US-12616942-B2 - Flat sheet membrane with integral posts

US12616942B2US 12616942 B2US12616942 B2US 12616942B2US-12616942-B2

Abstract

A membrane, for example a flat sheet membrane, has posts extending from a separation layer. The posts extend through one or more supporting structures such as a substrate layer and/or a permeate carrier, between two separation layers, or both. A post may help to attach the separation layer to a supporting structure, attach two supporting structures together, strengthen a supporting structure and/or attach two separation layers together. In some examples, one or more supporting structures, which may be temporary or remain in the membrane, are made with openings for posts. A liquid containing the separating layer material is cast over the supporting structure or structures and some of the liquid flows at least part way through the openings before the liquid is solidified. A temporary supporting structure may be removed, for example dissolved. In other examples, two supporting structures are held apart in a casting knife while posts are formed.

Inventors

Alexandru Valeriu TOMESCU

Assignees

THETIS ENVIRONMENTAL INC.

Dates

Publication Date: 20260505
Application Date: 20200227

Claims (9)

1 . A membrane comprising, a pair of separation layers; and a plurality of posts, each post extending between and connecting the pair of separation layers wherein: each of the plurality of posts is integral with each of the pair of separation layers; the posts and the separation layers are made of a porous membrane forming dope; the posts consist essentially of the porous membrane forming dope.
2 . The membrane of claim 1 wherein comprising one or more supporting structures, and wherein the posts extend through the at least one or more supporting structures.
3 . The membrane of claim 2 wherein the one or more supporting structures comprises a substrate layer.
4 . The membrane of claim 2 wherein the one or more supporting structures comprise a permeate carrier.
5 . The membrane of claim 1 without a permeate carrier.
6 . The membrane of claim 1 wherein the first and second separation layers are supported directly on a 3D spacer.
7 . The membrane of claim 1 having two substrate layers, wherein each of the first and second separation layers is supported on one of the substrate layers.
8 . The membrane of claim 7 further comprising a permeate carrier between the two substrate layers.
9 . The membrane of claim 7 without a permeate carrier.

Description

RELATED APPLICATIONS This application is a National Stage Entry of International Application No. PCT/CA2020/050263, filed Feb. 27, 2020, which claims the benefit of, and priority to, U.S. provisional patent application No. 62/811,689, Flat Sheet Membrane with Integral Posts, filed on Feb. 28, 2019, which is incorporated herein by reference. FIELD This specification relates to filtration membranes, for example microfiltration, ultrafiltration, nanofiltration or reverse osmosis membranes optionally in the form of flat sheets. BACKGROUND Flat sheet filtration membranes may be made by casting a liquid (which may be a mixture of liquids) onto a substrate and then solidifying the liquid to form a separation layer. The liquid may be a polymer solution (often called a dope) or a two-part polymer-forming solution. The substrate may be for example a woven, knitted or non-woven fabric. The substrate is formed tightly relative to the viscosity of the liquid such that the liquid does not flow through the entire thickness of the substrate. The curing mechanism may be, for example, interfacial polymerization, non-solvent induced phase separation or temperature induced phase separation. Porous membranes are formed as a dope is solidified in a bath after casting. The resulting separation layer may have pores be in a range from nanofiltration to microfiltration, frequently ultrafiltration or microfiltration. Interfacial polymerization may be used to form a dense (i.e. substantially non-porous) separating layer in the reverse osmosis or nanofiltration range. In some cases, in particular for reverse osmosis membranes, there may be two liquid application steps, the first producing a porous membrane on the substrate and the second producing a dense membrane on the porous membrane. Flat sheet membranes may be used, for example, in spiral wound, plate and frame or immersed flat sheet modules. In a typical spiral wound membrane, the membrane is formed with a separation layer on a non-woven fabric substrate. The membrane is folded and/or sealed around its edges to create an envelope around a permeate carrier. The permeate carrier is a structure able to resist compression but with an arrangement of voids, for example wales in a tricot fabric, that permit the flow of permeate into and through the permeate carrier. One or more envelopes are wrapped around a central tube with layers of feed carrier between adjacent layers of membrane. The entire structure is compressed and the membrane is further compressed against the permeate carrier by the applied feed liquid when in use. Conventional plate and frame modules have similar envelopes of membrane around permeate carrier but the envelopes are assembled into a stack of parallel planar forms typically (though not always) with intervening sheets of feed carrier. Immersed flat sheet membrane modules also have envelopes of membrane material surrounding a permeate carrier in a planar form but do not have intervening feed carrier layers. The spiral wound membranes and plate and frame membranes include a housing that confines a flow of feed water past the membranes whereas the immersed membranes are immersed in a relatively large tank of water with a free surface and less defined flow patterns. Immersed membranes tend to be assembled into large structure modules, for example 2-5 m2 in area in at least one elevation view, whereas individual spiral wound and plate and frame modules tend to be more compact structures. The term flat sheet membrane may refer to a single sheet with a separation layer or to an envelope or other structure having two sheets, each with a separation layer, around a permeate collecting space. The permeate carrier keeps the two sides of the membrane envelopes spaced apart from each other while providing a channel for permeate to flow to at least one collection point. The permeate carrier resists compression of the envelope due to transmembrane pressure applied during filtration. In some cases, particularly with immersed membranes, the membranes are backwashed periodically. In these cases, the membrane is typically attached in at least some places within its edges to the permeate carrier and the permeate carrier, and any other substrates, adhesives or other intervening materials, must also resist expansion of the membrane envelope if there is no sufficiently close feed carrier. The various materials must also resist delamination (or other separation) within or between them. In one example of a backwashable immersed membrane sold by Microdyn-Nadir, a separating layer is cast onto a non-woven fabric substrate. The substrate is bonded with a dis-continuous adhesive sheet to a permeate carrier in the form of a 3D spacer fabric. This material is reasonably successful in use as an immersed membrane, but may become unstable during filtration under large transmembrane pressures or separate under frequent or high-pressure backwashes. In another example of a backwashable immersed membra