WO1996004978A1

WO1996004978A1 - Pressure swing adsorption apparatus and process for recovery of organic vapors

Info

Publication number: WO1996004978A1
Application number: PCT/US1995/010081
Authority: WO
Inventors: Scott J. Collick; Herbert A. Johnson; Daniel J. Pezolt; Lanny A. Robbins
Original assignee: The Dow Chemical Company
Priority date: 1994-08-12
Filing date: 1995-07-25
Publication date: 1996-02-22
Also published as: AU3361995A

Abstract

A pressure swing adsorption process and method using a vacuum pump (4) to desorb organic vapors from an adsorption bed (11) and then a liquid-ring compressor (27) to compress the desorbed vapor stream to a pressure above atmospheric pressure to better recover compounds that have an atmospheric pressure boiling point below thirty five degrees centigrade. The process is especially suitable for recovering gasoline vapors from the headspace of a gasoline tank when the tank is being filled.

Description

PRESSURE SWING ADSORPTION APPARATUS AND PROCESS FOR RECOVERY OF ORGANIC

VAPORS

TECHNICAL FIELD This invention relates to apparatus and processes for the recovery of organic vapors such as the recovery of gasoline vapors from the headspace of a gasoline storage tank when the tank is being filled. BACKGROUND ART

The pressure swing adsorption system of United States Patent 4,857,084 issued to Lanny A. Robbins and Timothy C. Frank in August of 1989 is a commercially successful and relatively energy efficient process. However, this process was not designed to remove components in the vapor stream from the headspace of a gasoline tank that have an atmospheric pressure boiling point of less than about thirty five degrees centigrade.

In the past when a gasoline tank truck was filled, the displaced headspace vapors from the tank were merely vented to the atmosphere. This practice is increasingly environmentally unacceptable. One presently successful commercial process for recovering gasoline vapors from such gasoline tank trucks is to use the process of United States Patent 4,066,423 issued to McGill et al. in January of 1978. However, this process uses more energy than is desired to cool the absorption liquid used by this process. The process of United States Patent 5,154,735 issued to Dinsmore et al. in October of 1992 uses a booster pump and a liquid ring compressor to remove even more of the gasoline vapors.

It would be an improvement in the art of recovering gasoline vapors from the headspace of a gasoline storage tank if a process could be developed which recovered more of the gasoline than the process of United States Patent 4,857,084 using less energy than the process of United States Patent 4,066,423 or 5,154,735.

DISCLOSURE OF INVENTION

The instant invention is a process for the energy efficient recovery of most all of the gasoline vapors from the headspace of a gasoline storage tank. The instant invention is a process for recovering solvent, monomer or hydrocarbon vapor from a gaseous feedstream that includes five steps. The first step is to pass said gaseous feedstream containing said vapor through a first adsorption bed containing a material that is effective to adsorb said vapor under conditions at which more than one half of said vapor is adsorbed. The second step is to redirect the flow of said gaseous feedstream to a second adsorption bed containing a material that is also effective to adsorb said vapor under conditions at which more than one half of said vapor is adsorbed. The third step is to place said first adsorption bed under reduced pressure generated by a vacuum pump in the presence of a backpurge gas stream running counter to the direction in which said gaseous feedstream flowed, under conditions such that vapor adsorbed upon said bed is desorbed and flows out of said bed with said backpurge stream. The fourth step is to compress said desorbed vapor and backpurge gas stream using a liquid-gas compressor to a pressure above atmospheric pressure. The last step is to pass the compressed desorbed vapor and backpurge gas stream to a vapor receiving step wherein the desorbed vapor is used, recovered or disposed of.

The instant invention is also an apparatus for recovering a solvent, monomer or hydrocarbon vapor from a gaseous feedstream including at least two adsorption beds each containing a material that is effective to adsorb said vapor which material is present in an amount sufficient to adsorb substantial amounts of said vapor. A feed means is used for controllably directing said feedstream into said beds. A backpurge means is used for controllably permitting a flow of backpurge gas through each said bed in a direction counter to the flow of said feedstream when said bed is not receiving said feedstream. A vacuum pump is used having an inlet and an outlet. A conduit means is controllably connected to each adsorption bed and to the inlet of said vacuum pump, so that said vacuum pump can place each bed under reduced pressure while it is not receiving said feedstream, thereby desorbing at least some of said vapor into said backpurge gas and through said conduit means into the inlet of said vacuum pump. A liquid-gas compressor is also used and the inlet of said liquid-gas compressor is connected to the outlet of said vacuum pump. A vapor receiving means is used for receiving desorbed vapor and backpurge gas from the outlet of said liquid-gas compressor for use or disposal of said vapor. In addition, a means for controlling the pressure of desorbed vapor and backpurge gas in the vapor receiving means at a pressure above atmospheric pressure is used, the means for controlling the pressure of desorbed vapor and backpurge gas in the vapor receiving means being in fluid communication with the vapor receiving means.

In its broadest scope the instant invention is useful for the recovery of almost any solvent, monomer or hydrocarbon vapor including a relatively low boiling point solvent, monomer or hydrocarbon vapor or low boiling point fraction thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic drawing of one embodiment of the instant invention that includes a hot-oil vacuum pump (4) and a liquid-ring compressor (27).

MODES FOR CARRYING OUT THE INVENTION

The instant invention is used to separate a solvent, monomer or hydrocarbon vapor from a gas stream. Although the invention may be used to separate any solvent, monomer or hydrocarbon vapor which can be adsorbed and desorbed, it is in one aspect intended for recovering vapors which are soluble in the various oils used in oil sealed vacuum pumps at ordinary operating temperatures of such pumps. The instant invention in this regard is an improvement upon the invention of United States Patent 4,857,084. The invention of United States Patent 4,857,084 is particularly suited for use with organic vapors of compounds whose boiling point is at least about 35' C. at atmospheric pressure; and most particularly for use with vapors of compounds having a boiling point of at least about 40" C. The invention of United States Patent 4,857,084 is highly suitable for recovering haiogenated hydrocarbons and aromatic hydrocarbons, more highly suitable for haiogenated alkanes and aromatic hydrocarbons, and most highly suitable for 1,1,1 - trichloroethane and styrene monomer. Some examples of vapors which may be separated using the invention of United States Patent 4,857,084 are 1,1,1 -trichloroethane, methylene chloride, benzene, toluene, pentane, hexane, carbon tetrachloride, bromochloromethane, 1,2- butylene oxide, styrene, and ethanol.

In contrast, the instant invention is particularly suited for recovering organic vapors of compounds whose boiling point is less that about 35'C or 40'C at atmospheric pressure. The instant invention is highly suitable for recovering not only primarily single low boiling point compounds but also the myrid of low boiling point compounds found for example in refined and unrefined petroleum. The instant invention is highly suited for recovering gasoline vapors.

The vapor is recovered from a gas stream. The gas may be any gas which does not adversely effect the apparatus used to practice the process and which tends to adsorb upon the adsorbent material of the beds to a substantially lesser extent than does the vapor under process conditions. It more preferably condenses at lower temperatures and higher pressures than does the vapor. The gas may be, for instance, air, oxygen, nitrogen or argon. The gas is most typically air.

The vapor is removed from the feed gas stream by passing the stream through an adsorption bed which comprises a material that is effective to adsorb said vapor and is present in an amount sufficient to adsorb substantial amounts of vapor, i.e., more than fifty percent of said vapor. For the purposes of the present application, the term adsorption means that the vapor becomes associated with the adsorbent material and removed from the feedstream in a manner which can be readily reversed by reduction of pressure in the presence of a backpurge stream of gas. Desorption indicates the reverse process of adsorption. Techniques and materials to make adsorption beds are known in the art, and useful beds are commercially available. Useful materials for making the beds are listed in Kuri et al., United States Patent 4,104,039, at column 5, lines 33-47. The proper choice of adsorbent material varies in a manner familiar to persons of ordinary skill in the art depending upon the vapor to be recovered. The beds preferably comprise porous carbon or styrene/di vinyl benzene macroporous resin beads.

Because vapor adsorbed upon the bed must be desorbed, it is preferable to have a plurality of beds. In that way, the gas stream may be passed over a second bed while vapor is desorbed from the first bed. Adsorption and desorption steps may be alternated in each bed so that at least one bed is adsorbing at all times. Systems having only one bed could be practiced, but are less practical since adsorption would have to be shut down during desorption of that bed.

The concentration of vapor in the gas stream leaving the adsorption bed is preferably at least 95 percent less than the concentration of vapor in the feedstream, more preferably at least 99 percent less, and most preferably at least 99.9 percent less. The gas may be used for purposes which can tolerate the remaining vapor or vented or further treated.

Preferably, the adsorption step is continued in each bed for a period of time short enough that the heat of adsorption is substantially retained in the bed until the desorption o step commences. By adsorbing for only a short time, the desorption of vapor can later be carried out in the presence of retained heat without adding additional heat. The best length of time for adsorption steps will vary with individual systems in a manner readily ascertainable by experimentation, depending upon factors such as the bed size and material, the vapor, the temperature of the bed, and the pressures applied in adsorption and desorption. Preferably, a 5 single adsorption step is continued for no more than about 30 minutes, more preferably no more than about 20 minutes, and most preferably no more than about 10 minutes. The minimum time for an adsorption step is limited primarily by practical considerations. The minimum is preferably at least about 30 seconds, more preferably at least about 2 minutes, and most preferably at least about 5 minutes. Preferably, the bed's capacity to adsorb vapor is not 0 completely exhausted when the adsorption step ceases.

After the adsorption step, vapor is desorbed from the bed. Desorption is carried out at a reduced pressure low enough for the vapor to desorb at the temperature of the bed in the presence of a flow of backpurge gas. Optimal pressures for desorption vary in a manner familiar to persons skilled in the art, depending upon factors such as the size of the bed, the 5 material used in the bed, the amount and nature of the vapor adsorbed upon the bed, the temperature of the bed and the rate of back purge flow. The pressure is preferably no more than about 300 mm Hg and most preferably no more than about 200 mm Hg. For some applications it may be desirable to go as low as 40 mm Hg. For others, operation at the high end of the preferred pressures may be desirable. For the system of the Example below, the 0 pressure ranged from about 100 mm Hg to about 160 mm Hg.

During desorption, a backpurge means permits a slight stream of backpurge gas to flow counter the direction of the feed gas flow so that desorbed vapor is carried out of the bed. The backpurge gas, like the gas of the feedstream, may be any gas which does not adversely effect the apparatus and which is adsorbed upon the adsorbent material 5 substantially less strongly than is the vapor. Preferably, the backpurge gas is drawn from the gas stream exiting the other adsorption bed.

The desorption step is continued for a length of time sufficient to restore, at least in part, the previous adsorption capacity of the bed. Preferably, that length of ti me is short enough that desorption can be accomplished using heat retained in the bed without other auxiliary heating. More preferably, the desorption step is carried out for a time short enough that one bed can be brought to desorption pressures, desorbed, and brought back to adsorption pressures while the other bed is in the adsorption step. The desorption step need not be continued for a time equal to the time of adsorption. The desorption step may be run for a shorter time than adsorption, so that both beds operate simultaneously in the adsorption step for a short period of time. Within those constraints, the preferred maximum and minimum time constraints for the desorption step are similar to those for the adsorption step. A concentrated steam of desorbed vapor and backpurge gas is drawn through the inlet of a vacuum pump which creates the reduced pressure and is expelled from its outlet to the inlet of the liquid-gas compressor. In the instant invention, the specific type of vacuum pump used is not critical. For example, the vacuum pump can be a liquid-ring vacuum pump not unlike that used in United States Patent 4,066,423. However, the vacuum pump is preferably an oil-sealed vacuum pump, such as an oil-sealed rotary vane vacuum pump, rotary piston vacuum pump or rotary screw vacuum pump.

To prevent absorption of an oil-soluble vapor into the oil, oil in the oil-sealed vacuum pump is preferably maintained at a temperature high enough that its ability to absorb the oil-soluble vapor is restricted. The temperature of the oil is preferably above the dew point at which oil-soluble vapor condenses in the gas and vapor stream leaving the outlet of the pump. The temperature of the oil is more preferably at least about 30^* C. above that dew point. The temperature of the oil is most preferably at least 45' C. above that dew point. The temperature is preferably below the temperature at which the oil or oil-soluble vapor decompose or substantially degrade. It is more preferably no more than about 190" C. For example, when the oil-soluble vapor is 1 ,1 ,1 -trichloroethane, the temperature is preferably at least 75' C, more preferably at least 80' C, and is preferably no more than about 120' C, due to thermal decomposition of the oil-soluble vapor above that temperature.

Oil-sealed vacuum pumps specifically designed to operate at temperatures required by the present invention are commercially advertised and available. Ordinary oil- sealed pumps can be converted to operate at temperatures required by the present invention simply by insulating the pump with commercially available insulation and heating by known means, such as with electrical heating tape or by heat tracing.

The vapor and backpurge gas pass from the outlet of the liquid-gas compressor to a vapor receiving means which receives the vapor and uses or disposes of it. For instance, the vapor receiving means may comprise a conduit leading to a workplace where the concentrated vapor stream may be used, or a conduit leading to an incinerator where the vapor is destroyed, or an apparatus for condensing and recovering said vapor.

Preferably, the vapor receiving means further comprises the following elements: a condenser connected to the outlet of the liquid-gas compressor such that it receives and condenses at least some of said desorbed vapor; a condensate recovery means connected to said condenser into which condensed vapor passes; and a recycle means connected to said condenser or condensate recovery means which returns uncondensed desorbed vapor to the feedstream. The condenser is maintained at temperature and pressure conditions sufficient to condense at least a portion of the vapor. The pressure in the condenser is preferably greater than the pressure of the feed gas stream passing to the adsorption beds. In addition, the pressure in the condenser should be above atmospheric pressure. The condensed vapor is captured by a condensate recovery means, such as a recovered condensate tank. When gasoline vapors are being recovered, then it is preferable to use a shell and tube condenser and to connect the outlet of the liquid-gas compressor to the tube side of the condenser.

The backpurge gas containing uncondensed desorbed vapor is returned to the feedstream by a recycle means such as a recycle line. Preferably, a flow restricting valve is placed in the recycle line to maintain the pressure of the vapor and backpurge gas in the 5 condenser.

The use of a liquid-gas compressor is at the center of the instant invention. A liquid-gas compressor compresses a gas in the presence of a liquid. The quantity of liquid used is sufficient to absorb most of the heat of compressing the gas. Almost any gas compressor can be made to work as a liquid-gas compressor by feeding it with both a liquid and a gas. o However, most gas compressors are not preferable as liquid-gas compressors. For example, a reciprocating piston gas compressor fed a liquid and a gas must be designed and operated so that the volume of liquid in the compression chamber does not exceed its minimum closed chamber volume.

It should be possible to feed liquid and gas to a gear pump type of compressor as 5 well as a screw type of compressor in the instant invention. For example, an oil sealed screw type of compressor could be fed relatively cool seal oil, or other liquid such as condensed vapor, along with the gas. However, a liquid-ring compressor is highly preferred in the instant invention as the liquid-gas compressor. Liquid-ring compressors are recommended for "handling highly saturated vapors, wet vacuums, and corrosive and exothermal gases", Marks' 0 Standard Handbook for Mechanical Engineers, Eighth Edition, section 14-43. Liquid-ring compressors are also known as liquid-piston compressors, see Perry's Chemical Engineer's Handbook.

The use of a liquid-gas compressor such as a liquid-ring compressor in the instant invention dramatically increases the recovery of organic compounds having an atmospheric 5 pressure boiling point below thirty five or forty degrees centigrade. Even C3 hydrocarbons such as propane and propene, which have an atmospheric pressure boiling point of about minus forty five degrees centigrade, can be recovered from gasoline vapors with greater than 99.999 percent efficiency by the instant invention as discussed in greater detail in the Example below. The reason that a liquid-ring compressor or its equivalent is so dramatically effective in the instant invention is probably related to its design and operation.

A liquid ring compressor encases an impeller in an oblate chamber. The seal liquid is slung against the walls of the chamber trapping gas between the blades of the impeller and the wall of the chamber. Compression of the gas occurs when the blades rotate closer to the wall of the chamber. If sufficient seal liquid is constantly fed to the liquid-ring compressor, then the heat of compressing the gas can be removed by the seal liquid. If the seal liquid is cooled and if the seal liquid is a good absorption medium for the vapor to be condensed, then at least a portion the vapor can probably condense and absorb into the seal liquid in the liquid-ring compressor.

As discussed above, the amount of liquid compressed with the gas must be sufficient to absorb most ofthe heat of compressing the gas. Preferably, the amount of liquid compressed with the gas is sufficient to limit the temperature rise upon compression to less than twenty degrees centigrade and more preferably to less than ten degrees centigrade. In addition it is preferable to limit the temperature of the compressed gas exiting the liquid-gas compressor. When gasoline vapors are being recovered, it is preferable to limit the temperature of the gas exiting the liquid-gas compressor to less than forty degrees centigrade and more preferably to less than twenty degrees centigrade.

Cooling the liquid fed to the liquid-gas compressor is a preferred means of not only limiting the temperature of the gas exiting the liquid-gas compressor but also ensuring that the vapor pressure of the liquid fed to the liquid-gas compressor is less than the inlet pressure of the liquid-gas compressor. Preferably, the vapor pressure of the liquid fed to the liquid-gas compressor is sixty percent or less than the inlet pressure of the liquid-gas compressor. Referring now to Fig. 1, therein is shown a preferred apparatus of the present invention for the recovery of gasoline vapors, in which the vapor receiving means comprises a shell and tube condenser 5, a recovered condensate tank 6 and a recycle line 18. If a different receiving means were desired, those elements and the lines connecting them would be replaced by a conduit leading, for instance, to a boiler or a furnace. The apparatus depicted contains a feed line 1 which passes a feed gas stream containing gasoline vapors from the headspace of a gasoline storage tank, not shown, through open valve 12 and into adsorption bed 11. Clean gas, i.e., gas substantially free of gasoline vapor, passes out through valve 14 along outflow line 16 and out vent 17 to the atmosphere or to subsequent processing. Line 26 connects vent 17 with valve 24. Oil-sealed pump 4 reduces the pressure in adsorption bed 21 through open valve 23. A slight flow of backpurge gas flows through backpurge line 2 through valve 3 and through valve 25 into adsorption bed 21. The backpurge gas and desorbed gasoline vapor travel from bed 21 through open valve 23 and through heated oil-sealed vacuum pump 4 and liquid ring compressor 27 to the tube side of the condenser 5. Gasoline vapor is condensed in condenser 5. Condensed gasoline vapor is trapped in recovered condensate tank 6. Condensate in tank 6 is recovered through condensate outflow 7. Backpurge gas containing uncondensed vapor passes through recycle line 18, via a backpressure regulation valve 32, back into feed line 1. Valves 13, 15, 22 and 24 are closed when bed 11 is in the adsorption stage and bed 21 is in the desorption stage.

The backpressure regulation valve 32 controlls the pressure in the condenser 5 and the tank 6 at a pressure above atmospheric pressure, i.e., 760 mm Hg, and preferably above 1000 mm Hg. The use of valve 32 is preferred but a restrictor, such as an aperture plate or length of reduced diameter tubing, can be used instead of valve 32. Of course, valve 32 or the o like can be positioned in the line between the condensor 5 and the tank 6 but preferably it is positioned as shown in Fig. 1. Valve 32 is preferably not positioned in the line between the compressor 27 and the condenser 5 because such an arrangement would decrease the condensation of the vapor in the condenser 5. However, if the vapor stream from the compressor 27 is sent to a furnace to be burned, then valve 32 should be positioned in the line 5 between the furnace and the compressor 27.

When bed 21 is in the adsorption stage, valves 22 and 24 are open, and valves 23 and 25 are closed. When bed 11 is in the desorption stage, valves 12 and 14 are closed, and valves 15 and 13 are open. To control the flow of backpurge gas, valve 3 is preferably one whose opening can be accurately varied to points between full open and full shut, such as a 0 needle valve. Valves 12, 22, 13, 23, 14, 24, 15, and 25 need not offer fine control of the flow. For instance, they may be ball valves or butterfly valves. When switching from one bed to another, it is preferable to do so over several seconds so as not to mechanically shock the bed.

The preferred seal liquid for the liquid-ring compressor 27 is the condensed vapor in the tank 6 by way of the valve 29 and line 30. The recovered condensate tank 6 has an 5 internal partition 28. The top of the partition 28 is positioned so that it is level with the center of the liquid-ring compressor 27 so that the flow rate of condensed vapor from the tank 6 to the liquid-ring compressor 27 is more constant. However, even more of the lower boiling point vapors of gasoline can probably be recovered if the valve 29 is closed and chilled liquid gasoline is flowed through valve 31 to the seal liquid inlet of the liquid-ring compressor 27. 0

EXAMPLE

A demonstration unit like that shown in Fig. 1 is assembled. The beds 11 and 21 are one third meter in diameter and two meters long and consist of granulated activated carbon having a particle size of about 2-4 millimeters. Wedge-wire screen nozzles are used at 5 the top and bottom of the beds for gas distribution. The temperature of the beds 11 and 21 are monitored using inserted thermowells. Line 17 is connected to a blower, not shown, driven by a one half horse power electric motor. This blower has a maximum capacity of about one thousand liters per minute at a pressure of fourty milimeters of mercury. The vacuum pump 4 is a rotary screw hot-oil sealed unit. The pump 4 is driven by a seven and one half horse power electric motor and has a capacity of two thousand one hundred liters per minute. Polyalphaolefin seal oil is recirculated to the pump 4 with a small gear pump from an oil/vapor separator, not shown. Thetemperature of the oil in the oil/vapor separator is controlled at a temperature of about ninety to ninety five degrees centigrade by heating the oil/vapor separator with electrical heating tape. A heat exchanger, not shown, cools the seal oil being pumped into the pump 4 if the seal oil temperature is above the set point of about one hundred degrees centigrade.

The following variables are monitored for the pump 4: inlet pressure; oil filter outlet pressure; oil temperature at the discharge of the screws; oil temperature at the seal oil inlet; and oil level in the oil/vapor separator. The vapor inlet to the pump 4 is protected with a filter. A recycle line around the pump 4, not shown, is installed to control the inlet pressure to the pump 4. A control valve on the vacuum pump inlet, not shown, is installed to control the pressure between the pump 4 and the compressor 27 during the time when the bed pressure is lowered from atmospheric pressure to the desorption pressure.

A liquid-ring compressor 27 having a capacity of six hundred and fifty liters per minute and using condensed gasoline vapor as the seal liquid at a flow rate of fourty five liters per minute and a temperature of five to fifteen degrees centigrade is used. The impeller of the compressor 27 is driven by a seven and one half horsepower electric motor at 3,500 RPM. The inlet of the compressor 27 is ordinarily at about one atmosphere of pressure while the outlet is ordinarily at about two atmospheres of pressure. A recycle line, not shown, is installed around the compressor to avoid cavitating the compressor during adsorption bed switching when the flow rate from the vacuum pump 4 will substantially decrease.

The condenser 5 is a 316L stainless steel U-tube unit having two square meters of tube surface, each tube being ninteen milimeters in diameter, with the feed to the tube side. The condenser is cooled by a recirculated stream of heat exchange fluid which in turn is cooled by a twenty two horse power air cooled refrigeration unit. The tank 6 is a 316L stainless steel unit having a capacity of three hundred and eighty liters.

The demonstration unit is tested during a six hour period during which five tank trucks each haaving a capacity of thirtythousand liters are filled with gasoline. The average emission from the line 17 during this time is less than one milligram total organic carbon per liter of gasoline loaded into the tank. This level of performance can be compared to the current United States Environmental Protection Agency specification which is believed to be ten milligrams per liter of gasoline loaded. The performance of the demonstration unit at specific times and vent flow rates is discussed below.

When the blower is set to vent two hundred and fifty liters per minute, then the feed stream is flowing at three hundred and sixty liters per minute. The vent stream contains 780 milligrams of total organic carbon per cubic meter while the feed stream contains 31 volume percent gasoline. C1 hydrocarbon, i.e., methane, is essentially not removed from the feed stream. About two thirds of the C2 hydrocarbons are removed from the feed stream. More than 99.99 percent of the C3 hydrocarbons, e.g., propane, are removed from the feed stream. More than 99.999 percent the C4, e.g., butane, and higher hydrocarbons are removed from the feed stream .

When the blower is set to vent one hundred and seventy liters per minute, then the feed stream is flowing at two hundred and thirty five liters per minute. The vent stream contains 600 milligrams of total organic carbon per cubic meter while the feed stream contains 26 volume percent gasoline. C1 hydrocarbon is essentially not removed from the feed stream. o About 97 percent of the C2 hydrocarbons are removed from the feed stream. More than 99.999 percent of the C3 and higher hydrocarbons are removed from the feed stream.

The above example is made to better disclose the instant invention. However, it should be understood that the instant invention is much broader in scope than outlined in this specific example. 5

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Claims

WHAT IS CLAIMED IS:

1. A process for recovering solvent, monomer or hydrocarbon vapor from a gaseous feedstream, the process including the steps of: (a) passing said gaseous feedstream containing said vapor through a first adsorption bed containing a material that is effective to adsorb said vapor under conditions at which more than one half of said vapor is adsorbed;

(b) redirecting the flow of said gaseous feedstream to a second adsorption bed containing a material that is effective to adsorb said vapor under conditions at which more o than one half of said vapor is adsorbed:

(c) placing said first adsorption bed under reduced pressure generated by a vacuum pump in the presence of a backpurge gas stream running counter to the direction in which said gaseous feedstream flowed, under conditions such that vapor adsorbed upon said bed is desorbed and flows out of said bed with said backpurge stream; 5 (d) characterized by the step of compressing said desorbed vapor and backpurge gas stream in the presence of sufficient liquid to absorb most of he heat of compression to a pressure in excess of atmospheric pressure; and

(e) passing the compressed desorbed vapor and backpurge gas stream to a vapor receiving step wherein the desorbed vapor is used, recovered or disposed of. 0 2- The process of Claim 1 , wherein in step (d) the desorbed vapor and backpurge gas stream is compressed using a liquid-ring compressor to a pressure above 1000 mm Hg.

3. The process of Claim 2, wherein the solvent, monomer or hydrocarbon vapor is an oil-soluble solvent, monomer or hydrocarbon vapor, wherein an oil-sealed vacuum 5 pump is used in step (c) to place said first adsorption bed under reduced pressure, and wherein the oil of said oil-sealed vacuum pump is maintained at an elevated temperature such that adsorption of the oil-soluble vapor into the oil is restricted.

4. The process of Claim 3, wherein said vapor receiving step further comprises the steps of: subjecting said desorbed oil-soluble vapor and backpurge gas to temperature and 0 pressure conditions under which at least ten percent of the oil-soluble vapor condenses; collecting said condensed vapor; and returning uncondensed vapor and backpurge gas to said feedstream.

5. The process of Claim 2, wherein the seal liquid of said liquid-ring compressor is condensed vapor and the temperature and amount of seal liquid of said liquid- 5 ring compressor is sufficient to limit the increase in temperature of the desorbed vapor and backpurge gas stream upon compression to less than twenty degrees centigrade. 6. The process of Claim 3, wherein said oil-soluble vapor is gasoline vapor and wherein the reduced pressure of said first adsorption bed is more than 40 mm Hg and less than 300 mm Hg.

7. The process of Claim 4, wherein the conditions under which at least some oil-soluble vapor condenses occur in the tubes of a shell and tube condenser and the sealing liquid of the liquid-ring compressor comprises said condensed vapor.

8. The process of Claim 7, wherein the sealing liquid of the liquid-ring compressor comprises gasoline.

9. An Apparatus for recovering a solvent, monomer or hydrocarbon vapor from a gaseous feedstream, the apparatus including:

(a) at least two adsorption beds each containing a material that is effective to adsorb said vapor which material is present in an amount sufficient to adsorb substantial amounts of said vapor;

(b) a feed means for controllably directing said feedstream into said beds; (c) a backpurge means for controllably permitting a flow of backpurge gas through each said bed in a direction counter to the flow of said feedstream when said bed in not receiving said feedstream;

(d) a vacuum pump having an inlet and an outlet;

(e) a conduit means controllably connected to each adsorption bed and to the inlet of said vacuum pump, so that said vacuum pump can place each bed under reduced pressure while it is not receiving said feedstream, thereby desorbing at least some of said vapor i nto said backpurge gas and through said conduit means into the inlet of said vacuum pump;

(f) a liquid-gas compressor having an inlet and an outlet, the inlet of said liquid- gas compressor being in fluid communication with the outlet of said vacuum pump; (g) a vapor receiving means for receiving desorbed vapor and backpurge gas from the outlet of said liquid-gas compressor for use or disposal of said vapor; and

(h) characterized by a means for controlling the pressure of desorbed vapor and backpurge gas in the vapor receiving means at a pressure above atmospheric pressure, the means for controlling the pressure of desorbed vapor and backpurge gas in the vapor receiving means being in fluid communication with the vapor receiving means.

10. The apparatus of Claim 9, wherein said liquid-gas compressor is a liquid- ring compressor.

11. The apparatus of Claim 10 for recovering an oil-soluble solvent monomer or hydrocarbon, wherein said vacuum pump is an oil-sealed vacuum pump. 12. The apparatus of Claim 1 1 , wherein said vapor receiving means further comprises; a condenser in fluid communication with the outlet of said liquid-ring compressor so that the condenser receives and condenses at least ten percent of said desorbed oil-soluble vapor; a condensate recovery means connected to said condenser into which condensed vapor can pass; and a recycle means connected to said condenser or condensate recovery means which returns uncondensed desorbed vapor to the feedstream.

13. The apparatus of Claim 12, wherein the condenser is a shell and tube condenser, the outlet of said liquid-ring compressor being connected to the tube side of the shell and tube condenser.

14. The apparatus of Claim 12, wherein the means for controlling the pressure of desorbed vapor and backpurge gas in the vapor receiving means at a pressure above atmospheric pressure is a flow control valve.