USOO8409542B2

(12) United States Patent (10) Patent No.: US 8,409,542 B2 Lalancette et al. (45) Date of Patent: Apr. 2, 2013

(54) METHOD AND SYSTEM FOR THE 7,604,792 B2 * 10/2009 Fairchild ...... 423,551

PRODUCTION OF POTASSUMSULEATE 299;sy R $28.9 E.KCS ca.al FROM CHILORIDE 2002/0114759 A1 8/2002 Cabello-Fuentes ...... 423 (482 (75) Inventors: Jean-Marc Lalancette, Sherbrooke FOREIGN PATENT DOCUMENTS (CA); David Lemieux, Thetford Mines CA 521086 A 1, 1956 (CA); Bertrand Dubreuil, CA 633,571. A 12, 1961 Trois-Rivieres (CA) CA 879581 A 8, 1971 CA 93.1325 A2 8, 1973 (73) Assignee: Nichromet Extraction Inc. (CA) CA 1142324938O81 A1 12,3/1983 1973 CA 2040109 A1 10, 1991 (*) Notice: Subject to any disclaimer, the term of this CA 2464642 A1 5.2003 patent is extended or adjusted under 35 DE 2O29984 A1 12, 1971 U.S.C. 154(b) by 59 days. OTHER PUBLICATIONS (21) Appl. No.: 13/160,040 “Big Quill Resources Inc. HomePage', on-line). retrieved Jun. 23. 22) Filed: 14, 2011 2011. Retrieved from the Internet:

Preparation of a saturated of KCI in at 60°C (Solution A)

Preparation of a saturated water- solution of MgSO47H2O at 60°C (Solution B) f

Mixing Solution A with Solution B

Filtering

Rising with methanol

Recovering magnesium sulfate and hydrochloric acid 22

Collecting of hydrochloric acid 2. U.S. Patent Apr. 2, 2013 Sheet 1 of 2 US 8,409,542 B2

Preparation of a saturated Solution of KC in Water at 60°C (Solution A) 12

Preparation of a saturated Water-methanol Solution of MgSO4.7H2O at 60°C (Solution B) 74

Mixing Solution A with Solution B 16

Filtering 18

Rising with methanol 20

Recovering magnesium Sulfate and hydrochloric acid 22

Collecting of hydrochloric acid 24 U.S. Patent Apr. 2, 2013 Sheet 2 of 2 US 8,409,542 B2

?--EE-ET US 8,409,542 B2 1. 2 METHOD AND SYSTEM FOR THE then under stirring and cool them down into a slurry; a filter PRODUCTION OF POTASSIUMSULFATE collecting and filtering the slurry from the third reactor; deliv FROM POTASSIUM CHILORIDE ering, after rinsing of the Solid part with methanol, chloride free , and a combined filtrate and rinsings; a FIELD OF THE INVENTION column receiving and distilling the combined filtrate and rinsings, delivering methanol back to the second reactor and The present invention relates to . More specifi to the filter and a concentrated Solution of magnesium chlo cally, the present invention concerns the production of a chlo ride; a fourth reactor, adapted to receive the concentrated rine-free potassium sulfate from potassium chloride. Solution of magnesium chloride, which crystallizes upon 10 BACKGROUND OF THE INVENTION cooling, and to treat the concentrate with Sulfuric acid, deliv ering hydrochloric acid and a residual mass; a collector, Potassium is an important and it is found in nature adapted to absorb the hydrochloric acid delivered form the as such as Sylvinite (NaCl. KCl), fourth reactor; and a fifth reactor, adapted to collect and (KC1.MgC1.6HO) or kainite (KC1.MgSO3H2O). Most of 15 crystallise the residual mass from the fourth reactor, for recy the potassium made available for fertilizer uses is in the form cling to the second reactor as magnesium Sulfate heptahy of potassium chloride. But with intensive cultures, the chlo drate. rine combined with the potassium in potassium chloride has Other objects, advantages and features of the present undesirable effects on soil, and therefore a -free invention will become more apparent upon reading of the potassium is desirable, generally a sulfate of potassium and following non-restrictive description of embodiments magnesium. In many instances, however, pure potassium Sul thereof, given by way of example only with reference to the fate, KSO, would be desirable because of its high potassium accompanying drawings. COntent. This has led to the development of techniques for the BRIEF DESCRIPTION OF THE DRAWINGS production of potassium sulfate from naturally occurring 25 Sources of potassium. One of these methods (Treatise on In the appended drawings: Inorganic Chemistry, H. Remy, Vol. 1, p. 199, Elsevier Pub FIG. 1 is a flowchart of a method according to an embodi lishing Co., 195) calls for the treatment of schönite with a ment of an aspect of the present invention; and Solution of KCl according to the following reaction: FIG. 2 is a schematic diagram of a system according to an 30 embodiment of an aspect of the present invention. In practice, it has been found very difficult to obtain a DESCRIPTION OF EMBODIMENTS OF THE potassium sulfate essentially free of magnesium chloride INVENTION with this approach, the mother liquor of this crystallization leaving several percent of chloride in the end product 35 In a nutshell, the present invention provides a method and KSO. a system for the production of chlorine-free potassium Sulfate More recently, a thermal method (Mannheim process, (KSO) from a source of potassium, Such as potassium chlo Chemical Process Industries, R. N. Shreeve, McGraw-Hill, ride (KCl) for example, and a magnesium sulfate-containing 3rd ed., 1967, p. 346) has been implemented to obtain potas Substance, such as magnesium Sulfate heptahydrate sium sulfate directly by the reaction of potassium chloride 40 (MgSO.7HO) for example. with sulfuric acid, as follows: The method generally comprises reacting KCl with MgSO.7HO in the presence of a low alcohol such as methanol (MeOH) to yield KSO and magnesium This reaction is conducted at 450° C. in silica reactors, with chloride hexahydrate (MgCl2.6H2O). MgCl2.6H2O is further very poor thermal efficiencies and fast degradation of the 45 treated with sulfuric acid (HSO) to yield back reactor, the species involved, Sulfuric acid, potassium hydro MgSO4.7HO which is re-used in the process and also hydro gen sulfate and potassium Sulfate being highly corrosive. chloric acid (HCl). Moreover, the alcohol is distilled off and Another existing approach to obtain potassium Sulfate re-used in the process. The method allows for the production from and Sulfuric acid calls upon the use of of KSO, and HC1. exchange resin (Big Quill Resources Inc. website homepage: 50 More precisely, as illustrated in FIG. 1, a method according www.bigquill.com). This approach leads to a multiplicity of to an embodiment of the present invention comprises the , which renders this approach costly and complex. preparation of a saturated solution of KCl in water at 60° C. Therefore, there is still a need in the art for a method and a (Solution A) (step 12), then the preparation of a saturated system for the production of potassium Sulfate. water solution of MgSO.7HO at 60° C., with addition of 55 methanol until the apparition of cloudiness (Solution B) (step SUMMARY OF THE INVENTION 14). Then, by mixing Solution A with Solution B at 60° C. with good stirring and cooling to room temperature, a pre More specifically, there is provided a method for the pro cipitation of KSO is obtained (step 16), which is filtered duction of potassium sulfate comprising reacting a source of (step 18) and rinsed with methanol (step 20). The combined water Soluble potassium with a magnesium Sulfate-contain 60 filtrate and rinsings are distilled to recover the methanol and ing Substance in presence of an aqueous alcoholic Solution. crystallize out magnesium chloride hydrate (step 22). This There is further provided a system for the production of magnesium chloride hydrate is then treated with sulfuric acid potassium sulfate, comprising a first reactor for dissolving a in order to recover the initial magnesium Sulfate along with water Soluble potassium in water into a first Solution; a second hydrochloric acid, a useful product (step 24). reactor for dissolving magnesium Sulfate hydrate in water and 65 The method is based on the following reaction (I): adding methanol into a second solution; a third reactor, adapted to receive the first and the second solutions, mixed US 8,409,542 B2 3 4 As known in the art (Remy, Ibid., p. 199), the presence in temperature in a range comprised between about 50 and about solution of KSO and KCl leads to the formation of a spar 65° C. and an amount of methanol 70 at a temperature in a ingly soluble double , schönite (KSO.MgSO4.6H2O). range comprised between about 35° C. and 45° C., for Therefore, as soon as some potassium sulfate is formed from example 40°C., is added to the second reactor 40 so as to be the KCl and MgSO.7H2O, a precipitation of mixed sulfate of 5 near precipitation point. The content of the first 20 and second potassium and magnesium is expected. 40 reactors are then rapidly, i.e. in a range of seconds, mixed Surprisingly, it has been found that if the mixing of the in a third reactor 80 with good stirring, typically at between potassium chloride solution with the magnesium Sulfate solu about 100 and about 150 rpm for example, and then allowed tion is done in the presence of methanol, sparingly soluble to cool down as soon as possible to a temperature in a range schönite does not form. Rather, the whole sulfate group is 10 comprised between about 0 and about 5°C. The slurry is then displaced from the magnesium to the potassium in an essen filtered in a filter 90, and the solid 100 is rinsed with methanol tially quantitative way. 110 to give pure, chloride-free potassium sulfate 120. The The fact that magnesium chloride forms a rather stable combined filtrate and rinsings 130 are then distilled with a complex with methanol (MgCl2.6MeOH) might be the reason column 140, first to isolate methanol 150 which is recycled to why the system represented by reaction (I) is displaced com 15 70 and 110. Further distillation of water 160 gives a concen pletely to the right. Potassium sulfate is insoluble in metha trated solution of magnesium chloride 170, which crystallizes nol, while magnesium chloride is rather soluble in this sol upon cooling. The concentrate 170 is placed in a fourth reac vent. Therefore, by rinsing the potassium sulfate with tor 180 and is treated there at a temperature in a range com methanol, this salt is freed of most of the magnesium chloride prised between about 90° C. and about 120° C. with sulfuric and the resulting KSO is essentially a chloride-free product, acid 190. The resulting hydrochloric acid 200 is absorbed in i.e. a product with a chloride content of less than 1%. a collector 210 as a 32% HCl solution 220. The residual mass The precipitated KSO is filtrated and the resulting filtrate in the fourth reactor 180 is collected with a minimum (at a contains magnesium chloride in methanol and water. Metha ratio of 0.4 w/w water to MgSO.7HO for example), of hot nol can be distilled off and recycled, and magnesium chloride water 230, between about 90° C. and 100°C. for example, and crystallized out after evaporation of excess water. It has been 25 allowed to crystallize in a fifth reactor 240 and recycled to the noted that the hydrate of magnesium chloride reacts Smoothly second reactor 40 as magnesium sulfate heptahydrate 250. with Sulphuric acid to give magnesium Sulfate and hydrochlo This system allows the production of potassium sulfate of ric acid at a temperature comprised in a range between about high purity, containing less than 1% . The tempera 110 and about 120°C., as per reaction (II) below: tures of operation are low, typically below about 65° C., and 30 the recycling of magnesium sulfate takes places at tempera tures typically below about 120° C., with the production of The hydrochloric acid thus formed can be collected by hydrochloric acid as a useful secondary product. standard procedures, and the magnesium sulfate recycled for With the recycling of magnesium sulfate as intermediate the production of potassium sulfate, after recristallisation to step, the high temperature, low energy efficiencies and cor get the heptahydrate form. 35 rosive situations along with chloride contamination common Therefore, in the present invention, a closed loop approach to existing processes are thus avoided. The use of a broad is taken as far as magnesium Sulfate is concerned. By com spectrum of potassium sources also adds to the flexibility of bining reaction (I) and reaction (II), reaction (III) below is the process. obtained: The following examples illustrate particular ways of 40 implementing the present invention. KCl+HSO->K-SO-HCl (III) In a first example, for the production of magnesium sulfate, As a source of potassium, potassium chloride (KCl) can be starting with 300 g of magnesium chloride hexahydrate used, or carnallite (KC1.MgCl2.6H2O). In the last case, a obtained from previous potassium Sulfate production, this larger amount of magnesium chloride is recovered after the chloride is treated with 175.8g of sulfuric acid 96% in a one filtration of potassium sulfate (reaction IV below). 45 litre beaker. The temperature is raised to 120° C. and the operation is accompanied with the evolution of HC1. Twice a 20 mL portion of water is added and distilled in order to complete the stripping of hydrochloric acid. The weight of the Other relatively low boiling alcohols can be used, such as residual solid is 255g. This solid is taken up with water (500 or propanol, but methanol may be preferred for its 50 mL) in order to re-cristallise the magnesium sulfate heptahy ease of separation from water Solution. drate after evaporation of 100 mL of water. After drying at 70° As people in the art will be in a position to appreciate, the C., a crop of 244 g of magnesium Sulfate heptahydrate is present invention thus provides a closed-loop method for the obtained. The mother liquor from this crystallisation can be production of KSO using a source of potassium such as KCl recycled in further operation. and a magnesium sulfate-containing Substance Such as 55 In another example, for the preparation of a potassium MgSO.7HO, in the presence of a low boiling point alcohol chloride solution, 121 g of potassium chloride is dissolved in Such as MeOH, and which involves recycling and re-using 335 mL of water at 60° C. in a 1.4 L beaker. MgSO.7HO. In still another example, for the preparation of a magne A system according to an embodiment of another aspect of sium sulfate solution, a 200 g sample from (1) is dissolved in the present invention is illustrated for example in FIG. 2. 60 142 mL of water at 60°C., in a one litre beaker. Then, 230 mL A source of water soluble potassium 10 is dissolved in a of warm methanol (40°C.) is added slowly with good stirring first reactor 20 with a minimum amount of water 30, for to the solution of magnesium Sulfate. example at a ratio of water to KCl of about 2:8, at a tempera For the precipitation of potassium sulfate, a warm metha ture in a range comprised between about 50° C. and about 65° nolic Solution of magnesium Sulfate is poured into the warm C. In a second reactor 40, magnesium sulfate hydrate 50 is 65 potassium chloride (2) rapidly with good stirring There is a dissolved in a minimum amount of water 60, for example with partial precipitation and the mixture is cooled at a tempera a ratio of 0.7 water to MgSO4.7H2O of about 0.7 w/w, at a ture comprised in a range between about 0 and about 5° C. US 8,409,542 B2 5 6 The crystalline mass is filtered, rinsed with 600 mL of metha 5. The method as in claim 4, where the source of potassium nol and dried at about 100° C., giving a crop of 113 g of is KC1. KSO. The determination of chlorides indicated 0.3% CI in 6. The method as in claim 4, where the source of potassium the KSO. is carnallite. For recycling of materials, by evaporation of the mother 5 7. The method as in claim 4, where the aqueous alcoholic liquor and methanol rinsings, the methanol was recovered Solution comprises a low boiling alcohol. (800 mL) and the residual water solution evaporated to yield 8. The method as in claim 4, where the aqueous alcoholic magnesium chloride hexahydrate as per (1). Solution comprises one of methanol, propanol and ethanol. 9. A system for the production of potassium sulfate, com Although the present invention has been described herein prising: above by way of embodiments thereof, it may be modified, 10 a first reactor for dissolving a water Soluble potassium in without departing from the nature and teachings of the Subject water into a first solution; invention as defined in the appended claims. a second reactor for dissolving magnesium Sulfate hydrate in water and adding methanol into a second solution; The invention claimed is: a third reactor, adapted to receive the first and the second 1. A method for the production of potassium sulfate, com 15 Solutions, mixed then under Stirring and cool them down prising reacting a chloride of potassium with a magnesium into a slurry; Sulfate in an aqueous alcoholic solution, with recycling of a filter collecting and filtering the slurry from the third magnesium sulfate and production of hydrochloric acid, reactor; delivering, after rinsing of the Solid part with wherein the recycling of magnesium is done by a reaction of methanol, chloride-free potassium sulfate, and a com Sulfuric acid on resulting magnesium chloride with corre bined filtrate and rinsings; sponding production of magnesium sulfate and hydrochloric a column receiving and distilling the combined filtrate and acid. rinsings, delivering methanol back to the second reactor 2. The method as in claim 1, where the temperature of the and to the filter and a concentrated Solution of magne reaction of Sulfuric acid on the resulting magnesium chloride sium chloride; is a range comprised between 90 and 120° C. 25 3. The method as in claim 1, where hydrochloric acid is a fourth reactor, adapted to receive the concentrated Solu collected as a solution of about 15 to 32% HCl in water. tion of magnesium chloride, which crystallizes upon 4. A method for the production of potassium Sulfate com cooling, and to treat the concentrate with Sulfuric acid, prising reacting a source of water soluble potassium with a delivering hydrochloric acid and a residual mass; magnesium Sulfate-containing Substance in presence of an 30 a collector, adapted to absorb the hydrochloric acid deliv aqueous alcoholic Solution, wherein said reacting the Source ered form from the fourth reactor; and of water soluble potassium with the magnesium sulfate-con a fifth reactor, adapted to collect and crystallise the residual taining Substance in presence of the aqueous alcoholic solu mass from the fourth reactor, for recycling to the second tion is performed at a temperature in a range comprised reactor as magnesium sulfate heptahydrate. between 50 and 65° C. k k k k k