US3549312A - Process and apparatus for recovering sterilization gas for reuse - Google Patents

Description

R. R. ERNST Dec. 22, 1970 PROCESS AND APPARATUS FOR RECOVERING STERILIZING` GAS FOR REUSE Filed May 6, 1968 Mm @QM ATTORNEY United States Patent O 3,549,312 PROCESS AND APPARATUS FOR RECOVERING STERILIZATION GAS FOR REUSE Robert R. Ernst, Rochester, N.Y., assignor to Sybron Corporation, a corporation of New York Filed May 6, 1968, Ser. No. 726,974 Int. Cl. A611 3/00, 13/ 00 U.S. Cl. 21-58 9 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus for sterilizing an object (eg. material and/ or equipment) with a gaseous sterilizing agent wherein the gaseous sterilizing agent (e.g., an alkylene oxide) is recovered from the sterilizing chamber for reuse in subsequent sterilizing operations.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to vapor sterilization and in particular to a sterilizing process using volatile alkylene oxides which includes recovering the gaseous alkylene oxide and mixtures thereof for reuse in a subsequent sterilizing operation.

Description of the prior art The term sterilant as used in this application means a sterilizing agent capable of completely inactivating or destroying the viability of all types of micro-organisms and insects and their eggs and larvae contained on or in 'inanimate objects. A volatile sterilant is one that acts chieily in the vapor state.

Steam sterilization at high temperature is a conventional gas sterilization treatment, but certain pieces of equipment that are used in hospitals are deleteriously affected, or are attacked, by steam; and consequently sterilization of these articles with steam is either not practical, or not entirely satisfactory. For example, the high heat of steam sterilization attacks, and may destroy, materials such as plastics, rubber, waxes, certain adhesives, and many drugs. Then, too, the high moisture content of steam causes tarnishing, dulling, and rusting, of surgical instruments, knives and other metallic surgical instruments. Steam too, is not suitable for sterilizing such articles as temperature gauges that are affected by heat. In some instances, too, it is diflicult to make certain goods bacteriologically safe with steam, as, for instance, tubing for intravenous Work. Here the inside of the tubing may not be reached to the required degree Iby the steam.

For these reasons, in recent years attempts have been made to develop processes and equipment for effective sterilization through the use of non-corrosive gases that are effective at ordinary temperatures or at temperatures below the temperature at which steam is effective.

Ethylene oxide has many desirable characteristics as a sterilizing agent. For example, it is non-corrosive and does not damage the substance or equipment being sterilized. It is usable at low temperature. Moreover, it is destructive to all forms of organisms; and it has a relatively rapid action. Furthermore, after it has been used, it can be removed by aerating the sterile material.

However, the use of ethylene oxide as a sterilizing agent is subject to several disadvantages. For example, ethylene oxide is quite flammable and explosive when mixed with air in certain proportions. Some measure of relief has been obtained from the explosive and flammability characteristics of ethylene oxide by diluting it with carbon dioxide, Freons, Ucons, or chemically similar inert compounds, to render the mixture inert, and storing ICC it as a liquid solution under high pressure and/or low temperature. Other non-flammable, mutually non-reactive diluents are known for combining with ethylene oxide such that the mixture is non-flammable and non-explosive. One of the principal disadvantages of using inerted ethylene oxide as a vapor sterilizing agent is its high cost.

It is a primary object of the present invention to reduce the cost of sterilizing processes using a gaseous alkylene oxide as the vapor sterilizing agent.

It is another object of the present invention to provide a sterilizing process which uses gaseous ethylene oxide and mixtures thereof as the sterilizing agent and which recovers such mixtures for reuse in the sterilizing process.

It is a further object of the present invention to remove the sterilant mixture from a sterilizer, to separate air and moisture from it, and to condense it for reuse.

SUMMARY OF THE PRESENT INVENTION In the process of sterilizing material and equipment to produce biocidal action using volatile alkylene oxide sterilants which have preferably been rendered non-Hammable and non-explosive, the improvement comprising removing the gaseous sterilizing mixture from the sterilizing chamber, separating air and moisture from the mixture, condensing it to the liquid state, and storing the recovered sterilant mixture in a liquid sterilant reservoir for reuse in the process whereby the cost of the process is reduced.

BRIEF DESCRIPTION OF THE DRAWING These and other objects and advantages of the present lnvention will be more fully understood by reference to the attached drawing in which like reference numerals refer to like elements, and in which:

The figure is a schematic iiow diagram of the process and apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Conventional gas sterilization treatment processes wherein the used sterilant mixture is discharged into the atmosphere are old and well-known as disclosed for example in U.S. Pat. No. 3,068,064, issued Dec. 11, 1962, to Robert L. McDonald, and assigned to the same assignee as 1s the subject application. Such processes therefore need not be described in detail here.

The figure illustrates the preferred embodiment of the present invention wherein a sterilant mixture comprising 12% by weight ethylene oxide in Freon 12 dichlorodifluoromethane is removed from a sterilizing chamber 10, condensed, and fed to a sterilant supply reservoir 12 for reuse in the sterilizing chamber 10. An object (such as some material or a piece of equipment) is positioned in the chamber 10 and sterilized by supplying a gaseous sterilizing agent thereto from the reservoir 12 through a valve 13, 'feed line 14, a gas metering unit 16, a heat exchanger 18, and a valve 20, as is well known in the art. However, according to the prior art the gaseous sterilant mixture when then pumped out and discharged to atmosphere from chamber 10 through, for example, a pump 21 and a valve 22 before opening up the chamber to remove the sterilized subject. As described above this is an expensive procedure because of the total loss of the expensive sterilant mixture.

According to the present invention this disadvantage is eliminated by recovering the gaseous sterilizing agent, which can be pure sterilizing gas but which is preferably a sterilant mixture, from chamber 10 for reuse in subsequent sterilizing operations. This is accomplished by opening a valve 23 in a line 26 connected to the bottom of the chamber 10 to feed the gaseous sterilizing agent out of chamber 10 to a cooler 24 by means of a pump 28.

Alternatively the pump can be positioned as a vacuum pump to exhaust the condenser (infra). At the same time that Valve 23 is opened (valve 20 is of course closed), a vent valve 30 connected to vent line 31 adjacent the top of chamber is preferably opened to replace the gaseous sterilizing agent which has been removed from `the sterilizer 10 through line26 with air or some other lower density gas; a filter is preferably positioned in line 31 to allow for the admission of sterile air. The gaseous sterilizing agent is effectively removed from chamber 10 by taking advantage of the fact that it hasa density about four times greater than that of air whereby it-can be pumped out of the sterilizing chamber 10 near the bottom thereof While air is allowed to enter at the top thereof without any substantial mixing therebetween due to the stratification that occurs between the two different density gas phases.

The gaseous sterilant mixture flows from the preliminary cooler 24 to a drier 32 where excess moisture is removed therefrom. The dryer can be one ofthe type which uses a moisture absorbent material such as calcium chloride arranged, for example, in a column; this type of dryer also provides `a visual color change when the effectiveness of the material has terminated. Since the primary function of the cooler is to condense out moisture, which function is also served by the dryer, it is possible to eliminate the cooler from the system. The gas then flows to a main condenser 36 (flow rate being measured by means of a rotometer 34), where it is liquified by means of a plurality of cooling coils supplied with a refrigerant from a refrigeration unit 38. A non-return valve (not shown) `is Vpreferablypositioned downstream from the rotometer 34 to `prevent ow from the line 44 to the rotometer 34. Connected to the bottom of the main condenser 36 is a collecting tank 40 for collecting the liquified sterilizing agent which drains by gravity into the tank. r .t

Itfshould be notedthat it is not absolutely necessary tovhave a pump to move the gases vsince the condensing process will keep the gases flowing. However, if airis present in the system a vacuum pump can be used to remove air from the condenser. The condenser will have residual sterilant mixture vapor therein at all times and possibly will remain underfvacuum `when the refrigeration unit ison. The condenser will probably befunder ethylene oxide- Freon-12 pressure when the refrigeration unit` is off. The air in the condenser will be displaced by the sterilant mixture and will be removed by means of Va pressure controlled safety valve 41 connectedto the condenser 36 the reservoir 12. At this timea valve 42 in a pressure equalizing line 44 and a valve 46 in a-drain line-47 are opened. At this time the liquid which has been collected in tank 40 will drain into the reservoir 12. As shown in the ligure, the drain line 47 is connected to thepressure equalizer line 44 for draining liquidfrom the tank 40 into thereservoir 12, however, the drain line 47 can alternatifely be connected directly to the reservoir 12.

A float control 48 maintains the liquid level in the'reservoir 12 ata predetermined height. If the liquid level falls below said predetermined height the float control 48 will open a solenoid control valve 50 whereby a fresh supply of the liquid sterilant mixture enters the reservoir 12 from a sterilant mixture supply cylinder 52 via line 54. The sterilant mixture in cylinder52 at room temperature (75 F.) isgunder a pressure of about 70 p.s.i.g. The sterilant mixture thus feeds from the. cylinder 52 to the reservoir 12 under its own pressure when the pressure in 75 thereservoir 12 is reduced, such as when the operating temperature of the reservoir 12 is below room temperature due to the low temperature of the liquid returning to the reservoir 12 from the main condenser 36, and/or when the reservoir 12 pressure is otherwise reduced, such `as when the sterilizer 10 is being filled. The valve 50 is preferably a unidirectional valve permitting flow only from the cylinder 52 to the reservoir 12. Cylinder 52 is provided with an internal tube which opens adjacent the bottom of the cylinder 52.

Also connected to the reservoir 12 is an inert gas (in the preferred embodiment, Freon-12) supply cylinder 56, `by means of a line 58 and a pressure controlled solenoid valve 60. The inert gas is also under its own vapor pressure and it feeds as a liquid to reservoir 12 when the vapor pressure in the reservoir falls below a pre-set level. The vapor pressure of Freon-12 is always higher, at the same temperature, than that of the mixture in the reservoid. When the vapor pressure in the reservoir falls below an expected pressure level, for example for a 10% ethylene oxide-% Freon-l2 mixture,which it is desired to maintain in the reservoir, this indicates an ethylene oxide rich mixture. The pre-set pressure controlled switch 60 at such time places the Freon-12 make-up supply cylinder on demand until the Vapor pressure in the reservoir increases up to the desired range. The make-up supply cylinder 56 helps to maintain the proper mixture range of inerted ethylene oxide and prevents flammable mixtures from occurring.

In addition to the above described connection to reservoir 12 of the make-up supply cylinder 56 through pres- `sure controlled valve 60, the reservoir also is provided with a line 61 and a solenoid, pressurecontrol vent valve 62 which is set to open at a predetermined pressure. The valve 60 determines the lower end and valve 62 determines the upper end of the pressure range under which the vapor in the reservoir is maintained. Inv the preferred embodiment (l0-12% mixture of ethylene oxide in Freon- 12), this pressure range is below 70 p.s.i.g.

In the preferred embodiment the commercial mixture contained in the sterilant mixture supply cylinder 52 is a 12% by Weight mixture (27.3% molar) of ethylene oxide in Freon-12 (dichlorofluoromethane). A 10-l2% mixture can be maintained in reservoir 12 from the 12% supply cylinder. By keeping the solenoid, pressure control vent valve 62 set to open at a predetermined pressure, and by maintaining the temperature in the reservoir 12 within well defined limits (70 F. i5 F. in this embodiment) the liquid in the reservoircan be kept within the 10-l2% ethylene oxide range. The sterilizing agent can then be supplied to the sterilizer 10 directly from the reservoir 12 upon demand. The efficiency of this system is estimated to bein excess of 90%. The temperature can be maintained by means of a temperature controller 63, such. as a `water jacket or externalstrip heaters with insulation. The valve 62 vents pre-condensed air and serves as a safety valve. Also, the object(s) (eg. material and/or equipment) being sterilized may preferentially absorb ethylene oxide thus leaving excess Frech-12 to be condensed. Subsequently, the excess Freon-12 will provide an excessive vapor pressure, above that expected for the designated 12% mixture. Thus, the valve 62 will open under the excess pressure and vent the excess Freon-12.

The process of the subject invention is applicable for use with sterilizing agents such asi ethylene oxide and inerted ethylene oxide and with otherV sterilants than ethylene oxide; for example, other alkylene oxide sterilants such as propylene oxide can also be used. The used sterilizing agent which is recovered for` reuse according to the present invention is preferably condensed back to its liquid state but can be recovered and reused, all while still in the gas state. The process is preferably a batch process but a continuous process of sterilizing, recovering, and reusing is also possible. The system of the present invention reduces the high cost usually associated with gaseous sterilization processes. ln the case of ethylene oxide, the present invention makes the use of the safe non-hazardous mixtures thereof comparable in cost to the use of the less expensive explosive, flammable 100% ethylene oxide. This is especially true since the use of the ammable explosive gases require higher insurance costs and very high capital cost for explosion-proof components and isolated, make-safe quarters. V

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim: 1. A process for sterilizing an object with a gaseous sterilizing agent comprising an inerted mixture of alkylene oxide, said process comprising:

exposing an object to be sterilized to said gaseous sterilizing agent,

recovering said gaseous sterilizing agent for reuse, and

condensing said recovered sterilizing agent to its liquid state.

2. A process for sterilizing an object with a gaseous sterilizing agent comprising an inerted mixture of ethylene oxide, said process comprising:

exposing an object to be sterilized to said gaseous sterilizing agent,

recovering said gaseous sterilizing agent for reuse, and

condensing said recovered sterilizing agent to its liquid state. p

3. The process according to claim 2 including the step of:

feeding the condensed, liquid sterilizing agent to a liquid sterilizing agent supply reservoir.

4. The process according to claim 3 including the step of:

controlling the percentage range of said ethylene oxide in said inerted mixture.

5. The process according to claim 4 wherein said controlling step comprises:

introducing a fresh supply of said inerted sterilizing mixture to said reservoir when the liquid level in said reservoir falls below a predetermined level, and introducing into said reservoir, when the vapor pressure in said reservoir falls below a predetermined value, suflicient gas to raise said pressure back up to another predetermined Value, said introduced gas comprising the inert gas of said inerted mixture.

6. In a process for sterilizing an object with gaseous ethylene oxide, the improvement comprising:

recovering said ethylene oxide for reuse,

condensing the recovered ethylene oxide to its liquid state, and

feeding the condensed ethylene oxide to a supply reservoir.

7. A process for sterilizing an object with a sterilizing agent in its vapor state comprising an inerted mixture of ethylene oxide comprising the steps of:

storing said sterilizing agent in the liquid state in a supply reservoir;

vaporizing a quantity of said sterilizing agent;

sterilizing an object with said vaporized sterilizing agent;

condensing the resulting used vaporized sterilizing agent back into its liquid state; and

returning said condensed sterilizing agent to said reservoir.

8. A vapor sterilizing apparatus comprising:

a sterilizing chamber;

a reservoir adapted to contain a liquid sterilizing agent comprising a mixture of a sterilant in an inert substance in a predetermined percentage range of sterilant to inert substance;

means for feeding said sterilizing agent from said reservoir to said sterilizing chamber in its vapor state including means for vaporizing said liquid sterilizing agent;

means for removing said vaporous sterilizing agent from said sterilizing chamber;

means for condensing said vaporous sterilizing agent removed from said chamber back into its liquid state;

means for feeding said condensed sterilizing agent to said reservoir; and

means for maintaining said mixture in said reservoir at substantially said predetermined percentage range.

9. The apparatus according to claim 8 wherein said maintaining means comprises:

means for maintaining the temperature of said reservoir within a predetermined temperature range, and means for maintaining the pressure within said reservoir within a predetermined pressure range.

References Cited UNITED STATES PATENTS 2,131,134 9/1938 Baer et al. 21-58 2,526,974 10/ 1950 Schiponski 21-94UX 3,042,533 7/ 1962 McConnell et al. 21-58X 3,068,064 11/ 1962 McDonald 21-58 3,088,179 5/1963 Leuthner 1 21--58X 3,107,975 10/1963 Linder 21-94 3,341,280 9/1967 Bolkin 21-58 3,361,517 1/1968 Skaller 21-94X 3,372,980 3/1968 Satas 21-58 MORRIS O. WOLK, Primary Examiner B. S. RICHMAN, Assistant Examiner

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