KR20050071655A - Method of separating olefins from mixtures with paraffins - Google Patents

Abstract

A process for the separation or concentration of olefinic hydrocarbons from mixtures of olefinic and paraffinic hydrocarbons uses a polyimide membrane. The process is well suited to separating propylene from propylene/propane mixtures. The novel method The membrane exhibits good resistance to plasticization by hydrocarbon components in the gas mixture under practical industrial process conditions.

Description

Method for Separation of Olefin in Paraffin Mixture {METHOD OF SEPARATING OLEFINS FROM MIXTURES WITH PARAFFINS}

The present invention relates to a process for separating or concentrating a mixture of olefins and paraffins using a selective permeable membrane. More specifically, it relates to the use of certain polyimide membranes for the selective separation of olefinic hydrocarbons from gas or liquid mixtures of olefinic and paraffinic hydrocarbons occurring in the petroleum refining industry, petrochemical industry and related industries.

Olefins, in particular ethylene and propylene, are important chemical feedstocks. Generally they are produced as primary products or by-products in mixtures containing hydrocarbons and other components found in nature or saturated. Before using the raw olefins, they generally have to be separated from these mixtures.

In general, the separation of the olefin / paraffin mixture was carried out by distillation. However, due to the similar volatility of the components, this process is expensive and complicated, requiring expensive distillation tubes and energy intensive processes. Javelin reports that fractional distillation of propylene / propane mixtures is an energy intensive distillation in the United States (Harri Javelin & James R. Fair, Adsorptive separation of propylene / propane Mixtures , Ind. Eng. Chem. Research 32 (1993). ) 2201-2207). More energy conservation separation processes are needed.

Membranes were considered instead of distillation for the separation of olefins from paraffins. However, separation is most difficult due to the similar molecular size of the components. Another difficulty is that the feed stream conditions are generally close to the gas / liquid phase boundary of the mixture. In addition, the membrane must be operated in a hydrocarbon environment under conditions of high pressure and temperature. Such harsh conditions adversely affect the durability and stability of most membrane material separation performance. For example, certain contaminants can cause plasticization of selective permeable membrane materials and reduce selectivity and / or permeability. Despite long contact with hydrocarbon streams under high pressure and temperature, membranes with sufficiently high olefin / paraffin selectivity and durability are required.

Membrane materials for the separation of olefinic hydrocarbons from olefinic and saturated hydrocarbon mixtures have been reported, but none are readily or economically produced membranes that provide a special combination of high selectivity and durability under industrial process conditions.

For example, several inorganic and polymer / inorganic membrane materials with good propylene / propane selectivity have been studied. M. Teramoto, H. Matsuyama, T. Yamashiro, Y. Katayama, Separation of ethylene from ethane by supported liquid membranes containing silver nitrate as carrier , J. Chem Eng. Japan 19 (1986) 1 and RD Hughes, JA Mahoney, EF Steigelmann, Olefin separation by facilitated transport , in: NN Li, JM Calo (eds.), Membrane Handbook, Van Nostrand, New York, 1992. Such materials are difficult to manufacture with practical industrial membranes. Liquid facilitation-transport membranes are illustrated as exhibiting high separation performance in the laboratory, but are difficult to produce on a large scale, and have been reported to degrade in the normal environment of industrial propylene / propane streams.

Solid polymer-electrolyte promoting-transport membranes have been shown to require more deformation in stable thin film fabrication. Ingo Pinnau & LG Toy, Solid polymer electrolyte composite membranes for olefin / paraffin separation , J. Membrane Science, 184 (2001) 39-48. Such membranes are illustrated in US Pat. No. 5,670,051 (Pinnau et al, 1997), wherein silver tetrafluoroborate / poly (ethylene oxide) membranes exhibited ethylene / ethane selectivity of at least 1000. However, these membranes have several limitations due to poor chemical stability in the olefin / paraffin industrial environment.

Carbon hollow fiber membranes are promising in laboratory tests (" Propylene / Propane Separation ", Product Information from Carbon Membranes, Ltd., Israel), but have the disadvantage of being prone to degradation by the presence of condensable organics present in industrial streams. In addition, carbon films are brittle and difficult to form into commercially valid membrane molecules.

Rubbery polymeric membranes typically have low olefin / paraffin selectivity for economically effective separation. For example, Tanaka et al. Reported a single gas propylene / propane selectivity of 1.7 for polybutadiene membranes at 50 ° C. (K. Tanaka, A. Taguchi, Jianquiang Hao, H. Kita, K. Okamoto, J. Membrane Science 121 (1996) 197-207), Ito reported that propylene / propane selectivity was only slightly over 1.0 in 40 ° C silicone rubber (Akira Ito and Sun-Tak Hwang, J. Applied Polymer Science , 38 (1989) 483 -490).

Glassy polymeric membranes have the potential to provide high olefin / paraffin selectivity, which is effective by the selective diffusion of olefins, which have a smaller molecular size than paraffins.

Glassy polymers already used in gas separation generally have a suitable olefin / paraffin selectivity. For example, Ito reported that polysulfone, ethyl cellulose, cellulose acetate and cellulose triacetate films showed propylene / propane selectivity below 5 (Akira Ito and Sun-Tak Hwang, Permeation of propane and propylene through cellulosic polymer membranes , J. Applied Polymer Science, 38 (1989) 483-490).

U. S. Patent No. 4,623, 704 describes a process using a cellulose triacetate membrane to recover ethylene from the reactor outlet of a polyethylene plant. However, the outlet stream containing 96.5% ethylene rose by only 97.9% in the permeate stream for recovery to the reactor.

The poly (2,6-dimethyl-1,4-phenylene oxide) film membrane exhibited a pure gas propylene / propane selectivity of 9.1. (Ito & Hwang, Ibid.) High selectivity is described by Ilinitch et al. ( J. Membrane Science 98 (1995) 287-290, J. Membrane Science 82 (1993) 149-155, and J. Membrane Science 66 (1992) 1-8), but values at high pressures are definite. Without entailing unwanted firing of the membrane with propylene.

Polyimide membranes have been extensively studied for gas separation and olefin separation from paraffins. Lee et al. (Kwang-Rae Lee & Sun-Tak Hwang, Separation of propylene and propane by polyimide hollow-fiber membrane module , J. Membrane Science 73 (1992) 37-45) have low feed pressures (2-4 barg) Is disclosed a hollow fiber membrane of polyimide exhibiting a mixed gas propylene / propane selectivity in the range of 5-8. The composition of the polyimide is not disclosed.

Krol et al. (JJ Krol, M. Boerrigter, GH Koops, Polyimide hollow fiber gas separation membranes: preparation and the suppression of plasticization in propane / propylene environments , J. Membrane Science.184 (2001) 275-286) are pure gas propylene / propane selectivity. The co-fiber film | membrane of the polyimide which consists of this 12 biphenyl tetracarboxylic dianhydride and diaminophenyl indane was reported; However, the membrane is accompanied by unwanted calcination by propylene in propylene at pressures lower than 1 barg.

It has been found that polyimides based on 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and aromatic diamines provide a suitable combination of propylene permeability and propylene / propane selectivity. Permeation data for high density film membranes of two types of 6FDA-containing polyimide have been reported to have a pure gas selectivity of propylene / propane in the range of 6 to 27 (C. Staudt-Bickel et al, Olefin / paraffin gas separations). with 6FDA-based polyimide membranes , J. Membrane Science 170 (2000) 205-214). High selectivity of pseudo 6FDA polyimide is reported in US Pat. No. 5,749,943 (Shimazu et al); However, at high pressures, the mixed-gas selectivity is expected to be much lower by firing the propylene-excess feed gas.

US Patent No. 4,532,041; 4,571,444; No. 4,606,903; No. 4,836,927; No. 5,133,867; No. 6,180,008; And 6,187,987 from polycondensation of a mixture of benzophenone 3,3 ', 4,4'-tetracarboxylic dianhydride (BTDA) with di (4-aminophenyl) methane and a mixture of toluene diamine useful for liquid separation. Membranes based on derived polyimide copolymers are disclosed.

US Patent No. 5,605,627; 5,683,584; 5,683,584; And polycondensation of a mixture of benzophenone 3,3 ', 4,4'-tetracarboxylic dianhydride (BTDA) with di (4-aminophenyl) methane and a mixture of toluene diamine useful for liquid filtration or dialysis membranes in heading 5,762,798. Asymmetric, microporous membranes based on polyimide copolymers derived from the sum are disclosed.

US Pat. No. 5,635,067 from 4,4'-methylene bisphenylisocyanate (MDI) and benzophenone-3,3 ', 4,4'-tetracarboxylic dianhydride (BTDA) and toluene diisocyanate (TDI) condensation Disclosed are fluid separation membranes based on polyimide derived and / or polyimide and phenylindane containing polyimide polymer blends derived from the condensation of BTDA with pyromellitic dianhydride with TDI and MDI.

An important drawback of published data for separation of olefins from paraffins using membranes is that there is no data under practical industrial conditions: for example, pressure of high feed permeate and high temperatures. This is a condition where the plasticity of the membrane material can be significant and the membrane performance is significantly reduced for a long time. Despite considerable efforts to provide industrially viable membranes for the separation of olefins from paraffins, none have proven to meet the performance criteria required for industrial applications.

Summary of the Invention

(a) providing a double sided selective permeable membrane comprising a polymer or copolymer having repeating units of formula (I)

(b) contacting one side of the membrane with a feed mixture comprising a mixture of olefin compounds and paraffins having at least as many carbon atoms as the olefin compound,

(c) allowing the feed mixture to selectively permeate through the membrane, thereby forming an olefin rich permeable membrane having a higher concentration of olefin compounds than the feed mixture on the second side of the membrane,

(d) removing the olefin rich permeable membrane composition from the second side of the membrane,

(e) a membrane separation process for separating olefins from an olefin and paraffin mixture comprising recovering the olefin deficient composition from one side of the membrane:

Wherein R ₂ is a structural unit selected from the group consisting of Formula A, Formula B, Formula C, and mixtures thereof,

Z is a structural unit selected from the group consisting of the following formula (L), (M), (N) and mixtures thereof;

R ₁ is a structural unit selected from the group consisting of Formula Q, Formula T, Formula S and mixtures thereof:

The present invention provides a method for the selective separation of olefinic hydrocarbons from paraffinic hydrocarbons using membranes comprising certain polyimide polymers, copolymers and mixtures thereof. The polymer forming the polyimide has repeat units of formula (I)

Formula I

Wherein R ₂ is a structural unit selected from the group consisting of Formula A, Formula B, Formula C, and mixtures thereof,

Formula A

Formula B

Formula C

Z is a structural unit selected from the group consisting of the following formula (L), (M), (N) and mixtures thereof;

Formula L

Formula M

Formula N

R ₁ is a structural unit selected from the group consisting of Formula Q, Formula T, Formula S, and mixtures thereof.

Formula Q

Formula T

Formula S

In a preferred embodiment, the polyimide forming the selective layer of the membrane has repeat units of formula II:

In this embodiment, the unit R ₁ is formula Q, 0-100% of the repeating unit, formula T 0-100% of the repeating unit, and formula S in an amount such that the total amount of repeating units is 100%. Polymers having this structure are available from HP Polymer GmbH under the trade name P84 and are highly preferred for use in the present invention. P84 has a repeating unit according to formula II, wherein R ₁ is considered to be formula Q which is about 16% of the repeating unit, formula T which is about 64% of the repeating unit and formula S which is about 20% of the repeating unit. P84 is 2,4-toluene diisocyanate (2,4-TDI, 64 mol%), 2,6-toluene diisocyanate (2,6-TDI, 16 mol%) and 4,4'-methylene-bis (phenyl It is considered to be derived from the condensation reaction of benzophenone tetracarboxylic dianhydride (BTDA, 100 mol%) with a mixture of isocyanate) (MDI, 20 mol%).

In another preferred embodiment, the polyimide with which the selection layer is formed has a repeating unit of a structure selected from formulas IIIa and IIIb:

The repeating unit may be only one of Formula IIIa or Formula IIIb. Preferably, the repeating unit is a mixture of formulas IIIa and IIIb. In this embodiment, part R ₁ has a composition of Formula Q wherein about 1-99% of the repeating units and Formula T such that the total amount of repeating units is 100%, a being about 1- of the total amount of a and b Is in the 99% range.

Preferred polymers having this structure are available from HP Polymer GmbH under the trade name P84-HT325. P84-HT325 has a repeating unit according to formulas IIIa and IIIb, wherein R ₁ has a composition of formula Q which is about 20% of the repeating unit, formula T which is about 80% of the repeating unit, and a is the total amount of a and b About 40% of the time. P84-HT325 contains benzophenone tetracarboxylic dianhydride (BTDA, 60 mol%), 2,4-toluene diisocyanate (2,4-TDI, 80 mol%) and 2,6-toluene diisocyanate (2, Condensation reaction of pyromellitic dianhydride (PMDA, 40 mol%), including 6-TDI, 20 mol%).

In addition, in another preferred embodiment, the selective permeable part of the membrane may be formed of a material comprising a mixture of the aforementioned polymers. For example, the membrane may comprise a first polymer having a repeating unit of formula IIIa, IIIb or a mixture of formulas IIIa and IIIb as defined above, and a second polymer having a repeating unit of formula II as defined above It is anticipated that it may be formed from the blends included. Most preferred are membranes consisting of a mixture of first and second polymers. This preferred configuration is such that the second polymer should comprise about 10-90% by weight of the total amount of the first and second polymers.

The polyimide must have the appropriate molecular weight and flexibility to form the film so that a continuous film or film can be formed. The polyimide of the present invention preferably has a weight average molecular weight in the range of about 20,000 to 400,000, more preferably about 50,000 to 300,000. Polymers can be formed into films and films by a variety of techniques known in the art. The polymers are generally glassy and hard, and are hard, as a result, used to form monolayer films of unsupported films or fibers of the polymer. Such monolayer films are generally too thick to yield an acceptable transmembrane fluid of the selective permeable component of the feed mixture. In order to be more economically viable, the separator may include a very thin selection layer that forms part of a thicker structure. This structure can be, for example, an asymmetric membrane, which includes a thin and dense surface of a selective permeable polymer adjacent to and integral with the surface and a thick microporous support layer. Such membranes are disclosed, for example, by Ekiner in US Pat. No. 5,015,270.

In a preferred embodiment, the membrane can be a composite membrane, i.e. a membrane having multiple layers, typically having a different composition. Recent synthetic membranes typically include porous and non-selective support layers. This preferentially provides mechanical strength to the composite film. Selective layers of other selectively permeable materials are disposed in the same space in the support layer. The selective layer preferentially provides separation properties. Typically, the support layer of the composite membrane is produced by solution casting a film or spinning hollow fibers. The optional layer is then generally coated with the solution on the support layer in a separate step. Alternatively, the hollow fiber composite membrane can be produced by simultaneously blow molding the support material and the separation layer as described by Ekiner in US Pat. No. 5,085,676.

Membranes of the invention can be housed in any convenient form of separation unit. For example, flat sheet membranes may be laminated in plate-and-frame modules or wound in spiral wound modules. Hollow fiber membranes are typically made with a thermoset resin in a cylindrical housing. The final membrane separation unit may comprise one or more membrane modules. They may be housed in individual pressurized containers or may be mounted together in a conventional housing in which multiple modules have the appropriate diameter and length.

In practice, a mixture of at least one olefin compound and at least one paraffin compound is brought into contact with one side of the membrane. Under the proper driving force for permeation, such as adding a pressure difference between the feed and the permeate side of the membrane, the olefin compound passes through the permeate side at a higher rate than paraffin compounds having the same number of carbon atoms. That is, C ₃ olefins are permeated faster than C ₃ paraffins. This produces an olefin-rich stream exiting the permeate side of the membrane. Olefin-depleted residues, sometimes referred to as "reserves", are recovered from the feed side.

The new process can run under a wide range of conditions and is modified to accommodate feed streams from a variety of sources. If the feed stream is a gas already present at a pressure sufficiently above atmospheric pressure and the pressure gradient is maintained across the membrane, the driving force for separation may be sufficient without further increasing the feed stream. Otherwise, the feed stream may be compressed to high pressure and / or vacuum may be withdrawn at the permeate side of the membrane to provide adequate propulsion. The driving force for separation is preferably a pressure gradient across the membrane of about 0.7 to about 11.2 MPa (100-1600 psi).

The novel process may allow the feed stream in gaseous or liquid state. The state of the material depends on the composition, pressure and temperature of the olefin / paraffin feed stream. When the feed stream is in the liquid state, separation is carried out by a transparent evaporation mechanism. In essence, in pervaporation, the components of the liquid feed mixture in contact with the membrane are permeated and evaporated through the membrane, thus separating the components into the gas phase.

The present invention is particularly useful for the separation of propylene from propylene / propane mixtures. Such mixtures are produced, for example, by the effluent stream of the olefin production operation and by the various process streams of the petrochemical plant. In this preferred embodiment, the process comprises passing a stream comprising propylene and propane in contact with the feed side of the membrane which is selectively permeable to propylene and propane. Propylene is concentrated in the permeate stream, so the retentate stream is deficient in propylene. The membranes of the present invention exhibited unexpectedly high propylene / propane selectivity that is distinct from the membranes of the prior art. In addition, the membrane of the present invention showed stable performance for a long time under conditions in which the performance of the membrane of the prior art is significantly reduced.

The basic step of the separation process is that a feed mixture comprising an olefin compound and a paraffin compound having at least carbon atoms greater than the olefin compound is in contact with one side of the membrane; The feed mixture selectively permeates the permeate through the membrane to form an olefin-rich permeate composition having a higher olefin compound concentration than the feed mixture on the second side of the membrane; Removing the olefin-rich permeate composition from the second side of the membrane; And evacuating the olefin-deficient composition having a lower olefin compound concentration than the feed mixture from one side of the membrane.

The present invention has described examples of representative embodiments thereof, and all parts, percentages and percentages are by weight unless otherwise indicated. Not all weight units and units of measurement are obtained in SI units, which are converted to SI units. All disclosures of US patents mentioned in the Hari examples are incorporated herein by reference.

Example 1 Propylene / Propane Gas Separation Using P84 Membrane

Asymmetric hollow fiber membranes of P84 are a solution of 32% P84, 9.6% tetramethylenesulfone and 1.6% acetic anhydride in N-methylpyrrolidone (NMP) using the methods and apparatus described in US Pat. Nos. 5,034,024 and 5,015,270. Was spun from. The initial filament was extruded at a rate of 180 cm ³ / hr through a spinneret having a fiber channel size of 559 μm outer diameter and 254 μm inner diameter at 75 ° C. Fluid containing 85% NMP in water was injected into the pores of the fiber at a rate of 33 cm ³ / hr. The initial fibers were transferred through a 5 cm air gap at room temperature into a water coagulation bath at 24 ° C. and the fibers were wound at a speed of 52 m / min.

The wet fibers are washed in running water at 50 ° C. to remove residual solvent for about 12 hours and is US Patent No. The methanol and hexanes are exchanged sequentially as disclosed in 4,080,744 and 4,120,098 and then dried under vacuum at room temperature for 30 minutes. The fibers are then dried at 100 ° C. for 1 hour. Fiber specimens were formed of four experimental membrane modules of 52 fibers each. The fibers in the module were treated to seal defects in the separation layer in a similar manner as described in US Pat. No. 4,230,463. The fibers are contacted with a solution of 2% by weight of 1-2577 Low-VOC Conformal Coating (DowCorning Corporation) in 2,2,4-trimethylpentane for 30 minutes and then dried.

The module was measured at the supplied permeation of mixed propylene / propane (50: 50 mole%). The feed mixture was provided gas phase by controlling a feed pressure of 2.8 MPa (400 psig) and a feed temperature of 90 ° C. The feed mixture was fed to contact the outside of the fibers and the permeate stream was collected at atmospheric pressure. Permeate flow rate is measured by volumetric movement using a foam flow meter. The feed flow rate is kept higher than 20 times the permeate flow rate. This rate allows the feed mixture to permeate the membrane while keeping the composition of the feed side approximately constant. This is to simplify the calculation of the membrane permeability. The composition of the permeate stream was measured by gas chromatography using a flame ionization detector. The average permeate composition is 92.2% propylene and 7.8% propane.

The performance of the membrane was expressed in terms of propylene permeation and propylene / propane selectivity. Permeation is the flow rate of propylene across the membrane normalized by the membrane surface area and the propylene partial pressure difference across the membrane. The gas permeation unit was recorded as "GPU". One GPU is ^10-6 cm ³ (at standard temperature and pressure “STP”) / (sec * cm ² * cmHg). Propylene / propane selectivity is the ratio of permeation rate of propylene divided by permeation rate of propane. The performance of the four modules is shown in Table 1.

Example 2: Propylene / Propane Gas Separation Using P84 Untreated Membranes

The fiber sample of Example 1 is processed and made into the experimental module of Example 1 except that the fibers are not treated to seal the defects in the separation layer. Propylene transmission is 1.7 GPU and propylene / propane selectivity is 7.5. Although the selectivity is lower than the selectivity of the fibers treated in Example 1, it is sufficient to suggest that it is possible to produce P84 fibers with acceptable performance characteristics as an asymmetric membrane without sealing aftertreatment.

Example 3: Propylene / Propane Gas Separation Using P84 Membrane

Asymmetric hollow fiber membranes of P84 were prepared as in Example 1 with two variations: (a) lowering the bath temperature to 8 ° C., and (b) raising the spinneret temperature to 87 ° C .: washing the fiber, drying, experimental Modulated and tested by permeation of the 50:50 mol% mixed propylene / propane feed mixture of Example 1. Propylene transmission is 0.61 GPU and propylene / propane selectivity is 15.

Example 4: Durability of P84 Membrane in Propylene / Propane Gas Separation Using P84 Membrane

An asymmetric hollow fiber membrane of P84, similar to the fiber of Example 3, was subjected to a durability test at 90 ° C. for 4 days using a 50:50 mol% propylene / propane feed mixture at 2.8 MPa (400 psig). Experiments were modified to resemble normal operating conditions. The results are shown in Table II below. No decrease in selectivity was observed. After 2 days, a slight decrease in propylene permeation was observed and at 2 days stabilized.

Example 5: Separation of Propylene / Propane Liquid Feed Using P84 Membrane

One of the modules of Example 1 was tested using a 50:50 mol% propylene / propane feed mixture. The feed pressure and temperature are respectively used to make the feed mixture liquid It was adjusted to 2.8 MPa (400 psig) and 50 ° C. Permeability was reduced at atmospheric pressure, so that the permeate became vapor phase. For this type of separation, the concentration difference across the membrane is generally regarded as the driving force for separation instead of the partial pressure difference used in gas or vapor permeation. For a comparison of the results of this example with permeability under vapor phase feed conditions, see JG Wijmans & RW Baker, A simple predictive treatment of the permeation process in pervaporation , J. Membrane Science 79 (1993) 101-113). The simplified mathematical treatment described was applied. This analysis assumes that the liquid feed is evaporated to produce a saturated vapor phase on the feed side of the membrane and then permeated through the membrane driven by a partial pressure gradient. This analysis provides a mathematical model that includes permeability and selectivity comparable to those used for separation of gaseous feed mixtures and conditions for feed and permeate vapor pressures. The model also includes conditions relating to liquid-vapor equilibrium. Using a feed mixture of liquid 50:50 mol% propylene / propane, the membrane produces a permeate stream of 93% propylene. For the application of the model, the propylene transmittance was 0.46 GPU and the propylene / propane selectivity was determined to be 16. In a separate experiment using a feed mixture of the same composition in the vapor phase at 2.8 MPa (400 psig) and 90 ° C., the propylene permeability is 0.95 GPU and the propylene / propane selectivity is 13. This shows that the membrane of P84 may be useful for the separation service of liquid propylene / propane.

Example 6: Propylene / Propane Gas Separation Using a Mixed Membrane of P84-HT325 and P84

1: Mixed asymmetric hollow fiber membrane of P84 and P84-HT325 was spun from a solution of 16% P84, 16% P84-HT325, 9.6% tetramethylene sulfone and 1.6% acetic anhydride in NMP by the method described in Example 1 . Spinning conditions and equipment are similar except that the spinneret temperature is 85 ° C, the bath temperature is 8 ° C and the air gap is 10 cm. The fibers were formed into modules that were tested for permeation of the propylene / propane (50:50 mol%) feed mixture of Example 1. The transmission performance is 1.9 GPU propylene transmission and 11.9 propylene / propane selectivity.

Example 7: Separation of Propylene / Propane Liquid Feed Using Mixed Membrane of P84-HT325 and P84

The 1: 1 mixing module of P84 and P84-HT325 of Example 6 was tested using a feed mixture of 50:50 mol% propylene / propane. The feed mixture is subjected to the conditions described in Example 5, ie the feed pressure is 2.8 MPa (400 psig) and the temperature is maintained at 50 ° C. in the liquid phase. The permeate is recovered as steam at atmospheric pressure.

The membrane produces a permeate comprising 93.6% propylene; Propylene transmittance is 0.6 GPU and propylene / propane selectivity is 15.5. This shows that a 1: 1 mixed membrane of P84 and P84-HT325 can provide effective separation of the liquid propylene / propane feed.

Example 8: Separation of propylene / propane liquid feed using a mixture of P84-HT325 and P84

The test of Example 7 (ie, using a 1: 1 mixed membrane of P84 and P84-HT325) evaluated the performance stability of the membrane under conventional conditions simulated continuously for a period of 100 hours. The results are shown in Table III below. No significant decrease was observed.

Example 9: Propylene / Propane Gas Separation Using P84 Dense Film Membrane

A dense thin film of P84 polymer was cast into a solution containing 20% P84 in NMP. The film was dried at 200 ° C. in a vacuum oven for 4 days. Samples of the polymer film were tested in a fresh 47-mm ultrafiltration permeation cell (Millipore) using a 50:50 mol% propylene / propane feed mixture at 2.8 MPa (400 psig) pressure and 90 ° C. temperature. Permeate pressure was 2-5 mm Hg. The feed flow rate is high enough to lower the conversion of the feed to the permeate so that the composition is constant in terms of feed. The composition of the feed and permeate streams was determined by gas chromatography using a flame ionization detector. Permeate flow rate is determined from the increase in pressure over time in a fixed volume permeate chamber of the permeate cell.

The permeation performance of the polymer is characterized by two parameters: propylene permeability and propylene / propane permeation selectivity. The transmittance is the flow rate of propylene across the film normalized by the film surface area and the thickness of the film and the partial pressure difference across the film. The transmittance unit is Barrer. 1 Barrer is l0 ^-l0 cm ³ (STP) * cm / (sec * cm ² * cm Hg). Propylene / propane permeability is the ratio of propylene and propane permeability. The propylene transmission of P84 film at 90 ° C. and 2.8 MPa (400 psig) is 0.24 Barrer; And propylene / propane transmission selectivity is 15.5. The permeation selectivity is consistent with the selectivity measured using the hollow fiber membrane of P84 polymer.

Example 10 TDI + BTDA: Propylene / Propane Separation Using BPDA (1: 1) Membrane

Toluene isocyanate (TDI, a mixture of 20% 2,6-toluene isocyanate and 80% 2,4-toluene isocyanate), benzophenone-3,3 ', 4,4'-tetracarboxylic dianhydride (BTDA) A dense film of a copolymer of a 1: 1 mixture of 3,3 ', 4,4'-biphenyl tetracarboxylic dianhydride (BPDA) was prepared at 2.8 MPa (400 psig) and 50:50 mol at 90 ° C. as in Example 9. Permeation experiments were performed using a% mixed propylene / propane feed. The propylene transmittance of the film is 0.48 Barrer, and the propylene / propane transmission selectivity is 16 or more.

Comparative Example 1: Polypropylene / Propane Separation Using Fibrous Membranes of Common Composition

Matrimid® 5218 aerial of 5, x-amino- (4-aminophenyl) -1,1,3 trimethyl indane and 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (Vantico, Inc.) Samples of the composite hollow fiber membranes of coalescence were tested for at least 72 hours using a feed mixture of 1.7 MPa (250 psig) and 50:50 mol% propylene / propane at 90 ° C. as in Example 1. The purpose of the experiment is to determine the membrane performance stability under simulated normal conditions. This membrane, described in US Pat. No. 5,468,430, is a commercial gas separation membrane produced by MEDAL, LP. The results are shown in Table IV below.

As can be seen from the above results, the membrane shows that, unlike the membrane of the present invention, the low selectivity and the initial permeability decreased by 50% or more during the experiment.

Comparative Example 2: Propylene / Propane Separation Using Polyamide Membrane

Samples of asymmetric hollow fiber membranes were mixed with two aromatic polyamides to test the permeability of a feed mixture of 2.8 MPa (400 psig) and 50:50 mol% propylene / propane at 90 ° C. as in Example 1. This membrane is described in US Pat. No. 5,085,774 (Example 15). The fibers were spun at an elongation of 7.3. This is a conventional gas separation membrane applied to the separation of hydrogen from a mixture of hydrocarbons or carbon monoxide. This shows 0.23 GPU propylene transmittance and propylene / propane selectivity of 9.5. This performance is lower than the novel membranes having the composition of formula (I). Since the aromatic polyamide film of the other mixes of, for example, at 90 ℃ the selectivity of H ₂ / CH ₄ had the very high selectivity of more than 200 The result was outside the expected.

Although the specific forms in the present invention have been chosen for illustration in the above description by taking specific terms in order to fully and completely explain embodiments of the present invention to those skilled in the art, the equivalents may be substantially equivalent or It is to be understood that various substitutions and modifications that yield good results and / or performances fall within the spirit and scope of the following claims.

Claims (13)

(a) providing a double sided selective permeable membrane comprising a polymer or copolymer having repeating units of formula (I) (b) contacting one side of the membrane with a feed mixture comprising a mixture of olefin compounds and paraffins having at least as many carbon atoms as the olefin compound, (c) allowing the feed mixture to selectively permeate through the membrane, thereby forming an olefin rich permeable membrane having a higher concentration of olefin compounds than the feed mixture on the second side of the membrane, (d) removing the olefin rich permeable membrane composition from the second side of the membrane, (e) A membrane separation method for separating olefins from an olefin and paraffin mixture comprising recovering the olefin deficient composition from one side of the membrane: Formula I Wherein R ₂ is a structural unit selected from the group consisting of Formula A, Formula B, Formula C, and mixtures thereof, Z is a structural unit selected from the group consisting of the following formula (L), (M), (N) and mixtures thereof; R ₁ is a structural unit selected from the group consisting of Formula Q, Formula T, Formula S and mixtures thereof: Formula A Formula B Formula C Formula L Formula M Formula N Formula Q Formula T Formula S The method of claim 1 wherein the repeating unit is of formula II: Formula II In the above formula, the unit R ₁ is the formula Q of 0-100% of the repeating unit, the formula T of 0-100% of the repeating unit and the formula S in an amount such that the total amount of the repeating units is 100%. The method of claim 2, wherein the unit R ₁ is Formula Q, which is about 16% of the repeat units, Formula T which is about 64% of the repeat units, and Formula S, which is about 20% of the repeat units. The method of claim 1, wherein the repeating unit comprises a unit of a configuration selected from the group consisting of Formula IIIa, Formula IIIb, and mixtures thereof. Formula IIIa Formula IIIb Wherein R ₁ is Formula Q, which is about 1-99% of the repeating units, and Formula T in an amount such that the total amount of repeating units is 100%, and a is in the range of about 1-99% of a + b. 5. The method of claim 4, wherein unit R ₁ is formula Q of about 20% of repeat units, formula T of about 80% of repeat units, and a is about 40% of a + b. The process of claim 4 wherein the membrane comprises a mixture of said polymer and a second polymer having repeat units of formula II: Formula II In the above formula, R ₁ is formula Q of 0-100% of the repeating unit, formula T of 0-100% of the repeating unit and formula S in an amount such that the total amount of repeating units is 100%. The method of claim 6, wherein the second polymer consists of about 10-90 weight percent of the mixture of the polymer and the second polymer. The process of claim 1 wherein the feed mixture comprises ethylene and ethane. The process of claim 1 wherein the feed mixture comprises propylene and propane. 8. The process of claim 7, wherein the feed mixture is liquid. The process of claim 1, further comprising the step of continuously performing the steps (a) to (d) for a period after the initial time of contacting the feed mixture, wherein the membrane exhibits permeation of the olefin compound, and steps (a) to The 72 hour continuous transmission of (d) is at least 60% of the transmission at the initial time. The method of claim 1, wherein the membrane provides a selectivity of at least 10 of the olefin compound to the paraffin compound. The method of claim 10, wherein the membrane provides a transmission of at least about 0.4 GPU of the olefin compound.