IL39235A - Method of making distillation apparatus - Google Patents

Description

pipn ipnn n'.'isyV no's? METHOD OP MAKING DISTILLATION APPARATUS This invention rela ea to dis illation, of liquids, and mor e particularly to methods of making ' di:¾tilla.tion apparatus wh ch is used for transferring the vapour of a solution through a membrane without transferring a liquid from the solut on through the same membrane.

V"· .:. Distillation of certain solutions, such as salt water., is very efficiently carried out b the use of vapour permeable membranes wherein a solution to. be distilled is heated with the vapour therefrom migrating through the permeable membrane without allowing the passage of liquid therethrough. Such a membrane is shown in Israeli Patent Application No.. 26866 in which polyvinyl chloride, cellulose nitrate, cellulose acetate, cellulose triacetate, nylon' or. polytetrafluorethylene are described as being useful as materials for such, membranes . In another proposal pol ini'lidene f uoride is set forth as being a suitable material for such. 'vapour permeable membranes.. The proposals also teach the use of elongated channels formed by corrugations on the surface a vapour impermeable film in conjunction with adjacent vapou permeable membranes to • provide flow spaces on both sides of the film. The corrugated ■design was primarily intended to improve flow through a. multiple stage still, i.e. a still comprising a series of vapour permeable -nembra es and vapour impermeable films in face to face relationship. In other words, the disposition of two- very thin sheets such as are appropriate in such a still construction have a tendency to adhere to one another, possibly inhibiting flow between these two faces. The addition of the elongated- depressions or corrugations in that structure have the effect of allowing relatively unrestricted flow from end to end across a given sheet.

This invention relates to the manufacture of distillation apparatus incorporating this principle of construction and according to the invention a method of making distillation apparatus comprises stacking a number of sheet-like elements, consisting of vapour permeable, liquid impermeable membranes and corrugated impermeable films, face-to-face in a predetermined order to form liquid conducting channels between adjacent sheet-like elements, forming sealing elements of an organic polymeric material in a plastic state and, as the sheet-like elements are being stacked, positioning the sealing elements 'between adjacent sheet-like elements at predetermined locations where the channels formed between the sheet-like elements are to be blocked, and subjecting the stack of sheet-like elements with the interposed sealing elements to heat and pressure to bond each of the sealing elements to the surfaces of its sandwiching sheet-like elements.

By' sealing the vapour permeable membranes and impermeable films together in this way so that the channel therebetween are blocked as desired, the apparatus may be constructed entirely from polymeric materials, which leads to ease of manufacture and also. to a relatively long and efficient working life for the ap aratus.

Preferably, the sealing elements are arranged so that when! following the application of heat and pressure to the stack of sheet-like elements and sealing elements, a series of aligned holes are made through the stack in the - region of the sealing elements, the holes form conduits which pass through some sealing elements and are thus blocked from the channels between the sheet-like elements sandwiching those sealing elements but which communicate with the channels between the other pairs of sheet-like elements. The conduits communicate wit the channels which in use will be arranged to carry the distillate which condenses across the vapour permeable membranes from the channels on the other side which will be arranged to carry a distilland liquid. The conduits therefore..provide outlets for the distillate from the apparatus If desired, further conduits may be formed in a similar fashion but which oomm.unicate^with the distilland channels and not the distillate channels.

Preferably the method in accordance viith the invention further comprises forming sheet material, which may also be of organic polymeric material, into a pair •of complementary shaped housing structures each having a main wall, which is preferably corrugated, and side walls dependent therefrom, locating the stack of sheet-like elements and sealing elements between the housing structures with the outer sheet-like elements disposed face-to-face with the two main walls to form outer channels therebetween, positioning sealing elements formed of an organic polymeric material in a plastic state between the main walls and the outer sheetlike elements at predetermined locations where the outer channels are to be blocked, subjecting the assembly to beat and compressive pressure to bond at least the sealing elements within the outer channels to the adjacent sheet-like elements a d main walls, and securing the dependent walls of the two housing structures together to form a housing containing the stack and having peripheral chambers at the sides of the stack.

In order for the conduits from the selected channels within the stack to communicate with the outside of the housin the aligned holes forming the conduits must also be made through one of the housing main walls and the sealing elements blocking the outer channels bounded by this main wall.

In the specification of our application No. 31 05/7O v?e describe and claim a distillation apparatus which comprises a housing formed by two comple.mentary shaped housing structures made of a liquid and vapour impermeable material and joined face-to-face to provide an enclosure having facing main walls and side walls, a stack of distillation stages contained in the housing and each includin a vapour permeable, liquid Impermeable rectangular membrane face-to-face with a rectangular impermeable film, the stages being arranged with their edges in substantial alignment secured to the housing by means which forms four periphery . chambers betwean the sides of the stack and the side valls of the housing., and means for introducing liquids into first and second peripheral chambers at adjacent sides of the stack' and withdrawing the liquids from the third and fourth peripheral chambers at the opposite sides of the stack.

By appropriately feeding and interconnecting the chambers, heating and cooling fluids can be arranged to circulate within and around the stack to set up desirable thermal facilitates gradients across the stack v/hich =^4=©a ©s= efficient operation of the apparatus.

An example of a method in accordance wit the present invention is described in the following description of a distillation apparatus with reference to the accompanying drawings, i which . - : • Figure i iS a. perspective view of the apparatus with parts broken away to illustrate some internal detail; '■" Figure 2 is a perspective view of a >section of the stack of membranes and films contained in the apparatus shewn in Figure 1, the components being cut away in a step fashion to illustrate constructional detail; Figure 5.is a partially exploded perspective ~ ■-. view of the stack section shown in Figure 2; Figure h is a section, through the apparatus on a distorted scale taken on the lines In Figure 1; and Figure 5 is a section through the apparatus on a distorted scale taken on the line 5:5 in Figure 1. - There is illustrated a multiple stage distillation apparatus, or still, embodying the invention, being shown in.' Figure 1 as generally designated 10. The still includes as basic -components-' thereof, a multiple - stage distillation unit - . housing designated 14. The membranes and films are sheet~¾ce . elements all substantially rectangular and having the same dimensions and are arranged with their edges in alignment so • that the unit 12 takes the form of a relatively thin parallel- epipedon...

In more detail, the unit component 12 includes a multiplicity of microporous, vapour permeable membranes 16 ■ m and liquid and vapour impermeable barrier films lo. The mebranes and barrier films are arranged in face-to-face relation in alternating order to form two rectangular stacks which are joined together in a manner to be described to form the unit 12. Each membrane l6 is preferably formed with a smooth or plane. surface and its other surface having a corrugated appearance being formed with alternating parallel depressions and raised sections having a generally sinusoidal configuration. Each membrane is formed with a high proportion, e.g. in "the order of 8c , of microscopic through passages or pores for conducting the vapour of a liquid, such as water, while preventing the passage 'of liquid by capillary action. Although polymeric materials useful for the membranes and methods of manufacture are disclosed in the aforementioned patent, particular mention should be made of polyvinylidene fluoride as a preferred membrane material and the so-called "solvent-non- solvent" casting process as the preferred method of forming the membrane.

Although the construction and composition of barrier films l8 is described in the aforementioned patent, it should be noted that the preferred polymeric material for the barrier films is a polycarbonate such as sold by General Electric Co. under the trademark "Lexan". Films l8 are corrugated so that when interposed between adjacent porous membranes 16, as shown in the porous " membranes forming channels for the flow of liquids in contact with the membranes. As indicated in the drawings, the corrugated barrier films IS cooperate 'with porous membranes _ .16 to form a multiplicity of distilland channels 20 through which a feed or distilland liquid such as salt water is circulated; and a multiplicity of distillate channels 22 in which ■ vapour of the distilland liquid is condensed to form distillate liquid.

The essential components of a distillation stage of the still comprise a microporous membrane l6 through which the vapour ■ of the distilland is transferred and means such as a pair of barrier films l8 cooperating' with the membrane to form distillate and distilland channels on opposite sides of the membrane. For the purpose. of clarity of illustration, the thickness of the components has been exaggerated and he still is shown in the. drawings as including only four distillation stages. However, it should be understood that in actual practice, such a still would normally -comprise a very large number of distillation stages, for example, as many as l8o. The actual number of stages, however, will depend upon the temperature differential between the hottest and coldest stages and the temperature differential between succeeding stages. In the multiple stage still, (see Figures and 5) heat is transferred to the distilland liquid in the distilland channel (or channels) 20 of the first or hottest stage (or stages) to vaporize the distilland liquid. Heat is transferred from the distillate liquid of the last', cr coldest stage (or stages) of the st,±Xl to condense the vapour, transferred through .the adjacent membrane to form distillate in a distillate channel 22. in each stage, energy is transferred as flux, i.e. vapour, through the porous' membrane and then transferred by conduction through the adjacent barrier film from the distillate to the distilland. liquid of the next succeeding stage, in the preferred form shown in the drawings, the still comprises two series of distillation stages with the first or hottest stages being located innermost and successive cooler stages arranged outwardly therefrom. Thus, distillation unit 12 comprises tv/o inner porous membranes 16 and, alternating outwardly therefrom, barrier films l8 and additional porous membranes, four membranes and four barrier films being illustrated in the drawings.

The distillate and distilland channels are formed and separated from one another to confine and conduct the flow of the liquids within the channels by damming or" blocking the channels in selected regions. The channels are dammed o blocked by sealing elements located within the channels between adjacent membranes and barrier films and bonded to the facing surfaces of the membrane and films. The distilland channels are located on the inner or hot side of each mlcroporous membrane 16 and the distillate channel are located on the opposite sides of the membranes from the distilland channels. The channels are blocked in such a way that the flow of the distilland and distillate liquids is in parallel irections from end-to-end of the unit 12 and in the form shown, sealing elements 24 are bonded to the opposite lateral margins of adjacent membranes and barrier films to prevent the admission or escape of liquids from the distilland and distillate channels at the sides thereof. The distillate channels 22 are blocked' at opposite ends by sealing elements 26 and 28 secured between and to the end marginal surfaces of adjacent membranes and barrier films between the cold side of each membrane and the hot side of the adjacent barrier film. The distilland channels 20 are blocked at one end., termed the exit e d, by sealing elements 50 also bonded to the end marginal surfaces of adjacent membranes and barrier films. The opposite ends of the distilland channels remain open at the edges of the membranes to permit the introduction of distilland liquid into the distilland channels.

Means are provided for withdrawing liquid from any particula channel at or near an end thereof at which the channel is blocked. These means incliide outlets or conduits provided by holes formed in alignment through the stack of membranes, barrier films and sealing elements. VJhere a hole is formed in a sealing element within a particular channel, there is no communication between the channel and the hole because the channel is blocked in regions surrounding the hole. However, where the channel remains unblocked in regions surrounding the hole, there will be communication between the hole and the channel. In this way, each set of aligned holes through stacked membranes, films, and sealing elements forms a conduit through the stack communicating with selected channels.

The distillation unit 12 comprises two sets of. mem^?anes and barrier films secured together in face-to-face stacked relation by sealing elements bonded to the membranes and barrier films. · . Each of these sets, one of which is shown in exploded form in Figure 2, is bounded on one face by a microporous membrane 6, on its opposite face by a barrier film 18 and includes a multiplicity (one of each are shown) of barrier films and membranes arranged in alternating order between the outer membrane and barrier film. A pair of these sets are arranged with membranes 16 in spaced face-to-face relation separated by a corrugated spacer sheet 32. The spacer 32 is formed of a liquid and vapour impermeable polymeric sheet material such as a polycarbonate and is corrugated so as to cooperate with the adjacent membranes 16 ,' to form heating channels y\ through which a heating liquid is circulated for transferring heat to the still to help establish thermal gradients from the inside of the still outwardly towards the exterior thereof. The thickness of the sheet material comprisin the spacer y~≥ may be substantially greater than the thickness of the sheet material comprising the barrier films l8 and the corrugations in the spacer 32 are substantially deeper, e.g. have a greater amplitude than the corrugations in the barrier films 18, so that the flow capacity of the channels is substantially greater than the flow capacities of the channels 20 and 22 defined by the corrugations in the barrier films. The corrugations of the spacer are parallel with the corrugations of the barrier · films, and the spacer 32 is secured to the adjacent membranes l6, can be introduced into the channels 3 at one end edge of ^ he stack and withdrawn from the channels at the opposite end edge thereof after giving up heat to the liquids within the distillate and distilland channels during its passage through the channels 34. in the preferred example of the invention, the heating liquid is the feed or distilland liquid, e.g. salt water, so that a portion of the heating liquid circulated through the channels 34 is transferred as vapour through the microporous membranes l6 defining the outer sides of the heating channels.

The distillation unit 12 is enclosed within a housing 14 providing for circulation of the various liquids including the feed liquid utilized both for heating arid the distilland, and a cooling liquid. In the form shown in Figures 1, 4 and 5. the housing 14 comprises first and second complementary sections 38 and 4θ, each having a generally rectangular main wall h2 and dependent side walls hh each formed with a flange 46. The housing sections 38 and 4o are secured to one another at the flanges 46 to form a. shallow, enclosure having length and width dimensions exceeding the length and width of the unit 12 and a depth dimension, measured between the main walls 42, approximately equal to the depth of the unit 12. To facilitate fabrication and assembly, housing sections 38 and 4o are preferably identical in size, shape and conformation. Thus, only one set of tools is required and selective assembly is made unnecessary. dependent corner wall designated 48 disposed at °' ang?¾s with respect to the dependent side walls 44 and including projecting sections .50 for receiving the corners of the unit '. ' 12 located within the enclosure provided by the housing 14. Λ sealant adapted to adhere to the housing sections and to the edges of the distillation unit 12 is introduced into the projecting sections 50 to form a seal between the corners of the unit 12 and the corner walls 48 of the housing to form four chambers between the side walls of the housing and the edges of the unit 12, these chambers being designated first, second, third and fourth and numbered 56, 52, 58, and 5 respectively. The second chamber 52 is located at the edge of the unit 12 at. which the distilland channels 22 are unblocked or open, and the fourth chamber 5 is located at the opposite edge of the unit 12 where all of the channels, except the heating channels 34 are blocked. Thus, feed or distilland liquid introduced "into the second chamber 5 will enter and flow through the distilland channels 20 and the heating channels j5 toward the opposite edge of the unit.

The portion of the heated distilland liquid which passes through the heating channels 3 and is cooled during its passage, is collected in the fourth chamber ^ from "whlie h it is conducted from the still .

The first and third chambers 5β and 8 are located at the other two sides of the still; that is, at the sides thereof at which all of the distilland, distillate, and heating channels are through which a coolant liquid may be -circulated in conta^ with the outer barrier films 18 of the unit 12, The main walls 2 of the housing are formed with corrugations similar to those in the spacer sheet 32, but disposed at right angles to the latter, which cooperate with the outer barrier films 18 to form the coolant channels 60. The coolant channels are blocked at the edges of t e unit adjacent the second and fourth chambers 5 and 54 b sealing elements 62 bonded to the facing surfaces of the outer barrier films 18 and the main walls 42 to prevent the exchange of liquid between the cooling channels and the second and fourth chambers. By virtue of this construction, a coolant liquid introduced into the first chamber 56 will be conducted through the channels 60 against the outer surfaces of the unit 12 to the third chamber 8 from which the coolant liquid may be withdrawn, thus establishing thermal gradients across the sections of the unit 12 between the heating channels 4 and the coolant channels 60. - The structure of the still is especially designed to facilitate fabrication and assembly of the components as well as to optimise liquid transfer, heat exchange, and free flow of liquids particularly insofar as these factors effect efficiency. With regard to fabrication and assembly of the still 10, all of the components thereof are preformed or fabricated as sheets and films so that assembly is essentially a positioning and stacking operation followed by the application of heat and pressure to the assembly to bond the elements to one another to fori;) an integral unit 12 which is then sealed within the housing.

The membranes 16, barrier films 18, and sealing elements are. constructed and positioned to provide for the necessary channels and conduits for the various liquids and to reduce resistance to flow of the liquids.

In the operation of the still, the heated distilland liquid, e.g. saline water, is caused to 'flow through the distilland channels' between adjacent membranes and barrier films in a direction parallel to the direction of the corrugations of the barrier films. The distillate or product is formed by condensation of vapour which passes through the membranes into the distillate channels, and, in the preferred form of still shown, is withdrawn from the end of the still at which the distilland liquid is introduced so that the' flow of distillate is counter to the flow of distilland. The distilland liquid is introduced into the distilland channels at one end of the unit 12 from the second chamber 52 and flows through the distilland channels to conduits 88 formed by aligned holes also designated 88 in the membranes 16, the barrier films 18, and the sealing elements 26 and 62, as, well as additional sealing elements 90 located within heating channels and bonded to the opposite surfaces of the spacer sheet 32 and the adjacent membranes 16. The sealing elements 90 a^e spaced from one another to permit flow of the heating liquid from the heating channels into . the fourth chamber 5^ while blocking the channels in regions surrounding the holes 88 thereby preventing flow of the heating liquid into the holes 88.

Similar conduits 92 are provided at the opposite .end of the still for Withdrawing distillate liquid from the distillate channels 22. The conduits 92 are constituted by . , the holes,, also designated 92, formed in the membranes , the barrier films, the sealing elements 62 and additional sealing elements 4, similar to the elements 90 „ provided within the distilland channels 20 and heating channels 34. The elements 94 function to block the channels 20 and 4 in the regions surrounding the holes 92 to prevent the flow of feed liquid into the conduits 92 through which the distillate is withdrawn from the still. The conduits 88 and 9 are offset from one another so that each of the conduits 88 is aligned with a space between a pair of conduits 92 and vice versa, for reasons which" will appear hereinafter. It will be noted that the sealing elements 28 and 30, which block the ends, respectively, of the distillate and distilland channels ara. formed with sinusoidally shaped inner edges located so that the conduits 88 and 92 open into the distilland and distillate channels respectively. Because of the spacing of the conduits there is required to be some flow of the distillate and distilland liquids transverse to the direction of the corrugations in the barrier films 18 in order for the liquids to flow into the conduits, and the sinusoidal edge configuration of the elements 28 and 30 tends to guide the flow of the liquids towards the conduits 88 and 92 as required.

IS.

■As previously mentioned, the surface of each poi¾jjis membrane 16 defining one side of each distilland channel is formed with alternating parallel ridges and grooves or -corrugations, extending perpendicularly to the corrugations of the barrier films 18. This construction is provided to reduce the possibility of, and loss of efficiency due to, blockages within the distilland channels which occur, for example, through scaling, and to facilitate the flow of the distilland transverse to the barrier fil corrugations in the regions of the conduits 80. The crossed corrugations or grooves in the facing surfaces which bound each distilland channel 20 perform several functions tending to achieve, the desired aims. First, the crossed corrugations tend to increase turbulence within the distilland liquid which in turn tends to prevent scale accumulation and adherence thereof to the membrane and barrier film surfaces. Should" any scale buildup occur within a channel formed by a groove in a barrier film, the grooves in the membrane and adjacent grooves~.in the film will provide alternative paths or channels around the obstruction, thereby eliminating regions of stagnant liquid in which the concentration of the scale producing agents might tend to build-up and produce additional scale. The turbulent flow and alternative flow paths provided by the crossed grooves also tend to prevent particulate matter from becoming lodged in the distilland channels and, in the event that a particle does-become lodged in a distilland channel, alternative paths are . -I? again formed around the particle to prevent the occurrence of stagnant regions resulting in scale build-up. Furthermore the grooves in the porous membranes provide channels for the -transverse flow of the distilland liquid in the regions of conduits 88, This is particularly important in these regions since it is there that the temperature and the concentration of dissolved solids in the distilland are greatest, thus making conditions more conductive to scale formation.

The sealing elements are preformed of an adhesive material adapted to bond to adjacent membranes, barrier films, the main walls of the housing and the spacer sheet 32. The sealing elements may be preformed to the desired shape and thickness from an organic polymeric material in a thermoplastic state which is caused to bond by the application of heat and pressure.

The distillation unit 12 is then assembled by alternately positioning and stacking the membranes, and barrier films, and inserting the sheet 32 and the sealing elements as appropria and then subjecting the stack of the assembled components . to heat and pressure to activate and cure the adhesive sealing elements to bind the membranes, films, and spacer sheet to one another to form the various channels. The conduits 88 and 92 are then formed by the simple expedient of drilling through the unit in the appropriate places, a conventional paper drill being suitable for this purpose.

Except for connections to the conduits 08 and 92^>and to the chambers 5 , 5 ^ » 56 , and 58 , the remainder of the assembly process involves locating the unit 12 between the housing sections 38 and ¾0 together with the sealing elements 62 , and subjecting the assembly, i,e. the still 10 , to heat and pressure to bond the sealing elements 62 in place between the main walls l\ 2 of the housing and the outer faces of the unit 12 . The flanges kG of the two housing sections are secured to one another either by conventional methods such as the use of an adhesive or' by welding. An adhesive sealant in fluid form is introduced into the projecting sections 50 to form a seal between the corner walls of the housing and the corners of the unit 12 to divide the housing into the chambers 52 , 56 , and 58 . Sealants suitable for this purpose include water insoluble cements or heat curable rubber solutions having their a low enough viscosity to permit 4 ©= ntroduction into the projecting sections 50 , such as by way of a hollow needle or syringe , · .

Means are provided for introducing liquids into and withdrawing liquids from the still 10 , specifically fo introducing heated and deaerated feed liquid (distilland) into the second chamber , withdrawing the cooled and partially depleted heating liquid from the fourth chamber 5^1 , withdrawing the effluent liquid from the distilland channels 20 by way of the conduits 88 , withdrawing distillate liquid from the distilla channels 22 by way of the conduits 92 , introducing coolant liquid into the first chamber 56 , and withdrawing the coolant liquid from the third chamber 58 . These means involve drilling holes in the main wall 2 of the housing section 38 which open one into each of the chambers 52, ^, 56 and 58, and further holes through the main wall 2 and the elements 62 which open into the conduits 88 and 92. In the example shown, nipples or short, tubes 1Q0, 102, 104, 106, 108, 110 are then attached to the main wall H2 around the holes. The nipples 100, 102, 10^1, 106, are secured around the holes opening into the' chambers 52, 51, 56, and 58 respectively. The nipples 108 are secured around the holes 88 in the main wall ^12 and the nipples 110 are secured around the holes 92. The nipple 100 therefore becomes the inlet for the feed distilland liquid and since the flow rate through it must be greater than the flow through any other nipple, the internal diameter of the nipple 100 is larger than the diameter of. the other nipples. The nipples 108 and 110 may have substantially the same diameter in examples where the effluent flow rate approximates the product flow rate.

The nipples may be formed of the same material as the housing and may be attached to the main wall 2 in any conventional manner such as by welding or by a suitable adhesive. In use, the nipples are connected to external supply and return conduits of a distillation system of which the still 10 forms a part.

It will be seen from the foregoing that the distillation apparatus described provides a structure which is relatively simple to fabricate and assemble to form a relatively complex liquid distribution system providing for desirable heat exchange and temperature gradients; minimum resistance to liquid flow; poor conditions for scale formation; and optimum conditions for preventing flow blockages. The still structure is designe to permit fabrication entirely of polymeric materials in sheet form and provide for quick and easy connection to the other components of an overall distillation system including means for circulating liquids to and from the still. .

Claims (7)

1. A method of making distillation apparatus,- comprising stacking a number of sheet-like elements, consisting of vapour permeable, liquid impermeable membranes and corrugated impermeable films, face-to-face in a predetermined order to form liquid conducting channels between adjacent . sheetlike elements, forming sealing elements of an organic polymeric material in a plastic state and as the sheet-like elements are being stacked, positioning the sealing elements between adjacent sheet-like elements at predetermined locations where the channels formed between the sheet-like elements are to be blocked, and subjecting the stack of sheet-like elements with the interposed sealing elements to heat and pressure to bond each of the sealing elements to the surface of its sandwiching sheet-like elements.

2. A. method according to Claim 1, in which the sealing elements are arranged so that when, following the application of heat and pressure to the stack .. of sheet-like elements and sealing elements, a series of aligned holes are made through the stack in the, region of the sealing elements, the holes form conduits which pass through some sealing elements and are thus blocked from the channels between the sheet-like elements sandwiching those sealing elements but which communicate with the channels between the other pairs of sheet-like elements.

3. A method according to Claim 1 or Claim 2, ' further comprising forming sheet material into a pair of complementary shaped housing structures each having a main wall and side walls dependent therefrom, locating the stack of sheet-like elements and sealing elements "between the housing structures with the outer sheet-like elements disposed face-to-face with the. two main walls to form outer channels therebetween, positioning sealing elements formed of an organic polymeric material in a plastic state between the main walls and the outer sheetlike elements at predetermined locations where the outer channels are to be blocked, subjecting':- the assembly to heat and compressive pressure to bond at least the sealing elements vrithin the outer channels to the adjacent sheet-like elements and main walls, and securing the dependent walls of the two housing structures together to form a housing containing the stack and having peripheral chambers at the sides of the stack. k. .

4. A method according to Claim 3, in which the main walls are corrugated.

5. A method according to Claim 3 or Claim , in which each housing structure is formed from a sheet of organic polymeric material.

6. A method according to any one of Claims 5 to 5 when dependent upon Claim 2 , in which the aligned holes are m.ade after the stack, is sealed in the housing, the holes also being n ide through one of the housing main walls and the sealing elements blocking the outer channels bounded by this main wall so that the conduits communicate selected channels with outside the housing.

7. A method of making distillation apparatus substantially as described with reference to the accompanying drawings. Tel-Aviv, dated '16,4.1972