I'/
United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S2-88/028 Nov. 1988
v°/EPA Project Summary
Ethylene Oxide Control
Technology Development for
Hospital Sterilizers
A. Meiners
Hospital sterilize heat-sensitive
items in gas sterilizers which use a
mixture of ethylene oxide (EO) (12
wt%) and a chlorofluorocarbon
(CFC), dichlorodifluoromethane (88
wt%). The active sterilizing agent is
EO. The CFC is added as a
flameproofing diluent
Articles to be sterilized are placed
in a sterilization chamber and
exposed to this mixture (referred to
as 12/88) until sterile, at which time
the gas is drawn from the chamber
by a vacuum pump and emitted to
the environment The sterile articles
are then placed in an aeration
camber where fresh air is continually
circulated to allow residual EO to
diffuse from them. This air (which
contains low concentrations of EO)
is also emitted to the environment
The potential sterilizer emission
control systems were tested,
catalytic oxidation and acid
hydrolysis. In catalytic oxidation,
relatively dilute mixtures of air and
EO (12/88) are passed through a
catalyst bed at 149-177°C. The EO is
oxidized to COj and water; the CFC
passes through unchanged. Field
tests showed that the EO destruction
efficiency of a system which had
been installed in a hospital was
greater than 99% of the EO that
reached the control system.
However, for sterilizers that use a
water jacket seal, 61-78% of the EO
was absorbed by the water of the
once-through, water-sealed
vacuum pump. The investigation
focused on the efficiency of the
control devices; therefore, other
system losses were outside its
scope. However, the potential for
release of EO to the environment
from the water should be considered
in any overall system design. There
was no detectable decomposition of
the CFC.
In acid hydrolysis, EO is
hydrolyzed to ethylene glycol using
sulfuric acid (the CFC is unaffected).
A full-scale system was tested
under laboratory conditions,
simulating a system that could be
used for hospital sterilizers. The tests
showed that the EO destruction
efficiency was 99.99-99.999% of the
EO reaching the control system.
However, 45 - 60% of the EO was
absorbed by the ethylene glycol used
in the closed-circuit, liquid-ring
vacuum pump. This requires a longer
sterilizer cycle to permit desorption
of the EO from the ethylene glycol
into the emission stream to the
control system.
In considering the relative costs of
these systems, the advantages and
limitations of each must be con-
sidered.
This Project, Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Ethylene oxide (EO) has been
identified as a major toxic air pollutant.
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EPA's Office of Air Quality Planning and
Standards (OAQSP) designated EO as
an Intent to List Compound in the
Federal Register in early 1986. One of
the major uncontrolled sources of EO
emissions is hospital and clinic
sterilizers. More than 400 Mg/yr of EO is
estimated to be released to the
atmosphere each year from these
sources.
In the program to identify, develop,
and evaluate viable control options for
EO emissions from medical facility
equipment: Phase I (Work Assignment 5)
identified three potential devices for the
control of EO emissions from hospital
and clinical sources, and Phase II (Work
Assignment 10) involved tests of se-
lected technologies identified in Phase I.
Phase I - Potential Control
Systems
Hospital Sterilizers
Almost all hospitals sterilize heat-
sensitive items in gas sterilizers which
use a mixture of ethylene oxide (EO) and
a chlorofluorocarbon (CFG), dichloro-
difluoromethane. The active sterilizing
agent is EO. The CFC is a flameproofing
diluent. This mixture, 12% by weight EO
and 88% by weight CFC, is referred to
as 12/88.
Hospital sterilizers are essentially
enclosed chambers which can be
pressurized with 12/88 to sterilize
medical equipment. At the conclusion of
the sterilization phase, the chamber is
evacuated by a vacuum pump and
brought to atmospheric pressure by
introducing clean, filtered air. The
combination of evacuation and air flushes
is repeated. After the last air wash, the
chamber door is opened, and the sterile
products are removed and placed in an
aeration cabinet. Aeration allows residual
EO to diffuse out of the sterilized articles.
Ethylene Oxide Emissions
In the absence of control systems, EO
emissions come primarily from four
sources: the camber vacuum pump (75-
95% of the total emission), the aeration
cabinet (5-25%), the sterilizer door area
(varies widely), and the EO storage tanks
(from accidental leaks). If the vacuum
pump is a once-through, water-sealed
pump, substantial quantities of EO (60-
80% of the total emission) can be
discharged to the sewer in the vacuum
pump water.
Potential Control Technologies
The chemical reactions of EO and the
CFC were reviewed to evaluate sterilizer
emission control options. Catalytic
oxidation and acid hydrolysis were
shown to be especially suitable. The
following selection criteria were
developed for EO control technology
options (in order of priority): (1) cost, (2)
effectiveness and environmental safety,
(3) state of development, (4) complexity,
(5) space requirements, and (6) safety.
Nine potential control options were
examined. Six options were eliminated
for the following reasons: carbon
adsoption (high operating cost), thermal
incineration (toxic by-product),
condensation (explosion hazard),
ozonation (high cost), corona discharge
(toxic by-product), and ultraviolet
photolysis (toxic by-product).
1. Catalytic Oxidation
A control system has been developed
in which relatively dilute mixtures of air
and EO (12/88) are passed through a
catalyst bed at 149-177°C. The EO is
oxidized to COg and water; the CFC
passes through unchanged. The system
is characterized by relatively high flow
rates (14,000-28,000 L/min-- or
500-1000 cfm- and relatively dilute
concentrations of EO (5-500 ppm). The
system treats EO emissions in both the
sterilizer exhaust and the ventilation air
from the aeration cabinets and other
areas. The system has had 2 years of
apparently trouble-free operation at a
hospital in Philadelphia. The unit is
claimed to be 99.9 efficient in controlling
EO.
2. Acid Hydrolysis
Another control system has been
developed which consists of a counter-
current packed column in which EO (in
12/88) is hydrolyzed to ethylene glycol
using sulfuric acid at pH 1 (the CFC is
unaffected). The system is characterized
by relatively high concentrations of EO
(250,000 ppm) and very low and highly
variable flow rates, 2.8-42.5 L/min
(0.1-1.5 cfm). Many industrial-sized
units have been installed, and test data
on these units show that they are 99 + %
efficient. A hospital system was installed
in March 1987. Another type of acid
hydrolysis system has been developed
in which EO is bubbled through diffusers
into aqueous sulfuric acid. A unit of this
kind has been designed for hospitals and
is claimed to be 99.2% efficient.
3. Adsorption/Reaction
Some exploratory work has been done
on a proprietary process which uses a
combination of adsorption and reaction
The process is in the developmenta
stage and is not ready for full-scak
application.
Phase II - Control System
Evaluation
Two potential control technologies
catalytic oxidation and acid hydrolysi;
were selected for testing. Both system;
demonstrated very high efficiencie;
(99 + %) in destroying EO emission;
discharged from hospital sterilizers
However, only the catalytic oxidatior
system can treat EO emissions frorr
hospital aerators, which typically accoun
for 5-10% of all EO emitted.
Field Tests of Catalytic
Oxidation
Field tests were performed to measure
the EO destruction efficiency of <
catalytic oxidation system which hac
been installed in a hospital. This systerr
handled emissions from the sterilizei
vacuum pump, an aeration cabinet, the
sterilizer door area, and the EO storage
tank area. Two types of experiments
were performed: one involved the
treatment of the sterilizer discharge; anc
in the other, sterilizer gas was addec
directly to the system.
In the sterilizer discharge experiments
the observed EO destruction efficiency
was high, 99 + %. As expected for thi;
type of system, the concentration of EC
entering the catalyst system variec
widely, reaching a maximum of 400-45C
ppm. Flow rates were about 14,000 L/mir
(500 cfm).
In the sterilizer discharge experiments
only about 10-13% of the EO in the
sterilizer actually reached the catalys
system. A major fraction of the EO was
absorbed by the water which was used ir
the once-through, water-sealec
vacuum pump. Analysis of the aqueous
discharge indicated that an unexpectedly
large proportion of the EO in the sterilizei
(61-78%) was discharged to the sewei
in the water from the vaccum pump.
Additional experiments were
performed to supplement the analytica
data obtained during sterilizer discharge
EO was added (at a controlled rate) tc
the system at a point upstream from the
catalyst. Sufficient EO was added tc
bring the concentration of the stream tc
selected levels of EO. Three levels
125-250, 400-600, and 750-150C
ppm were tested. The results of these
experiments indicated high catalys
efficiencies, 99.8% or better.
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Of importance is that the EO addition
experiments demonstrated that the
catalytic oxidation system was capable of
operating very efficiently at con-
centrations of sterilizer gases
comparable to those developed if the
total discharge from the sterilizer were
directed into the system.
All of the tests were performed using
the common sterilizing gas mixture
(12/88) which is 12% ethylene oxide and
88% CFC. Separate tests demonstrated
that there was no detectable
decomposition of the CFC under the
conditions of the catalytic oxidation.
Laboratory Tests of Acid
Hydrolysis
A full-scale acid hydrolysis system
was tested under laboratory conditions
which closely simulated a system that
could be used for hospital sterilizers.
This system handled only the discharge
from the vacuum pump (it was not
designed to handle aeration discharges
or other airflows containing low
concentrations of EO). The tests
demonstrated that the system was very
efficient, destroying 99.99-99.999% of
the EO that entered the control system.
Four tests involved actual discharges
from a hospital-type sterilizer, and three
tests involved the direct addition of EO
(12/88). In the sterilizer discharge
studies, only about 25-26% of the EO in
the sterilizer was observed to reach the
system. Evidence indicated that most of
the EO was absorbed by the ethylene
glycol used in the closed-circuit,
liquid-ring vacuum pump, thus reducing
the amount of EO reaching the system.
The concentrations of EO reaching the
system were 20,000-140,000 ppm (2-
14%) and the flow rates were 2.8-42.5
L/min (0.1-1.5 scfm).
Of the EO reaching the system, more
than 99.99% was removed from the
gaseous stream.
Ethylene oxide (12/88) was also
added directly to the system to
determine efficiencies at levels of flow
rate near the maximum for which the
system was designed. 70.8 L/min (2.5
cfm). These studies also demonstrated
the high efficiency of the hydrolysis
system, 99.999 + %.
Cost Effectiveness
Table 1 shows the estimated costs for
the two potential control technologies,
catalytic oxidation and acid hydrolysis.
In considering the relative costs of
these systems, the advantages and
limitations of each should be considered.
The catalytic oxidation system is capable
of treating all of the gaseous EO
emissions from the sterilizer vacuum
pump, the aeration cabinets, the sterilizer
door area, the EO storage tanks, and any
other areas that can be ventilated.
However, there are EO emission
problems related to the relatively large
amounts of EO (60-80% of sterilizer
charge) which can be lost to the
environment through the aqueous
discharge from once-through, water-
sealed vacuum pumps. Recirculating
vacuum pumps may prevent this
emission, but most hospital sterilizers are
apparently not currently equipped with
recirculating vacuum pumps. (Installation
of recirculating vacuum pumps will result
in costs nearer the high side of the above
capital cost estimates.) Furthermore,
even with recirculating vacuum pumps,
the substantial absorption of EO into the
recirculating fluid produces a potential
emissions problem.
The present acid hydrolysis system
can treat only the direct discharge from
the sterilizer (through the vacuum pump).
EO emissions from the aeration cabinets,
sterilizer door area, and other dilute
emissions could probably not be handled
efficiently by the acid hydrolysis
systems. Recirculating vacuum pumps
would ordinarily be used with acid
hydrolysis systems; this would eliminate
an immediate discharge of EO-
contaminated sealant liquid, but methods
of disposing of the contaminated sealant
liquid would need to be devised.
As Table 2 shows, the catalytic
oxidation system has a greater overall
EO destruction efficiency than the acid
hydrolysis system. This is primarily
because the acid hydrolysis system
cannot treat discharges from the aeration
chamber or other dilute sources.
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Table 1. Estimated Costs for Catalytic Oxidation and Acid Hydrolysis
Catalytic Acid
Oxidation Hydrolysis
Capital costs
Equipment $25,000-$40,000 $15,000-320,000
Installation 5,000-10,000 4,000-6,000
Total equipment cost $30,000-$50,000 $19,000-$26,000
Annual operating cost $5,700-$16,000 $600-56,000
Table 2. Comparison of System Efficiencies
Emission
reduction potential*1
EO source
Sterilizer^
Aerator
Sterilizer room ventilation air
Total reduction potential
percentage
of total EO
emissions3
75-95
5-25
<1
Catalytic
oxidation
(%)
99.5 +
99.5 +
99.5 +
99.5 +
Acid
hydrolysis
("/')
99.9 +
0.0
0.0
75-95
*The estimated percentages of total EO emissions were developed in Phase I of
this program.
bTrte catalytic oxidation system has a greater overall EO emission reduction
potential primarily because the acid hydrolysis system cannot treat the
discharge from the aerator or other dilute sources.
cln these sterilizer discharge experiments, about 75% of the EO from the
sterilizer wasabsorbed by the vacuum pump fluids and did not reach the
control systems. However, other experiments demonstrated that the control
systems were capable of handling the full discharge of the sterilizer The
efficiencies indicated for both types of control devices are based on the
assumption that the vacuum pump fluids are not discharged.
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U
A. Meiners is with Midwest Research Institute, 425 Volker Blvd., Kansas City,
MO 64110.
Charles H. Dan/in is the EPA Project Officer (see below).
The complete report, entitled "Ethylene Oxide Control Technology Development
for Hospital Sterilizers," (Order No. PB 88-211 792/AS; Cost: $19.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-88/028
•000C329 PS
230 S OfARBORW STREET
CHICAGO IL 60604
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