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WO1992019359A1 - Procede servant a retirer de flux gazeux des constituants condensables - Google Patents

Procede servant a retirer de flux gazeux des constituants condensables Download PDF

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Publication number
WO1992019359A1
WO1992019359A1 PCT/JP1991/000609 JP9100609W WO9219359A1 WO 1992019359 A1 WO1992019359 A1 WO 1992019359A1 JP 9100609 W JP9100609 W JP 9100609W WO 9219359 A1 WO9219359 A1 WO 9219359A1
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WO
WIPO (PCT)
Prior art keywords
membrane
stream
permeate
condensable component
feed
Prior art date
Application number
PCT/JP1991/000609
Other languages
English (en)
Inventor
Johannes G. Wijmans
Original Assignee
Membrane Technology And Research, Inc.
Nitto Denko Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Membrane Technology And Research, Inc., Nitto Denko Corporation filed Critical Membrane Technology And Research, Inc.
Priority to JP03508271A priority Critical patent/JP3023802B2/ja
Priority to PCT/JP1991/000609 priority patent/WO1992019359A1/fr
Publication of WO1992019359A1 publication Critical patent/WO1992019359A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/225—Multiple stage diffusion
    • B01D53/226—Multiple stage diffusion in serial connexion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/229—Integrated processes (Diffusion and at least one other process, e.g. adsorption, absorption)

Definitions

  • Gas streams containing condensable components arise from numerous industrial and commercial processes. Venting such gases to the atmosphere wastes resources and causes pollution problems. Industries throughout the world are, therefore, under increasing pressure to clean up waste gas emissions.
  • a widely used treatment method is condensation. The idea is to cool and/or compress the gas beyond the dewpoint of the condensable constituent. A portion of the condensable component will then condense out and can be drawn off in liquid form for reuse or disposal. The degree of removal that can be achieved in this way will depend on the initial concentration, the boiling point of the condensable, and the operating conditions of the process.
  • the invention is a combination, or "hybrid", process that can reduce the concentration of a condensable component in a gas stream to 5% or less of its original value, and because of the inherent complementary features of the two processes, can do this in a highly efficient, economic manner.
  • the process involves two main steps, a condensation step and a membrane concentration step.
  • the condensation step may be followed by the membrane step, or vice versa.
  • Streams containing low concentrations of the condensable component will typically benefit from membrane concentration followed by condensation.
  • Streams close to saturation with the condensable component are preferably treated by condensation followed by membrane concentration.
  • the hybrid process can be designed to yield only two product streams: one, the condensed liquid, ready for use, reuse or discard, and two, a gas stream containing only 5% or less of the original condensable content, which in most cases will be clean enough for direct discharge or reuse. This result is achieved by recycling other streams within the process. If the membrane concentration step is performed after the condensation step, then the permeate stream from the membrane step can be returned and fed back into the condensation process. If the condensation step is performed after the membrane concentration step, then the non-condensed gases can be returned to the feed of the membrane concentration step. Thus, no secondary wastes or pollution problems are created by the process.
  • condensation and membrane separation may be used alone for treating gases containing condensable components.
  • Table 1 summarizes the representative features of the individual processes. As can be seen, each process has its strengths and weaknesses. In particular, the operating costs of a condensation process are strongly dependent on the boiling point of the condensable material. Compounds with relatively high boiling points, for example room temperature or above, can be handled much more efficiently than those with lower boiling points, particularly those with boiling points below 0oC. Condensation becomes increasingly expensive with decreasing feed concentration. At high feed concentrations, condensation is cheaper than membrane separation. In contrast, membrane separation process costs are independent of feed concentration, and membranes are known that exhibit useful selectivities in separating volatile, low-boiling organics and other compounds from air, for example.
  • Condensation is frequently performed by first compressing the gas stream to be treated to an elevated pressure, such as 2-15 atmospheres. Consequently, the non-condensed fraction of gas leaving the condenser is often at high pressure. This high pressure can be used to provide the driving force for membrane permeation.
  • the membrane separation step can be carried out without the need for any additional energy use whatsoever.
  • a process that combines the two individual treatment methods can utilize the advantages of each one to create an optimized process that achieves better results, at higher efficiency, than could be gotten from either method alone. Table 1. Comparative Features of Condensation and Membrane Separation
  • the combination process can be designed to offer energy and cost savings compared with other treatment methods.
  • the combination process can improve five-fold or more on the degree of removal of condensable components achievable with condensation alone. 4. No secondary streams.
  • the process can be designed to generate only two product streams, a condensed liquid stream and a gas stream sufficiently free of condensable compounds for discharge or reuse.
  • the process can be designed to operate without the need for prior pooling, dilution or concentration of the waste stream.
  • the gas stream to be treated by the process of the invention may be an effluent stream that would otherwise be discharged into the atmosphere untreated, or would be subject to some other treatment method or methods.
  • it may be an internal process stream from which it is desirable, for example, to recover an organic solvent for reuse.
  • the process could be carried out by fitting a membrane unit to existing condensation units, or by installing a new combined condensation/membrane unit. Adding membrane units, either in front of, or behind, existing condensation units, is a relatively simple engineering task. The capital cost of the membrane equipment could be recovered within months in the most favorable applications.
  • the process of the invention involves running a feed gas stream containing a condensable component through two treatment steps, a condensation step and a membrane separation step.
  • the membrane separation step involves running the gas stream containing a condensable component across a membrane that is selectively permeable to that component.
  • the condensable component is therefore concentrated in the stream permeating the membrane; the residue, non-permeating, stream is correspondingly depleted in condensable content.
  • the driving force for permeating across the membrane is the pressure difference between the feed and permeate sides, which can be generated in a variety of ways.
  • the membrane separation process produces a permeate stream enriched in the condensable component compared with the feed and a residue stream depleted in the condensable component.
  • the membrane separation process may be configured in many possible ways, and may include a single membrane stage or an array of two or more units in series or cascade arrangements. Eighty to 909. or above removal of the condensable content of the feed to the membrane system can typically be achieved with an appropriately designed membrane separation process, leaving a residue stream containing only traces of the condensable material.
  • the permeate stream is typically concentrated 5- to 100-fold compared with the feedstream.
  • the membrane used in the membrane separation step will typically be selectively permeable to the condensable component of the feedstream, so that the permeate stream from the membrane is enriched many-fold in the condensable component.
  • the condensation step may be performed by simply chilling the gas stream down to a temperature at which a substantial fraction of the condensable content of the stream will condense. Simple chilling may be efficient in situations where the boiling point of the condensable material is relatively high.
  • the condensation step will involve running the gas stream through a compressor, then chilling it to a temperature below the dewpoint temperature at that pressure. Eighty percent or above removal of the condensable content can typically be achieved by the condensation system.
  • Figure 1 is a graph showing the relationship between permeate vapor concentration and pressure ratio for membranes of varying selectivities.
  • Figure 2 is an embodiment of the invention using a condensation step, involving compressing and cooling the gas stream, followed by a membrane separation step using a single membrane unit.
  • Figure 3 is an embodiment of the invention using a condensation step, involving compressing and cooling the gas stream, followed by a membrane separation step using a two-stage cascade arrangement.
  • Figure 4 is an embodiment of the invention using a condensation step, involving compressing and cooling the gas stream, followed by a membrane separation step using a two-step series arrangement.
  • Figure 5 is an embodiment of the invention using a membrane separation step with a single membrane unit, followed by a condensation step, involving compressing and cooling the gas stream.
  • Figure 6 is an embodiment of the invention using a condensation step, involving compressing and cooling the gas stream, followed by a membrane separation step using a single membrane unit, selectively permeable to a non-condensable component of the gas stream.
  • Figure 7 is an embodiment of the invention using a membrane separation step with a single membrane unit, selectively permeable to a non-condensable component of the gas stream, followed by a condensation step, involving; compressing and cooling the gas stream.
  • Figure 8 is an embodiment of the invention where a condensation step is performed between two membrane separation steps.
  • Figure 9 is a graph showing the relationship between feed and permeate concentrations of acetone, 1,1,1-trichloroethane, toluene and octane.
  • Figure 10 is a graph showing the relationship between feed and permeate concentrations of perchloroethylene.
  • Figure 11 is a graph showing the relationship between feed and permeate concentrations of CFC-11 at low CFC feed concentrations.
  • Figure 12 is a graph showing the relationship between feed and permeate concentrations of CFC-11 at CFC feed concentrations up to about 35vo1%.
  • Figure 13 is a graph showing the relationship between feed and permeate concentrations of CFC-113 at CFC feed concentrations up to about 6vol%.
  • Figure 14 is a graph showing the relationship between feed and permeate concentrations of HCFC-123 at feed concentrations up to about 8%.
  • Figure 15 is a graph showing the relationship between feed and permeate concentrations of methylene chloride at feed concentrations up to about 8%.
  • condensable and condensable component refer to fluids below their critical temperatures and having boiling points greater than -100°C. In the event that a mixture containing two or more condensable components is to be treated, the terms condensable and condensable component refer to the more readily condensable component or components.
  • permselective refers to polymers, or membranes made from those polymers, that exhibit selective permeation for at least one gas or vapor in a mixture over the otehr components of the mixture, enabling a measure of separation between the components to be achieved.
  • multilayer means comprising a support membrane and one or more coating layers.
  • selectivity means the ratio of the permeabilities of gases or vapors as measured with mixed gas or vapor smaples under the normal operating conditions of the membrane.
  • residue stream means that portion of the feedstream that does not pass through the membrane.
  • permeate stream means that portion of the feedstream that passes through the membrane.
  • membrane unit means one or more membrane modules arranged in parallel, so that a portion of the incoming gas stream passes through each one.
  • series arrangement means an arrangement of membrane modules or units connected together such that the residue stream from ome module or unit becomes the feedstream for the next.
  • cascade arrangement means an arrangement of membrane modules or units connected together such that the permeate stream from one module or unit becomes the feedstream for the next.
  • membrane array means a set of one or more individual membrane modules or membrane units connected in a series arrangement, a cascade arrangement, or mixtures or combinations of these.
  • product residue stream means the residue stream exiting a membrane array when the membrane separation process is complete. This stream may be derived from one membrane unit, or may be the pooled residue streams from several membrane units.
  • product permeatestream means the permeate stream exiting a membrane array when the membrane separation process is complete. This stream may be derived from one membrane unit, or may be the pooled permeate streams from several membrane units.
  • a feed gas stream containing a condensable component is passed through a condensation step and a membrane separation step.
  • the sources of the gas streams to be treated are diverse. Many industrial processes produce waste gas streams containing organic vapcrs. For example, solvent-containing airstreams are produced as a result of solvent vaporization in the drying of synthetic fibers and films, plastics, printing inks, paints and lacquers, enamels and other organic coatings. Solvents are also used in the preparation of adhesive coatings and tapes. Waste gases containing organic vapors are generated by solvent degreasing operations in the metal and semiconductur industries. Hydrocarbon vapors are released from petroleum storage tanks during transfer operations.
  • CFCs Chlorinated fluorocarbons
  • Other sources of extensive CFC pollution are refrigeration operations, air conditioning and fire extinguisher filling and use.
  • concentration of these streams varies widely, from a few ppm to as high as 40-50% or more organic.
  • Organic vapors that can be handled by the process include, but are not limited to, chlorofluorocarbons such as CFC-11 (CC l3 F), CFC-12 (CCl 2 F 2 ), CFC-113 (C 2 Cl 3 F 3 ), CFC-114 (C 2 Cl 2 F 4 ), CFC-15 (C 2 ClF 5 ), HCFC-21 (CHCl 2 F), HCFC-22 (CHClF 2 ), HCFC-23 (CHF 3 ), HCFC-123 (C 2 HCl 2 F 3 ), HCFC-142b (C 2 H 3 CIF 2 ), Halon-1211 (CF 2 ClBr), Halon-1301 (CF 3 Br) and Halon-2402 (C 2 F 4 Br2); chlorinated hydrocarbons, such as tetrachloroethylene, trichloroethylene, methylene chloride, 1,1,1-trichloroethane, 1,1,2-trichloroethane, carbon tetrachloride, chlorobenzene,
  • organic-component- containing streams will comprise the organic material in air.
  • Mixtures of organic components in nitrogen are also commonly encountered, because nitrogen is frequently used as a blanketing gas.
  • Streams of organic compounds in other gases, or streams comprising mixtures of organics are also found.
  • hydrogenation reactions in the chemical industry yield off-gas streams containing hydrogen and various hydrocarbons.
  • Treatment of such streams could be carried out using a membrane type preferentially permeable to the hydrocarbon component or a membrane type preferentially permeable to hydrogen.
  • Mixed organic component streams might arise, for example, from natural gas processing or petrochemical refining, where the stream could contain a mixture of methane, ethane, propane, butane and so on.
  • the process of the invention has two main steps, the membrane separation step and the condensation step.
  • the membrane separation step preferably uses a membrane that is relatively permeable to a condensable component of the stream, but relatively impermeable to other gases in the stream.
  • Preferred embodiments of the invention employ a composite membrane. This has two layers, a microporous support, which provides mechanical strength, and an ultrathin permselective coating, which is responsible for the separation properties.
  • the microporous support membrane should have a flow resistance that is very small compared to the permselective layer.
  • a preferred support membrane is an asymmetric Loeb-Sourirajan type membrane, which consists of a relatively open, porous substrate with a thin, dense, finely porous skin layer.
  • the pores in the skin layer should be less than 1 micron in diameter, to enable it to be coated with a defect-free permselective layer.
  • the support membrane should resist the solvents used in applying the permselective layer.
  • Polymers that may be used to form the microporous support membrane include polysulfone, polyimide, polyvinylidene fluoride, polyamide, polypropylene or polytetrafluoroethylene.
  • the membranes may be prepared by the processes for making finely microporous or asymmetric membranes known in the art.
  • NTU ® 4220 crosslinked polyimide
  • NTU ® 3050 polysulfone
  • the thickness of the support membrane is not critical, since its permeability is high compared to that of the permselective layer. However the thickness would normally be in the range 100 to 300 microns, with out 150 microns being the preferred value.
  • the suspport membrane may be reinforced by casting it on a fabric or paper web.
  • the multilayer membrane then comprises the web, the microporous membrane, and the ultrathin permselective membrane.
  • the web material may be made from polyester or the like.
  • the permselective layer could not be cast directly on the fabric web, because it would penetrate the web material, rather than forming an unbroken surface coating.
  • the permselective layer should be made very thin.
  • the permselective layer must also be free of pinholes or other defects that could destroy the selectivity of the membrane by permitting bulk flow-through of gases.
  • the preferred membrane is one in which the permselective coating is deposited directly on the microporous support.
  • optional embodiments that include additional sealing or protective layers above or below the permselective layer are also intended to be encompassed by the invention.
  • the preferred method of depositing the permselective layer is by dip coating.
  • the polymer material that forms the permselective layer should be a film-forming material that is soluble in an organic solvent.
  • the dip coating method is described, for example, in U.S.Patent 4,243,701 to Riley et al., incorporated herein by reference.
  • a support membrane from a feed roll is passed through a coating station, then to a drying oven, and is then would onto a product roll.
  • the coating station may be a tank containing a dilute polymer or prepolymer solution, in which a coating, typically 50 to 100 microns thick, is deposited on the support. Assuming a 1% concentration of polymer in the solution, then after evaporation a; film 0.5 to 1 micron thick is left on the support.
  • the permselective membrane may be cast by spreading 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 onto the microporous support. This method is more difficult in practice, but may be useful if the desired support is attacked by the solvent used to dissolve the permselective material.
  • the thickness of the permselective layer should normally be in the range 0.1 to 20 microns, preferably 10 microns or less, and more preferably 0.1 to 5 micron.
  • the form in which the membranes are used in the invention is not critical. They may be used, for example, as flat sheets or discs, coated hollow fibers, or spiral-wound modules, all forms that are known in the art. Spiral-wound modules are a preferred choice. References that teach the preparation of spiral-wound modules are S.S. Kremen, "Technology and Engineering of ROGA Spiral Wound Reverse Osmosis Membrane Modules", in Reverse Osmosis and Synthetic Membranes, S.Sourirajan (Ed.), National Research Council of Canada, Ottawa, 1977; and U.S.Patent 4,553,983, column 10, lines 40-60. Alternatively the membranes may be configures as microporous hollow fibers coated with the permselective polymer material and then potted into a module.
  • the membrane may take the form of a homogeneous membrane, a membrane incorporating a gel or liquid layer, or dispersed particulates, or any other form known in the art.
  • the choice of permselective membrane material will depend upon the separation to be performed.
  • a number of rubbery polymers could be used.
  • Examples include nitrile rubber, neoprene, silicones rubbers, including polydimethylsiloxane, chlorosulfonated polyethylene, polysilicone-carbonate copolymers, fluoroelastomers, plasticized polyvinylchloride, polyurethane, cis-polybutadiene, cis-polyisoprene, poly(butene-1), polystyrene-butadiene copolymers, styrene/butadiene/styrene block copolymers and styrene/ethylene/butylene block copolymers.
  • Particularly preferred rubbers are silicone rubbers.
  • Thermoplastic polyolefin elastomers and block cpolymers of polyethers and polyesters would also be useful.
  • Suitable polymers include, for example, cellulose and derivatives, such as cellulose diacetate, cellulose triacetate, cellulose nitrate and ethylcellulose; polyvinyl chloride, polyvinylidene fluoride or polyacrylate.
  • Other suitable membranes could be made from polymers or copolymers that combine glassy and rubbery segments. Examples include polyamide-polyether block copolymers such as those having the formula: where PA is a polyamide segment, PE is a polyether segment, and n is a positive integer.
  • Such polymers have both high selectivity and high flux for sulfur dioxide.
  • Such membranes are described in detail in copending application number 295,686, incorporated herein by reference.
  • Liquid membranes such as polyethylene glycol, also exhibit high flux and selectivity for sulfur dioxide and could be used in the process of the present invention.
  • glassy membranes that are highly selective to hydrogen over ammonia, such as polyimide membranes, could be used. The ammonia would then be concentrated in the residue stream.
  • Ammonia-selective membranes could be made from rubbery materials.
  • Other suitable membranes would be the molten salt membranes described in U.S. Patent 4,758,250 to Air Products.
  • membranes that are selectively permeable to the non-condensable or less condensable component (s) of the feed gas are also possible.
  • membranes made from glassy polymers are preferable.
  • Such polymers include, for example, polysulfone, polyethersulfone, polyimides, polycarboantes, brominated polyestercarbonates and the like.
  • J is the membrane flux (cm 3 (STP)/cm 3 ⁇ s ⁇ cmHg)
  • D is the diffusion coefficient of the gas or vapor in the membrane (cm /sec) and is a measure of the gas mobility
  • l is the membrane thickness
  • k is the Henry's law sorption coefficient linking the concentration of the gas or vapor in the membrane material to the pressure in the adjacent gas (cm3 (STP) /cm3.cmHg)
  • ⁇ p is the pressure difference across the membrane.
  • the product Dk can also be expressed as the permeability, P, a measure of the rate at which a particular gas or vapor moves through a membrane of standard thickness ( 1 cm) under a standard pressure difference (1 cmHg).
  • a measure of the ability of a membrane to separate two components, (1) and (2), of a feedstream is the ratio of their permeabilities, ⁇ , called the membrane selectivity
  • the permselective membranes used in the present invention should preferably have a selectivity for the preferentially permeating component of at least 5, more preferably at least 10, and most preferably at least 20.
  • the first is the extent of removal of condensable component from the feed.
  • the concentration of condensable component in the feedstream decreases as it passes through the membrane module.
  • the average concentration of the condensable component on the feed side of the membrane will determine the average concentration of that component on the permeate side of the membrane.
  • the average feed stream concentration will be low.
  • the enrichment in the permeate stream will be low also.
  • the average concentration of condensable component in the permeate decreases.
  • a second factor affecting the performance of a membrane system is the pressure of feed and permeate gas streams.
  • the driving force for permeation is the difference between the partial pressures of the components; on the feed and permeate sides.
  • the ratio of the feed to the permeate pressures defined as total permeate pressure (p)
  • total feed pressure (p') (3) is important.
  • the partial pressure of the condensable component on the permeate side of the membrane must never exceed the partial pressure on the feed side, or the permeation process would stop.
  • the concentration of condensable component on the permeate side of the membrane can never be greater than 1/ ⁇ times the concentration in the feed.
  • the relationship between pressure ratio and selectivity can be derived from the Fick's law expression for the membrane fluxes, J 1 and J 2 , given as
  • P 1 and P 2 are the permeabilities of components 1 and 2
  • l is the membrane thickness
  • p' 2 and p" 1 , P" 2 are the partial pressures of the two gases or vapors in the feed and permeate streams, respectively.
  • the total gas pressure is equal to the sum of the partial pressures, i.e.,
  • Figure 1 plots the calc ulated permeate condensable component concentration, C" 2 , ag ainst pressure ratio, ⁇ ,for membranes of selectivities 20,50, 100,200 and 500.
  • the pressure drop across the membrane can be achieved by pressurizing the feed, by evacuating the permeate or by both. If the membrane separation step follows the condensation step, and the condensation step includes compression, then the feed to the membrane step may already compression, then the feed to the membrane step may already be at a high pressure compared with atmospheric, such as 1-10 atmospheres. Therefore, drawing a vacuum on the permeate side may not be necessary. If the membrane separation step precedes the condensation step, it may be preferable to keep the feed at atmospheric pressure and to lower the permate pressure by means of a vacuum pump. At pressure ratios between 0.01 and 0.001, very large differences in performance with differing selectivity can be achieved. In large-scale operations, the cost of maintaining a hard vacuum on the permeate side may be very high.
  • the preferred operating zone for the processes of the invention is generally in the middle region of Figure 1, where a good separation can be achieved by combining a membrane with a good, but not excessively high, selectivity, typically in the range 5-200, with a pressure ratio in an economically sustainable range, such as 0.005-0.5. This limits the maximum enrichment of condensable component obtained in a single-stage industrial system to this range.
  • the ratio of the permeate flow to the feed flow is called the stage cut.
  • the degree of depletion of the more permeable component from the feed depends on the stage cut.
  • the feed gas becomes substantially depleted in the more permeable components.
  • the average concentration of the more permeable component seen by the membrane is substantially lower than the initial feed gas concentration.
  • the result is a fall in the concentration of the more permeable component in the permeate stream.
  • a stream contains 4% condensable component and it is desired to reduce the concentration to 0.5%. If only the condensable component, and would be 3.5% of the total feed flow.
  • the minimum stage cut to achieve this degree of separation would be 3.5%.
  • stage cut will always be higher than this, because the other gases in the feed will also permeate the membrane to some extent.
  • the stage cut should be kept low, preferably below 40% and most preferably below 30%.
  • the membrane separation step should preferably be designed to achieve removal of at least 50% of the condensable component present in the feed to the membrane system, more preferably at least 70% and most preferably at least 80%.
  • the condensation step may involve chilling, compression or a combination of these.
  • the goal of the condensation step is to bring the gas stream to the dewpoint of the condensable component, so that a portion of the condensable component will condense out of the gas stream in liquid form.
  • the amount of the condensable component that can be removed from the gas stream in this way will depend on the boiling point of the condensable component, its concentration in the feed, and the operating conditions under which the condensation is performed.
  • the gas stream to be treated by the condensation step should preferably contain above about 10-20% of the saturation concentration of the condensable component at ambient temperature and pressures. Very dilute streams are difficult to treat efficiently.
  • the gas stream will pass first through a compresser, where it is pressurized to a pressure in the range 1-15 atmospheres. Compression above about 15 atmospheres, and particularly above 20 atmospheres is less desirable, because of the energy demands and consequent high cost.
  • the gas is cooled, for example by running it through a condenser.
  • the condenser may be water cooled, or may employ refrigerants that can take the gas down to lower temperatures.
  • chilling without compression may be adequate to recover the bulk of the condensable material.
  • the chiller temperature should be no lower than about 10 °C because this permits simple water cooling.
  • the second limit also very desirable, is that the chiller temperature be no lower than 0°C, because ice formation in the condenser is then avoided. Many, if not most, streams to be treated will contain water vapor. If the condenser temperature is below 0°C, periodic defrosting or dehydration pre-treatment will always be necessary.
  • the third limit occurs at around -45°C. Temperatures down to about -45°C should be possible to reach in a single-stage chilling operation, but costs will be relatively high compared with the two preferred options above.
  • the fourth, and least preferred, mode of operation is to chill down to as low as -100°c or below. This will normally require at least two chillers operating at progressively lower temperatures. The increase in energy requirements and costs is now sharp in comparison with the preferred modes.
  • the hybrid membrane separation/condensation processes taught herein can often be tailored so that the condensation step can be performed above 0oC. This is a major advantage of such processes.
  • the fraction of condensable component remaining in the condenser vent gas after the condensation step depends on the vapor/liquid equilibrium at the operating conditions under which the condensation step is performed. From the economic and energy consumption viewpoints, it is preferable that the dewpoint be reached at a combination of modest pressures and temperatures. If the dewpoint is reached at 2 atmospheres and 10oC for example, then compressing the stream to 10 atmospheres and cooling will remove approximately 80% or more of the organic vapor. If the concentration and boiling point are such that the stream is already saturated at atmospheric pressure and ambient temperature, then compressing the stream to 10 atmospheres will remove at least 90% or more of the organic vapor. If is theoretically possible to obtain 95% or more removal of any volatile component from the feed gas stream by creating appropriate conditions of high pressure and low temperature.
  • the condensation step be designed to remove at least 50% or more of the condensable component present in the feed to the condenser. Most preferably, the condensation step should be designed to remove at least 70% or more of the condensable component present in the feed to the condenser. Operation under extreme conditions to achieve 90% ro more condensable removal is usually unnecessary, because of the presence of the membranestep. If the condensation step necessitates cooling to below 0°C, and the gas stream contains water vapor, then optionally the condensation step may use two chillers in series.
  • the first chiller is maintained at a temperature close to 0°C, and removes most of the entrained water.
  • the second chiller is maintained at the lower temperature necessary to remove a substantial fraction of the condensable component. Some water vapor will inevitably pass into the second chiller but the use of the first chiller will significantly reduce the need for defrosting the second.
  • the condensation step may include another type of dehydration process through which the gas stream passes before it enters the condenser.
  • the overall degree of condensable removal and recovery that can be achieved by the hybrid process of the invention will depend on the combined effects of the condensation step and the membrane separation step. For example, suppose the condensation step removes 50% of the condensable component of the feed gas. If the condensation step is followed by a membrane separation step that can remove 80% of the condensable component reaching it, then the total removal obtained by the process is 90%. If the condensation step removes 80%, and is followed by a membrane separation step that also removes 80%, then the total removal obtained by the process is 96%. If the condensation step removes 80% and the membrane separation step 90%, the total removal is 98%.
  • the above discussion is intended to show that the process can be tailored to achieve a desired degree of condensable removal in a highly efficient manner.
  • the tailoring can be done by comparing estimates of the energy and dollar costs with several sets of system configurations and operating conditions. For example, the costs and energy requirements to achieve 95% total removal, using an initial condensation step removing 50, 75 or 90% of the condensable component, followed by a membrane separation step removing 90, 80 or 50% of the remaining condensable component, could be compared,
  • Figures 2-7 show some representative examples.
  • the process of the invention may be configured so that the condensation step is followed by the membrane separation step, or vice versa. If the concentration of the condensable component in the gas stream is above about 20-50% of the saturation concentration under ambient conditions, then it is normally preferable to subject the incoming gas stream first to the condensation step and then to the membrane separation step.
  • a basic embodiment of the invention according to this sheme is shown in Figure 2. Referring now to this figure, incoming gas stream, 1, containing a condensable component, is passed through compressor, 2, to form compressed gas stream, 3. This stream passes through condenser, 4, to yield a condensed liquid stream of the condensable component, 5.
  • the non-condensed fraction, 6, of the gas stream passes to membrane separation unit, 7, which contains membranes selectively permeable to the condensable component.
  • the non-permeating, residue stream, 8, is thus depleted in the condensable component.
  • a pressure difference across the membrane is provided by optional vacuum pump, 9. If the feed gas to the membrane is at high pressure, then the vacuum pump may not be necessary because a sufficient pressure drop across the membrane already exists.
  • the permeate stream, 10, is enriched in the condensable component and can be returned and mixed with the incoming gas stream for recompression and condensation.
  • This type of process could be used, for example, when the vent stream from the condensation process step contains the condensable component in a low concentration.
  • the second stage of the membrane array minimizes the amount of non-condensable component recirculated to the condenser system.
  • incoming gas stream, 11, containing a condensable component is passed through compressor, 12, to form compressed gas stream, 13.
  • This stream passes through condenser, 14, to yield a condensed liquid stream of the condensable component, 15.
  • the non-condensed fraction, 16, of the gas stream passes to first membrane separation unit, 17, which contains membranes selectively permeable to the condensable component.
  • the non-permeating, residue stream, 18, is thus depleted in the condensable component.
  • a pressure difference across the membrane is provided by optional vacuum pump, 19.
  • the permeate stream, 20, is enriched in the condensable component, but still contains significant amounts of non-condensables.
  • the permeate from the first membrane unit is therefore fed to second membrane unit, 22, after recompression in compressor, 21.
  • a pressure difference across the second membrane unit is provided by vacuum pump, 25.
  • the permeate stream, 24, from the second membrane unit is now highly concentrated in the condensble component and can be returned and mixed with the incoming gas stream for recompression and condensation.
  • the residue stream, 23, from the second membrane unit, depleted in the condensable component compared with stream 20, may optionally be recycled to the feed side of the first membrane unit. In this way the process produces only two streams, the liquid stream of the condensable component, 15, and the relatively clean residue stream, 18.
  • FIG. 4 A second alternative embodiment of the invention, employing a membrane array consisting of a two-step series arrangement, is shown schematically in Figure 4.
  • This type of process could be used, for example, when the vent stream from the condensation process step contains the condensable component in a relatively high concentration and if the desired removal by the membrane separation unit is high.
  • incoming gas stream, 31, containing a condensable component is passed through compressor, 32, to form compressed gas stream, 33.
  • This stream passes through condenser, 34, to yield a condensed liquid stream, 33.
  • This stream passes through condenser, 34, to yield a condensed liquid stream of the condensable component, 35.
  • the non-condensed fraction, 36, of the gas stream passes to first membrane separation unit, 37, which contains membranes selectively permeable to the condensable component.
  • a pressure difference across the membrane is provided by optional vacuum pump, 39.
  • the permeate stream, 40 is enriched in the condensable component and can be returned and mixed with the incoming gas stream for recompression and condensation.
  • the non-permeating, residue stream, 38 is depleted in the condensable component compared with stream 36, but still contains too much of the co ⁇ densable component for discharge.
  • Stream 38 is therefore fed to second membrane unit, 41.
  • a pressure difference across the second membrane unit is provided by vacuum pump, 44.
  • the residue stream, 42, from the second membrane unit is now sufficiently depleted in the condensable component for discharge .
  • the permeate stream, 43, from the second membrane unit, enriched in the condensable component compared with stream 38, may optionally be recompressed by compressor, 45, and recycled to the feed side of the first membrane unit. In this way the process produces only two streams, the liquid stream of the condensable component, 35, and the relatively clean residue stream, 42.
  • gas stream, 51 containing a condensable component
  • membrane separation unit, 52 which contains membranes selectively permeable to the condensable component.
  • the non-permeating, residue stream, 53 is thus depleted in the condensable component.
  • a pressure difference across the membrane is provided by vacuum pump, 55.
  • the permeate stream, 54 is enriched in the condensable component. .
  • recycle of streams within the membrane separation step can be performed.
  • the residue stream from the second membrane unit in the cascade arrangement may be returned to feed side of the first unit.
  • the permeate stream from the second membrane unit in the series arrangement can be returned to the feed side of the first unit.
  • FIG. 6 shows such an embodiment.
  • the incoming gas stream, 61 containing a condensable component, is passed through compressor, 62, to form compressed gas stream, 63.
  • This stream passes through condenser, 64, to yield a condensed liquid stream of the condensable component, 65.
  • the non-condensed fraction, 66, of the gas stream passes to membrane separation unit, 67, which contains membranes selectively permeable to the non-condensable component.
  • the non-permeating, residue stream, 68, is thus enriched in the condensable component, and can be returned to the condenser inlet without recompression.
  • a pressure difference across the membrane is provided by optional vacuum pump, 59.
  • the permeate stream, 70 is depleted in the condensable component and can be discharged or reused as desired. Variations of this embodiment include those in which the single membrane unit shown in Figure 6 is replaced by a cascade or a series arrangement.
  • Figure 7 shows an embodiment also using non-condensable selective membranes, in which the membrane separation step precedes the condensation step.
  • the incoming gas stream, 71 containing a condensable component, is passed through compressor, 72, to form compressed gas stream, 73, and thence to membrane separation unit, 74, which contains membranes selectively permeable to the non-condensable component.
  • the non-permeating, residue stream, 77 is thus enriched in the condensable component, and is passed to condenser, 78, to yield a condensed liquid stream of the condensable component, 79.
  • the non-condensed fraction, 80, of the gas stream from the condenser is returned to the feed side of the membrane unit without recompression.
  • a pressure difference across the membrane is provided by optional vacuum pump, 75.
  • the permeate stream, 76 is depleted in the condensable component and can be discharged or reused as desired.
  • variations in which the single membrane unit shown in Figure 7 is replaced by a cascade or a series arrangment, are possible.
  • Processes of the type shown in Figures 6 and 7 are particularly suited to the treatment of volatile, but condensable, component stream containing minor amounts of relatively non-condensable gases.
  • volatile, but condensable, component stream containing minor amounts of relatively non-condensable gases For example, in the production of vinyl chloride, off gases are produced containing 90% or more vinyl chloride contaminated with carbon dioxide, nitrogen and oxygen. Membranes preferentially permeable to carbon dioxide, nitrogen and oxygen could be used to leave behind a an essentially pure vinyl chloride residue stream.
  • the process of the invention may also be carried out by using two discrete membrane separation steps, between which the condensation step is performed.
  • Process designs of this type enable different membrane materials to be used in the two membrane separation steps. Also the membrane area used in the two steps, and hence the gas processing capacity, can be different.
  • An embodiment of this type is shown in Figure 8. Referring now to this figure, feed gas stream, 81, containing a condensable component, passes through optional compressor, 82, to form compressed gas stream, 83. This stream is passed to first membrane separation unit 84, which contains membranes selectively permeable to the condensable component. The non-permeating, residue stream, 86, is thus depleted in the condens ble component. A pressure difference across the membrane is provided by optional vacuum pump, 85.
  • the permeate stream, 87 is enriched in the condensable component.
  • This stream is passed through compressor, 88, and thence to condenser, 89, to yield a condensed liquid stream of the condensable comopnent, 90.
  • the non-condensed fraction, 91, of the gas stream is passed to second membrane separation unit, 92.
  • the residue stream, 94, from this unit is returned to the feed side of the first membrane unit.
  • the permeate stream, 93 is sufficiently enriched to be returned to the condensation step.
  • first and second membrane arrays may be used instead of single membrane units, if necessary.
  • similar process designs to that shown in Figure 8 can be devised using membranes that are selective for the non-condensable component.
  • a particular advantage of the process of the invention relates to the driving forces for the individual condensation and membrane separation processes. Condensation is frequently facilitated by at least a moderate degree of compression of the gas stream. Compression of the gas stream to be treated also facilitates the membrane separation step. If the feed to the membrane system is at high pressure compared to atmospheric, this may completely obviate the need for a vacuum pump or other means of lowering the pressure on the permeate side.
  • Typical emissions from storage tanks are C 3 through C 6 hydrocarbons.
  • the total capacity of refining storage systems is on the order of 35 to 50 million tons of crude oil and 20 to 30 million tons of gasoline. The hydrocarbon lost per year thus amounts to 1-2% of the storage capacity.
  • Streams produced during the storage and transfer of volatile petroleum products typically contain hydrocarbons in air or hydrocarbons in nitrogen. These streams usually contain 20-50% hydrocarbons.
  • the composition of an airstream contaminated with gasoline vapor might typically be approximately as follows: Component Percentage 0 2 12.6
  • hydrocarbon content of such a stream could be reduced from 40% to 0.5% by a - process such as that of Figure 2.
  • CFC-laden emissions represents a major immediate potential application for the process of the invention.
  • Large sources of CFC emissions include air conditioning and refrigeration (mostly CFC-11 and CFC-12), plastic foam manufacture (mostly CFC-11 and CFC-12) and solvent degreasing (mostly CFC-113).
  • Emissions of all types of CFCs also arise from CFC manufacture, storage and transfer operations. Emissions from manufacture, storage and transfer, from foam blowing, and from solvent operations, are all possible candidates for the presently proposed treatment methods.
  • the total volume of all CFC emissions from all sources in the United States was at least 0.7 million tons in 1980 and has grown substantially over recent years.
  • Airstreams contaminated with chlorinated solvents are also widely encountered throughout large and small industries.
  • the streams arise from chemical manufacture and processing operations, film and laminate preparation, coating and spraying, solvent degreasing, industrial and commercial dry cleaning and many other sources. Storage and handling of all these solvents gives rise to contamianted airstreams similar to those discussed in the sections above.
  • methylene chloride which is widely used as a standard solvent in chemical reactions, for degreasing and cleaning of metal parts in many industries, in casing operations, and as a blowing agent in foam production.
  • Methylene chloride has a boiling point of 40oC.
  • Condensation processes are already fairly widely used for methylene chloride recovery, but nevertheless annual emissions of methylene chloride in the U.S. are believed to be in the region of 200,00-300,000 tons. Retrofitting of existing condensation processes with an additional membrane separation unit could reduce emissions from the condensation process by 90% or more.
  • the examples are in four groups.
  • the first group covers the results obtained in a series of experiments carried out according to the general procedure described below. These experiments were performed to determine that separation of organic vapors from gas streams, with adequate selectivity, can be achieved. The experiments were performed with a single membrane module, usually operated at low stage cut, to optimize the concentration of organic vapor in the permeate stream. There was no attempt made in these simple experiments to control the concentration of organic in the residue stream. Having demonstrated that adequate separation is possible, the other groups of examples take representative separations and illustrate how hybrid systems for carrying out the process of the invention can be designed.
  • a small bypass stream was used to take the samples at atmospheric pressure instead of the elevated pressure in the lines.
  • Two liquid nitrogen traps were used to condense "the organic contained in the permeate stream.
  • a non-lubricated rotary-vane vacuum pump was used on the permeate side of the module.
  • the permeate pressure used in the experiments was in the range 1-5 cmHg.
  • the nitrogen permeate flow rate was determined by measuring the vacuum pump exhaust flow rate. This provided a quality check on the module.
  • the organic input was started and the feed concentration was monitored with frequent injections into the GC.
  • the permeate pressure was adjusted if necessary.
  • Step 6 was repeated after 10-20 minutes. The feed concentration was monitored after each parameter change to ensure steady state had been reached.
  • the experimental procedures described above were carried out using a membrane module containing a composite membrane with an area of 1,100 cm 2 .
  • the feedstream comprised nitrogen and acetone, the acetone concentration in the feed varying from about 0.4% to 2%.
  • a plot of acetone concentration in the feed against acetone concentration in the permeate is given by the lowest curve in Figure 9.
  • the permeate was enriched about 18-fold compared with the feed.
  • a feedstream containing 0.45% acetone yielded a permeate containing 8% acetone.
  • the selectivity for acetone over nitrogen was found to be in the range 15-25, depending on the feed concentration of acetone and other operating parameters.
  • the experimental procedures described above were carried out using a membrane module containing a composite membrane with an area of 1,100 cm 2 .
  • the feedstream comprises nitrogen and 1,1,1-trichloroethane, the trichloroethane concentration in the feed varying from about 0.5% to 1.5%.
  • a plot of trichloroethane concentration in the feed against trichloroethane concentration in the permeate is given by the second lowest curve in Figure 9.
  • the permeate was enriched about 24-fold compared with the feed.
  • a feedstream containing 0.5% trichloroethane yielded a permeate containing 13% trichloroethane.
  • the experimental procedures described above were carried out using a membrane module containing a composite membrane with an area of 1,100 cm 2 .
  • the feedstream comprised nitrogen and toluene, the toluene concentration in the feed varying from about 0.2% to 1%.
  • a plot of toluene concentration in the feed against toluene concentration in the permeate is given by the third curve in Figure 9.
  • the permeate was enriched about 48-fold compared with the feed.
  • a feedstream containing 0.65% toluene yielded a permeate containing 30% toluene.
  • the experimental procedures described above were carried out using a membrane module containing a composite membrane with an area of 1,100 cm 2 .
  • the feedstream comprises nitrogen and octane, the octane concentration in the feed varying from about 0.1% to 0.6%.
  • a plot of octane concentration in the feed against octane concentration in the permeate is given by the uppermost curve in Figure 9.
  • the permeate was enriched at least 50-60 fold compared with the feed.
  • a feedstream containing 0.3% octane yielded a permeate containing 14% octane.
  • the experimental procedures described above were carried out using two different membrane modules containing composite membranes with different rubbers as the permselective layer, but both with membrane areas of 3,200 cm 2 .
  • the feedstream comprises nitrogen and perchloro- ethylene, the perchloroethylene concentration in the feed varying from about 0.2% to 0.8%.
  • a plot of perchloroethylene concentration in the feed agaisnt perchloroethylene concentration in the permeate is given in Figure 10. The open circles are for one module; the triangles for the other. Typically the permeate was enriched at least 10-12 fold compared with the feed.
  • a feedstream containing 0.2% perchloroethylene yielded a permeate containing 2.2% perchloroethylene.
  • a feedstream containing 0.5% perchloroethylene yielded a permeate containing 8.3% perchloroethylene.
  • the experimental procedures described were carried out using a feedstream containing CFC-11 (CCl 3 F) in nitrogen in concentrations from 1-35%.
  • the module contained a composite membrane with an area of approximately 2,000 cm .
  • the experimental procedures described above were carried out using a membrane module containing a composite membrane with an area of 2,000 cm 2 .
  • the feedstream comprised nitrogen and methylene chloride, the methylene chloride concentration in the feed varying from about 0.1% to 8%.
  • a plot of methylene chloride concentration in the feed against methylene chloride concentration in the permeate is given in Figure 15.
  • the permeate was enriched about 30-fold compared with the feed at low feed concentrations. At higher concentrations the degree of enrichment dropped to about 10-20 fold.
  • a feedstream containing 2% methylene chloride yielded a permeate containing 44% methylene chloride.
  • a feedstream containing 8% methylene chloride yielded a permeatecontaining 84% methylene chloride.
  • a composite membrane was prepared by coating a support membrane with a permselective membrane made from a polyamide-polyether block copolymer having the following formula:
  • PA is a polyamide segment
  • PE is a polyether segment
  • n is a positive integer.
  • a stamp of the membrane having an area of 12.6 cm 2 was tested at 61°C with a gas mixture containing sulfur dioxide. The pressure on the permeate side of the test cell was maintained at 6.5 cmHg.
  • This set of examples compares treatment of a CFC-11 laden stream by condensation alaone and by the process of the invention.
  • the stream has a flow rate of 100 scfm and contains 50% CFC-11 in all cases.
  • the membrane calculations are all based on CFC-11 selectivities determined in single module experiments of the type described in the first group of examples. The calculations were performed using a computer program based on the gas permation equations for cross flow conditions described by Shindo et al., "Calculation Methods for Multicomponent Gas Separation by Permeation, "Sep. Sci. Technol. 20, 445-459 (1985). The membrane area required was generated by the computer program.
  • the chillercapacity was extrapolated from product literature provided by Filtrine Manufacturing Company, of Harrisville, New Hampshire.
  • the capacities of the vacuum pumps and compressors were obtained or extrapolated from performance specification charts and other data from the manufactures. Energy calculations were done by calculating the adiabatic ideal work of compression and dividing by the efficiency of the unit. Compressor efficiency was taken to be 60%: vacuum pump efficiency was taken to be 35%.
  • the CFC-11 laden stream is compressed to 5 atmospheres, then chilled to 7°C and condensed.
  • the performance is characterized as shown in Table 3. Table 3.
  • Non-condensed off- gas from condenser 10.9% CFC-11 56.1 scfm
  • the CFC-11 laden stream is compressed to 25 atmospheres, then chilled to 7oC and condensed.
  • the performance is characterized as shown in Table 4.
  • Non-condensed off-gas from condenser 2.18% CFC-11 51.1 scfm
  • Non-condensed off- gas from condenser 2.18% CFC-11 51.1 scfm
  • a process was designed to achieve the same level of performance as in Examples 13 and 14.
  • the process involved a condensation step followed by a membrane separation step.
  • the condensation step the CFC-11 laden stream is compressed to 5 atmospheres, then chilled to 7°C and condensed.
  • the non-condensed off-gas from the condensation step is then subjected to a membrane separation step, using a membrane with a selectivity for CFC-11 over air of 30.
  • a pressure drop across the membrane is provided only by the elevated pressure of the compressed feed.
  • the permeate stream from the membrane separation step is returned for treatment in the condensation step.
  • the performance is characterized as shown in Table 6.
  • Example 15 The process as in Example 15 was again considered. The only difference was the inclusion of a small vacuum pump on the permeate side of the membrane to lower the permeate pressure to 15 cmHg. The performance is characterized as shown in Table 7.
  • Vacuum pump 4.4 Comparing this example with Example 15, several differences are apparent. To reduce the residue concentration to 2.18% in Example 15 requires a relatively high stage cut of 40%. The permeate volufme flow is high, 33.3 scfm, so a more powerful compressor is needed to handle the additional load returned from the membrane unit. The membrane area, 41 . 7 m 2 , is also large compared with Example 15. The use of a vacuum pump to lower the pressure on the permeate side means that the same degree of CFC removal can be achieved with a much smaller membrane area, 8.1 m 2 , and a much lower stage cut, 18%. There is a corresponding saving in the energy requirements of the compressor. However, the energy used by the vacuum pump makes the overall energy demand of the system about the same in both cases. Both schemes achieve major improvements in performance compared with condensation alone.
  • This set of examples compares treatment of a gas stream containing sulfur dioxide in air by condensation alone and by the process of the invention.
  • the stream has a flow rate of 1,000 scfm and contains 50% sulfur dioxide in all cases.
  • the calculations are performed in similar manner to those for the Group 2 examples.
  • the membrane calculations were based on the performance of composite membranes having a permselective layer of polyamide-polyether block copolymer.
  • the membrane selectivity for sulfur dioxide over air was taken to be 100, and the normalized sulfur dioxide flux was 6 ⁇ 10 -3 cm 3 (STP) /cm 2 ⁇ s ⁇ cmHg.
  • the sulfur dioxide laden stream is compressed to 8 atmospheres, then chilled to 6°C and condensed.
  • the boiling point of sulfur dioxide is -10°C, so under these compression/chilling conditions, 25% sulfur dioxide remains in the vent gas from the condenser.
  • the performance is characterized as shown in Table 8.
  • Non-condensed off-gas from condenser 25% SO 2 625 scfm
  • the sulfur dioxide laden stream is compressed to 40 atmospheres, then chilled to 6°C and condensed.
  • the sulfur dioxide content of the vent gas is reduced to 5% under these conditions, but the energy and cost requirements of the system are more than double those of Example 17.
  • the performance is characterized as shown in Table 9.
  • Non-condensed off- gas from condenser 5% SO 2 526 scfm
  • a process was designed employing the condensation step exactly as in Example 17, followed by a membrane separation step to treat the condensation step vent gas stream, using a membrane with a selectivity for sulfur dioxide over air of 100. A pressure drop across the membrane is provided only by the elevated pressure of the compressed feed. The performance is characterized as shown in Table 10. Table 10,
  • Non-condensed off-gas from condenser 25% SO 2 625 scfm
  • the permeate from the membrane separation step is richer in sulfur dioxide content than the original gas stream to be treated, and can be returned for treatment by the condensation step.
  • the hybrid process is able to reduce the concentration of sulfur dioxide in the vented gas stream from 25% to 1%, with no extra energy consumption whatsoever, because the driving force for membrane permeation is provided by the relatively high pressure of the already compressed feed.
  • a process was designed, employing a two-stage membrane separation step followed by a condensation step, to treat a 1,000 scfm stream containing 0.5% CFC-113 (C 2 Cl 3 F 3 ).
  • the feedstream is compressed to 15 psig and passes through the first membrane is provided by a vacuum pump on the permeate side.
  • the residue stream contains 250 ppm CFC-113 at 995 scfm and the permeate stream produced by this first stage contains 2.3% CFC-113.
  • This permeate stream passes to the second membrane stage, having an area of 200 m 2 , where the
  • the residue stream from the second stage is recirculated to the inlet of the first membrane stage.
  • the permeate stream produced by the second stage contains 11.2% CFC-113 and is passed to the condensation step, where it is compressed to 100 psig and chilled to 5°C,
  • the non-condensed stream from the condensation step is returned to the inlet of the second membrane stage. Table 11 summarizes the process performance.
  • the process as configures yields only two streams: a residue stream containing 250 ppm CFC and a clean liquid CFC permeate stream.
  • the capital cost of the system, including pumps, compressors and membrane system, was estimated to be $680,000 or $600/scfm feed. Operating cost was estimated at $316,000 per year or 33 cents/lb CFC-113 recovered.
  • a process was designed, employing a two-step membrane separation step followed by a condensation step, to treat a 1,000 scfm stream containing 10% methylene chloride.
  • the stream is compressed to 15 psig and pases through the two membrane steps in series.
  • the membrane units have areas of
  • Vacuum pumps on the permeate sides of the membranes provide a pressure drop across the membranes.
  • the final residue stream contains
  • the permeate from the second step contains 9.8% methylene chloride and is returned to the inlet to the first membrane step.
  • the permeate from the first step contains 50.6% methylene chloride and is passed to the condensation step.
  • the condensation step involves no compression.
  • the stream is chilled to -12oC.
  • Table 12 summarizes the performance of the system.

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Abstract

Procédé servant à traiter un flux gazeux afin d'enlever dudit flux gazeux ou de récupérer à partir dudit flux gazeux un constituant condensable. Ledit procédé comprend une étape de condensation et une étape de concentration par membrane. L'étape de condensation peut être suivie de l'étape de concentration par membrane ou vice et versa. Le procédé peut être conçu de façon à obtenir seulement deux flux: un flux constitué du liquide condensé, prêt à être utilisé, réutilisé ou jeté, et un flux de gaz résiduel qui dans la plupart des cas est suffisamment propre pour être déchargé ou réutilisé directement. Ce résultat est obtenu par le recyclage d'autres flux au cours du procédé. On peut récupérer jusqu'à 90 % ou plus du constituant condensable. Grâce à ce procédé, l'on fait d'importantes économies d'énergie si l'on compare avec le procédé de simple condensation.
PCT/JP1991/000609 1991-05-07 1991-05-07 Procede servant a retirer de flux gazeux des constituants condensables WO1992019359A1 (fr)

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JP03508271A JP3023802B2 (ja) 1991-05-07 1991-05-07 気体流から凝縮可能成分を分離する方法
PCT/JP1991/000609 WO1992019359A1 (fr) 1991-05-07 1991-05-07 Procede servant a retirer de flux gazeux des constituants condensables

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GB2282082A (en) * 1993-09-05 1995-03-29 Carbon Membranes Ltd Method for improving the efficiency of cryogenic-membrane seperation hybrids
EP0839568A1 (fr) * 1996-10-31 1998-05-06 Air Products And Chemicals, Inc. Récupération et recyclage de composés chimique fluorés utilisant des membranes
US7837877B2 (en) 2006-06-09 2010-11-23 Air Products And Chemicals, Inc. Process for separating components of a multi-component feed stream

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JP2010111405A (ja) * 2008-11-05 2010-05-20 Tominaga Oil Pump Mfg Co Ltd ガソリンベーパー回収システム
KR102145061B1 (ko) * 2020-03-17 2020-08-14 한국산업기술시험원 막 투과 응축장치

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US4553983A (en) * 1984-07-31 1985-11-19 Membrane Technology And Research, Inc. Process for recovering organic vapors from air
EP0389126A2 (fr) * 1989-03-23 1990-09-26 Membrane Technology And Research, Inc. Procédé à membrane pour le traitement de courants de gaz chargés d'hydrocarbures fluorées
US4963165A (en) * 1987-04-27 1990-10-16 Membrane Technology & Research, Inc. Composite membrane, method of preparation and use
WO1991006363A1 (fr) * 1989-11-07 1991-05-16 Membrane Technology And Research, Inc. Procede d'elimination d'un constituant condensable dans des courants gazeux

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Publication number Priority date Publication date Assignee Title
US4553983A (en) * 1984-07-31 1985-11-19 Membrane Technology And Research, Inc. Process for recovering organic vapors from air
US4963165A (en) * 1987-04-27 1990-10-16 Membrane Technology & Research, Inc. Composite membrane, method of preparation and use
EP0389126A2 (fr) * 1989-03-23 1990-09-26 Membrane Technology And Research, Inc. Procédé à membrane pour le traitement de courants de gaz chargés d'hydrocarbures fluorées
WO1991006363A1 (fr) * 1989-11-07 1991-05-16 Membrane Technology And Research, Inc. Procede d'elimination d'un constituant condensable dans des courants gazeux

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2282082A (en) * 1993-09-05 1995-03-29 Carbon Membranes Ltd Method for improving the efficiency of cryogenic-membrane seperation hybrids
EP0839568A1 (fr) * 1996-10-31 1998-05-06 Air Products And Chemicals, Inc. Récupération et recyclage de composés chimique fluorés utilisant des membranes
US7837877B2 (en) 2006-06-09 2010-11-23 Air Products And Chemicals, Inc. Process for separating components of a multi-component feed stream

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