Spiral wound membrane element for high temperature filtration

Abstract

A spiral wound membrane module is suitable for use with high temperature water that may also have a high pH, for example steam injection produced water. The module uses a membrane with a polyphenylene sulfide (PPS) backing material. The feed spacer of the module may be made from polyphenylene sulfide (PPS) or ethylene chlorotrifluoroethylene (ECTFE). The permeate carrier may be made of a woven nylon (i.e. nylon 6, 6) fabric coated with high temperature epoxy. The core tube and anti-telescoping device may be made of polysulfone. In some examples, the module may be used at a temperature of up to 130° C. Optionally, the module may be used at a pH of 9.5 or more. In a filtration method, the module may be operated at a pressure in the range of 150 to 450 psi. The module may be operated at a generally constant pressure.

Claims

1. A spiral wound membrane module comprising, a membrane envelope comprising a membrane and a permeate spacer; a feed spacer adjacent the membrane envelope; a center tube, wherein the membrane envelope and feed spacer are wrapped around the center tube; and, an anti-telescoping device attached to the center tube beside the membrane envelope and feed spacer, wherein the membrane comprises a polyphenylene sulfide backing, the feed spacer comprises ethylene chlorotrifluoroethylene or polyphenylene sulfide, and the permeate spacer comprises a nylon fabric coated with epoxy, wherein the membrane further comprises a polyamide separation layer.

2. The membrane module of claim 1 wherein the membrane further comprises an intermediate polyethersulfone layer.

3. The membrane module of claim 1 wherein the center tube is made of polysulfone.

4. The membrane module of claim 3 wherein the anti-telescoping device is made of polysulfone.

5. A filtration process comprising steps of, providing a membrane module according to claim 1; feeding water to the membrane module at a temperature in the range of 90° C. to 130° C.

6. The process of claim 5 comprising feeding water to the membrane module at a temperature above 100° C.

7. The process of claim 5 comprising feeding water to the membrane module at a pH of 9.5 or more.

8. The process of claim 5 comprising feeding produced water to the membrane module.

9. The process of claim 5 comprising feeding water to the module at a pressure in the range of 150 psi to 450 psi.

10. The process of claim 9 comprising feeding water to the module at a constant pressure.

11. The membrane module of claim 1 wherein feed spacer comprises ethylene chlorotrifluoroethylene.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a partially cut away isometric view of a spiral wound module.

DETAILED DESCRIPTION

(2) A spiral wound membrane module (alternatively called an element) can be thought of as being composed of two or more groups of materials. The first group is the membrane. The membrane is the functional component within the module that does the work of separating the feed water into filtered (permeate) and waste (brine or retentate) streams. A membrane is typically comprised of three layers of decreasing porosity starting with a fabric (i.e. nonwoven) backing, then a supporting or intermediate layer, and then a separation or membrane layer. The supporting layer may be made of polysulfone, made porous by casting a dope and forming pores by a phase-inversion process. The separation layer may be a polyamide layer made by interfacial polymerization.

(3) A typical membrane might not fail when operated at 90° C. for a short period of time, but the lifetime of the materials can be significantly shortened by high temperature operation, especially when operating at high pH. For example, in tests by the inventors poly(butyl terephthalate) was almost dissolved and poly(ester terephthalate) was materially degraded after soaking in water at 130° C. and a pH of 9.5 for two weeks. Polyesters such as these are commonly used as membrane backing layers. In contrast, the polysulfone and polyamide layers in samples of typical membranes survived exposure to water at 130° C. and a pH of 9.5 for two weeks, as did samples of polyphenylene sulfide (PPS).

(4) In some embodiments, a module is constructed of materials to allow operation at 90° C. or more or 100° C. of more. Optionally, the module may be constructed to allow operation at a temperature up to 130° C. Optionally the module may operate at up to a pH of 9.5 or more.

(5) Examples of high temperature membranes were made having a non-woven backing substrate of polyphenylene sulfide. Polysulfone UF films were cast on the backing from a dope solution of 22% (wt.) polysulfone in n,n-dimethylformamide, with 1% (wt.) lithium bromide. The UF films were cast with a 0.010″ gap doctor blade onto a sheet of the backing substrate that was taped to a glass plate. The cast films were submerged into a room temperature de-ionized (DI) water bath to quench. They were stored in the water bath overnight, after which the water was changed and they were stored in the water batch for about another 5 days. Casting took place under ambient conditions (room temperature, about 10% humidity) under a laboratory fume hood. After being removed from the water bath, excess water was removed from the surface of the UF films and they were coated with a polyamide RO layer.

(6) Coupons of the membranes with PPS backing were soaked in a synthetic feed solution at 135° C. for 2 weeks in an autoclave. The feed solution contained 200 ppm sodium chloride, 20 ppm calcium chloride and 200 ppm silica and had a pH of 9.5. Samples were removed from the autoclave at the end of the first and second weeks and tested for flux (A-value) and NaCl selectivity with a crossflow test procedure.

(7) The coupons had an average A-value of 3.79 and 46% salt passage. An A-value of 3.79 is roughly equivalent to a full-sized (8-inch diameter) element with a permeate flow of 975 LPH. This flux is reduced by about 40% from typical commercially available modules. The high salt passage is believed to be the result of pinhole defects in the coupons. It is expected that optimizing the membrane making process would likely yield improved flux and selectivity, but the coupon results demonstrate that useful membranes were produced on the PPS backing.

(8) A second group of materials includes the feed spacers, permeate carriers, core tube and anti-telescoping device which serve to give the module structure and support while creating the flow paths for water through the module. These components are typically fabricated from commodity plastics such as polyester, polypropylene and ABS. These materials are not designed for use at elevated temperatures and may begin to fail at even moderately elevated temperatures, for example 60 or 70° C.

(9) Examples of materials suitable for operation at high temperature, optionally above 100° C. are shown in Table 1.

(10) TABLE-US-00001 TABLE 1 Component Material Membrane Polyamide UF Support Polysulfone or Polyethersulfone Backing PPS Permeate Carrier Epoxy-coated nylon knitted fabric Feed Spacer ECTFE or PPS Core Tube Polysulfone Adhesive Epoxy ATD Polysulfone

(11) Examples of module structural elements and adhesive samples were immersed in water at 135° C. and a pH of 9.5 for a minimum of 2 weeks. Adhesive samples were configured in a lap sheer format between layers of polyester backing and tested for tensile strength. All other materials were inspected visually for changes in shape and for mass loss.

(12) Module structural elements tested included, feed spacers made from PPS and ECTFE (HALAR™); coated PET permeate carrier; high temperature epoxies; and core tubes made of polysulfone; polyproylene and EPTFE feed spacer; and, Polyset polyurethane adhesive. All of the components survived the test.

(13) FIG. 1 shows a spiral wound membrane module 10. One primary component is the separation membrane 12, which is formed into a flat sheet. Other primary internal components are a feed channel spacer 14, a permeate spacer (or permeate collection material) 16, a permeate collection tube or center tube 18 and an end surface holder or anti-telescoping device 20 at each end of the module 10. The membrane 12 is arranged to form an envelope around the permeate spacer 16. The edges of the envelope are sealed except that at an inside edge the permeate spacer 16 is open to perforations 22 of the center tube 18. The feed channel spacer 14 is placed over the envelope. The envelope and feed channel spacer 14 are wound around the center tube 18. Feed water can access the surface of the membrane 12 by flowing into the edge of and across the feed channel spacer 14. Permeate passes through the membrane 12, then flows through the permeate spacer 16 and center tube 18 to leave the module 10. Concentrate flows out of the downstream edge of the feed channel spacer 14 to leave the module. The anti-telescoping devices 20 are glued or taped to the center tube 18 and also held in place by an outer wrap 24. The anti-telescoping devices 20 prevent the envelopes from being pushed along the length of the center tube 18 by the feed water. An outer wrap 24 surrounds the envelopes to keep them from unwinding in use.

(14) One or more of various other components may also be present in the module 10. For example, the membrane 12 typically comprises a membrane support or backing layer. The envelopes may be sealed with an adhesive. In a multi-stage module, two or more center tubes 18 may be connected in series by element interconnectors. The module typically has O-rings, brine seals or other end-seal gaskets and other seals. Folds in the envelope may be reinforced with a tape or film. A film or tape may also be used to provide an inner wrap. Tape may also be used to help hold the anti-telescoping devices 20 in place.

(15) The membrane 12 may be a polyamide-based membrane with a backing material of, for example, PPS. The backing material may be coated with an intermediate layer of polysulfone or polyethersulfone, made porous by a phase inversion process. Thereafter, the surface of the coated backing material is coated with a reverse osmosis or nanofiltration membrane.

(16) In other components, the membrane module 10 makes use of one or more of the following materials, or blends of the following materials: polyamide (PA, nylon); polyphenylene oxide (PPO, NORYL™); polyphenylene sulfide (PPS); polysulfone (PSO); polyethersulfone (PES); polysulfonamide; and, polyvinylidene fluoride (PVDF), EPDM, fiberglass, epoxy and mylar. Polypropylene may be used in minor components such as a backing for a tape.

(17) In an example of a spiral would module 10 intended for use in treating SAGD or other high temperature produced water. The feed channel spacer 14 is made of PPS or ethylene chlorotrifluoroethylene (ECTFE). The permeate spacer 16 is made from a knitted yarn of nylon 6-6 and epoxy. Epoxy is used for an adhesive in other parts of the module 10. The center tube 18 is extruded from polysulfone. An element interconnector is also extruded from polysulfone. The anti-telescoping device 20 is injection molded from polysulfone. The outer wrap 24 is made of fiber-reinforced plastic, for example fiberglass embedded in epoxy. An inner wrap is made from a polypropylene backed pressure sensitive adhesive (PSA) tape. The same tape is used on other parts of the module 10 requiring tape. Creased mylar film is used for a fold reinforcement. A concentrate seal and O-rings are made from molded EPDM rubber.

(18) Optionally, the center tube of the module 10 may be provided with 3 or more rows of holes having a diameter of 0.1″ or less, or perforations of other shapes having an equivalent area, for example 4 rows of 0.063″ diameter holes. The module 10 may also be rolled under a tension of 20 psig or more, for example about 25 psig. The central tube 18 is mounted in a driven chuck assembly that is first used to roll up all of the leaves or elements of the module. Inner wrap tape is then wrapped around the element. The tension of the tape inner wrap is controlled by the tension at which the tape is allowed to unwind from a roll that it is mounted on. The tension and numerous small holes assist the heated materials in resisting mechanical stresses.

(19) While the module as described above is suitable for use in service with water having a high temperature and pH, it may also be used with water under other conditions. The ability of the module to withstand extreme conditions can also be used when cleaning the module. In particular, the module may be cleaned with a hot caustic solution, for example a highly concentrated and heated solution of NaOH. The solution may be used, for example, according to known clean in place procedures. However, due to an increased reaction rate relative to typical cleaning solutions, one or more of the time, energy, water, or other consumables required for cleaning may be reduced.

(20) U.S. Pat. No. 8,940,169 is incorporated herein by reference.