US2592139A

US2592139A - Continuous process for the production of anhydrous glauber's salt

Info

Publication number: US2592139A
Application number: US97414A
Authority: US
Inventors: Horace J Hegan
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1948-07-02
Filing date: 1949-06-06
Publication date: 1952-04-08
Anticipated expiration: 1969-04-08
Also published as: FR990016A; BE489948A; NL70236C; DE853937C; GB646111A

Description

April 8, 1952 H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS GLAUBERS SALT Filed June 6, 1949 //7 van for Horace James Hagan By his attorneys April8, 1952 H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANI-IYDROUS GLAUBERS SALT 6 Sheets-Sheet 2 Filed June 6, 1949 lvlllll/Ill/l/ ljI/I/ I/llI/I/ //7venf0r Horace JamesHegan By his oflomeys April 8, 1952 H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS GLAUBERS SALT 6 Sheets-Sheet 5 Filed June 6. 1949 f m w M 5 0y mm 00 umh m April 8, 1952 H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS GLAUBERS SALT 6 Sheets-Sheet 4 Filed June 6, 1949 //7 vemor Horace James Hagan By his attorneys April 8, 1952 H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS GLAUBERS SALT 6 Sheets-Sheet 5 Filed June 6, 1949 I I I l'w zllllllllllll A V lhven/or Horace James Hagan By his attorneys April 8, 1952 2,592,139

H. J. HEGAN CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS GLAUBERS SALT FIG].

//7 van for Horace James Hagan By his aftomeys Patented Apr. 8, 1952 GONTINUOUS PROCESS FOR THE PRODUC- TION F ANHYDROUS GLAUBERS SALT Horace J. Hegan, Coventry, England, assignor to Courtaulds Limited, London, England, a British company Application June 6, 1949, Serial No. 97,414 In Great Britain July 2, 1948 4 Claims. (o1.- 23-121) This invention relates to the conservation, re- I covery and purification of chemicals from viscose rayon spinning baths.

In the viscose spinning industry it is standard practice to extrude viscose into coagulating baths containing sodium sulphate, sulphuric acid and zinc sulphate; the chemical processes taking place in the bath result in the formation of water and further quantities of sodium sulphate so that the composition of the bath is continuously changing. It is customary therefore to withdraw some of the bath, either continuously 01' intermittently, to evaporate water from the bath and to crystallise Glaubers salt (Na2SO410I-I2O) from the bath after the evaporation; the crystallised salt is then separated from the liquor which is usually returned, if necessary after adjustment of its composition, to the coagulating bath. The Glaubers salt obtained contains small amounts of sulphuric acid and zinc sulphate and for economic reasons it has been the practice hitherto in the viscose industry to discharge the crystallised salt, together with the small amount of sulphuric-acid and zinc sulphate associated with it, to waste.

It is known that Glaubers salt can be converted into anhydrous sodium sulphate, which has a higher commercial value than Glaubers salt, by heating it above its transition temperature (about 325 centigrade). either alone or in a saturated solution of sodium sulphate, the mother liquor being run off and cooled to provide further quantities of Glaubers salt.

The application of these processes to the viscose industry has not hitherto proved to be an economical commercial proposition. Thus the known proposals effect the conversion of a relatively small proportion of the total sodium sulphate in the Glaubers salt to the anhydrous salt since only about 16 parts of the 4.4 parts of NazSO4 contained in 100 parts of Glaubers salt (parts being by weight) are converted to anhydrous sodium sulphate on heating Glaubers salt to its transition point. It is therefore only by repeatedly carrying out the steps of heating the to anhydrous sodium sulphate can be raised to a reasonable figure for example, 60 per cent. Such repeated steps have been proved to be uneconomical.

Again in the prior proposals the anhydrous sodium sulphate tends to deposit in hard, cakelike form on hot surfaces in the evaporators or heaters used, and also in certain circumstances in the pipes connecting the various pieces of apparatus used in the recovery process. This caking is believed to be mainly due to the fact that sodium sulphate has a negative solubility coefficient and consequently, heating sodium sulphate solutions from a low temperature, for example 32 centigrade to a high temperature, for example 80-90 centigrade, causes deposition of sodium sulphate in the heaters.

In United States patent of Ebert No. 2,374,004 it is proposed to avoid entirely or to minimize and localize the effects of caking by using a concentrated solution of a sodium salt other than sodium sulphate, for example the chloride, bromide or nitrate, as the hot solution used to convert the crude Glaubers salt into anhydrous sodium sulphate.

The object of the present invention is to provide an improved, economic process for converting crude Glaubers salt into anhydrous sodium sulphate in the viscose industry.

In accordance with the present invention, a continuous process for the production of anhydrous sodium sulphate from Glaubers salt comprises continuously feeding the Glaubers salt into a stream of a saturated aqueous solution of sodium sulphate of gradually increasing temperature, the salt being introduced at a point where the temperature of the solution is below 325 centigrade, converting the Glaubers salt into anhydrous sodium sulphate by drawing it through the stream of solution into a heated zone of solution, that is a zone of solution maintained at a temperature above 32.5 centigrade, in a direction opposite to the direction of flow of the solution, which solution is continuously formed solely as a result of the heating of the Glaubers salt in the heated zone so that it thereafter flows continuously from the heated zone -through the advancing Glaubers salt and so forms the stream of solution of gradually increasing temperature and, while cooling and flowing, it washes the Glaubers salt and also deposits pure Glaubers salt crystals, and continuously recovering the anhydrous sodium sulphate formed. The temperature of the solution at the point where the Glaubers salt is fed in I is preferably about 12-l4 centigrade.

The present invention also includes apparatus for the production of anhydrous sodium sulphate from Glaubers salt comprising in combination,

an elongated vessel, mechanism for continuously feeding the Glaubers salt into one end of the elongated vessel, at least one mechanical device for drawing the Glaubers salt through the vessel from one end to the other, and heating means at the other end of the vessel to where the Glaubers salt is fed in, which heating means forms a heating zone to convert the Glaubers salt into anhydrous sodium sulphate and saturated sodium sulphate solution, the vessel being so arranged and constructed that the saturated sodium sulphate solution so formed flows towards the Glaubers salt feeding end of the vessel and forms a stream of solution the temperature of which gradually decreases as it flows through the vessel. In a preferred form of apparatus, cooling means is also provided from the beginning of the heated zone to the Glaubers salt feeding point so that the temperature of the flowing solution may be readily adjusted to give .the desired temperature gradient. Both the heating and .oooling of the vessel are preferably effected by jacketing the vessel and circulating either a heating fluid such as hot water or steam or a cooling medium such as water, as the case may be, through the jackets.

In one form of apparatus according to the invention, the vessel consists of a long tank or trough. The part of the tank or trough which forms the heating zone may be inclined if desired so that the washed crystals are allowed to drain before being converted into the anhydrous salt. In a further form of the invention, the conversion of the washed Glaubers salt to the anhydrous salt is effected in a heated container provided at the end of the tank or trough, and into which the salt is drawn, preferably after draining, by the mechanical device, the sodium sulphate solution which is simultaneously liberated being continuously fed back to the vessel at the beginning of the heated zone for example by an over-flow pipe. The pipe may be jacketed so that the temperature of the liquid can be. adjusted to as near 325 centigrade as possible.

In a further form of apparatus according to the invention, the vessel is formed by a series of inter communicating circular tanks connected so that there is a step of the foot of each tank communicating with the succeeding tank. Each tank is provided with a rotating paddle which turns the Glaubers salt crystals round till they fall over the step into the next tank.

In carrying out the process according to the invention, the Glaubers salt may be drawn through the solution by an Archimedean screw; or a system of rakes, paddles, scrapers or other mechanical devices. The mechanical devices used to draw the Glaubers salt through the solution may also be used to draw the anhydrous sodium sulphate into a suitable collecting device, for example a separating tank or a centrifuge, or a separate mechanical device may be used for this purpose. The liquor adhering to the crystals is separated by the centrifuge and if necessary is reheated and fed back into the stream of sodiumof the anhydrous sodium sulphate. The tank or trough in front of the heated zone is preferably immersed in a stream of cooling water moving in the same direction as the direction in which the Glaubers salt is raked. By a suitable adjustment of the dimensions of the tank, the rate of feeding and drawing of the Glaubers salt and the temperature and rate of flow of the cooling Water, the process may be carried out so that anhydrous sodium sulphate is collected at one end of the tank while a cooled saturated solution of sodium sulphate of such low concentration runs away at the other end that it is possible continuously to recover about per cent or more of the sodium sulphate in the crude Glaubers salt in the form of the anhydrous salt, depending on the temperature to which the solution is ultimately cooled.

In an alternative form of the invention, the tank extends so that the solution of sodium sulphate flows beyond the feeding point of the crude Glaubers salt so that the'further cooling beyond this point for example to 2-14 centrigrade deposits substantially pure crystals of Glaubers salt and the crystals so deposited are recovered by drawing them by a second mechanical device in the same direction as the direction of the flow of the solution to a suitable collecting device such as a centrifuge. In this case, the point of addition of the crude Glaubers salt to the tank will be nearer to the heated zone of sodium sulphate solution than in the case in which only sodium sulphate solution is collected beyond the feeding point of the Glaubers salt and the temperature of the solution at the point of entry of the Glaubers salt will be correspondingly higher. This embodiment of the invention permits the simultaneous and continuous production of commercially pure anhydrous sodium sulphate and commercially pure Glaubers salt from crude Glaubers salt such as is obtained by evaporation 1 and crystallisation of viscose spinning baths.

As a modification, sodium sulphate solution may be maintained by withdrawing part of the stream of solution at a point where its temperature is below 325 centigrade, heating the withdrawn solution and feeding it back into the stream at the point where the anhydrous sodium sulphate is recovered. The solution withdrawn in this manner is preferably reheated to a temperature at which the solubility of sodium sulphate in water is not below its solubility at the temperature at the withdrawal point. In this manner deposition of anhydrous sodium sulphate in the heater and in the pipes connecting the heater to the tank may be prevented. For example, if the solution is withdrawn at a temperature of 31.5 centigrade it may be heated to a temperature of 60 centigrade since the solubility of sodium sulphate in water is 31.2 per cent at both 31.5 centigrade and 60 centigrade. Information on the solubility of sodium sulphate is given by A. Seidell on page 1301 of his book entitled Solubilities of Inorganic and Metal Orgenie Compounds, 3rd edition, volume 1, and published in 1940 by D. Van Nostrand' Co. Inc. The withdrawn solution may also be treated to remove impurities such as sulphuric acid or zinc sulphate before it is returned to the tank.

When starting the process according to the invention it is not essential that there should be any saturated sodium sulphate solution in the tank since such solution will eventually be formed when the Glaubers salt reaches the heated zone but it is advantageous to have the this solution will serve to wash someof the impurities from the crude Glaubers salt and so help to improve the purity of the anhydrous sodium sulphate initially precipitated in the heated zone. As soon as the tank has become filled with saturated sodium sulphate solution no further sodium sulphate solution is added to the tank as the solution will be subsequently provided continuously as the Glaubers salt is simultaneously transformed in the heated zone into anhydrous sodium sulphate and saturated sodium sulphate solution.

In the case of acid-contaminated Glaubers salt it may be desirable to neutralise the solution with alkali. Such neutralisation is preferably carried out in the neighbourhood of the heated zone.

In carrying out the process according to the invention it is important to establish a sodium sulphate solution of gradually increasing temperature and concentration in the tank or trough in front of the heated zone so that the highest temperature, which should be about 325 centigrade but not higher, will be immediately before the heated zone and the lowest temperature will be at the exit end of the tank where the cooled solution flows to waste.

It is also important that the action of the paddles or rakes should be so adjusted as to bring the crystals of Glaubers salt into substantial equilibrium with the solution at every stage of increasing temperature and concentration; this is particularly important at the last stage where the temperature is at or near to 325v centigrade for at this temperature the solubility of sodium sulphate is at its maximum. If therefore any of the solution is carried over with the Glaubers salt into the heating or decomposition zone, none or only a small proportion of the Glaubers salt is dissolved and a maximum yield of anhydrous sodium sulphate is attained. It is particularly in this respect that the process according to the invention differs from any of the known processes of converting Glaubers salt to anhydrous sodium sulphate for in the known processes it is usual to crystallise out the Glaubers salt at relatively low temperatures and therefore any adhering mother liquor when heated above the transition temperature of Glaubers salt is capable of dissolving some of the anhydrous sodium sulphate formed by the decomposition process thus decreasing the yield for a given consumption of heat. This eiiect may be shown by an actual example; if Glaubers salt is crystallised at, say, l2-13 centigrade in accordance with standard practice and after separating the crystals these latter contain say 19 per cent of adhering mother liquor, then 111 grams of damp crystals would have contained 44 grams of NazSOi and 56 grams of water in the crystalline decahydrate and approximately 1.1 grams of NazSOr and 9.9'grams of water in the adhering solution. Therefore on heating these damp crystals to 32.5" centigrade at which temperature 100 grams of solution contain 33 grams of NazSO4 and 67 grams of water, the 9.9 grams of adhering water would be capable of dissolving:

=4.9 grams of Na SO 'drate yielding 16 grams or anhydrous sodium sulphate the yield would be reduced to: V

' l64.9+1.1=12.2 grams to the point of maximum solubility (32 centrigrade) just prior to entering the decomposition zone no or very very little sodium sulphate is dissolved in the adhering solution and therefore no especial care is necessary to dry the crystals between the crystallizing and the decomposition zones.

In accordance with a further feature of the present invention, the continuous production of anhydrous sodium sulphate, with or without the simultaneous production of pure Glaubers salt, is employed as part of a continuous process for the conservation and recovery of chemicals from viscose rayon spinning baths containing sulphuric acid, sodium sulphate and-zinc sulphate. Thus spinning bath liquor may be withdrawn either continuously or intermittently and water evaporated from the liquor so that on cooling, Glaubers salt will crystallise out. In accordance with the invention, the cooling of the liquor, after the evaporation, is effected in a tank while the liquor is moving in a stream in the same direction as the rakes, scrapers orother device employed to move the Glaubers salt, and when the desired degree of cooling has been obtained, the-mother liquor is allowed to drain away from the tank over a suitably placed weir and is returned to the spinning bath, if necessary after adjustment of its composition, while the crude crystals of Glaubers salt are continuously raked forward past the exit weir of the mother liquor into the moving stream of sodium sulphate solution. Thus, the crystallisation of the crude Glaubers salt from the evaporated liquor and also its conversion to anhydrous sodium sulphate may be effected in one long tank.

In order to prevent excessive contamination with acid of the saturated sodium sulphate solution flowing away from the heated zone it is desirable. to slope the bottom of the tank upwards beyond the exit weir of the cooled evaporated acid solution in order to allow the Glaubers salt to drain a little before it is raked into the stream of saturated sodium sulphate solution moving in the opposite direction. The top of the'slope should be above the level of the two solutions so that there is no tendency for the acid solution to mix with the other solution. After passing over the top of the slope the Glaubers salt is raked in the same direction along the tank into the heated zone where the anhydrous sodium sulphate is produced in accordance with the invention.

If des'ued the weak sodium sulphate solution containing any small quantities of acid and zinc sulphate which had adhered to the crude Glaubers salt may be passed over a weir of the tank and may be added to the mother liquor as it returns to the spinning bath. p

The evaporated spinning bath liquor is preferably introduced into the tank at a temperature of the order of 40-45 centigrade and cooled in the tank to a temperature of about 12-14 centigrade immediately before the weir.

The invention is illustrated by way of examples in the accompanying diagrammatic drawings in which Figure 1 is a vertical section of an apparatus for converting Glaubers salt to anhydrous sodium sulphate in a long straight tank,

Figure 2 is an enlarged section on the line 11-11 of Figure 1,

Figure 3 is a vertical section of a modification of the apparatus of Figure 1 in which the washed Glaubers salt crystals are allowed to drain before being converted into the anhydrous salt,

Figures 4 and 5 illustrate a further modification in which a series. of intercommunicating cirview of part only of the tanks,

Figure 6 is a vertical section of an apparatus for producing both pure Glaubers salt and anhydrous sodium sulphate, and

Figure '7 is a vertical section of an apparatus for the continuous recovery of anhydrous sodium sulphate and other chemicals from viscose spinning baths.

Throughout the drawings, like reference numerals are included to indicate like parts.

Referring to Figures 1 and 2, crude Glaubers salt I is fed continuously from a hopper 2 into a long jacketed tank 3. A series of scrapers 4, carried by a bar 5. is continuously oscillated as shown so that the crystals within the tank 3 are slowly drawn from left to right through a stream of saturated sodium sulphate solution 6 flowing through the tank 3 from right to left and finally are drawn into the heated container 1 in which -the washed Glaubers salt is converted into anhy- -drous sodium sulphate 8.

j ,The tank 3 consists of two zones AB and BC,

:the zone AB being the cooled or crystallizing zone of gradually increasing temperature up to 325 centigrade and the zone BC being the heated or decomposition zone at a temperature above 32.5" centigrade, preferably about centigrade. Higher temperatures may be used but are undesirable as they cause scaling on the container walls as a result of the negative solubility coefficient of sodium sulphate above 325 centigrade. Zone AB is provided with a bafiled jacket 9 through which cooling water is continuously circulated, the water being fed in through an inlet pipe I 0 and flowing out through an exit pipe ii. The heated zone BC has a surrounding jacket I2 which also surrounds the lower part of the container 1. Jacket I2 is heated by steam -or hot Water pipes 13, the heating medium flowing from pipe [4 to pipe l5 at such an initial temperature and at such a rate that at point B the temperature is about 32.5 centigrade.

The crude crystals I fed in at the end A are slowly drawn by the scrapers 4 through the stream of solution 6 and as they are advancing they are washed by the solution. At the point 'B the washed crystals enter the decomposition solution formed then flows from the end C towards the end A thus automatically and continuously forming the stream of solution 6. As the stream flows down the tank it is cooled after passing point B, where the temperature is regulated at or about 325 centigrade, and washes the advancing crystals and also deposits pure Glaubers salt to augment the crystals I. At the same time its temperature gradually decreases as a result of cooling by the advancing crystals and the cooling water in jacket 9, the temperature and rate of flow of which is regulated to give the necessary temperature gradient having regard to the length of the tank. By the time the solution reaches point A its temperature will preferably be about 12-14 centigrade and it then flows away through pipe I! to waste; if desired the pipe i! may be replaced by an open channel so that any crystals which become deposited are accessible for removal. When using acid-contaminated Glaubers salt it is desirable to neutralise the solution and this is preferably effected at point B just before the washed crystals enter the decomposition zone.

In the embodiment shown in Figure 3, the procedure is the same as that described with reference to Figures 1 and 2 with the following exceptions:

(a) In the decomposition zone BC the tank is inclined so that the washed crystals passing point B at or near 32.5 centigrade are allowed to drain before being decomposed. A separate set of oscillating scrapers l8 carried by a bar I9 is provided and is preferably oscillated in the same way and at the same speed as the scrapers 4.

(b) The drained crystals are fed into a. separate container 20 to effect the decomposition. Container 20 is provided with a jacket 2|, heated, for example to about 40 centigrade, by hot water or steam pipes 22.

(c) The saturated sodium sulphate solution formed as a result of the decomposition continuously overflows from container 20 and is fed by an open inclined channel 23 back into the tank 3 near to point B, the temperature of the solution at point B being approximately 32.5 centigrade when it enters the tank 3.

Instead of using scrapers 4 for drawing the Glaubers salt through the tank 3, a system of slowly moving rakes or an Archimedean screw system may be used.

Referring to Figures 4 and 5, the tank is formed by a series of intercommunicating tanks 24 having the desired temperature gradient from about 1244 centigrade at point A up to 325 centigrade at point B. The propulsion of the Glaubers salt crystals is carried out by a series of rotating paddles 25, one for each tank, which turn the crystals round until they fall over a step 26 into the succeeding tank. The paddles as shown are arranged to scrape the sides of the tanks to prevent undue scaling of crystals on the tank walls. The procedure is otherwise the same as that described with. reference to Figures 1 and. 2.

Referring to Figure 6, crude Glaubers salt'l is fed from a hopper 2 into a jacketed tank 3 as described with reference to Figures 1 and 2 but in this case the hopper is arranged nearer to the heated zone of the tank so that the crude salt I is fed into the stream of solution at a higher temperature, for example about 20 centigrade and the tank 3 and the cooling jacket 3 are extended beyond the Glaubers salt feeding point, that is to the left of the hopper 2. The apparatus to the right of the hopper 2 for producing the anhydrous salt is not shown in full since it corresponds with that shown in either Figure 1 or Figure 3. The saturated sodium sulphate solution 6 after flowing past the hopper 2 continues to cool and in cooling deposits pure Glaubers salt crystals 21. These crystals are drawn by further systems of scrapers 28 and 29, in the same direction as the direction of flow of solution 5 into a container 30. The tankis sloped slightly at the end as shown so that excess liquid is removed from the pure Glaubers salt crystals and run to waste through a pipe 3|. The cooling of the solution 6 to the left of the hopper 2 is preferably carried as low as possible for example down to 4". centigrade.

Referring to Figure 7, evaporated spinning bath liquor while still hot, for example at a temperature of 40 to 45 centigrade is fed from a pipe 33 into one end of a jacketed tank 34. The solution in the tank 34 begins to deposit crude Glaubers salt 35 which is drawn, together with its associated mother liquor, by a system of scrapers 35, carried by a bar 31, towards a weir 38. The crude Glaubers salt and mother liquor while being drawn along by the scrapers 38 are cooled by means of cooling water flowing from an inlet pipe 39 into a jacket '30, out through an exit pipe 4!, and while so cooling further crystals of Glaubers salt are deposited. The temperature of the weir 38 is preferably about 12 to 14 centigrade. When the crude salt and the mother liquor reach the weir 38, they are drawn by an Archimedean screw 42 up and over the weir which is provided with holes or perforations 43 through which the mother liquor drains away down pipe 44. At the top of the weir the crude crystals are drawn by a second Archimedean screw 45 into a countercurrent flow of sodium sulphate solution 6 where the crude salt is washed and converted into an- ;hydrous sodium sulphate as described with reference to Figure 1 or Figure 3. The excess cold, saturated sodium sulphate solution at the weir 38 drains away through holes 46 into a pipe 4'! and, as shown, is mixed with the mother liquor for return. if necessary after adjustment of the composition of the mixture, to the spinning bath.

What I claim is:

1. A continuous process for the production of anhydrous sodium sulphate from Glaubers salt which comprises heating Glaubers salt to a temperature above 32.5 centigrade to form anhydrous sodium sulphate and a saturated solution of sodium sulphate by passing the Glaubers salt longitudinally through a substantially horizontal tank having at one end a cold zone at a temperature below 32.5 C. and at the other end a hot zone above 325 C., continuously separating the saturated solution from the anhydrous sodium sulphate and recovering the anhydrous sodium sulphate by withdrawing it from the tank at the hot zone, causing the saturated sodium sulphate solution so formed to flow continuously as a confined stream along a substantially horizontal path away from the hot zone to the cold zone,

gradually cooling said stream of saturated solution so that its temperature gradually and uniformly falls to a temperature below 32.5 C. as it flows from the hot zone to the cold zone whereby the stream as it cools deposits Glaubers salt, continuously feeding additional Glaubers salt into said stream in the cold zone, continuously moving both the additional and the deposited Glaubers salt counter-current through said stream into the hot zone where the Glaubers salt is continuously converted to anhydrous sulphate and saturated sodium sulphate solution.

2. A continuous process for the production of anhydrous sodium sulphate from Glaubers salt which comprises heating Glaubers salt to a temperature above 325 C. in a hot zone to form a saturated solution of sodium sulphate and anhydrous sodium sulphate, causing the saturated sodium sulphate solution so formed to flow as a confined stream along a substantially horizontal path from the hot zone having a temperature above 325 C. to a cold zone at a temperature below 325 C. gradually cooling said stream of solution so that its temperature gradually and uniformly fallsv as it flows from the hot zone whereby the stream as it cools deposits Glaubers salt, continuously feeding additional Glaubers salt into said stream in the cold zone, continuously moving both the additional and the deposited Glaubers salt counter-current through said stream into the hot zone wherein the Glaubers salt is continuously converted to anhydrous sodium sulphate and saturated sodium sulphate solution, causing continuous flowing ofif of the saturated NazSO i solution from the cold zone and removing anhydrous sodium sulphate from the system at the hot zone.

3. A process as claimed in claim 2 wherein the temperature of the stream of solution at the point where the additional Glaubers salt is fed in is about 12 to 14 centigrade.

4. A process as claimed in claim 2 wherein the temperature of the stream of solution at the point where the additional Glaubers salt is fed in is about 20 centigrade.

HORACE J. HEGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 400,983 Williams et al. Apr. 9, 1889 1,004,858 Dow Oct. 3, 1911 2,121,208 Milligan June 21, 1938 2,374,004 Ebert Apr. 17, 1945 2,459,302 Aronson Jan. 18, 1949 2,504,097 Wiseman et a1 Apr. 11, 1950 FOREIGN PATENTS Number Country Date 13,983 Great Britian of 1887 518,671 France Jan. 7, 1921

Claims

1. A CONTINUOUS PROCESS FOR THE PRODUCTION OF ANHYDROUS SODIUM SULPHATE FROM GLAUBER''S SALT WHICH COMPRISES HEATING GLAUBER''S SALT TO A TEMPERATURE ABOVE 32.5* CENTIGRADE TO FORM ANHYDROUS SODIUM SULPHATE AND A SATURATED SOLUTION OF SODIUM SULPHATE BY PASSING THE GLAUBER''S SALT LONGITUDINALLY THROUGH A SUBSTANTIALLY HORIZONTAL TANK HAVING AT ONE END A COLD ZONE AT A TEMPERATURE BELOW 32.5* C. AND AT THE OTHER END A HOT ZONE ABOVE 32.5* C. CONTINUOUSLY SEPARATING THE SATURATED SOLUTION FROM THE ANHYDROUS SODIUM SULPHATE AND RECOVERING THE ANHYDROUS SODIUM SULPHATE BY WITHDRAWING IT FROM THE TANK AT THE HOT ZONE, CAUSING THE SATURATED SODIUM SULPHATE SOLUTION SO FORMED TO FLOW CONTINUOUSLY AS A CONFINED STREAM ALONG A SUBSTANTIALLY HORIZONTAL PATH AWAY FROM THE HOT ZONE TO THE COLD ZONE, GRADUALLY COOLING SAID STREAM OF SATURATED SOLUTION SO THAT ITS TEMPERATURE GRADUALLY AND UNIFORMLY FAILS TO A TEMPERATURE BELOW 32.5* C. AS IT FLOWS FROM THE HOT ZONE TO THE COLD ZONE WHEREBY THE STREAM AS IT COOLS DEPOSITS GLAUBER''S SALT, CONTINUOUSLY FEEDING ADDITIONAL GLAUBER''S SALT INTO SAID STREAM IN THE COLD ZONE, CONTINUOUSLY MOVING BOTH THE ADDITIONAL AND THE DEPOSITED GLAUBER''S SALT COUNTER-CURRENT THROUGH SAID STREAM INTO THE HOT ZONE WHERE THE GLAUBER''S SALT IS CONTINUOUSLY CONVERTED TO ANHYDROUS SULPHATE AND SATURATED SODIUM SULPHATE SOLUTION.