher. However, with gravity sedimentation,
the product oil had acceptable ash and lead contents, and this method does
have its advantages in lower operation and maintenance costs.
With filtration a good solids-removing efficiency was obtained; however
the filtration rates were very low for DAP-treated used oil. In order to
evaluate the use of a diluent (No. 2 fuel oil) to improve filtration rates,
another DAP demetallation run was carried out in a 1000 ml distillation flask
under the reaction conditions shown in Table 12 (Run DF3). After the
reaction, the reaction product including spent DAP was evenly divided into
four fractions; a specified amount of filter aid or No. 2 fuel oil or both
20
-------
were thoroughly blended in three of the four fractions. Viscosity of each
fraction was first measured using a Cannon-Manning viscometer before
filtration (using the house vacuum). The filtration rate for each fraction
was determined, and so was the viscosity of the filtrate from each fraction.
The results showed that the viscosity of the product oil drastically decreased
from 90 to 33 cP at 25°C when diluted with 20% No. 2 fuel oil by weight of
total liquid as shown in Table 19 (No. 2 fuel oil has a viscosity of 3.5 cP at
25°C). The filtration rate, after dilution, approximately doubled (from 11.5
to 25.0 ml/min). With the addition of 1% by weight of the total liquid, the
filtration rate was further increased from 25.0 to 34.0 cm3/min; however, the
viscosity of the resulting liquid increased from 32.8 to 38.4 cP due to the
presence of extra solids (i.e., filter aid).
Conclusion
Used oil treated with NaBH4 aqueous solution (i.e., SWS solution) was
characterized by high sludge production and ash content. High sludge
production could be circumvented by substituting SWS solution with NaBH4 or
KBH4 powder. However, the lead reduction efficiency decreased. Demetallation
performance with metal borohydride treatment could be greatly improved by
distilling off water contained in the used oil before the reaction.
As for DAP demetallation, water present (about 5 wt%) during the early
stages of the demetallation reaction was found to be beneficial. This
beneficial effect was felt to be due to the additional interfacial contact
area available for DAP particles to react with oil. Overall, mass transfer
(DAP dispersion) was observed to be important; however, by extending the
reaction time (. 2 hr), even with mild reaction conditions, thermodynamic
equilibrium (. 100% lead removal) could be approached, thereby minimizing the
significance of any mass transfer related parameters.
In liquid/solid separation, a better quality of oil was obtained by
• : --~-t • 21 "
-------
filtration as compared to gravity sedimentation. (Nevertheless, an EPA
specification-grade oil was produced using gravity sedimentation.) The oil
filtration rate was doubled by dilution with 20 wt% of No. 2 fuel oil.
Acknowledgements
The authors would like to thank Morton Thiokol, Inc. for providing metal
borohydride chemicals. The information in this document has been funded in
part by the United Stated Environmental Protection Agency (EPA) under
cooperative agreement CR 812090 to Auburn University, it has been subjected
to the agency's peer and administrative review, and it has been approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
22
-------
References
[1] M.M. Johnson, "Reclaiming Used Oil by Chemical Treatment with
Ammonium Phosphate," U.S. Patent 3,879,282, 22 April 1975.
[2] Code of Federal Regulations, Title 40, Part 266.40.
[3] Process Stream Purification With Sodium Borohydride Technical Manual and
Users Guide, Morton Thiokol, Inc., Ventron Division.
[4] Metal Removal & Recovery With Sodium Borohydride, Morton Thiokol Inc
Ventrol Division. '
[5] Personal communication with Ventrol Division of Morton Thiokol, Inc.
[6] Miller, T.M., "An Investigation of the Demetallization Chemistry
Associated with the Re-refining of Used Motor Oil," M.S. Thesis, North
Carolina State University, Raleigh, N.C. (1983).
[7] "The Use of Disposable Catalysts in Coal Liquefaction Activities for Oil
Production", presented at the National AIChE Meeting, Houston, Texas
March, 1981. '
[8] Gollakota, S.R., "An Investigation of Mass Transfer Phenomena in Coal
Liquefaction: Assessment of Resistances and Reactor Types," Ph.D.
Dissertation, Auburn University, Auburn, AL (1984).
23
-------
Table I--Reaction conditions for typical TBMR runs
Demetallation reagent
Reaction temperature,°C
Heat-up time, sec
Reaction time, hr
Agitation rate, cpm
Metallic Borohydrides
110, 150
60
2.0
860
DAP
150-160
60
0.5-2.0
860
24
-------
Table 2--Demetallation results using metal borohydrides (for type B oil)
Run No.
-50% NaOH Added to
the Oila, wt%
SWS, wt%
NaBH4 Powder, wt%
Phase Transfer
Catalystb, wt%
After Reaction:
Sludge Production,
wt%
Product Oil Analysts:
Ash Content, wt%
Lead Content, ppm
Lead Reduction, %
1.2 1.2 0.8 0 0.8 0 0.8
0.65 0.65 0.43 0000
000 0.05 0.05 0.05 0.05
0 0 0 0 0 0.10.1
16
16 15
0.36 0.36 0.58 - 0.77 0.40 0.53
70 69 240 430 300 350 330
85.4 85.6 50.0 10.4 37.5 27.1 31.3
aOil charge - 20g Oil Type: B (lead content
water content — 1.8 vol%).
Tri-n-butyl-methyl ammonium chloride.
— 480 ppm, ash content «•> 0.52 wt%
25
-------
Table 3--Effect of oil type on demetallation
Run No. i
Oil Type B
Lead Content, ppm 480
Oil Charge, g 20
5% NaOH Added to
the Oil, wt% 1.2
SWS, wt% 0.65
Product Oil Analysis•
Ash Content, wt% 0.36
Lead Content, ppm 70
Lead Reduction, % 85.4
8
A
660
20
1.2
0.65
0.57
500
24.2
26
-------
Table 4--Demetallation results using metal borohydrides (for type A oil)
Run No.
50% NaOH. Added to the
oila, wt%
SWS, wt%
KBH4 Powder, wt%
NaBH4 Powder, wt%
Phase Transfer Catalystb,
wt%
8 9
1.2 1.2
0.65 1.3
0 0
0 0
10
1.8
0
0
0.15
11
1.8
0
0
0.15
12
1.8
0
0.15
0
0.10
0.35
Product Oil Analysis;
Ash Content, wt%
Lead Content, ppm
Lead Reduction, %
0.62
500 280
24.2 57.6
0.56
300
54.5
0.50
180
72.7
0.68
270
59.1
aOil charge - 20 g Oil Type: B (lead content - 660 ppm, ash content - 0 S9%
water content - 5 volume %) . •-=>•*,
Tri-n-butyl-methyl ammonium chloride.
27
-------
Run No.
Oil Type
Reaction Temp., °c
50% NaOH, wt%
SWS in the
oil, wt%
After.
Lead Content, ppm
Lead Reduction, %
0.65
Sludge Production, wt% 15.5
Product: Oil
70
85.4
. 0.65
100% (Gel)
400
16.7
B
110
1.2
B
150
1.2
B
150
1.2
0.65
100% (Gel)
28
-------
Table 6--Effect of caustic solution on gel formation
Run No.
Oil Type
50% NaOH in
the oil, wt%
SWS, wt%
NaBH4 Powder, wt%
15
Cotton Seed
Oila
•1.2
0.65
0
16
Cotton Seed
Oil
0
0.05
17
Cotton Seed
Oil
0
0
0.10
18
Motor
1.2
0.65
0
Oilb
After Reaction-
Sludge Production,
Vol%
29
-------
Table 7--Effect of NHjOH on sludge production
Run No.
50% NaOH, wt% 0.8
NH^OH, wt% 0
NaBH4 Powder, wt% 0.05
NH3, psig 0
Before Reaction:
Lead Content, ppm 480
Ash Content, wt% 0.52
After Reaction:
Sludge Production, wt% 4.3
Product Oil Analysis:
Ash Content, wt% 0.77
Lead Content, ppm 300
Lead Reduction, % 37.5
19
0
1.5
0.05
25
3.4
0.31
260
45.8
20
0
1.5
0.05
0
3.2
0.37
400
16.7
Note:
Oil type: B
Oil charge: 20 g
Reactor: 45 ml TBMR
Agitation: 860 cpm
30,
-------
Table 8--Properties of type oils used
Oil Type A B C D
Water content, vol.% 5.0 1.8 0 0
Ash content, wt.% 0.59 0.52 0.75 1.02
Lead Content, ppm 660 480 700 640
E
0.8
0.65
180
31 -•
-------
Table 9--Effect of water on demetallation with SWS
Run no.
Oila type
50% NaOH, wt%
SWS, wt%
Phase transfer
catalyst^,
wt%
9
A
1.2
1.3
21
C
-
0.90
22
C
-
0.40
23
C
-
0.90
24
C
-
0.25
25
D
-
0.35
26
D
.
0.^
0
Product Oil0 Analysis:
Ash content, wt% 0.62 0.53 0.68
Lead content, ppm 280 100 180
Lead reduction,% 57.6 85.7 74.3
^Oil charge - 20 g
Tri-n-butyl-methyl ammonium chloride.
cSludge production in all the runs was high (about 15-20 wt%).
0.1
0.63
120
82.9
0.1
0.77
300
57.1
0.93
280
56.3
0.69
220
65.6
-------
Table 10--Results from autoclave (3785 ml) runs using metallic borohydrides
Run No.
Atmospheric Distillation Conditions
used for oil preparation.;
AS2 AS3 AS4 ASS AS6
890 1000 1000 600 600 600
0.25 0.25 0.25 0.25 0.25 0 25
129 175 175 150 150 150
Type Aa oil charge, g
50% NaOH, wt%
Distillation cut'point, °C
Reaction Mixture:
Residue13 from distillation, g
SWS, wt%
NaBlfy Powder, wt%
KBH4 Powder, wt%
Phase transfer catalyst0, wt%
Product Oild Analysis:
Ash content, wt%
Lead content, wt%
Lead reduction, %
aWater content - 5.0%
Lead content - 660 ppm
Ash content - 0.59%
Lead content — 700 ppm
Ash'content - 0.86%
ctri-n-butyl-methyl ammonium chloride
dSludge production in all the runs was high (about 15-20 wt%).
890
0.90
0
0
0
0.74
440
37.1
900
0.91
0
0
0
0.50
25
96.4
900
0.46
0
0
0
0.51
420
40.0
545
0
0.10
0
0.20
0.57
440
37.1
545
0
0
0.10
0.20
0.56
345
50.7
545
0
0.15
0
0.20
0.53
200
71.4
33
-------
Table 11--.Reaction conditions for
Demetallation Reagent
Reaction Temperature, °G
Heat-Up Time, hr
Reaction Time, hr
Agitation Rate, rpm
Metallic Borohydrides
110
1.5
2
2000
DAP
160
2
1
2000
34
-------
Table
No.
Type A Oil3 charge, g
Water content in
the oil, vol %
Percent DAP added
Product mib Analvseg
Lead Content, ppm
Lead reduction, %
Ash content, wt%
DF2
60
5
0
640
3
0.47
18
97
0.06
DF3
60
5
2
DF1
60
5
8
24
96
0.02
aType A oil:
Lead Content - 660 ppm
Ash Content - 0.59 % (no filtration>>
Water Content - 5 vol% tiltration)
bReaction Conditions:
Reaction temp, °c
Heat-up time, min
Reaction time, ' hr - j_
Reaction Pressure -.Atmospheric
solids
75
35
-------
Table 13- -Effect of DAP dispersion (steel ball addition) for TBMR runs
Run NO. Dl D2 D3 D4
No. of Steel Balls Added 0 3 g 6a
Product Oilb Analyse-
Lead Content, ppm 200 153
Lead Reduction, % 70 77
TBMR Reaction Conditions:
127 156
81 78
Reaction Temperature 150°C
Reaction Time 1
Agitation 730 cpm
Type A oil charge 20 g
DAP added 2 wt%
aDry Oil (lead content - 700 ppm)
bLess than 1 wt% solids (excluding DAP added) was produced in all the runs
36
-------
Table 14--Effect of heating time and reaction
temperature on demetallation
Run No.
TBMR Reaction Conditions15!
Reaction Temp, °C
Heat -Up Time, min
Reaction Time, hr
Agitation, cpm
Product Oilc Analyses :
Lead Content , ppm
Lead Reduction, %
Dl
150
1
1
800
200
70
D5
150
75
1
800
62
91
D8
160
1
2
800
64
90
D9a
160
1
2
800
81
88
D10
200
1
1
800
76
88
aDry Oil (lead content - 700 ppm) was used.
bOil type: A
DAP charge: 2 wt%
No. of steel balls used: 0
cLess than 1 wt% solids (excluding DAP added) was produced in all the runs
37-
-------
Run No.
Autoclave Size, ml
Oil Charge3, g
DAP Added, wt%
Reaction Conditions:
Reaction Temp,°C
Heat-Up Time, hr
Reaction Time, hr
Reaction Pressure, psi
Agitation, rpm
Product Oilb Analysis:
Lead Content, ppm
Lead Reduction, %
Table 15--Effect of reactor configuration on demetallation
D8 AD7 AD2
45
20
2
160
0
2
N/A
800
64
90.0
300
60
2
160
2
1
150
2000
21
96.8
3,785 (1 ga
554
1.5
160
2
1
atmosphere
2000
2
99.7
used: type A
bLess than 1 wt% solids (excluding DAP added) was produced in all the runs,
38
-------
Table 16--Reaction conditions for autoclave (3785 ml) run using DAP
Temperature - 160°C
Heat-Up Time - 2 hr
Time - 1 hr
Agitation - 2000 rpm
39
-------
Table 17--Demetallation with DAP using autoclave (3785 ml)
Run Noa
Oil Type
Oil Charge, g
Percent DAP Added, %
Product Ollc Analyses :
Lead Content, ppm
Lead Reduction, %
Ash Content, wt%
ADI
A*.
541
4.0
180
74.3
0.310
AD2
A
554
4.0
0
100
0.020
ADS
A
554
1.5
0
100
0.030
AD4
A
554
1.5
2
99.7
0.026
ADS
£
554
1.5
18
96.3
0.016
AD6
E
554
1.5
2
98.9
0.036
AD7
A^
560
1.5
580
17.1
0.464
aRuns ADI And AD2: The autoclave was completely sealed.
Runs AD3-7: One port of the autoclave was intentionally opened
to allow the water vapor to escape in an effort to
simulate the distillation process.
bDry Oil: Lead Content - 700 ppm
cLess than 1 wt% solids (exlcuding DAP added) was produced in all runs
40
-------
Table IS--Effect of filter aid and/or diluent on oil quality
Run No.
I.-Sedimentation in 60°C:
Water bath for 24 hr
Oil only
Oil+1 wt% filter aid
Oil+20 wt% No. 2 fuel oil
Oil+1 wt% filter aid+
20 wt% No. 2 oil
II. Vacuum Filtration:
Oil only
Oil+1 wt% filter aid
Oil+20 wt% No. 2 fuel oil
Oil+1 wt% filter aid+20
wt% No. 2 fuel oil
AD 8
AD 9
Ash Content,
wt%
0.046
0.012
Pb Content,
ppm
20
10
0.012
0.008
0
0
Ash Content,
wt%
0.066
0.124
0.050
0.066
0.012
0.014
0.004
0.002
Pb Content,
ppm
52
46
36
32
4
6
2
4
41
-------
Table 19- -Effect of filter aid and diluent on
filtration rate and oil viscosity
Viscosity at 25°C Filtration Rate Filtrate Viscosity
(ml/min) at 25°C (cP)
Oil Only 89.9 11.5 87.7
Oil +
1 wt% Filter
Aid 95.5 12.0 87.3
Oil +
20 wt% No. 2
Fuel Oil 32.8 25.0 37.3
Oil +
20 wt% No. 2
Fuel Oil +
1 wt% Filter
Oil 38.4 34.0 37.6
42
-------
VARIABLE
SPEED
ELECTRIC
MOTOR
FLYWHEEL
&
PUSHROD
BEARING
TACHOMETER
AGITATOR SHAFT
M1CROREACTOR (TUBING BOMB)
FLUIDIZED SAND BATH
TEMPERATURE CONTROLLER
Schematic diagram of tubing bomb microreactor agitation assembly.
43
-------
240
200
E
\
o>
T3
O
O 8OO CPM
A 4OO CPM
00
Reaction Time, Min
Effect of reaction time and agitation rate on lead removal
44
-------
1
Q-
Q.
O
O
-o
O
Oil* Type B
Reactor Volume1 45 m£
DAP % in Oil* 8%
Water Added' 12%
30 45 60
Reaction Time, min.
75
Effect of reaction time on lead removal at various temperatures.
45 '
-------
o.
a.
a
------- |