JPH0557125A - Cooling method for purging and recovering cooling agent - Google Patents

Abstract

PURPOSE: To prevent emission of refrigerant into the air by purging a mixture of refrigerant and air, and recovering the refrigerant by treating the purged gas by film-separation process. CONSTITUTION: When a high content refrigerant is contained in the purge gas and in high pressure, the gas flow is cooled. The cooling cycle 1 is a single gaseous cycle, region of the high pressure refrigerant gas 3 is produced by the compressor 2, the gas is sent to the heat exchanging zone 4, after heat exchange, the gas is compressed to form a high pressure liq. zone 5. Otherwise refrigerant is sent to a low pressure liq. zone 7 through expansion valve 6. Then heat exchange between substances to be cooled and refrigerant in zone 8, the low pressure gases are recompressed in zone 9. The high pressure purged flow 12 is derived from cooling cycle, and compressed in concentrator 13. Then the purged flow is passed through film unit 16, the refrigerant is recovered. Thus the purge of refrigerant into air is prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cooling method. In particular, the present invention relates to a cooling method in which a cooling agent / air mixture is purged from a cooling cycle and treated by a membrane separation process to recover the cooling agent and control atmospheric pollution.

[0002]

BACKGROUND OF THE INVENTION Cooling is accomplished using mechanical or heat activated equipment for the purpose of cooling.
Cooling is usually done in a reverse Carnot cycle by using a liquid that evaporates and concentrates at a suitable pressure and temperature as a coolant so that practical equipment can be manufactured. In the gas compression cooling cycle,
As a typical example, the gas is compressed, then cooled by air or water to be concentrated, and then expanded through an expansion valve to a low pressure and a correspondingly low temperature. Cooling is effected by subsequently evaporating this coolant. In the absorption cooling cycle, cooling can be performed even if the high pressure gas is expanded into the low pressure region. The low-pressure gas thus obtained is absorbed in water and then separated at high pressure from the water by a separator.

Many liquids are known which can be used as coolants under suitable conditions. Coolants are generally divided into three groups by their toxicity and flammability. The third group of coolants is highly toxic and flammable, so that for example such coolants are obtained in situ as a chemical process product and the risk of their presence is not exacerbated by their use. It is used only in a variety of environments. Examples of such coolants include hydrocarbons such as methane, propane and butane. The second group of coolants has little toxicity and flammability, for example:
Ammonia, which is widely used, and sulfur dioxide are also included. The first group of coolants are non-toxic and non-flammable, and thus they are widely used for most widespread cooling purposes. Many of the first group of coolants are halogenated hydrocarbons that contain one or more chlorine, fluorine or bromine atoms in their structure. For example, industrial chillers use large amounts of CFC-12 and other chlorofluorocarbons (CFCs). And although they are non-toxic and non-flammable, they are now believed to cause serious environmental damage.

Cooling can be done as either a closed cycle or an open cycle. Open cycle operations are used in most chemical method industries. This method
There is the advantage of creating in a chemical process a product that can also be used as a cooling agent. For example, the natural liquid gas removed by cooling and compressing the natural feed gas can be expanded in a refrigeration cycle to lower the temperature of the feed gas and recover heavier hydrocarbons. The product stream to the cooled ammonia storage tank is used in the ammonia synthesis plant.

In most other industrial applications,
A closed cycle refrigerator is used. The coolant is substantially enclosed in a closed loop, where the coolant circulates from high pressure gas to high pressure liquid, low pressure liquid, low pressure gas. The low pressure vaporization portion of the system may be at atmospheric pressure or at a pressure below atmospheric pressure, depending on the thermodynamic properties of the coolant and the cooling temperature. For practical reasons,
Cooling systems that use CFC coolants are often operated at evaporation pressures as low as 2-5 psia.

Since most of the cooling system is at subatmospheric pressure, air enters from the low pressure side. Air ingress is almost unavoidable during the large industrial refrigeration period and therefore air contaminated with gaseous coolant must be regularly purged from the system. In the conventional purge system, the gas flow containing the coolant and air was taken out from the high pressure side of the cycle. This gas stream is maintained at a high purge pressure to eliminate the coolant loss and then, for example, -5
Cool to 0 ° F or below. Cryogenic coolants can be conveniently used to provide this cooling. Under these conditions, the volume of coolant contained in this gas stream is concentrated and returned to the chiller. The rest is released into the atmosphere. The frequency and degree of performing this purging operation may be determined from the energy and economical aspects. If the air content in the loop is kept increasing over a long period of time, the partial pressure of air in the system will increase. As a result, the total compressor pressure required to maintain the refrigerant partial pressure at an appropriate level is higher, and the energy consumption and cost are correspondingly increased.

The air content in the cooling system can be kept at a constant low level by performing continuous purging.
For example, when the purge gas is cooled, 90% or more of the coolant can be recovered from the purge stream by concentration. Still, the air released into the environment contains as much as 15% coolant. Operating the purge gas treatment concentrator under pressure and temperature conditions with substantially no loss of coolant puts an excessive heavy load on the concentrator, consumes excess energy, and is economically infeasible. Become. The need to severely curb or ban CFC emissions into the atmosphere has been recognized around the world and has become a subject of ever more pressing legislation. CFC coolants are becoming increasingly expensive in addition to being environmentally unacceptable. Refrigerator emissions pose serious environmental problems and are a waste of resources. C of 5% or more
The 10 scfm concentrator effluent stream containing FC, for example, is many of the typical ones found throughout the food and pharmaceutical industry. Such emissions are 0.16 lb / min,
That is, it corresponds to a CFC loss of about 80,000 lb / year. Hundreds of industrial refrigeration plants are in use on a nationwide scale, and when these are aggregated, the percentage of this loss is C
It becomes a large source of FC pollution and waste of resources. Therefore, there is an urgent need to improve the cooling technology to severely reduce or eliminate CFC emissions. To be more precise,
The same applies to other coolants. There is also a need for an improved method for keeping the air content of the refrigeration cycle as low as possible, because it is counterproductive to the operation of the refrigeration cycle.

Attempts have been made to monitor and / or treat the purge stream from the cooling operation using various means in addition to concentration. For example, Loland U.S. Pat. No. 4,485,286 describes a CFC from a cooler purge stream
A distillation method for recovering is described. Also, Zin
Smeyer, U.S. Pat. No. 4,531,375, describes a cooling system which includes means for monitoring the cooling device purge system and compensating for excessive release of purge gas. Nie
US Pat. No. 4,484,453 to ss describes a method of controlling the concentration of non-enriched gas in an ammonia chiller to a predetermined concentration by knowing the temperature at which the ammonia is concentrated.

It has been known for many years that gasses or gas mixtures can be separated by the use of permselective membranes. And gas separation systems using membranes are about to replace conventional separation techniques in many fields. Membranes are known to have the ability to separate organic or inorganic gases from air. For example, US Pat. No. 4,553,983, which shares the present invention, uses a membrane with high organic selectivity to separate an air stream containing a low concentration (up to 2%) of organic gas from air. The method is described. or,
Aine, U.S. Pat. No. 3,903,694, describes a concentrated working membrane process for recycling unburned hydrocarbons in engine exhaust gas. Jones U.S. Pat. No. 2,617,493 describes the separation of nitrogen from a concentrated hydrocarbon feed stream. The specification of the U.S. patent pending (Ser. No. 327,860) sharing the present invention is C
It describes a membrane separation process for treating air or other gas streams containing fluorinated hydrocarbons such as FC.

[0010]

SUMMARY OF THE INVENTION The present invention is a combination of a refrigeration cycle, a purging operation to remove air or other non-concentrating gas from a refrigeration system, and a purge gas treatment with a membrane separation system to recover the coolant. And an improved cooling method.

The cooling cycle is preferably performed in a closed cycle operation in which the coolant is brought to a low temperature, for example by gas compression or absorption. This refrigeration cycle comprises:
(B) a combined cycle in which more than one compression / expansion cycle is used, but with the normal coolant circulated during those cycles, or (c) sequential lower temperatures using a series of different cooling cycles. Can take any form of a cascade cycle, such that

Any cooling agent known in the art may also be used, for example, inorganic compounds such as ammonia, sulfur dioxide or carbon dioxide, saturated or unsaturated carbonizations such as propane, butane, ethylene or propylene. Mention may be made of hydrogen, as well as many halogenated hydrocarbons such as chlorofluorocarbons (CFC) and hydrogenated fluorocarbons (HCFC). The purpose of the purging operation is to remove air or other non-concentrating gases that have entered the cooling system. It is desirable to keep the amount of air circulating with the coolant at a very low level. The reason is that the presence of air in the gaseous coolant necessitates operating the compressor at unnecessarily high pressures.
The higher the level of air in the system, the more inefficient the system becomes. In the purging operation, a part of the gaseous coolant is continuously or periodically taken out. For example, the gaseous coolant can be withdrawn through a pressure actuated valve that is connected to the high pressure gas portion of the cycle and automatically opens when the pressure in the system exceeds a certain value. The purge gas may contain a very small amount, for example less than 1%, to a large proportion, for example 5%, 10%, 15% or more, of non-concentrating gas.

The treatment of the purge stream is designed to recover as much of the coolant as possible and to make the purge stream a sufficiently clean residual air stream to be released into the atmosphere without adversely affecting the environment. To do. The purge stream treatment operation is performed by separating the coolant and air by permeating the purge gas stream through a membrane that is selectively permeable to the coolant. The coolant is thus concentrated in the stream that has permeated the membrane, so that the amount of coolant in the unpermeated retentate stream is correspondingly reduced. The driving force for permeating the membrane is due to the pressure difference between its supply side and permeation side. If the purge stream is extracted from the high pressure part of the cycle as usual, no additional driving force is required for membrane permeation. The milling step produces a permeate stream that is rich in coolant compared to the feed stream and a residual stream that does not contain coolant.

The efficiency of the above process with respect to the relative proportions of coolant and air in the feed, permeate and residual streams depends on many factors, such as pressure differential, membrane selectivity, proportion of feed stream permeating the membrane. , And the film thickness. The present invention is adaptable to feed streams containing a wide range of concentrations of coolant. Effective membrane separation is possible even when the membrane selectivity is not very high. In one possible embodiment, this step can be further cooled and / or compressed to create a permeate stream from which the pure liquid refrigerant can be recovered. This liquid coolant may then be returned to the liquid portion of the cooling cycle. In another desired embodiment, the permeate gas can be returned directly to the refrigeration cycle on its low pressure gas side.

The membrane permeation step can be carried out in many possible ways, for example using a single membrane or using an array of two or more units in a co-current or counter-current arrangement. . 80% to 90% of the coolant content of the feed stream to the membrane system using a properly designed membrane separation method
% Or more can be removed and a residual stream with negligible traces of coolant can be created. As a typical example, the permeate stream is concentrated, for example, 5 to 100 times more than the feed stream.

The above describes aspects of the invention where the membrane used to separate the coolant from the air is preferentially permeable to the coolant. As another aspect of the invention, it is also possible that the membrane is selectively permeable to air. In this case, the non-permeable residual stream will be rich in coolant. The particular advantage of this method of operation is that depending on the membrane selectivity, the nature of the coolant, and the operating parameters, it is possible to achieve a considerable amount of cooling in the cooling system that can be economically achieved using optional equipment for the coolant-selective membrane. It is possible to maintain the lowered air level. In this case,
The sowing separation step can also be performed as a single or multiple operation.

When a coolant-selective membrane is used, in one preferred embodiment of the present invention, a purge gas treatment step is performed in which the purge gas is passed through a concentrator before being introduced into the membrane separation unit. The purge gas stream has been previously treated by concentrating, and for this purpose many industrial refrigeration systems already have a concentrating device.
The purge gas taken out of the cooling device is usually 1
It is at a high pressure on the order of 00 psi, so simply cooling the purge gas may cause some of the coolant to precipitate out due to condensation. A concentrating unit attached to a conventional refrigeration system is capable of removing up to about 90% of the coolant passing through it. If a membrane separation unit is connected to this concentrator, the degree of removal by the concentrator can be easily increased. Since the concentrator does not have to be operated at such low temperatures, there are energy and cost savings, and yet almost complete recovery of the coolant. This membrane system can, for example, remove 90 to 95% of the coolant from the concentrator. In this way, the combination of the concentrator and the membrane separator makes it possible to achieve higher coolant recovery rates than with the concentrator alone. For example,
If the removal rate of the cooling agent in the concentration step is 50% and a membrane separation step capable of removing 80% of the cooling agent is performed subsequent to the concentration step, the total removal rate by this method is 90%.
%. Also, assuming that the removal rate of the coolant in the concentration step is 80%, and a membrane separation step capable of removing 80% of the coolant is also performed subsequent to the concentration step, the total removal rate by this method is 96%. Becomes Also, 80% in the concentration process
Is removed, and 90% is removed in the next membrane separation step, in which case the total removal rate is 98%.

The method of the present invention has many advantages over conventional cooling methods. Membrane separation systems are characterized by lower energy consumption than other separation technologies. The driving force for permeating the membrane is given by the pressure difference between the supply side and the permeate side of the sock. In the method of the present invention, since the purge gas from the cooling device is already at a pressure higher than the atmospheric pressure, the membrane separation operation can be performed in various ways without further supplying any energy to it. The added value of the recovered coolant is especially CFC and HCF
In the case of C, it is high. Thus, according to the method of the present invention, the recovery rate of the coolant can be greatly improved, for example, 80% to 95%, or 90% to 9%.
It can be increased to over 9%, which ultimately results in lower net operating costs. Another important advantage is
This is also of particular importance for CFCs and HCFCs, where the amount of coolant released into the environment as exhaust gas is
It can be reduced by as much as 0% or more. Also, since the present invention provides a more efficient purge cycle, it is easier and most effective to keep the circulating air volume lower in the method of the present invention, so that the compressor in the cooling cycle is It can also reduce the amount of energy required.

[0019]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cooling method which eliminates or minimizes the release of coolant into the atmosphere.

It is also an object of the present invention to provide an improved method of treating chiller purge gas. Another object of the present invention is to provide an energy-saving cooling method.

It is also an object of the present invention to separate the coolant from the air. It is also an object of the invention to reduce the load on the compressor used in the refrigeration cycle.

It is also an object of the present invention to reduce the load on the concentrator to recover the purged coolant. Other objects and advantages of the present invention will be readily apparent to those skilled in the art from the description herein.

Further, the above description and the following description in the text explain the embodiments of the present invention, and the scope of the present invention is not limited thereby. In the text of "specific configuration of the invention", "gas" means an inorganic compound or an organic compound that is in a gaseous phase below its critical temperature.

"CFC" means a hydrocarbon containing at least one fluorine atom and at least one chlorine atom. "HCFC" means a hydrocarbon containing at least one fluorine atom, at least one chlorine atom and at least one hydrogen atom.

The term "hydrocarbon" means a saturated or unsaturated hydrocarbon. Also, "selective permeability (membrane)" means that at least one gas or gas in the mixture is selectively permeable to the other components of the mixture and allows for separation between those components. Such a polymer or a film made of the polymer.

The "permeability of the polymer film" means
It means a gas or a ratio of gas that permeates a unit cross-sectional area of the film having a unit thickness under a unit driving force condition. Also, "selectivity" means the rate of permeability of two gases or gases, and its permeability is determined by the concentration of the actual membrane separation system and the gas or gas mixture at the operating conditions. Is.

The term "air selectivity" means a higher nitrogen selectivity and a higher oxygen selectivity than a coolant. The term "plural layers" means a layer composed of a support membrane and one or more coating layers.

Also, "residual stream" means the portion of the feed stream that does not permeate the membrane. Also, "permeate stream" means the portion of the feed stream that has permeated the membrane. Also, "stage-cut" means the ratio of the membrane permeate volume flow to the membrane feed volume flow.

"Membrane unit" means one or more membrane modules arranged in equilibrium so that the fluid introduced therein passes through each other. or,
The “forward flow arrangement” means that a plurality of membrane modules or units are connected and arranged so that the residual flow from one module or unit becomes the next supply flow.

The term "cascade (countercurrent) arrangement" means that a plurality of membrane modules or units are connected and arranged so that the permeate flow from one module or unit becomes the next supply flow. means.

A "membrane array" means a set of one or more membrane modules or membrane units connected in a forward flow arrangement, a cascade (countercurrent) arrangement, or a combination thereof.

Also, "residual product stream" means the residual stream present in the membrane array at the completion of the membrane separation process. This "residual product stream" may be obtained from one membrane unit or may be multiple pooled residual streams from several membrane units.

"Permeate product stream" also refers to the permeate stream present in the membrane array at the completion of the membrane separation step. This "permeate product stream" may be obtained from one membrane unit or may be multiple pooled permeate streams from several membrane units.

In the text, all "%" are "% by volume" unless otherwise specified. The cooling method of the present invention comprises a combination of a cooling cycle, removal of the purge stream, and treatment of the purge stream. The cooling cycle of the present invention is a conventional mechanical cycle, either gas or absorption type. The gas cycle consists of, in sequence, a compressor, a concentrator, an expansion valve and an evaporator as its basic elements. In the compressor, the pressure of the coolant gas is increased so that its saturation temperature is higher than the temperature of the coolant in the concentrator. There is a heat exchange from this coolant gas to the coolant in the concentrator, and the former is concentrated. The liquid thus concentrated is sent through the expansion valve to the cold region of the cycle. Here, its saturation temperature is lower than the temperature of the substance to be cooled. Heat exchange occurs with the coolant, and the coolant evaporates. The low pressure gas is removed by the compressor and thus the cycle continues. The compressor and concentrator used in this refrigeration cycle may be of any type known in the art. For example, the compression device can be either reciprocating or centrifugal. Multiple compression devices arranged in series or in parallel may be used. The concentrator is conveniently a water cooled device, such as a basic shell / tube concentrator, or an air cooled device in which air is blown into the concentrator by a propeller fan. The evaporator can also be of the shell / tube type, where the exchange surface is immersed in or sprayed with a liquid coolant.

In the absorption cycle, the coolant, which is usually ammonia, is alternately absorbed into the water and then removed from the water at high pressure. This cycle consists of an extractor, a concentrator, an expansion valve, an evaporator and an absorber. The high pressure ammonia is withdrawn from the top of the extractor, concentrated and passed through an expansion valve to produce a low pressure liquid. It then passes through the evaporator as in the liquid sum, gas cycle. The low-pressure gas generated in this way is absorbed in the water in a normal absorption device,
Then, the generated liquid is returned to the extraction device by the pump.

The construction and operation of cooling cycles are well known in the art. For details, see "the Am".
ericianity of heatin
g, Refrigerating and Venti
rating Engineers "(Atlante
a, Georgia, USA), a four-volume handbook published by the publisher, provides a wealth of information on examples of cooling device configurations and equipment.

The cooling cycle used in the method of the present invention may be simple, complex, or also cascaded. Any coolant can be used in the method of the present invention. Typical coolants include, for example, carbon dioxide, CFC-from the first group.
11, CFC-12, CFC-13, CFC-22, C
FC-23, CFC-113 and CFC-114, H
CHF-123, HCFC-142b and HCFC-
134a; from the second group, carbon tetrachloride, ammonia and sulfur oxides; and from the third group, methane, ethane, propane, butane, isobutane, ethylene and propylene.

The purge stream containing the coolant and air that enters the cooling cycle is continuously or periodically withdrawn from the cooling cycle. The rate of withdrawal can be determined by the amount of air entering the system and the level of air content in the cycle (the level to be reduced to that level or to maintain that condition). If possible, it is preferable to withdraw the purge stream continuously or over an extended period of time. By doing this, the membrane unit can also be operated without having to be frequently stopped and started. A valve is used to control the coolant withdrawal. This valve can be operated manually or automatically, for example, at suitable intervals or under a defined pressure. The purge stream contains coolant and air, and preferably, but not necessarily, the purge stream contains air as a minor component. For example, the air content of the purge stream can range from less than 1% up to 50%. Preferably, the purge stream is withdrawn from the high pressure gas portion of the refrigeration cycle. In the case of a cascade cycle, different purge streams can be withdrawn from each stage.

A membrane system is used to treat the purge stream.
The gas or gas permeability through a membrane is the product of the diffusion coefficient (D) and the Henry's law sorption coefficient (k). D is a measure of the permeability of the permeant in the polymer and k is a measure of the sorption of the permeant in the polymer, which depends in part on the gas concentration. The diffusion coefficient tends to decrease as the molecular weight of the permeate increases.
The reason is that large molecules interact with more segments of the polymer chain, resulting in loss of mobility. Depending on the nature of the polymer, either diffusion or sorption of its permeable component predominates. In rigid glassy polymeric materials, diffusivity is usually the main factor controlling permeability, so glassy membranes tend to permeate nitrogen or oxygen, for example, faster than larger organic molecules. .. In those embodiments of the invention where an air selective membrane is required, membranes made from glassy polymers are therefore preferred.

In elastomeric membrane materials, the effect of the sorption coefficient predominates so that condensable coolants can permeate the membrane much faster than nitrogen and oxygen. Therefore, elastomeric membrane materials are preferred for embodiments of the invention where there is coolant selectivity. Hydrophobic elastomers are preferred for hydrophobic coolants and more hydrophilic substances are more suitable for hydrophilic coolants such as ammonia, carbon dioxide and sulfur dioxide.

In the process of the present invention, the purge stream from the chiller cycle (which may optionally be concentrated to recover a portion of the coolant, and also wipes the gaseous coolant and air). The selective permeation thin film is transmitted. The selectively permeable membrane forms a barrier that is relatively permeable to one component of the purge stream but relatively impermeable to the other components. The membrane may take the form of a homogeneous membrane, a membrane containing a gel or liquid layer, or any other membrane known in the art.

In order to achieve a sufficient flow of permeate components,
This permselective membrane should be as thin as possible. As a preferred embodiment of the present invention, a microporous support and a composite membrane having a permselective layer deposited thereon as an ultrathin coating can be used. The microporous support membrane should have very low flow resistance compared to the permselective layer. A preferred support membrane is an asymmetric membrane consisting of a skin layer having a thin, dense, fine pores and a substrate having a substantial opening. Suitable polymers for making asymmetric membranes include, for example, polysulfones, polyimides, polyamides and polyvinylidene chloride. Commercially available asymmetric polysulfone and polyimide membranes for ultrafiltration are also suitable as supports. Isotropic support membranes such as microporous polypropylene or polytetrafluoroethylene can also optionally be used. The thickness of the support membrane is not limiting. This is because its permeability is higher than that of the selectively permeable layer. However, its thickness is typically 100 to 300 microns, with about 150 microns being the preferred value.

In some cases, the support membrane may be reinforced by casting it onto a cloth or paper web made of polyester or the like. Thus, the multilayer film is composed of the web, the microporous film, and the ultrapermeable thin film.

The selectively permeable membrane is applied, for example by dip coating, on the dense skin layer of the support membrane. The dip coating method is described, for example, in Riley et al., US Pat.
No. 3,701. In a typical dip coating process, the support membrane from a feed roll is first passed through a coating zone, then wound into a drying oven and then onto a product roll. The coating zone may be a tank containing a solution of dilute polymer or prepolymer,
And here, for example, a coating with a thickness of 50 to 100 μm is applied to the support. If a 1% strength polymer solution is used, a film with a thickness of 0.5 to 1 micron is formed on the support after evaporation.

Alternatively, the permselective membrane can be formed by casting a thin film of the polymer solution on the surface of a water bath. After evaporation of the solvent, the permselective layer may be picked up on the microporous support. This method is actually more difficult, but it is useful when the desired support is attacked by the solvent used to dissolve the permselective material.

The thickness of the selectively permeable layer is usually in the range of 1.0 to 20 microns, preferably 5 microns or less, more preferably 0.1 to 2 microns. Preferred polymers for use as the coolant-selective membrane include, for example, rubbery amorphous polymers, that is, those having a glass transition temperature below the normal operating temperature of the system.
Further, a thermoplastic elastomer can also be used. These polymers have a combination of hard and soft segments or regions in their polymer structure. When the soft segment is rubbery at the temperature and operating conditions of the present invention,
Membranes suitable for use in the present invention can be made from this type of polymer. Examples of usable polymers include, but are not limited to, nitrile rubber, neoprene, polydimethylsiloxane (silicone rubber), chlorosulfonated polyethylene, polysilicone carbonate copolymer, fluoroelastomer, plasticized polyvinyl chloride, polyurethane, and cis. Polybutadiene, poly (butene-1), polystyrene-butadiene copolymers, styrene / butadiene / styrene block copolymers, styrene / ethylene / butylene block copolymers, thermoplastic polyolefinelastomers, and block copolymers of polyethers, polyamides and polyesters. .. The thickness of the selectively permeable layer should be as thin as possible to maximize the permeate flow. However, the permselective layer must also be free of pinholes and other defects that would destroy the selectivity of the membrane by permeating large volumes of gas flow. In the present invention, a particularly preferred rubber is silicone rubber. Silicone rubber solutions are capable of wetting fine, microporous substrates and, after solvent evaporation, can form uniform, defect-free coatings. Therefore, the preferred membranes are made by depositing the permselective coating directly onto the microporous support. However, as a desired embodiment of the present invention, a sealing layer or a protective layer may be further provided on or under the selectively permeable layer, and this is also included in the scope of the present invention.

Preferred polymers for use as air selective membranes include, for example, glassy materials such as polysulfones, polyimides, polyamides, polyphenylene oxides, polycarbonates, ethyl cellulose or cellulose acetate. Glassy materials are more difficult to make composite films than elastomers. In a preferred embodiment of the method of the present invention using an air selective membrane, an asymmetric glassy membrane is used, where the thin dense skin layer functions as the permeation selective layer. Such membranes are known in the field of gas separation technology and can be made, for example, by various modifications of the Loeb-Souriajan method. Loeb-Souriajan
The method consists of making a solution of the polymer in a suitable solvent, casting a thin film and then dipping the film in a settling bath. The membrane thus formed has an asymmetric structure consisting of open micropores on the surface of the support to non-porous or very fine micropores on the skin side. Such gas separation membranes are often covered by a sealing layer on their skin side to prevent large gas streams from passing through them through their pores or other defects. For the preparation of asymmetric gas separations and their properties, see, for example, Henis and Tripodi.
U.S. Pat. No. 4,230,463 or Dow Che
Mical, U.S. Pat. No. 4,840,646.

The selectively permeable membranes used in the present invention should have a selectivity of at least 5, more preferably at least 10, and most preferably at least 20 coolant / nitrogen, or nitrogen / coolant. I won't. Table 1
Shows experimentally measured results for the selectivity of many conventional coolants. In each case, the membrane used is a composite membrane with a silicone rubber selectively permeable layer. 20 measurements
It was performed at ° C. In general, decreasing temperature increases selectivity and vice versa. Coolants such as CHF ₃
Membrane selectivity is only 4 at room temperature and much better results are obtained by carrying out the membrane separation operation at low temperature. As shown in this table, the membrane selectivity is -39 ° C.
Increase to 14 at.

[0049]

[Table 1]

The form of the membrane used in the present invention is not limited. For example, a plain sheet or disk,
Any form known in the art can be used, such as coated hollow fibers or spiral modules. Among them, the spiral module is preferable.
For the manufacturing method of the spiral module, see S.
S. Kreman's "Technology and
Engineering of ROGA Spiral
Wound Reverse Osmosis Me
mbrane Modulus "(Reverse O
smosisand Synthetic Membr
ane, S.M. Sourirajan (editor), Nati
onal Research Council (Can
ada), 1997); and US Pat.
No. 53,983, col. 4, pages 40-60. Alternatively, the membrane may be made by making microporous hollow fibers coated with a permselective polymeric material and then making this a module.

The flow rate of the gas or gas passing through the polymer membrane is proportional to the pressure difference of the gas or gas passing through the membrane. In order to increase the permeation flow rate, it is desirable not only to make the permselective membrane very thin, but also to operate the system with a large pressure drop across the membrane. The purge gas stream is withdrawn from the high pressure gas region of the refrigeration cycle.
Therefore, the purge gas stream is usually at a pressure substantially above atmospheric pressure and is at 100 psia or 200 psia.
It can be as high as moderate pressure. As a result, by keeping the permeate side of the membrane at atmospheric pressure and using the high pressures inherently possible during the cooling cycle, the just right driving force used in many aspects of the invention can be obtained. .. The efficiency of the membrane system depends not only on the membrane selectivity and the pressure drop across the membrane, but also on the feed / permeate pressure ratio. Theoretically, even with a very highly selective membrane, the concentration of the component that preferentially permeates to the permeate side of the membrane should never be greater than φ times the concentration in the feed. It is shown. Where φ is the feed pressure / permeate pressure. In order to bring the permeate pressure to atmospheric pressure to obtain the proper pressure ratio, the feed pressure should preferably be above about 60 psi. Often, the purge gas stream withdrawn from the refrigeration cycle is at a pressure substantially above about 60 psi. If the feed pressure to the membrane is not high enough to produce a beneficial pressure ratio, the pressure drop across the membrane may be achieved by reducing the permeate side of the membrane to a partial vacuum. Also, in some cases, subatmospheric pressure on the permeate side can be maintained simply by continuously concentrating and withdrawing the permeate stream. In embodiments using a coolant selective membrane, the residual stream may be an air stream. The coolant content in the air should be reduced to a level where it can be released to the atmosphere with minimal loss of coolant or environmental pollution. Preferably, the residual stream is one of the coolants contained in the feed fed to the membrane unit.
It should contain less than 0%, more preferably less than 5% of coolant. If an air-selective membrane is used, the permeate can be a stream of air and must be clean enough to be released as well.

The process of the present invention may be carried out using a membrane system designed to meet the feed composition to the membrane unit, and the desired composition of the retentate and permeate stream, to meet their required properties. You can The purge gas stream may optionally be subjected to a concentration step to recover most of the coolant and then to a membrane treatment step. Next, some representative aspects of the present invention will be described. However, these aspects merely disclose the practice of the present invention and are not intended to limit the scope of the invention in any way. Those skilled in the art of cooling and its membrane arts will readily appreciate that many other embodiments of the invention are possible.

Representative of the Invention Using a Coolant Selective Membrane
Aspect 1, Purge gas treatment step consisting of concentration and then membrane separation. In a preferred embodiment of carrying out the present invention, the purged gas taken out is subjected to a concentration step and then to a membrane treatment step.
When the purge gas contains a high proportion of coolant and is at high pressure (and the purge gas is usually both), cooling the gas stream causes a portion of the coolant to concentrate. The cooling method using this treatment scheme is shown in FIG. In this first figure, the cooling cycle 1 is a single gas cycle. The compression device 2
Create a region of high pressure coolant gas 3. This gas is passed to the heat exchange zone 4, where heat is given to the coolant material therein and this gas is concentrated to create a high pressure liquid zone 5. The coolant is then passed through the expansion valve 6 to the low pressure liquid zone 7. The heat exchange between the substance to be cooled and the coolant takes place in the evaporation zone 8. The low pressure gas thus produced in zone 9 is compressed again and the cycle is repeated. High pressure purge flow 12
Is removed from the cooling cycle through outlet 10 and valve 11. The purge stream passes through the concentrator 13. This concentrator 13 is a simple water-cooled or air-cooled concentrator operating above 0 ° C., or is cooled using this cooling cycle or another smaller cooling device. It may be one.
Concentrator temperatures down to about -45 ° C can be achieved with a single cycle of cooling operation. If lower concentrator temperatures are used, a combined or cascade system may be used. However, this is a highly unfavorable approach because of its complexity and high energy consumption unless the cooling cycle itself is a combined or cascade cycle through which a purge stream can be readily provided. The use of a membrane treatment unit means that the amount of coolant removed by the concentrator is not a limiting factor in its form. The combination of the concentration step / membrane separation treatment step may be designed so that the concentration step can be performed at a temperature higher than 0 ° C. This is advantageous, for example, when the purge gas stream contains water vapor, for example in an embodiment using an absorption cooling cycle, because the defrosting of the concentration step does not have to be performed on a regular basis. On the one hand, the selectivity of certain polymers with an organic gas to air selectivity increases with decreasing temperature. If the coolant selectivity at room temperature is low, then a more efficient separation in the membrane separation process can be achieved by cooling the purge gas to a relatively low temperature before it passes through the membrane unit. The proportion of coolant remaining in the purge gas stream after the concentration step depends on the gas / liquid equilibrium at the operating conditions under which the concentration step is performed. If a concentration step is performed, it is generally preferred to design the step so that at least 50% of the coolant present in the withdrawn purge stream can be removed during the concentration step. 9
Operations under extreme conditions such as removal of as much as 5% or more of the coolant are usually unnecessary because of the membrane treatment steps involved.
The total rate of concentrating removal and recovery achieved by the combined concentration / membrane separation step is a multiple of the removal rate achieved by each step. For example, in the case of removing 50% of the cooling agent in the concentration step, if a membrane separation step of removing 80% of the cooling agent reaching the concentration step is performed, the total removal rate in this series of processes becomes 90%. Become. It also removes 80% in the concentration step, and also 80%
Assuming a subsequent membrane separation step to remove%, the total removal achieved in this process is 96%. Also, when 80% is removed in the concentration step and 90% is removed in the membrane separation step, the total removal rate is 96%.

The above description has shown that the method of the present invention can be designed to achieve the desired recovery of the coolant with high efficiency. The design can then be carried out by comparing the estimated energy and production costs with some combinations of system configurations and operating conditions. For example, 5
Achieves 95% overall removal using an initial concentration step that removes 0, 75 or 90% of the coolant component followed by a membrane separation step that removes 90, 80 or 50% of the residual coolant. Compare the production costs and energy needed to do so.

Liquid coolant stream 14 from the chiller is withdrawn for reuse in the cooling cycle. Flow 1
5 has a higher pressure than the atmosphere and contains a non-concentrated coolant and air, which is fed to a membrane unit 16 consisting of one or more membranes which are selectively permeable to the coolant. Be entered. Permeate stream 18 is thus stream 1
Rich in coolant compared to 5. If its selectivity is high,
And also, if the stream from the concentrator is not very dilute, the permeate stream 18 will be fully concentrated and returned to the refrigeration cycle. 2 and 3 illustrate the desired process. Here, the residual stream 17 from the membrane operation (which may still be at a pressure above atmospheric pressure) has its coolant concentration sufficiently low to allow it to be released into the atmosphere. Preferably, this residual stream is less than 1%,
More preferably it contains less than 0.5% of coolant.

2. Return the permeated gas to the cooling cycle. In FIG. 3, permeate stream 20 is compressed in compressor 20 and returned to concentrator 15. This is preferred over returning the permeate gas directly to the cooling cycle. because,
The compressor 20 is relatively small, and in this way no air is returned to the refrigeration cycle. The total energy consumption of this system is therefore lower than in the case of FIG.

Exemplary Embodiments of the Invention Using Air Selective Membranes
Situation 1, in the case of only treatment with an air selective membrane. As another aspect of the present invention, a membrane treatment process in which an air selective membrane is used to directly treat a purge gas stream without being subjected to a concentration process in advance can be mentioned. The basic system of this embodiment is shown in FIG. In FIG. 4, the cooling cycle and the purging operation are carried out in the same manner as in FIGS. 1, 2 and 3. That is, the purge stream 12 (which is above atmospheric pressure) is sent directly to the membrane unit 22 containing the air selective membrane. Permeate stream 24 is thus richer in nitrogen and oxygen than stream 12.
The residual stream contains concentrated coolant. If the purge gas concentration, membrane selectivity and operating parameters are such that very simple separation results can be obtained with this simple one-stage membrane operation, then in the case of the coolant-selective aspects of FIGS. 2 and 3 above. Similarly, it is possible to vent the permeate and return the residual stream to the refrigeration cycle with or without liquefying it. It is believed that at least the residual stream needs to be further processed if very highly selective membranes are not available, such as nitrogen selectivity to the coolant of 200, 500 or even higher. However, in the membrane separation process, it is generally preferable to reduce stage-cut in order to obtain a high separation result. Therefore, the amount of permeate stream is usually much less than the amount of feed stream and residual stream.
Therefore, the advantage of the air-selective embodiment of FIG. 4 is that the amount of permeate air stream containing the coolant gas that must be concentrated or otherwise treated is much greater than the total purge gas amount. It means that there are few. This means that it is economically feasible to operate this refrigeration cycle at a lower air content and lower head pressure to be achieved by the refrigerant cycle compressor. It is meant.

2. A combination of air-selective and coolant-selective membranes. The purge gas flow just removed from the cooling cycle is
For example, as an example, it contains 90% coolant and 10% air. If this purge stream is permeated, for example, through a membrane having a nitrogen selectivity for the coolant of about 20, the permeate stream will still be 20 to 30 even if waste wasted prematurely.
% Cooling agent. This level is too high to directly release this permeate into the atmosphere. However, permeation of this coolant 24 through the coolant selective membrane unit here can reduce its coolant concentration to a point where release is possible. The residual stream from the coolant selective membrane operation could thus be released and the permeate stream from the coolant selective control unit could be recycled to the feed side of the air selective unit.

In embodiments using an air-selective membrane unit followed by a coolant-selective membrane unit, it is usually necessary to have the pressure on the permeate side of the coolant-selective unit below atmospheric pressure. The reason is that the feed stream to this unit is at or near atmospheric pressure.

3. Combination of air-selective membrane and concentration means. a) When the purge gas treatment step consists of a membrane treatment step and a subsequent concentration step This process is the same as that described in Embodiment 1 above with respect to the cooling cycle, the purge gas extraction step and the permeation of the air-selective membrane. However, in this case, the permeate stream 24 is optionally recompressed and then cooled, preferably using the cooling portion of the refrigeration cycle, thus recovering a suitable liquid coolant stream for return to the refrigeration cycle. Non-enriched gases containing only a small amount of coolant gas can thus be released.

B) In the case where the purge gas treatment step comprises a concentration step and a subsequent membrane treatment step. In order to maximize the advantages of the above-described embodiments of the invention of using an air selective membrane in the membrane treatment process, it is highly preferred to use a membrane having a high nitrogen selectivity to the coolant gas.

However, if a membrane with nitrogen selectivity for 10 or 20 coolants, for example, is available, it is also possible to design a useful embodiment as shown in FIG. In FIG. 5, the coolant cycle and purge gas extraction operation are the same as in FIG. However, in this case, the purge stream 12 has a light pressure as compared with the atmospheric pressure and is sent to the concentrator 13. Similar to the coolant-selective embodiment, the concentrator is a water-cooled or air-cooled concentrator operating at temperatures above 0 ° C, or using a cooling cycle therefor or another smaller cooling. It may be cooled using an apparatus. Concentrator temperature adjustment down to about -45 ° C can be accomplished by a single cycle cooling operation. And lower temperatures require complex or cascade systems. It is convenient and cheap to use the cooling cycle there to cool the concentrator, as is the case with the desired means of coolant selectivity. The liquid coolant stream 14 from the concentrator is suitable for reuse. The non-concentrated fraction 15 from the concentrator, which is above atmospheric pressure, is sent to a membrane unit 16 containing an air-selective membrane. The permeate stream 28 from the membrane unit is predominantly air and contains a very low concentration of coolant gas. Residual stream 29 contains coolant and is at a pressure above atmospheric pressure. FIG. 5 illustrates the desired process, where this stream is returned to the high pressure gas portion of the refrigeration cycle. Circulating blowers or pumps may be used if desired to tailor the flow of the recycle gas stream. Alternatively, stream 29 could be liquefied and returned to the liquid portion of the refrigeration cycle.

From the above description, there are many different ways of purging gas treatment operations, and to obtain a highly efficient and economical recovery of the coolant, and to recycle the spent coolant gas to the atmosphere. It will be appreciated that various designs can be made to minimize emissions. And depending on the coolant used, the operating conditions of the refrigeration cycle, and the capacity of the compressor and / or concentrator used in combination, many different workable and practical aspects could be designed. The ultimate goal of all modes of operation is to produce only two streams with the purge gas treatment operation. And one of them is an exhaust gas flow that does not contain a coolant gas, so that even if it is released into the atmosphere, it does not adversely affect the environment. Product stream containing pure refrigerant.

For simplicity, all of the above cooling processes have been described in terms of a simple single stage membrane operation. As will be appreciated by those skilled in the art, there are many different methods for membrane separation operations, such as single-stage operation with a single membrane or an array of two or more units in a co-current or counter-current arrangement. Operations, etc. As an example,
FIG. 6 schematically shows a membrane array with a two-stage countercurrent (cascade) arrangement.
It was shown to. This type of membrane arrangement, for example, concentrates the purge stream first, and then concentrates it so that a single passage through the membrane unit does not adequately concentrate the coolant gas back into the coolant cycle. It can be used when the non-enriched gas from the device contains a low concentration of coolant.

In FIG. 6, the incoming purge stream 30 contains a coolant and air, and this comprises a first membrane separation unit 3 containing a membrane which is selectively permeable to the coolant.
Sent to 1. The retentate stream 32, which does not permeate here, is therefore free of coolant. Downstream 33 will be coolant rich, but will still contain significant amounts of nitrogen and oxygen. The permeate from the first membrane unit is at atmospheric pressure and is sent to the second membrane unit 34. The pressure difference with the second membrane unit is provided by the vacuum pump 35. In the permeate stream 36 from the second membrane unit, the coolant is fully concentrated and this stream is further concentrated in the concentrator 37 to produce a liquid coolant stream 38. If there is a non-concentrated fraction 39, it may be recycled to the second membrane unit. The residual stream 40 from the second membrane unit has a lower coolant content compared to stream 30, which may optionally be recycled to the feed side of the first membrane unit. In this way, the membrane operation produces only two streams, a liquid coolant stream 38 that can be returned to the refrigeration cycle and a substantially clean residual stream 32 that is discharged.

A second specific example of a membrane array consisting of a two-step forward flow arrangement is shown diagrammatically in FIG. This type of membrane unit can be used, for example, where substantially complete removal of the coolant is required prior to evacuation. For example, a two-step process removes over 99% of the coolant introduced therein. In FIG. 7, the incoming purge gas 42 contains a coolant and air, which is sent to a first membrane separation unit 43 which contains a membrane which is selectively permeable to the coolant. The permeate stream 49 becomes rich in coolant and, if desired, may be liquefied by a compression device 50 and a concentrator device 51 into a liquid coolant stream 52. This stream 52 is suitable for return to the cooling cycle. The residual stream 44 has a lower coolant content than stream 42,
It still contains large amounts of coolant and is not suitable for release. Therefore, the stream 44 is sent to the second membrane unit 45. The residual stream 46 from the second membrane unit is thus sufficiently cleaned and discharged. The permeate stream 48 from the second membrane unit is richer in coolant than stream 42,
It can be recompressed by the compression device 47 and recycled to the feed side of the first membrane unit. In this way, the membrane operation produces only two streams, the liquid coolant stream 52 and the fairly clean air stream 46.

Multi-stage and multi-step membrane operations, and combinations thereof, can be used in conjunction with embodiments that utilize a coolant-selective or air-selective membrane.

[0068]

The present invention will be described in more detail with reference to the following examples. These specifically disclose the embodiments of the present invention, and do not limit the scope of the present invention and the technical idea on which the invention is based. The examples are described separately in two groups. The first group of Examples 1 to 13 is a variety of conventional coolant separation processes performed using a typical composite thin film. Second Group Examples 14-27
Is a representative example of performing a purge flow treatment operation.

First Group of Examples Examples 1-13: Experimental Results Using Coolant Selective Membranes Experimental Method All feedstream samples had a membrane area of about 2,000 cm ^2.
Was evaluated using a laboratory test system with a single membrane module having a permselective silicone rubber membrane. The air in the feed cycle was replaced with nitrogen from a pressure cylinder prior to the experiment. To replace the lost nitrogen in the permeate,
Nitrogen was continuously fed into the system during the experiment. The gaseous solvent is vaporized by pumping the liquid solvent into the residue line using a syringe pump and heating it further, or the bypass stream of the residue is charged with the liquid solvent. It was continuously fed into the system by pumping through the containing wash bottle. The organic concentration in the feed and the residue can be determined by gas chromatography (G
C) It was measured by subjecting it to analysis. A small bypass stream was used so that the sample could be taken at atmospheric pressure instead of the elevated pressure in the line. Two liquid nitrogen traps were used to concentrate the solvent in the permeate stream.
For long-term experiments, a rotary turbine vacuum pump was used that did not require lubricating oil on the permeate side of the module. Samples from the permeate stream were removed using a removable glass container that was constantly purged with a permeate bypass stream. At the time of sampling, the container was removed and air was placed in the container. The concentration in the container was measured by gas chromatography. Thus, the transmission density was calculated from the following formula.

Transmission density = (concentration in container) X [(76c
mHg) / (permeation pressure cmHg)] The test method using this system is as follows. 1. Run the system without solvent under maximum permeation vacuum,
The air in the loop was replaced with nitrogen.

2. The nitrogen permeation flow rate was determined by measuring the vacuum pump exhaust flow rate. This allows you to check the quality of the module. 3. The feed stream, feed pressure and permeate pressure were adjusted to the desired values. The cold trap was filled with liquid nitrogen.

4. Start solvent introduction and feed
The feed concentration was monitored by frequent injections into C. Permeate pressure was adjusted as needed. 5. Run the system until feed analysis reveals a steady state.

6. All parameters are recorded and a permeate sample is removed and analyzed. 7. Step 6 was repeated after 10 to 20 minutes. The feed concentration was monitored after it became clear that a steady state was reached due to each parameter change.

Example 1 (CFC-11, low-concentration product) CFC-at a concentration of 100 ppm to 2,000 ppm
The above experimental process was carried out using a feed stream containing 11 (CCl ₃ F). The results are summarized in FIGS. 8 and 9. The calculated CFC / N ₂ selectivity of the module increased slightly from 22 at 100 ppm to 28 at 2,000 ppm. As can be seen from FIG. 6, even from a very lean stream in a very simple one-step process, about 4 lb / m ² . CFC-11 up to date can be recovered.

Example 2 (CFC-11, high-concentration product) CFC-11 at a concentration of 1 vol% to 35 vol%
The experimental process described above was carried out using a feed stream containing (CCl ₃ F). The results are summarized in FIGS. 10 and 11. The calculated CFC / N ₂ selectivity of the module increased from 30 at 1 vol% to 50 at 35 vol%. This effect is due to the plasticization of the membrane material by sorbed hydrocarbons. Both hydrocarbon and nitrogen streams increased with increasing hydrocarbon feed concentration.

Example 3 (CFC-113, low concentration product) CFC-at a concentration of 500 ppm to 2,000 ppm
The experimental process described above was carried out using a feed stream containing 113 (C ₂ Cl ₃ F ₃ ). The results are summarized in Fig. 12. The calculated CFC / N ₂ selectivity of the module is
A constant value of about 20 was maintained in the supply concentration range.

Example 4 (CFC-113, high-concentration product) CFC-11 at a concentration of 0.5 vol% to 6 vol%
The experimental process described above was carried out using a feed stream containing 3 (C ₂ Cl ₃ F ₃ ). The results are summarized in Fig. 13. The calculated CFC / N ₂ selectivity of the module remained constant at about 25 over its feed concentration range.

Example 5 (HCFC-123, low concentration material) HCFC at a concentration of 500 ppm to 2,000 ppm
-123 using a feed stream comprising _{(C 2 HCl 2 F 3)} , and performing the above experiments the process. The results are summarized in Fig. 14. The calculated CFC / N ₂ selectivity of the module remained constant at about 25 over its feed concentration range.

Example 6 (HCFC-123, high concentration product) HCFC-1 at a concentration of 0.5 vol% to 8 vol%
The experimental process described above was carried out using a feed stream containing 23 (C ₂ HCl ₂ F ₃ ). The results are summarized in Fig. 15. The calculated CFC / N ₂ selectivity of the module is
A constant value of about 25 was maintained in the supply concentration range.

Example 7 (HCFC-142b) HCFC at a concentration of 300 to 3,500 ppm
-142b using feed stream comprising _{(C 2 H 3 ClF 2)} , and performing the above experiments the process. The results are summarized in Fig. 16. The calculated CFC / N ₂ selectivity of the module is only slightly over 13 over its feed concentration range.
Increased from 15 to 15.

Example 8 (CFC-114) CFC-114 at a concentration of 2 vol% to 25 vol%
The experimental process described above was carried out using a feed stream containing (C ₂ Cl ₂ F ₄ ). The results are summarized in Fig. 17. The calculated CFC / N ₂ selectivity of the module increased very slightly from 9 to 12 over its feed concentration range.

Example 9 (Halon-1301) Halon-13 at a concentration of 0.1 vol% to 5 vol%
The experimental process described above was carried out using a feed stream containing 01 (CF ₃ Br). A halon / nitrogen selectivity of about 4 was obtained.

Example 10 (Carbon Dioxide) Membranes particularly suitable for separating carbon dioxide, sulfur dioxide and ammonia from air can be made from commercially available poly (ether amide ester) block copolymers. Composite thin film was prepared by coating a 1-3% solution of Pebax-4011 (a product of Atochem) in butanol on a polysulfone moldable support membrane. Permeability experiments were performed using a feed stream containing 8% carbon dioxide in an air mixture. The carbon dioxide flow permeation rate at 61 ° C. is 6.05 × 10 ⁻⁴ cm ³ (STP) / cm ² . s.
It was cmHg. Calculated (carbon dioxide) / (nitrogen)
The selectivity was 26.

Example 11 (Sulfur dioxide) A composite thin film was prepared in the same manner as in Example 10.
Permeability experiments were conducted using a feed stream containing 0.33% sulfur dioxide in an air mixture. Sulfur dioxide stream permeation at 61 ° C is 6.12 x 10 ^-3 cm ³ (STP) / cm ² .
s. It was cmHg. The calculated (sulfur dioxide) / (nitrogen) selectivity was 251.

Example 12 (Air Selective Membrane) Dissolved in 47.9% methylene chloride, 24% 1,1,2-trichloroethane, 6% formic acid, and 7.7% butanol. 14 .4 wt% polyether sulfone (Victrex 52009, ICIAmerica
asymmetric Loeb-S using a casting solution
Ouriajan film was prepared. First, the casting solution was spread on a glass plate using a manual spreading roller. Then, the glass plate was immersed in a methanol bath to deposit the polymer. After deposition was complete, the resulting film was peeled off and dried. A 0.5 to 2 micron thick layer of silicone rubber dissolved in octane was coated on top of this membrane. This layer of silicone rubber covered the defects of the membrane and thus the permeability of this membrane was close to the eigenvalues obtained with thick isotropic films made of the polymer.

The above permeation experiments were carried out using various dilute mixtures of CFC-11 in air. This membrane is 2.
85 × 10 ⁶ cm ³ (STP) / cm ² . s. cmHg
Permeation of oxygen and the flow rate of 4.75 × 10 ^-8 cm ³ (ST
P) / cm ² . s. It showed a CFC-11 flow permeation of cmHg. The (nitrogen) / (CFC-11) selectivity was 16.

Example 13 (Air Selective Membrane) As in Example 12, but with 85% of 1,1,2-
Asymmetric Loeb-Souriajan membranes were made using a casting solution of 10 wt% polyphenylene oxide dissolved in trichlorethylene and 5% octanol. First, the casting solution was spread on a glass plate using a manual spreading roller. Then, the glass plate was immersed in a methanol bath to deposit the polymer. After deposition was complete, the resulting film was peeled off and dried. A 0.5 to 2 micron thick layer of silicone rubber dissolved in octane was coated on top of this membrane. This layer of silicone rubber covered the defects of the membrane and thus the permeability of this membrane was close to the eigenvalues obtained with thick isotropic films made of the polymer.

The above permeation experiments were carried out using various diluted mixtures of CFC-11 in air. This membrane is 1.
20 × 10 ⁶ cm ³ (STP) / cm ² . s. cmHg
Permeation of oxygen by 3.68 × 10 ^-9 cm ³ (ST
P) / cm ² . s. It showed a CFC-11 flow permeation of cmHg. The (nitrogen) / (CFC-11) selectivity was 79.

Second Group of Examples Examples 14-18: Various Purge Gas Processing Modes of Operation and Analysis The following examples are for the treatment of CFC-11 load streams.
It is a comparison between the case of only the concentration treatment and the case of the purge gas treatment operation of the present invention. Examples 14 to 16
Is not the method of the invention. In all cases of Examples 14 to 16, the stream has a flow rate of 10 scfm and contains 50% CFC-11. Membrane calculations are all based on CFC-11 selectivity measured in single module experiments of the type described in the first group of examples. Moreover, the calculation is performed by Shindo et al.
calculation Methods for Multi
icone Gas Separation
by Permeation "(Sep. Sci. T
echnol. 20, 445-459 (1983)) using a computer program based on the gas permeation equation at cross-flow conditions. The required membrane area was determined by the computer program. Refrigerator capacity is Filtrine Manufacturing
Company (Harris Belay, New Hampshire)
It was determined by extrapolation from literature values provided by.

Further, the capacities of the vacuum pump and the compression device were obtained from the specification chart of each manufacturer and other data, or by extrapolation from them. Energy calculations were performed by calculating the adiabatic ideal compression work and dividing this by the efficiency of each unit. Compressor efficiency was 60% and vacuum pump efficiency was 35%.

Example 14 Compression to 5 atmospheres and cooling to 7 ° C. The CFC-11 on-board purge stream is believed to be at a pressure of 5 atmospheres and is cooled to 7 ° C. and concentrated. The implementation process is as shown in Table 2.

[0092]

[Table 2]

Example 15 Compression to 25 Atm and Cooling to 7 ° C The CFC-11 on-board purge stream is compressed to 25 atm and then cooled to 7 ° C and concentrated. The implementation process is as shown in Table 3.

[0094]

[Table 3]

Example 16 Compression to 5 atm and cooling to -27 ° C Similar to Example 15 except that a purge gas of 5 atm was used and the cooling temperature was lowered to -27 ° C. Done the way. The implementation process is as shown in Table 4.

[0096]

[Table 4]

Example 17 Purge Gas Treatment Operations According to Aspects of the Present Invention A process was designed to achieve similar levels of performance as Examples 15 and 16. That is, the process consists of a concentration step followed by a membrane separation step. In the concentration step, the 5 atm CFC-11 load stream is cooled to 7 ° C and concentrated. The non-concentrated exhaust gas from the concentration step is then subjected to a membrane separation step using a membrane with CFC-11 selectivity for 30 air. The pressure drop across the membrane is done only by increasing the pressure of the compressed flow. The permeate stream from the membrane separation step is returned for treatment in the concentration step. The implementation process is as shown in Table 5.

[0098]

[Table 5]

Comparing this example with Example 15 and Example 16, the process of the present invention showed that the energy required for the treatment system to remove and recover 98% of CFC was 7.
It can be seen that it can be reduced from 46 hp or 6.14 hp to 3.91 hp. In other words, the energy used in the method of the present invention is only 52% or 64% of the method including only the concentration step of the comparative example.

Example 18 Purge Gas Treatment Operation According to the Method of the Invention A method similar to that of Example 17 was performed. However, it differs from Example 17 only in that a small vacuum pump was attached to the permeate side of the membrane to lower the permeate pressure to 15 cmHg. The implementation process is as shown in Table 6.

[0101]

[Table 6]

Comparison of this example with Example 17 reveals some differences. In Example 17,
A fairly high percentage of waste disposal (40%) was required to reduce the residue concentration to 2.18%. The permeate stream volume is at most 3.33 scfm, so a more powerful compressor is needed to handle the additional load returned from the membrane unit. Also, the membrane area is as large as 4.17 m ² . Using a vacuum pump to reduce the pressure on the permeate side is comparable to a CFC with a much smaller membrane area (0.81 m ² ) and a much smaller intermediate waste (18%).
Means that can be removed. However, due to the energy required of the vacuum pump, the total energy requirement of the system in both of these cases is almost the same after all. And the process for both of these cases
There was a marked improvement as compared to the process of the comparative example only having the concentration step.

Examples 19-21 The following examples compare the treatment of a gas stream containing sulfur dioxide in the air with only a concentration treatment and with a typical purge gas treatment operation according to the invention. is there. In all cases of these examples, the flow is 10
It has a flow rate of scfm and contains 50% sulfur dioxide. Calculations were performed as in the CFC-11 example above. Membrane calculations were performed based on the performance of composite membranes with selectively permeable layers consisting of polyamide-polyether block copolymers. The membrane selectivity of sulfur dioxide to air is 100, and the normalized sulfur dioxide stream permeation is 6 × 10 ⁻³ cm ³ (STP) / cm ² . s. cmHg
Met.

Example 19 Compression to 8 Atm and Cooling to 6 ° C A sulfur dioxide loaded purge stream is believed to be available at a pressure of 8 atm and is cooled to 6 ° C and concentrated. The boiling point of sulfur dioxide is −10 ° C., so that under this condition 25% of sulfur dioxide remains in the exhaust gas from the concentrator. The implementation process of this example is as shown in Table 7.

[0105]

[Table 7]

Example 20 Compression to 40 Atm and Cooling to 6 ° C A sulfur dioxide charge stream was compressed to 40 atm and then 6
Cool to ° C and concentrate. The sulfur dioxide content in the exhaust gas is reduced to 5% under these conditions, but the required energy and cost of this system is more than double that of Example 19. The implementation process is as shown in Table 8.

[0107]

[Table 8]

EXAMPLE 21 Purge Gas Treatment Procedure According to the Method of the Invention Using a concentration step exactly the same as in Example 19, and then using a membrane having a sulfur dioxide selectivity to 100 air, the previous concentration was performed. A process was designed to perform a membrane separation process that treats the exhaust gas stream from the process. The pressure drop across the membrane is done only by increasing the pressure of the compressed flow. The implementation process is as shown in Table 9.

[0109]

[Table 9]

The permeate stream from the membrane separation step is richer in sulfur dioxide content than the original gas stream being treated, which can be returned for treatment by the concentration step. This method allows the concentration of sulfur dioxide in the exhaust gas stream to be reduced from 25% to 1% without the need for any additional energy consumption. The reason is that the driving force for membrane permeation is obtained from the much higher pressure of the already compressed feed.

Example 22 (Propylene / Ethylene Cascade Cooling Cycle) Cool to -145 ° F using a two stage cascade cooling cycle using ethylene and propylene. This type of system is called "Chemical Process E".
equipment Handbook "(Butter
worth's Series in Chemical
Engineering), page 226, 8.2.
It is described in FIG. In this system, the first stage propylene gas is compressed to 245 to 250 psia,
It is then cooled to 116 ° F with water to produce liquid propylene. Then this liquid propylene is 16 psia
It is expanded to make cold gas. This cold gas passes through the heat exchanger in the second stage of the cascade system to reach 230 to 24
The ethylene gas is liquefied by cooling at a pressure of 0 psia.
This liquid ethylene expands to 12 psia and -145 °
At F, ethylene gas is produced. The low pressure part of the ethylene cycle causes air leakage and is cheap. Let us assume that the purge stream from the ethylene cycle contains 2-10% air. As an example, this purge stream is first cooled to -140 ° F in a purge gas concentrator. The concentration operation at a purge gas pressure of 240 psia produces a liquid ethylene stream and a non-concentrated stream consisting of 90% air and 10% ethylene at a rate of about 10 scfm. This pressurized exhaust gas is passed over the surface of the silicone membrane in the most economical way. The membrane is 8 times more permeable to ethylene than nitrogen and 8 times more permeable to ethylene than oxygen. The membrane thus carries this gas with a residual stream of 5.2 scfm containing 99% air and 1% ethylene (which can be released to the atmosphere), 19.7% ethylene and 80.3% air. And a low pressure permeate stream containing. This permeate may be returned directly to the low pressure side of the refrigeration cycle, or recompressed to 240 psia and introduced to the front of the -140 ° F purge gas concentrator.

Example 23 (Ammonia Cooling Cycle) Ammonia is often used as a coolant in compression cooling systems such as cooling to the 20 to -50 ° F range. In these systems, non-concentrating gases collect on the high pressure side of the cycle and these gases must be removed as a purge stream. For example, consider a cooling device using ammonia such that the temperature of the liquid ammonia in the concentrator on the high pressure side is 95 ° F. At this temperature the gas pressure of ammonia is 197 psia. However, the actual operating pressure is on the order of 210 psia, which is not uncommon. This extra 13ps
ia is a 6% non-concentrating gas (air, hydrogen, nitrogen, etc.). This gas must be purged at a rate determined by the rate of non-concentrating gas evolution during the cooling cycle. Let us suppose that a purge gas stream containing 6% air or other non-concentrating gas is first subjected to a concentrating step, where the refrigeration cycle provides cooling to -40 ° C. The ammonia concentration in the exhaust gas discharged from the concentrator becomes 4.9%. And
The exhaust gas from the concentrator is passed through a membrane separation unit containing a composite thin film having a selectively permeable layer of silicone rubber. The membrane has an ammonia selectivity for nitrogen of 20 and an ammonia selectivity for oxygen of 10. Depending on the amount of waste in the middle, this membrane operation resulted in a residual stream containing 0.5% ammonia and a permeate stream containing 16% ammonia, and a lower stream containing 0.05% ammonia and a residual stream containing 10%. A permeate stream containing ammonia is produced. By using a two-step process, it is also possible to further reduce the concentration of ammonia in the residual stream if necessary.

Example 24 (CFC-12 Recovery) Regarding the embodiment of the present invention shown in FIG. 1, the case where CFC-12 is used as a coolant will be described. Here, based on the experimental data of the present inventors, CFC-
The membrane selectivity of 12 is 6 to 10. Also, 10 scf
Consider the case where a 87% CFC-12 stream is produced from a purge bath stream containing m air and contaminated with 67 scfm CFC-12. This CFC-12 stream is 90 psi
It results from the purge unloading operation in a and is first passed through a concentrator driven at -60 ° F. This concentrator reduces the CFC content of this gas to 5% CFC-12. The stream thus treated is sent to a membrane unit where the CFCs are selectively permeated. As a result, a stream of 10 scfm containing 0.5% CFC-12 is produced and released. The permeate from this membrane separation operation contains 11% CFC-12 and can be recompressed in a small compressor and returned to the cold concentrator.

Alternatively, the CFC-12 content of the discharge stream can be reduced to 0.05% using a two step membrane separation operation as shown in FIG. In this case, the permeate flow from the second step may be returned to the inlet of the first step. Therefore, this purge stream processing operation produces only two streams. One is the release gas stream containing 0.05% CFC-12 and the other is the liquid CF from the concentration step.
It is C-12 style.

Example 25 (Purge Gas Treatment Using Air Selective Membrane Step) For the embodiment of the invention shown in FIG. 4, this was 9.4%.
Mixed with 0.6% oxygen and 90%
When used to treat a purge gas stream at 100 psig pressure containing a non-specific coolant.
It is assumed that the membrane selectivity of oxygen with respect to nitrogen is 4, and the membrane unit is operated with an intermediate waste rate of 1%. or,
To create a pressure differential across the membrane, a vacuum pump should be used on the permeate side of the membrane to reduce the pressure on the permeate side to 1 cmHg. Computer control method of Shindo et al. (Shindo et al., “Calculation Met
hods for Multicomponent G
as Separation by Permeatio
n ”(Sep. Sci. Technol. 20, 445).
-459 (1985)), the amount of coolant remaining in the permeate stream from the membrane unit was calculated as a function of membrane selectivity. The results are shown in Table 10.
Are summarized in.

[0116]

[Table 10]

From the above results, it can be seen that a film having a very high air selectivity is required in order to reduce the content of the coolant in the purge gas to a level that can be passed at once.

Example 26 (Purge Gas Treatment Using Air-Selective Membrane Treatment and Concentration Step) For the embodiment of the invention shown in FIG. 5, a concentration step is performed to treat the purge gas stream prior to the membrane separation step. The case will be described. Here, the combination of these steps shall reduce the content of the coolant in the stream sent to the membrane separation operation to 5%. The supply flow to the membrane separation process is 100
psig, and pre-permeate pressure of 1c
A vacuum pump shall be used to reduce to mHg.
The calculation was performed as in Example 22. The results are summarized in Table 11.

[0119]

[Table 11]

As is evident from the results in the table above, the residual coolant in the evolved gas is reduced to very low levels by this method even when using a membrane with a modest selectivity.

Example 27 (Purge Gas Treatment Using Air Selective Membrane Treatment Step and Concentration Step) Example 26 except that no vacuum pump was used.
The same method was repeated. Therefore, in this case, the pressure on the dropping side of the soybean was 76 cmHg. The results are summarized in Table 12.

[0122]

[Table 12]

As is evident from the results in the above table, the residual coolant in the released gas is reduced to very low levels by this method even when using a membrane with a modest selectivity, Moreover, the pressure drop can be smaller.

[Brief description of drawings]

1 schematically illustrates an embodiment of the invention using a concentrator and a coolant selective membrane.

FIG. 2 schematically illustrates an embodiment of the invention in which the membrane permeate gas is returned directly to the cooling cycle.

FIG. 3 schematically illustrates an embodiment of the invention in which the membrane permeate is returned to the concentrator.

FIG. 4 schematically illustrates an embodiment of the invention incorporating a nitrogen selective membrane.

FIG. 5 schematically illustrates an embodiment of the present invention incorporating a concentrator followed by a nitrogen selective membrane device.

FIG. 6 is a schematic diagram showing a desired morphology of a two-stage membrane system.

FIG. 7 is a schematic diagram showing a desired morphology of a two-step membrane system.

FIG. 8 is a graph showing the relationship between the concentration of CFC-11 in the feed flow and the concentration of CFC-11 in the CFC supply at a low concentration.

FIG. 9: CFC-1 in CFC supply at low concentration
It is a graph which shows the relationship between 1 stream and supply stream concentration.

FIG. 10 is a graph showing the relationship of CFC-11 concentration between feed and permeate at CFC feed concentrations up to about 35 vol%.

FIG. 11 is a graph showing the relationship between membrane selectivity and CFC-11 supply concentration at CFC supply concentrations up to about 35 vol%.

FIG. 12 is a graph showing the relationship between the concentration of CFC-113 in the supply flow and the concentration of the permeation flow in CFC supply at a low concentration.

FIG. 13: CFC feed concentration up to about 6 vol%,
It is a graph which shows the relationship of the density | concentration of CFC-113 with a supply flow and a permeation | transmission flow.

FIG. 14 is a graph showing the relationship between the concentration of HCFC-123 between the feed flow and the permeate flow in the CFC supply at a low concentration.

FIG. 15: CFC feed concentration up to about 8 vol%,
It is a graph which shows the relationship of the density | concentration of HCFC-123 with a supply flow and a permeation | transmission flow.

FIG. 16 is a graph showing the relationship between the concentration of HCFC-142b in the supply flow and the permeation flow in the CFC supply at a low concentration.

FIG. 17 is a graph showing the CFC-114 concentration relationship between feed and permeate at CFC feed concentrations up to about 25 vol%.

[Explanation of symbols]

 1, Cooling Cycle 2, Compressor 3, High Pressure Coolant Gas 4, Heat Exchange Zone 5, High Pressure Liquid Zone 6, Expansion Valve 7, Low Pressure Liquid Zone 8, Evaporation Zone 8 9, Zone 10, Outlet 11, Valve 12 , High pressure purge stream 13, concentrator 14, liquid coolant stream 15, stream 16, membrane unit 17, residual stream 18, permeate stream

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Lichyard Davre Baker United States California California 94301, Palo Alto, Kingsley Avany 120

Claims (20)

[Claims] 1. A cooling step comprising (a) compressing and expanding a coolant, which is carried out in a cooling system,
A method comprising: (b) a purge step consisting of taking out a purge gas consisting of the coolant and air from the cooling system; and (c) a purge gas treatment step consisting of subjecting the purge gas to a membrane separation step. The membrane separation step permeates a feed gas comprising the coolant and air through a membrane having a feed side and a permeate side, and a permeate stream rich in the coolant relative to the feed gas from the permeate side. The method, which comprises removing. 2. The method of claim 1, wherein the permeate stream is recycled to the cooling step. 3. The method of claim 1, wherein the membrane comprises a microporous support layer and a thin permselective coating layer. 4. The method of claim 1, wherein the membrane has a selectivity to the coolant for nitrogen of at least 5. 5. The method of claim 1, wherein the membrane has a selectivity to the coolant for air of at least 10. 6. The method of claim 1, wherein the coolant is selected from the group consisting of chlorinated hydrocarbons, CFCs and HCFCs. 7. The method of claim 1, wherein the coolant is selected from the group consisting of sulfur dioxide and ammonia. 8. The method of claim 1 wherein the concentrating step comprises cooling the purge gas. 9. The method according to claim 1, wherein the membrane separation step is carried out at a feed gas temperature below atmospheric temperature. 10. The method of claim 9 wherein the feed gas is cooled to a temperature below ambient by subjecting it to heat exchange in the cooling step prior to permeating the membrane. 11. The method of claim 1, wherein at least 90% of the coolant present in the feed gas to the membrane separation step is recovered in the permeate stream. 12. The purge gas treatment step comprises (i) a concentration step, followed by (ii) the membrane separation step, and the concentration step comprises adding the purge gas to the coolant at a concentration of the coolant. A portion of the coolant is concentrated under conditions characterized by greater than its saturation concentration, a concentrated stream of said coolant in liquid form is withdrawn, and said coolant is compared to said purge gas. Is removed, and the membrane separation step provides a membrane having a feed side and a permeate side, the unconcentrated stream from the concentration step is passed from the feed side, and the unconcentrated stream is A process according to claim 1, which comprises withdrawing a permeate stream enriched in the coolant relative to the permeate side from the permeate side. 13. The method of claim 12, wherein the permeate stream is recycled to the concentration step. 14. The membrane separation step comprises providing a membrane array, and each membrane in the array having a feed side and a permeate side, a feed gas comprising the coolant and air being passed through the membrane array. The method of claim 1 comprising passing through and withdrawing the coolant rich product permeate stream relative to the feed gas from the membrane array. 15. The method of claim 14, wherein the membrane array comprises a plurality of membrane units connected in a forward flow arrangement. 16. The method of claim 14, wherein the membrane array comprises a plurality of membrane units connected in a countercurrent arrangement. 17. The membrane separation step comprises at least 60 ps.
The method according to claim 1, which is performed by supplying the supply gas at a pressure of ia. 18. The membrane separation step is carried out by supplying the feed gas at atmospheric pressure, and induces a coolant flow through the membrane by creating a partial vacuum on the permeate side. The method of claim 1. 19. A cooling step comprising (a) compressing and expanding a coolant, which is carried out in a cooling system,
A method comprising: (b) a purge step consisting of taking out a purge gas consisting of the coolant and air from the cooling system; and (c) a purge gas treatment step consisting of subjecting the purge gas to a membrane separation step. The membrane separation step permeates a feed gas comprising the coolant and air through a membrane having a feed side and a permeate side, and a residual stream enriched in the coolant relative to the feed gas from the feed side. The method, which comprises removing. 20. The purging gas treatment step comprises (i) a concentrating step, followed by (ii) the membrane separation step, and the concentrating step comprises purging gas at a concentration of the coolant. A portion of the coolant is concentrated under conditions characterized by greater than its saturation concentration, a concentrated stream of said coolant in liquid form is withdrawn, and said coolant is compared to said purge gas. Consisting of removing a lean non-concentrated stream, and the membrane separation step providing a membrane having a feed side and a permeate side, passing the non-concentrated stream from the concentrating step from the feed side, and 20. The method of claim 19, comprising withdrawing a residual stream rich in the coolant from the feed side as compared to a concentrated stream.