Liquid separation by membrane assisted vapor stripping process

Abstract

An improved process for separation of liquid mixtures involves vapor stripping followed by mechanical compression of the vapor which is then exposed to a permeation membrane for separation of the compressed vapor.

1 . An apparatus for separating a liquid mixture of two or more solvents comprising components through which streams of mixtures pass, a stripping column having at the top of said column, an inlet for a stream containing a feed liquid and an outlet for a stream containing vapor and, at the bottom of said column, an outlet for a stream of liquid that has passed through said stripping column and an inlet for a stream containing at least one vapor, said apparatus having further components located in relation to said stream exiting the top of said stripping column and arranged in sequence (1) at least one over-head compressor and, thereafter, (2) at least one selectively permeable membrane stage selective for water, arranged so that said stream exiting the said outlet at top of said stripping column passes through said compressor and contacts said membrane before exiting said apparatus. 
   
   
       2 . The apparatus of  claim 1  wherein, before exiting the apparatus of  claim 1 , there is, in the stream exiting said apparatus, a back-pressure component placed in the line containing said stream. 
   
   
       3 . The apparatus of  claim 1 , wherein said membrane is a composite membrane comprising at least one porous support layer and at least one permselective layer. 
   
   
       4 . The apparatus of  claim 3  wherein multiple types of membranes are incorporated in said membrane system including, but not limited to, membranes consisting of permselective layers of polymeric materials (glassy and/or rubbery), zeolite materials, ceramic materials, and silica materials, liquid membranes, and layered or mixed matrix combinations thereof. Examples of permselective materials which could be used to make membranes useful in the present invention, wherein permselective materials are chosen from among poly(vinyl alcohol), NaA zeolite, Y-type Zeolite, ZSM-5 zeolites, Silicalite-1, Zeolite Beta, poly(allyl amine hydrochloride), chitosan, functionalized chitosan, sodium alginate, silicone rubber, polysiloxane, poly(dimethylsiloxane), poly(methylhydrosiloxane), poly(octylmethylsiloxane), poly(methyl phenyl siloxane), polysilicone, fluorinated silicone rubber, fluoropolymers, poly(methyl methacrylate), poly(trimethylsilylpropyne) “PTMSP”, silica, surface-modified silica, polyurethane, poly(vinyl pyrollidone), zirconia, polyaniline, microporous alumino-phosphate, Viton, EPDM, styrene-butadiene copolymers, poly(vinylidene fluoride), cellulose, ion exchange materials, nitrile-butadiene copolymers, polyelectrolytes, polyacrylic acid, polyimide, poly(ether-block-amide) [PEBA] copolymer, poly(ethylene oxide), poly(siloxaneimide), polyethylene, polypropylene, polyphosphazene, poly(ether ether ketone) [PEEK], sulfonated poly(ether ether ketone) [SPEEK], poly(4-methyl-2-pentyne) [PMP], polyglycols, poly(ethylene glycol), poly(propylene gycol), polyethyleneimine, polyvinylamine, Nafion, BTDA-TDI/MDI (P84) co-polyimide, poly(ether imide), Interpenetrating Polymer Networks, amorphous copolymers of 2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole and tetrafluoroethylene (amorphous Teflons AF), poly(propylene oxide), amorphous fluoropolymers, and mixtures, copolymers, blends, and mixed-matrix compositions thereof. 
   
   
       5 . An apparatus for separating a liquid mixture of two or more solvents comprising components through which streams of mixtures pass, a stripping column having, at the top of said column, an inlet for a stream containing a feed liquid and an outlet for a stream containing vapor and, at the bottom of said column, an outlet for a stream of liquid that has passed through said stripping column and an inlet for a stream containing at least one vapor, said apparatus having further components located in relation to said stream exiting the top of said stripping column and arranged in sequence (1) at least one overhead vapor compressor and, thereafter, (2) at least one selectively permeable membrane stage selective for one of the solvents, arranged so that said stream exiting the said outlet at top of said stripping column passes through said compressor and contacts said membrane before exiting said apparatus wherein vapor permeating said selectively permeable membrane stage is returned to said stripping column as said at least one vapor entering said stripping column either directly as vapor or indirectly by vaporizing a portion of said stream of liquid that has passed through said stripping column, said vaporized liquid being returned to said stripping column. 
   
   
       6 . A process for separating a liquid mixture of two or more solvents in which one solvent (“A”) predominates with the other dilute solvent compounds present at concentrations less than 50 mole %, said process comprising:
 a. Introducing a flow of said liquid mixture at or near the top of a vapor stripping column comprising:
 i. a rising vapor phase which removes the more dilute solvent compounds from a falling liquid phase; 
 ii. a bottoms liquid stream depleted in the more dilute compounds; 
 iii. an overhead vapor stream depleted in solvent “A” relative to the feed liquid; 
 iv. devices inside the column which establish mass transfer surfaces for the interaction of the vapor and liquid phases; 
   b. increasing the pressure of said overhead vapor stream by at least about 100% using a mechanical overhead vapor compression device;   c. passing the compressed vapor stream to a vapor permeation membrane system comprising: i)
 i. a permselective membrane having a feed side and a permeate side; 
 ii. feed side of said membrane in contact with said compressed vapor stream; 
 iii. permeate side of said membrane in contact with a vapor at a pressure reduced by at least about 50% relative to that of said feed side; 
   d. withdrawing a permeate vapor stream from said permeate side enriched in solvent “A” relative to said feed side of the membrane;   e. withdrawing from said feed side a retentate, non-permeated, vapor depleted in solvent “A”   f. Introducing at least a portion of said permeate vapor to said stripping column at or near the bottom of said column.   
   
   
       7 . The process of  claim 6  wherein said column contains, as mass transfer surfaces, trays, wiped liquid films, falling liquid films, and high surface area structures and/or packing materials. 
   
   
       8 . The process of  claim 6  wherein, in step d, there are multiple individual membrane modules are plumbed in parallel and series relative to the fee vapor flow from which one or more permeate vapor streams are withdrawn. 
   
   
       9 . The process of  claim 6 , wherein said reduced permeate side pressure is achieved by passing all or a portion of said permeate vapor through one or more vacuum compressors plumbed in parallel and/or in series. 
   
   
       10 . The process of  claim 9  wherein said permeate vapor is passed through said vacuum compressors prior to introduction of all or a portion of the permeate vapor into said stripping column. 
   
   
       11 . The process of  claim 9  wherein said permeate vapor is passed through said vacuum compressors prior to introduction of all or a portion of permate vapor into the suction side of said overhead mechanical vapor compressor device. 
   
   
       12 . The process of  claim 9  wherein said permeate vapor is passed through said vacuum compressors prior to introduction of all or a portion of the any resulting condensate return to said stripping column. 
   
   
       13 . The process of  claim 6  wherein said retentate vapor is introduced into one of said reboiler heat exchangers so that all or a portion of the latent and/or sensible heat can be transferred from said retentae vapor to said reboiler. 
   
   
       14 . The process of  claim 6 , wherein auxiliary heat is provided at the bottom of said stripping column by:
 i) direct introduction of steam to column   ii) heating via one or more of said reboiler heat exchangers   
   
   
       15 . The process of  claim 6  wherein a portion of the sensible heat of said bottoms liquid stream is transferred to said feed liquid mixture using a heat exchange device. 
   
   
       16 . The process of  claim 6  wherein solvent A is water and the other solvents are organic compounds chosen from among methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, tert-butanol, istobutanol, 2=butanol, acetone, butyl acetate, ethyl acetate, methyl ethyl ketone, tetrahydrofuran, methyl isobutyl keton, dioxane and acetonitrile. 
   
   
       17 . The process of  claim 6  wherein said membrane system consists of one membrane stage. 
   
   
       18 . The process of  claim 6  wherein said membrane system consists of multiple membrane stages. 
   
   
       19 . A process for separating a liquid mixture of two or more solvents in which one solvent (“A”) predominates with the other dilute solvent compounds present at concentrations less than 50 mole %, said process comprising:
 b) Introducing a flow of said liquid mixture at or near the top of a vapor stripping column comprising:
 i) a rising vapor phase which removes the more dilute solvent compounds from a falling liquid phase; 
 ii) a bottoms liquid stream depleted in the more dilute compounds; 
 iii) an overhead vapor stream depleted in solvent “A” relative to the feed liquid; 
 iv) devices inside the column which establish mass transfer surfaces for the interaction of the vapor and liquid phases, including, but not limited to: trays, wiped liquid films, falling liquid films, and high surface area structures and/or packing materials; 
 v) optionally, including one or more heat exchangers thermally connected to the reboiler located at the bottom of column for transfer of heat from process streams into the reboiler. 
   c) Increasing the pressure of said overhead vapor stream by at least about 100% using a mechanical overhead vapor compression device;   d) Passing the compressed vapor stream to a vapor permeation membrane system comprising:
 i) A permselective membrane having a feed side and a permeate side 
 ii) Feed side of said membrane in contact with said compressed vapor stream 
 iii) Permeate side of said membrane in contact with a vapor at a pressure reduced by at least about 50% relative to that of said feed side 
 iv) Withdrawing a permeate vapor stream from said permeate side depleted in solvent “A” relative to said feed side of the membrane 
 v) multiple individual membrane modules plumbed in parallel and series relative to the feed vapor flow from which one or more permeate vapor streams are withdrawn 
 vi) Withdrawing from said feed side a retentate, non-permeated, vapor enriched in solvent “A” 
   
   
   
       20 . The process of  claim 19  wherein, after withdrawing retentate, non-permeated vapor enriched in solvent “A”, at least a part of said retentate vapor is introduced to said stripping column at or near the bottom of the column. 
   
   
       21 . The process of  claim 19  wherein said reduced permeate side pressure is achieved by passing all or a portion of said permeate vapor through one or more vacuum compressors plumbed in parallel and/or in series prior to introducing all or a portion of said permeate vapor into the suction side of said overhead mechanical vapor compression device. 
   
   
       22 . The process of  19  wherein said reduced permeate side pressure is achieved by passing all or a portion of said permeate vapor through one or more vacuum compressors plumbed in parallel and/or in series prior to introducing all or a portion of said permeate vapor into the suction side of said overhead mechanical vapor compression device.