Study on the production process of potassium chloride
Potassium chloride is the most important potassium compound, its production accounts for more than 95% of all potassium compounds, is the production of other potassium compounds raw materials . China's potassium deficiency, but with a large amount of potassium country, production and varieties of more and more attention to the optimization of potassium salt. In this paper, the main technology of potassium chloride, potassium sulfate, potassium nitrate and potassium carbonate at home and abroad are introduced. 1 potassium chloride into potassium sulfate production process of potassium sulfate is a kind of high quality potash fertilizer, especially suitable to avoid chlorine crop, is the current market in China, the shortage of fertilizer. The production of potassium sulfate by potassium chloride is about 70% of total potassium sulfate production. 1.1 Mannheim furnace method by famin furnace, potassium chloride and non volatile sulfuric acid in the reaction furnace in special indirect heating direct reaction of potassium sulfate. The production of potassium sulfate by the method accounts for the world's production capacity of 37%[2 ~ 4]. The method is divided into two steps: KCl+H2SO
4KHSO4+HCl = +10.4kJ (1) of the reaction can be carried out at low temperature, but potassium chloride into the KHSO4 reaction temperature must reach 120 to 140 DEG C. The temperature is related to the concentration of sulfuric acid and the ingredient of the . Second step reaction: KCl+KHSO
4 K2SO4+HCl = -70.0kJ (2) of the reaction must be heated to 500 DEG C to make sufficient reaction, due to the complicated situation in the actual industrial production, so the actual temperature to reach more than 500 DEG C. The production technology is mature and reliable, large yield scalability, production and product quality is stable, the reactor can produce more than two kinds of sulfate products . However, the technology has high investment, high quality requirements of the reaction furnace and difficulty in the construction of the furnace body. High reaction temperature, high energy consumption, fuel consumption of standard coal for 700kg/tK2SO4 (or 0.14t /tK2SO4 fuel). 1.2 solvent (for method ) in the reaction (1), (2) on the basis of changing the process conditions in order to make it more peaceful, adding organic solvent in the reaction system, greatly reduce the solubility of the reaction products or remove HCl, the reaction (1), (2) right and successfully potassium sulfate. Many scholars have done a lot of research on how to improve the conversion efficiency of the organic solvent, which can effectively improve the efficiency of . Aromatic amines or heterocyclic compounds; water soluble alcohols, such as methanol, ethanol, n-propanol, isopropanol, butanol, butanol, tert butyl alcohol, ethylene glycol, glycerol or mixtures thereof; low fat such as n-nonyl alcohol alcohol hydrophilic solvent; alkyl tertiary amine and organic amine in two ethanol amine, 1,6- hexanediamine Sanya, three ethyl amine, aniline and so can be used as solvent for the extraction of , and Association - dissociation, the Association for the production of potassium sulfate association. Methanol as a solvent in the production of potassium sulfate process is particularly prominent (Figure 1). The sulfuric acid and potassium chloride, the potassium liquor and residual liquid reaction after recovery, dissolved in water after adding methanol to the crystallization of potassium sulfate precipitation. The key to this process is the methanol recovery, because the boiling point of methanol to 65 degrees, a reasonable arrangement of hot and cold fluid flow will reduce energy consumption. But the increase of the distillation unit also increased the cost of investment and operation, and methanol toxic once the leak will cause harm to the environment.
As a kind of organic amine extractant and reaction products of HCl reaction and HCl RNH2 chloramine salt into the organic phase removed HCl, adding ammonia stripping out of amine by-product NH4Cl. This process of producing potassium sulfate (Fig. 2) enables the purity of potassium sulfate to reach the industrial grade. The purity of potassium sulfate was 52.2% (with K2O) as the extraction reagent, and the purity of the by-product NH4Cl was 99.1% (). But the general amine lower boiling point, toxic and expensive, industrialization should pay attention to sealing and safe operation.
1.3 complex decomposition method because of the solubility of potassium sulfate is far below the potassium chloride, the use of phase diagram, solubility data to achieve the purpose of separation and crystallization of potassium sulfate. In K+, Na+, Cl-, and SO2-4 - phase solubility data of multi H2O system based on the [8 ~ 13], with cheap Glauber's salt to produce potassium sulfate as raw materials for industrial transformation and potassium chloride. The transformation process is divided into two stages: into intermediate potassium sulfate, potassium sulfate and completely or partially into potassium sulfate. After the precipitation of potassium sulfate mother liquor can be processed by salt, Glauber's salt and potassium chloride and potassium mixture precipitation recycling returns. Li Po Cun  for their own raw materials are of the process was modified, select two routes: as shown in Figure 3, figure 4, carries on the material balance theory of the recovered potassium rate was 100% with the Enek index, the actual recovery rate reached more than 82%. Peng Saijun  will well mine salt water ten mirabilite reacted with potassium chloride through the "two period of transformation, the process of evaporation", select the optimum conditions for the economic and technical index can be improved greatly.
The process of potassium chloride and the transformation of the compound decomposition of the salt and the salt to potassium sulfate is similar to that of the transformation method. 2KCl+MgSO
4 MgCl2+K2SO4 (3) first step for the formation of picromerite, then treated with potassium chloride picromerite in aqueous medium, the potassium sulfate. Magnesium Sulfate method is a relatively good transformation method, in Germany, the United States, Canada and other countries, the application of a wide range of . But China's salt industry of bittern in Magnesium Sulfate utilization rate is not high, even if the production of potassium chloride by-product of Magnesium Sulfate use of all the year can only meet the production of potassium sulfate 1/10, so using the method of  resources limited. Potassium chloride and ammonium sulfate preparation of potassium sulfate with simple process, convenient operation, no corrosion, no waste, low energy consumption and equipment and materials easy to solve the advantages of [16 ~ 19], so many domestic manufacturers and research and Design Institute of technology design and production practice of relatively mature, reached the expected economic indicators. The reaction mechanism is as follows: 2 (n+1) KCl+ (n+1) () (NH4) 2SO
4 K2SO4 / (NH4) 2SO4+2n (NH)
(KCl) (4) K2SO4 (NH4) 2K2SO4+2NH4Cl 2SO4+2KCl
(5) by equation (4), (5) shows that the reaction is reversible, and [K2SO4 exists in equilibrium (NH4) and 2SO4] (NH4C1, KCl) solid solution, the product of potassium sulfate and potassium chloride purification to improve the conversion rate of difficult. Therefore, the use of K+, NH+ 4, C1-, SO2-4 - H2O system in [8 ~ 11] and the solubility data of multi phase [19 ~ 22], at higher temperature the solubility of potassium sulfate, potassium sulfate crystallization system fell in the area, at the same time in a certain amount of water, potassium chloride and ammonium sulfate added more on conversion rate, then take a quick cooling to reduce the formation of solid solution; solid-liquid separation at low temperature to improve the yield of. Tang Jianhua et al  using the process shown in Figure 5, select the best reaction temperature is 90 DEG C, the optimal separation temperature of 35 degrees Celsius in the appropriate proportion, the quantitative potassium chloride while stirring hot solution while slowly adding ammonium sulfate, potassium sulfate by superior products, the yield is up to 85%. But for without considering the recovery of potassium chloride in compound fertilizer by-product and reuse, and just as the additive of special fertilizer, can achieve good effect in economy. And in the recovery of ammonium chloride can not avoid the large amount of evaporation. Song Haining  uses the process of precipitation of ammonium chloride without evaporation (Figure 6), reduce energy consumption, reduce equipment investment to achieve the purpose of reducing costs. If the liquid phase concentration of ammonium chloride increased gradually, the solid content of potassium sulfate inevitably decreases if no evaporation conditions of potassium sulfate and ammonium chloride in the transformation temperature (45 DEG to 60 DEG) should be higher than that of ammonium chloride cooling crystallization temperature (20 DEG to 30 DEG), then the product can only be used as crude potassium sulfate, further water dissolved to obtain pure potassium sulfate. In the process in order to recycle the liquor to remove ammonium sulfate adding lime, the solubility and the use of free ammonia ammonia reduced effect of potassium sulfate, improve the conversion rate of potassium. However, the introduction of lime milk produced a large number of waste residue to cause environmental pollution. Wang Jianzhao  in Qinghai using potassium chloride and ammonium sulfate and is rich in resources, is a unique resource condition by-product of large-scale petrochemical, coking enterprises in the following screening process, as shown in Figure 7, although its products are for agricultural, resource utilization rate is not high, but the conditions of potassium sulfate production in China will play a positive role. Zhang Gang [18 ~ 19] et al. Similarly the potassium chloride and ammonium sulfate, their preparation method for high temperature saturated solution and then mixed reaction, different materials using different process of potassium sulfate production. Selection of potassium chloride and ammonium sulfate in the process of the best reaction ratio of 1: 1.2 the best reaction temperature of 95 degrees Celsius to 100 degrees Celsius, the best cooling temperature of 35 degrees, adding catalyst Q catalytic reaction, so that the yield of potassium reached 88.9%. But in order to reduce energy consumption, there is no water washing treatment of , so that the content of K2O is only 49%. Process two in the production of raw materials for the production of potassium chloride in the production of potassium sulfate two times the reaction of potassium sulfate production of potassium sulfate. As mentioned earlier, the potassium chloride and ammonium sulfate respectively prepared into high temperature saturated solution and mixed reaction, while adding A salting out agent, preparation of potassium ammonium sulfate, and ammonium potassium sulfate and potassium chloride solution with the catalyst B two conversion reaction to prepare potassium sulfate product. The yield of potassium was 80%. The greatest advantages of the above two processes are: (1) the first preparation of raw materials for their high temperature saturated solution, and then mixed reaction; (2) to add the catalyst to accelerate the reaction to maximize product precipitation. This and other transformation process is innovative and breakthrough. But the side products N, K fertilizer could further processing into higher value-added industrial products needs further research and development.
1.4 ion exchange method described above the production process of potassium sulfate has always been faced with the difficulty of the purity of potassium sulfate is not high enough, and the use of ion exchange to produce potassium, can obtain high purity products. According to the theory of ion exchange: sequential cation exchange resin for the following ions: Fe3+>Al3+>Ca2+>Mg2+>K+>NH+4>Na+>H+, Mg2+, K+, Na+ exchange capacity is very similar, the exchange medium can make their mutual exchange. The production of potassium sulfate by ion exchange method is based on the above principles. The mechanism of the process of potassium chloride and sodium sulfate as raw materials (Fig. 8): exchange reaction: 2RK+Na2SO
4 2RNa+K2SO4 (6) regeneration reaction: RK+NaCl RNa+KCl (7) R in the resin in the resin skeleton fixed part (), (6), (7) the reaction of alternating, then get the product potassium sulfate and sodium chloride. Li Hongling et al.  using U ion exchange column, type 732 strong acid cation exchange resin for the production process, to achieve industrial grade potassium sulfate standard. The biggest disadvantage of the ion exchange method is the low concentration of the solution, the concentration of evaporation, high energy consumption. Therefore, the technology is only suitable for coal and natural gas and other energy companies, and the low price of sodium chloride and potassium chloride containing a certain amount of potassium chloride is difficult to recycle waste.
Potassium chloride and Magnesium Sulfate ion exchange process and potassium chloride and sodium sulfate ion exchange process is similar. The Russian  K cation exchange agent and Magnesium Sulfate hot solution by following exchange reaction at 90 DEG C: exchange reaction: 2RK+MgSO4 R2Mg+K2SO4 (8) when the solution was cooled to 10 DEG C when the crystal precipitation, then the mother liquor with potassium chloride solution after treatment, recovery of cation exchange agent. Regenerative reaction: R2Mg+2
KCl2RK+MgCl2 (9) because of the process of high temperature exchange of low temperature crystallization separation, so the requirement for ion exchanger is higher. Process for production of potassium nitrate potassium nitrate 2 potassium chloride conversion is mainly used for military and fireworks, drugs, can also be used for ceramic glaze agent, chemical catalyst, food preservative, is a kind of important inorganic chemical raw materials. Potassium nitrate is a kind of high quality chemical fertilizer , which is a kind of plant nutrients. The production of potassium nitrate has been included in the development plan of China's chemical fertilizer production. 2.1 complex decomposition method (conversion method) the traditional production of potassium nitrate, sodium nitrate method, that is, KNO3+NaCl KCl+NaNO3 (10) due to raw material sodium nitrate prices make the method into 60s after the mainstream is no longer. The process of production of ammonium nitrate and potassium chloride has become the target of production enterprises and research institutes, and has made breakthrough progress [24 ~ 28]. The reaction is as follows: KCl+NH4NO3 KNO3+NH4Cl (11) by K+, NH+4, Cl-, NO-3 - H2O system in [8 ~ 11] and the solubility data of multi phase [24 ~ 31], the nitrate in low temperature zone is small solubility potassium crystallization crystallization temperature, high solubility of ammonium chloride crystal region. Therefore, the selection of reasonable process conditions can make the concentration of ammonium nitrate and potassium chloride mixed in the cooling of the majority of the precipitation of potassium nitrate, and then under the appropriate conditions of separation of ammonium chloride. Xiang Jianmin et al  the feeding process, and circulation method of potassium nitrate and ammonium chloride, and the introduction of a certain amount of additives, sodium chloride and sodium nitrate precipitation on potassium nitrate content has obvious effect, and does not affect the quality of the product, the potassium nitrate grade industry, the main product of potassium was 91%. Its process as shown in figure 9.
The process determines the amount of ammonium nitrate in the range of 2.25mol/L ~ 2.75mol/L, the amount of potassium chloride should be x=n (KCl): n (NH4NO3) in the range of 1.1 to 0.75. The final temperature of potassium nitrate crystallization should be at 27 + 1 C, and the final temperature of ammonium chloride crystal is 56 + 1. The additives of sodium nitrate, due to increase the concentration of [NO-3] is good for the crystallization of potassium nitrate into [Na+] for salting out effect to precipitate potassium nitrate, sodium nitrate and potassium nitrate solubility than the much larger, so adding 0.1mol/L to 0.58mol/L in the mother liquor I, potassium nitrate production increased by 5% ~ 30% and the purity of nitrate the effect of potassium. Sodium chloride on potassium nitrate also has a significant role in promoting, although the effect is better than that of sodium nitrate, sodium chloride is cheap, it is more suitable for economic. But the number of cycles in the process of 3 ~ 4 round, operating costs in the cost of a large proportion of. After 10 years of research and development of , Shen Huanghong and others, using ammonium nitrate and potassium chloride to produce potassium nitrate to obtain a more mature process and put into operation. The device is made up of the mature chemical unit operation, and realizes the large-scale continuous production in our country, which changes the backward situation of the production of potassium nitrate in China. Auby, France, is the first to open the 2.2 solvent extraction method, the so-called solvent extraction method, that is, using nitric acid and potassium chloride in low temperature to add organic extraction agent to produce potassium nitrate and by-product hydrochloric acid method. Since the successful development of the Haifa company in 60s, the cost of production of potassium nitrate has been greatly reduced, and it has been widely used in agriculture . The process principle is as follows: KCl (solid) +HNO3 (liquid)
(solid) +HCl (liquid) (12) () reaction to generate HCl at low temperature with solvent extraction removed, so that the reaction to the right to carry out. The extraction agent is separated from the hydrochloric acid, and then recycled into the original system. The key to the production technology is the choice of the solvent and the recycling of . Haifa company believes that the alcohol is the best solvent . Its technological process as shown in figure 11. Wang Guiyun et al.  in the choice of solvent extraction and innovative exploration. In the process of Haifa, the selectivity of HCl is good when the concentration of HCl and HNO3 is high, and the process of desorption is separated and the device is shown in Figure 10. The potassium chloride is dissolved in water, filtered into the tank, the tank added from ammonium chloride to filter section containing ammonium nitrate and potassium solution, after mixing into the vacuum evaporator, concentrated liquid into the first crystallizer of potassium nitrate cooling crystallization, centrifugal separation to obtain potassium nitrate; potassium nitrate crystallization mother liquor is returned is the outflow from the crystallizer mother liquid into II mixed with ammonium nitrate feeding trough. The solution tank within the II I return slot in the mold, spilled into the mother liquor tank III. However, the purity of a product of potassium nitrate was 94.40% (with the purity of 95% potassium chloride as raw material), it was necessary to get high purity product recrystallization.
Two acid is more difficult to put forward the following process (as shown in Figure 12). The process to avoid direct contact with the solvent and solid potassium nitrate, potassium nitrate reduced by solid surface adsorption caused by the loss of a large amount of solvent; with a solution of HNO3 I HCl and solvent extraction, solvent II through three stage countercurrent extraction of HNO3, the mixed acid has good separation effect. However, because the extraction and reverse extraction process is more complex, and the purity of the product can only be used in agriculture, industrial need to re crystallization purification, industrialization is still need to be further improved.
2.3 ion exchange method and the complex decomposition method, the solvent extraction method, ion exchange process can get high purity potassium nitrate products [28,34,35]. And the appearance, color, particle size, content and other aspects of ion exchange has obvious advantages. Based on the above mentioned ion exchange theory: K+, NH+4, H+ exchange capacity is very close, through the exchange of media can make them exchange. AST using potassium chloride and nitrate ion exchange of potassium nitrate production ; Shanxi Wentong potassium salt Group Co. Ltd. using ammonium nitrate and potassium chloride exchange of potassium nitrate production . The mechanism is: exchange reaction: KR+NH4NO
KNO3+NH4R (13) KCl+NH4RKR+NH4Cl (14): the regeneration reaction cycle by ion exchange resin exchange, each period can be close to the working exchange capacity of high purity product of potassium nitrate and ammonium chloride, but to obtain high conversion solution concentration is lower, so exchange effluent concentration is low, evaporation and concentration of high energy consumption, the the main drawback is the ion exchange, the implementation of the project is a special need to consider the problem of [28,35].
The production process of potassium carbonate, potassium carbonate, potassium chloride 3 transformation as an important inorganic chemical raw materials, widely used in glass, chemical, electronic and chemical fertilizer industry, also extended to medicine, welding rod, rubber and other fields, with the development of modern industry, the demand for more and more potassium carbonate, the market has been at home and abroad Jan Huojin price. However, due to the limitation of the production method, the production cost has been very high, which limits its application. At present, the main production methods of potassium carbonate are: electrolytic method, organic amine method and ion exchange method [14,36 ~ 39].
3.1 electrolysis electrolysis is obtained by carbonization of  potash solution electrolysis of potassium chloride. With potassium chloride electrolysis membrane could be made by a mixed solution containing potassium chloride and potassium hydroxide, the concentration of solution cooling precipitation separation of potassium chloride, potassium hydroxide solution will be diluted to about 30%, and then carbonized in filling the porcelain ring filler (if the potassium hydroxide solution obtained in electrolysis of potassium chloride mercury cathode in the electrolytic bath containing only trace potassium chloride, direct carbonation). In the process of carbonization of CO2 gas as the carbonization agent dosage should be reasonable distribution and accurate measurement, the effluent in 90% to enter the new countercurrent absorber, adding 10% potassium hydroxide solution, the effluent only allowed 10% inflow under one operating unit. The purity of potassium carbonate obtained by this method is about 98%, and the potassium chloride is 1%. In order to improve the purity of potassium carbonate, recrystallization and purification can be carried out.
3.2 amine organic amine method uses carbon dioxide pressure and potassium chloride as raw materials, organic amine medium mixing the following reaction: KCl+NR3+CO2+H2O KHCO3+NR3 HCl (15) after cooling precipitation of potassium hydrogen carbonate crystallization, then calcined potassium carbonate. Extraction of organic phase containing hydrochloric acid by using lime milk;
At room temperature up to more than 93% recycled . The utilization ratio of potassium chloride is 95% ~ 70%, which is difficult to deal with the pollution environment. The choice of organic amines also needs to be cautious with the economy. Zhang Renwei , Hou Qiushi  et al with high boiling point and low toxicity of organic amine as extractant, using liquid ammonia as regenerative agent to potassium chloride reached more than 95%, organic amine regeneration rate was 93.3%. Its technological process as shown in figure 13. 3.3 ion exchange ion exchange method is developed by our country, it has become the main production method of potassium carbonate in China.
, many scholars have carried out the exploration and innovation of the process optimization [35 ~ 41]. The basic principle is: exchange reaction: KCl+NH4RKR+NH4Cl (17) elution: KHCO3+NH4R KR+NH4HCO3 (18) roast: 2KHCO3=K2CO3+CO2+H2O (19) by the ion exchange theory foundation
K+ and NH+4 ionic radius is similar to that of a serious leak in the exchange and leaching of potassium, the yield is not high, Deng Jiancheng et al.  uses the multistage ion exchange column, single column, using potassium chloride solution by the first column of cation exchange resin, liquid outflow into the back of the cation exchange column to exchange, at last the outflow of liquid for high purity ammonium chloride by-product. After the exchange, get the potassium bicarbonate crude product with a certain concentration of ammonium bicarbonate solution with the first exchange column. The next round of exchange by the second column, followed by third column, the column...... Finally, through the first column discharge effluent ammonium chloride leaching, then second column to obtain the crude product, after repeated cycle. The crude product obtained by recrystallization is more than 99% of the potassium carbonate product, and the product of potassium carbonate is calcined. The utilization ratio of potassium chloride in the process can be as high as 95%. Wang and , Hou Qiushi  to join the carbonization process will be exchanged after about 10% of the potassium carbonate solution directly by evaporation and concentration, carbonization, separation, roasting potassium carbonate products. However, the ion exchange process has a great difficulty in the recovery of ammonium chloride and the reuse of potassium chloride in the mixed solution of ammonium chloride and potassium chloride. Although the application of  system ISEP recovery of ammonium chloride has obvious effect, but the system is very difficult to use a wide range of complex investment. 4 conclusion in this paper can have in part or potassium chloride in China's industrialization process into production of other potassium salts were studied and analyzed, some other [24,28,34] technology merit, or because of industrialization is very difficult, or because the process is too complex, the current level of production in China is difficult to achieve, but have not been discussed in detail. Overall, the current overall level of China's potash industry development is relatively backward; the production capacity is small, the high cost of the products; varieties of low grade, lack of research on Application development. Therefore, potash production enterprises should be combined with universities and research institutes, exert their talent and information advantages, make full use of the advanced testing facilities, the implementation of production, learning and research, accelerate the transformation of scientific and technological achievements, increase technical input, improve project, product technology content and added value. To encourage enterprises to introduce foreign advanced equipment and production technology development at the same time, pay attention to in the absorption, digestion and innovation efforts, to upgrade China's potash in the production technology, product quality grade, and enhance international competitive, so China's potash production in the short term is not impossible to reach the international level.