Apparatus and continuous process for synthesis of lsx zeolite using cation exchange

Abstract

The present invention relates to a continuous process for the synthesis of Low Silica X (LSX) zeolite using cation exchange method. Further, the present invention relates to an apparatus (100) for production of LSX zeolites by cation exchange method. Specifically, the present invention relates to an improved continuous process for production of Li- LSX zeolites based on cation exchange method by using a continuous process reactor system. Further, the present invention provides a process with shorter time period, easily recoverable and reusable salt-solution and good adsorption capacity of the synthesized Li- LSX zeolites.

Description

[0001] APPARATUS AND CONTINUOUS PROCESS FOR SYNTHESIS OF LSX ZEOLITE USING CATION EXCHANGE

[0002] METHODFIELD OF THE INVENTION

[0003] The present invention generally relates to low silica X zeolite (LSX zeolite) via a cation exchange method. Specifically, the present invention relates to an apparatus / reactor for production of cation-LSX zeolites via a cation exchange method. More specifically, the present invention relates to a continuous process for production of cation-LSX zeolites using said continuous process reactor. Additionally, the present invention provides said process with a shorter time of period, easily recoverable and reusable salt-solution with good adsorption capacity for producing the cation- LSX zeolites.

[0004] BACKGROUND OF THE INVENTION

[0005] Air contains a large amount of oxygen and nitrogen, and separating oxygen and nitrogen from air is a common method for obtaining high-purity oxygen or nitrogen. Before the pressure swing adsorption technology appeared, oxygen and nitrogen production by air separation was monopolized by the freezing separation technology, however, the method has the disadvantages such as complex process steps, large area of equipment required, high investment / cost, strict / specific environmental requirements and longtime consumption, making it not a suitable method for producing oxygen in small scale and for rapid preparation of oxygen on site, and this is maintained until 70 years. Later, pressure swing adsorption technology began to be applied to the field of air separation and has been rapidly developed. The Pressure Swing Adsorption (PSA) air separation oxygen generation technology, has the advantages of simple process, convenient operation, low investment, low energy consumption, high automation degree and the like, and has gained more and more attention, and the same is explained in patents such as USP2944627, USP5176722, CN1196273A and the like. Currently, pressure swing adsorption based air separation has been around 20% of the total output of the duty cycle and is still growing rapidly.

[0006] Pressure Swing Adsorption (PSA) and Vacuum Pressure Swing Adsorption (VPS A) are commonly used as air separation means, and the preparation of high-efficiency nitrogen or oxygen separation adsorbent is one of the key process feature of the pressure swing based oxygen production technology. At present, the most studied adsorbents are mainly nitrogenadsorbing materials, and typically, the most studied adsorbents comprise CaA, CaX, NaX, LiX and the like, and the separation principle is based on the selective adsorption of the adsorbents towards nitrogen and oxygen gases present in air, and the nitrogen and oxygen separation is done by utilizing the differences of the adsorption quantity, the adsorption speed and the adsorption force of nitrogen and oxygen, the characteristic that the adsorption quantity changes along with the pressure, and by adopting the characteristics of pressure adsorption and pressure reduction desorption. Lithium based LSX zeolite (Li-LSX) has huge demand as adsorbent in oxygen generation applications using Pressure Swing Adsorption (PSA)ZVPSA techniques. Currently there is no manufacturer in India and hence, there is high dependence on imports for this material. In COVID crises there was a significant shortage of this material for oxygen generation units.

[0007] Relevant researche find that the LSX is an excellent adsorbent, so that the LSX can be applied to the fields of oxygen enrichment, hydrogen storage, gas purification and drying, tail gas treatment, environmental protection, liquid phase adsorption separation of hydrocarbons and the like. The wide application prospect of LSX promotes each mechanism to continuously optimize and improve the production process flow, improves the product quality and reduces the process cost, thereby meeting the application requirements. LSX type zeolite has wide application in pressure swing adsorption separation and vacuum pressure swing adsorption separation. Baksh et al found that the adsorption capacity of LiX molecular sieve to nitrogen was much higher than that of NaX; when the X-type zeolite has lower silica to alumina ratio, more cations can be exchanged, thereby exhibiting better adsorption performance. Due to Li+, a minimum radius and maximum charge density, compared to Na+, Mg2+, and Ag+. The zeolite formed by plasma, Li LSX zeolite, has better oxygen enrichment performance and nitrogen-oxygen separation capability.

[0008] Currently, Li-LSX is prepared using a cation exchange process with sodium based LSX (Na-LSX). The exchange process is done by two methods, viz, batch reactor and in a column. As of now, both reported methods have limitations of significant time; water and Li-salt solution required for synthesizing Li-LSX. Also, recovery and recycling of the Li- salt and water is not addressed in the prior art. Also, after Li-exchange, zeolite needs significant water for washing to remove adsorbed salts. Nothing is reported about the disposal of the spent wash water or recyclability and reuse of the spent water. Also, no solution is reported so far for the cation exchange process which addresses recycling of both Li-salt and water. Also, the reported process needs significant processing time to synthesize the cation exchanged LSX.

[0009] The known methods / apparatus in the literature require significantly higher time period (MT 24 hrs), no water and salt recovery; recover zeolites with numerous side products / salt mixtures making it tedious for separation and purification, etc. Therefore, there is an unmet need in the art to solve the aforementioned problems and provides a process for the synthesis of cation-LSX (e.g. Li-LSX) zeolite with shorter time period, easily recoverable and reusable salt-solution and good adsorption capacity of the synthesized Li- LSX zeolites.

[0010] OBJECTIVES OF THE INVENTION

[0011] An objective of the present invention is to provide an apparatus / reactor for the production of cation-LSX zeolites via cation exchange method.

[0012] Another objective of the present invention is to provide a continuous process for production of cation- LSX zeolites via cation exchange method using said continuous process reactor.

[0013] Another objective of the present invention is to provide an improved process for production of cation-LSX (e.g. Li- LSX) zeolites with a shorter time of period, easily recoverable and reusable salt- solution, and good adsorption capacity, using the novel reactor setup.

[0014] SUMMARY OF THE INVENTION

[0015] The present invention relates to an apparatus for production of cation-LSX zeolites by cation exchange method. Further, the present invention relates to a continuous process for production of cation-LSX zeolites based on cation exchange method by using said continuous process reactor system.

[0016] In an aspect, the present invention provides a continuous process reactor (100) system for the production of cation-LSX zeolites, comprising: a. leaching vessel (112) connected with organic solvent tank (104) and crude / impure salt solution supply (126), to leach out salt from the crude / impure salt, obtaining a salt solution mixture in the vessel (112); b. liquid-liquid extraction (LLE) column (105) connected to said leaching vessel (112) via filter(s) (107), in order to perform liquid-liquid-extraction of the salt solution mixture to separate and obtain pure aqueous salt solution and organic solvent; c. aqueous salt solution tank (108) connected to said liquid-liquid extraction (LLE) column (105), to store said pure aqueous salt solution; d. plurality of cation exchange column(s) [(101) and (102)] connected to said aqueous salt solution tank (108), for cation exchange of LSX zeolites in presence of said aqueous salt solution; e. water tank (103) connected to the plurality of cation exchange column(s) [(101) and (102)] to supply water for washing of the cation exchanged LSX zeolites in said plurality of cation exchange column(s) [(101) and (102)]; f. spent wash water tanks [(109) and (110)] connected to the cation exchange columns [(101) and (102)], in order to store spent wash water received from the cation exchange columns [(101) and (102)] after washing; g. calcinator (116) connected to said plurality of cation exchange column(s) [(101) and (102)], to obtain calcined cation LSX zeolites; h. multiple effect evaporator with Agitated Thin Film Dryer (122) connected to said plurality of cation exchange column(s) [(101) and (102)] via spent salt solution supply line (128), to obtain water condensate and dry spent salt; i. one part of water condensate from said multiple effect evaporator with Agitated Thin Film Dryer (ATFD) [(122)] is fed back to liquid-liquid extraction (LLE) column (105) via condensate supply line (124), and second part of water condensate is fed back to said water tank (103) via supply line (123); and j. the dry spent salt obtained from multiple effect evaporator with Agitated Thin Film Dryer (ATFD) (122) is supplied to the leaching vessel (112) via a supply line (127) for re-use in the production of cation-LSX zeolites.

[0017] In an embodiment, the plurality of cation exchange column(s) [(101) and (102)] are cylindrical columns.

[0018] In another embodiment, the water tank (103) is also connected to a solution preparation tank (111) in order to supply water for the preparation of alkali solution. In another embodiment, the organic solvent tank (104) is connected to the leaching vessel (112) in order to supply organic solvent for leaching out impure salts and remove impurities via said filter(s) (107).

[0019] In another embodiment, the reactor system (100) further comprises: a) a solution preparation tank (111) comprising alkali solution, connected to said aqueous salt solution tank (108), in order to adjust pH of the aqueous salt solution in the range of 7.5 to 9.5 before supplying to the cation exchange columns [(101) and (102)]; b) vacuum pump line (125) connected to said plurality of cation exchange column(s) [(101) and (102)] for drying the cation exchanged LSX zeolites in the plurality of cation exchange column(s) [(101) and (102)] itself; c) one or more heating elements or preheaters (106) is / are placed between aqueous salt solution tank (108) and the plurality of cation exchange column(s) [(101) and (102)] in order to supply pre-heated aqueous salt solution; d) spent wash water from the spent wash water tanks [(109) and (110)] is fed back into the cation exchange columns [(102) and (103)], and / or to the liquid liquid extraction column (105); e) hold vessel (113) is provided to hold filtered cation exchange salt solution containing organic solvent and pure salt after passing through said filter(s) (107); f) the hold vessels (114 and 115) is provided to hold spent cation exchanged salt solution from the cation exchange columns [(102) and (103)]; g) decanter (117) connected to said liquid-liquid extraction column (105), to separate aqueous and organic layer coming from the top section of the liquid-liquid extraction column (105); h) jackets [(118) and (119)] onto said plurality of cation exchange column(s) [(101) and (102)] to maintain the temperature within the columns in the range of 75-95 °C; i) heat supply (120) to said jackets [(118) and (119)] to attain said temperature in the range of 75 -95 °C; j) LSX zeolite supply line (121) to said cation exchange columns [(102) and (103)]; and k) impurities of salt after filtration through the filter (107) is removed from supply line (129).

[0020] In another embodiment, the spent wash water from the spent wash water tanks (109) is recycled back for zeolite washing of the next batch, and spent wash water from the spent wash water tanks (110) is sent to liquid-liquid extraction column (105) for liquid-liquid extraction of organic solvent.

[0021] In another aspect, the present invention provides a method for production of cation-LSX zeolites by cation exchange process comprising the steps of: a) preparing pure aqueous salt solution via leaching and liquid-liquid extraction of cation salt solution having Na and K as impurities; b) reacting continuously flowing freshly prepared salt solution with LSX zeolite in cation exchange column(s) at temperature in the range of 75-95°C and for time period in the range of 5-8 hrs to obtain cation zeolite granules; c) washing cation zeolite granules with DM water to obtain washed cation zeolite and spent wash water; d) recycling spent wash water back for zeolite washing of next batch and / or sent to liquid-liquid extraction column for extraction of organic solvent; e) drying the washed cation zeolite within the column itself by applying vacuum or passing hot dry air through the column; and f) calcining the dried zeolite granules at temperature in the range of 350 to 450°C for time period in the range of 4-5 hours to obtain pure cation zeolite granules.

[0022] In another embodiment, the cation in the cation-LSX zeolites is selected from Na+, Li+,

[0023] In another embodiment, the cation in the cation-LSX zeolites is Li2+. In another embodiment, the LSX zeolite used in cation exchange column(s) in step b) is Na- LSX zeolite.

[0024] In another embodiment, the organic solvent in step d) is selected from isoamyl alcohol, n- hexanol and 2-ethylhexanol.

[0025] In another embodiment, the calcination of step f) is done at a temperature in the range of 350 to 450 °C for time period in the range of 4-5 hours.

[0026] In another embodiment, the step a) of said method comprises: a. adding a salt solution into leaching vessel (112), followed by leaching of cation salt using an organic solvent, which is added from organic solvent tank (104) through the pump (P-03), wherein said step effects a selective dissolving of cation salt in the leaching vessel (112) to obtain a salt slurry; b. pumping the slurry using pump P-14 through filter (107) to filter out undissolved sodium and potassium impurities, which produces an organic filtrate; c. collecting the organic filtrate in the hold vessel (113) and pumping the same to liquid-liquid extraction (LLE) column (105), followed by the extraction of cation salt from the organic filtrate using DM water initially and spent wash water from spent wash water tanks [(109) and (110)] to obtain an aqueous salt solution; d. sending the aqueous salt solution from LLE column (105) to aqueous salt solution tank (108), followed by adding aqueous alkali solution from solution preparation tank (111) for pH adjustment of around 7.5 to 9.5 to obtain pure aqueous salt solution; and spent organic solvent from top of liquid-liquid extraction (LLE) column is separated through decanter (117) and sent back to the organic solvent tank (104) for re-use.

[0027] In another embodiment, the step b) of said method comprises: a. passing cation zeolites in plurality of cation exchange column(s) [(101) and (102)]; b. feeding the plurality of cation exchange column(s) [(101) and (102)] [(101) and (102)] filled with LSX zeolite granules, pre-heated pure aqueous salt solution from aqueous salt solution tank (108) through a preheater (106) in an upflow mode; c. maintaining a temperature within the plurality of cation exchange column(s) [(101) and (102)] at 95°C by supplying heating utility selected from low pressure steam (LPS) or hot oil circulation (120) through a jacket (118); d. passing aqueous salt solution continuously through the plurality of cation exchange column(s) [(101) and (102)] for time period in the range of 5-8 hours to obtain cation exchanged-LSX zeolite granules; e. washing the cation exchanged-LSX zeolite granules with DM water from the water tank (103) in downflow mode to remove adsorbed salts, followed by collecting the spent wash water in two parts in spent wash water tanks [(109) and (110)], wherein the spent wash water from spent wash water tank (109) is recycled back for zeolite washing of the next batch in the cation exchange columns (101 and 102), and the spent wash water from spent wash water tank (110) is sent to the LLE column (105) for LLE of organic solvent; f. drying the washed cation exchanged-LSX zeolite granules within the cation exchange column itself by applying a vacuum or by passing hot dry air through a supply line (125); and g. removing and sending the dried cation exchanged-LSX zeolite granules to the calcinator (116), where a hot dry air is passed for performing calcination at temperature of 400 °C for time period in the range of 4-5 hours, followed by cooling and packing the cation exchanged -LSX granules.

[0028] In another embodiment, the salt solution is circulated in a single pass mode or in a recirculation mode in step b) and step d).

[0029] In another embodiment, the LSX zeolite is Na-LSX zeolite.

[0030] In another embodiment, the adsorbed salts removed during washing in the cation exchange columns (101 and 102) are NaCl and KC1. In another aspect, the present invention provides a process with shorter time period, easily recoverable and reusable salt-solution and good adsorption capacity of the synthesized Li- LSX zeolites.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 illustrates Process Flow Diagram (PFD) for production of Cation-LSX zeolite.

[0033] Figure 2 illustrates Process Flow Diagram (PFD) for production of specific Li ion based LSX zeolite.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0036] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0037] In a general embodiment, the present invention relates to a synthesis of LSX zeolite using cation exchange method. Specifically, the present invention relates to an apparatus / reactor for production of LSX zeolites by cation exchange method. Further, the present invention relates to an improved continuous process for production of Li- LSX zeolites based on cation exchange method by using a continuous process reactor system.

[0038] In a general embodiment, the present invention provides an apparatus for the production of cation-LSX zeolites, the apparatus comprising: a. plurality of cation exchange column(s) [(101) and (102)], b. water tank (103), c. organic solvent tank (104), d. liquid-liquid extraction (LLE) column (105), e. one or more pumps or valve pumps(P-01-P-17), f. one or more heating element or preheater (106), g. filter(s) (107), h. recovered salt solution tank (108), i. spent wash water tanks [(109) and (110)], j . solution preparation tank( 111), k. leaching vessel(l 12), l. hold vessels [(113), (114) and (115)], m. calcinator (116), n. decanter (117), o. jackets [(118) and (119)] onto said plurality of cation exchange column(s) [(101) and (102)], p. heating supply [(120)], q. commercial salt supply [(121)], r. multiple effect evaporator with Agitated Thin Film Dryer (ATFD) [(122)], s. MEE condensate recycle (123) and MEE condensate (124) to the LLE column (105) via pump P-05, t. vacuum pump line (125), u. Fresh salt solution supply (126), v. dry salt mixture supply (127), w. spent salt solution (128), and x. impurities of salt mixtures (129).

[0039] In another embodiment of the present invention, the spent wash water from spent wash water tanks (109) is recycled back for zeolite washing of the next batch and the spent wash water from spent wash water tanks (110) is sent to LLE column (105) for LLE of organic solvent.

[0040] In another embodiment of the present invention, the cation exchange column(s) [(101) and (102)] are cylindrical columns comprising a jacket for heating and insulation to keep the temperature around 75-95°C.

[0041] The heating element or preheater are present in different sections e.g. columns, preheater (106) between (108) tank and cation exchange column(s) [(101) and (102)].

[0042] In another embodiment of the present invention, the apparatus (100) for the production of cation- LSX zeolites as shown in Figure 1 comprises; adding fresh salts (126) into the leaching vessel (112) in which leaching of salt is done with suitable organic solvent from organic solvent tank (104) through the pump P-03. The salt slurry from the vessel (112) is then pumped using pump P-14 through filter (107) to filter out undissolved impurities. The fdtrate is collected in the hold vessel (113) and pumped using pump P-15 to liquid-liquid extraction (LLE) column (105) in the upflow mode. Aqueous solution from LLE column (105) is sent through the pump P-13 to salt solution tank (108) to which alkali solution is added from tank (111) through the pump P-17 for pH adjustment. The water is provided from water day tank (103) to the tank (111) to prepare alkali solution through the pump P- 02.

[0043] The cation exchange column(s) [(101) and (102)] are fed with the salt solution from (108) tank pumping using pump P-16 through preheater (106) in the upflow mode. The zeolite granules formed are washed with water from water day tank (103) in downflow mode through the pump P-01. Finally, the zeolite granules are dried and sent to the calcinator (116). The spent salt (LiCl) solution (128) from the cation exchange column (101) is collected in the hold vessel (114) and further passed through the pump P-07 to the multiple effect evaporator (MEE). Similarly, the spent LiCl solution from the cation exchange column (102) is collected in the hold vessel (115) and further passed through the pump P-09 to the multiple effect evaporator (MEE). The spent LiCl solution is passed through the multiple effect evaporator (MEE) to obtain dry salt mixture (to feed into the leaching vessel (112). The MEE condensate recycle (123) is passed through the pump P-04 to the water day tank (103) in the upflow mode. Also, the MEE condensate (124) is passed through the pump P-05 to the LLE column (105). Spent wash water is collected from cation exchange column (101) through the pump P-06 and column (102) through the pump P-08 in two parts in (109) and (110) tanks. The spent wash water from tank (109) is recycled back for zeolite washing of the next batch through the pump P-11 and the spent wash water from tank (110) is sent to LLE column (105) through the pump P-10 for LLE of organic solvent. The organic solvent from the LLE column (105) is passed through the decanter (117) and is pumped using pump P-12 to recycle back to the organic solvent tank (104).

[0044] In another embodiment, the present invention relates to a method for production of cation - LSX zeolites by cation exchange process, comprising the steps of: a) preparing aqueous salt solution via leaching and liquid-liquid extraction using a commercial salt having Na and K as impurities; b) reacting continuously flowing freshly prepared salt solution with a LSX zeolite in cation exchange column(s) at a temperature in the range of 75-95°C and for a time period of 5- 8 hrs to obtain a mixture of cation zeolite granules; c) washing said mixture of cation zeolite granules with a solvent to obtain a washed cation zeolite and a spent wash solvent; d) recycling said spent wash solvent back for zeolite washing of next batch and / or sent to liquid-liquid extraction column for extraction of organic solvent; e) drying the washed cation zeolite obtained in step c) or d) within the column itself to obtain dried zeolite granules (130); and f) calcining the dried zeolite granules to obtain pure cation zeolite granules.

[0045] In another embodiment of the present invention, the cation in the cation-LSX zeolites is selected from Li2+, Mg2+, Ca2+and K+.

[0046] Specifically, the cation in the cation -LSX zeolites is Li2+.

[0047] In another embodiment of the present invention, the commercial salt is selected from lithium chloride (LiCl), lithium bromide, lithium iodide, magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, calcium iodide, zinc chloride, barium chloride, silver bromide, silver chloride, nickel chloride, manganese chloride, cadmium chloride, cobalt chloride, rubidium chloride, Strontium chloride, Caesium chloride. In another embodiment of the present invention, the salt solution used in step a) and b) is selected from LiCl solution, LiBr solution, Lil solution, MgCh solution, MgBri solution, Mgl2solution, CaCh solution, CaBri solution, Cab solution, barium chloride solution, silver bromide solution, silver chloride solution, nickel chloride solution, manganese chloride solution, cadmium chloride solution, cobalt chloride solution, rubidium chloride solution, Strontium chloride solution, Caesium chloride solution.

[0048] In another embodiment, in step b) of the process of the present invention the LSX zeolite used in cation exchange column(s) is Na-LSX zeolite.

[0049] In another embodiment of the present invention, the solvent used in step c) is selected from water, de-mineralized water and de-ionized water.

[0050] In another embodiment, the organic solvent used in step d) is selected from isoamyl alcohol, n-hexanol and 2-ethylhexanol.

[0051] The preferred organic solvent is isoamyl alcohol.

[0052] In another embodiment, the drying of step e) is done by applying a vacuum and / or passing hot dry air through the column.

[0053] In another embodiment, the calcination of step f) is done at a temperature of 350 to 450 °C for 4-5 hours. Specifically, the temperature for said calcination is done at 400 °C.

[0054] In yet another embodiment of the present invention, the cation exchange process is carried out in a column by forming a fixed bed of the Na-LSX granules and passing the Li-salt solution with suitable superficial liquid velocity. The optimized process parameters gave a good nitrogen adsorption capacity of around 20 ml / gm within 5 hours of the Li -exchange process. The spent solution of Li-salt after cation exchange process is processed to recover Li-salt solution by separating the Na and K-salts which are formed in the process.

[0055] In an embodiment of the present invention, a complete Process Flow Diagram (PFD) for the production of Li-LSX from Na-LSX through the cation exchange process along with LiCl separation and LiCl-solution recovery and recycles is shown in Figure 1. The overall PFD for the production of Li-LSX starting with Na-LSX comprises of:

[0056] 1. LiCl salt solution preparation, recovery and recycle; and

[0057] 2. Cation exchange process. In another embodiment of the present invention, the detailed process description as shown in Figure 1 is given below:

[0058] 1. LiCl salt solution preparation, recovery and recycle: a. Fresh commercial salt has higher Na & K content which is not suitable for the cation exchange process. Hence, it is purified before use. b. Initially fresh salts are added into the vessel (112) in which leaching of LiCl salt is done with suitable organic solvent like isoamyl alcohol. Isoamyl alcohol is added from the (104) day tank through the pump P-03. c. Sodium and potassium impurities do not dissolve in the solvent; however, LiCl gets selectively dissolved in the solvent in the (112) mixing vessel. d. The salt slurry is then pumped using pump P-14 through filter (107) to filter out undissolved sodium and potassium impurities. e. The filtrate is collected in the hold vessel (113) and pumped to liquid-liquid extraction (LLE) column (105) where LiCl salt from the organic filtrate is extracted using DM water. f. Initially fresh DM water is used for LLE and later condensate from the evaporator and spent wash water from (109) can be used to reduce water consumption. g. Aqueous solution from LLE column (105) is sent to LiCl solution day tank (108) to which aqueous LiOH solution is added for pH adjustment from (111) tank. The desired pH of aqueous LiCl solution for the exchange process is in the range of 8.5-9. h. The organic phase from the LLE column (105), which is almost pure isoamyl alcohol, is sent to the day tank (104). i. For recovery of LiCl salt in dry form from spent aqueous solution, Multiple Effect Evaporator is used with Agitated Thin Film Dryer (ATFD). Also, spray dryers can be used to recover LiCl salt in completely dry form. j. Once recycling of LiCl salt is started through the Multiple Effect Evaporator with Agitated Thin Film Dryer (ATFD) to (112) vessel, fresh salt requirement will be reduced. . Cation exchange process: a) The Na-LSX zeolites are filled in the Li-exchange columns [(101) and (102)]. In the present configuration two columns are considered. However, the number of columns to be used depends on the desired throughput of the plant. Multiple Li-exchange columns can also be used. b) The column [(101) and (102)] filled Na-LSX zeolite granules are fed with the aqueous LiCl solution from (108) day tank through preheater (106). Solution flows into the column in the upflow mode. c) Both exchange columns are jacketed (118 and 119) to maintain the process temperature within the column at around 95°C by supplying heating utility such as low pressure steam (LPS) (120) or hot oil circulation (120). d) Once desired temperature is achieved LiCl solution is passed continuously through both columns for appropriate time, typically 5-8 hours. e) Once the cation exchange process is completed, formed Li-LSX zeolite granules are washed with DM water to remove adsorbed salts. It is done by feeding water from DM water day tank (103) in downflow mode for efficient washing. f) Spent wash water is collected in two parts in (109) and (110) hold tanks. Initially, approximately one third of total spent wash water is collected in (110) tank and remaining in (109) tank. g) Spent wash water from (109) is recycled back for zeolite washing of the next batch. h) Spent wash water from (110) is sent to LLE column (105) for LLE of organic solvent. i) The washed Li-LSX zeolite granules are then dried within the column itself by applying vacuum. Drying can also be done by passing hot dry air through the columns. j) The dried Li-LSX zeolite granules are then removed and sent to the calcinator (116) in which hot dry air is passed during calcination. Calcination is performed at around 400°C for 4-5 hours. k) After calcination the Li-LSX granules are allowed to cool and then removed and packed in an airtight container. 1) In the Li-exchange process described in point no. b-d, the LiCl solution is circulated in a single pass mode. It is also possible to circulate the LiCl solution in recirculation mode i.e fixed quantity of salt solution is kept on circulating through the column with Na-LSX zeolite.

[0059] In another embodiment of the present invention, a similar process can also be used for other cation exchange processes such as calcium exchange using CaCh salt.

[0060] In another embodiment, the present invention is useful to generate Li-LSX with good nitrogen gas adsorption capacity within a short exchange time of the order of 5 hrs. The process of the present invention allows recycling of Li-salt, but also allows the complete water recycle in the process. The key advantage of the improved process is reduction in salt and water requirement for cation exchange process along with good adsorption capacity of the synthesized Li- LSX zeolites.

[0061] In simple terms, the present apparatus and process is in continuous mode considering salt solution for cation exchange is passed continuously, and the LSX zeolite are fdled initially in one go in cation exchange columns. Once they are exchanged, they have to be removed and next lot of LSX zeolite is taken. As there are multiple columns, the production is continuous as while one column is doing cation exchange, other column is giving final exchanged zeolite, hence, it is a continuous production.

[0062] EXAMPLES

[0063] The present invention is further explained in the form of the following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.

[0064] Example 1 - General procedure for the preparation of Li-LSX zeolites.

[0065] 200 g of commercial Na-LSX zeolite is filled in a jacketed glass column such that a granules bed is formed in the center of the column. The bed is supported by perforated teflon plate at bottom and top. The jacket of the column is connected to a hot oil circulator with temperature control. A solution of 5 molar LiCl concentration is prepared with pure LiCl salt and DM water. Small quantity of LiOH is added to the solution to adjust solution pH to 8.5. The outlet of the vessel having LiCl solution is connected to the bottom inlet of the jacketed glass column through a preheater and a pump. Outlet at the top of the jacketed glass column is connected to a solution collection vessel. To start the Li-exchange process, initially the column is filled with LiCl solution using the pump such that the granules bed is completely filled with the solution. Hot oil circulator is started to circulate hot oil through the column jacket to heat the solution in the column. The hot oil temperature is maintained at such a temperature that temperature within the column bed reaches around 95°C. Once the desired temperature is achieved within the column, the solution is fed continuously at a flow rate of 1.8 liters per hour. The cation exchange process continues for 2 hours. After 2 hours the LiCl solution feed is stopped by turning off the pump and hot oil circulator. The granules within the column are washed by feeding DM water from the top of the column. Granules are washed with 5 liters of DM water. The granules are then dried at 100°C for 4 hours within the column. The temperature for drying is achieved by starting the hot oil circulator. Vacuum is also applied to the column to remove moisture effectively. After drying, Li-LSX granules are taken out for calcination. Li-LSX granules are calcined at 400°C for hours in the furnace. After calcination, granules are stored in a moisture free container. Synthesized Li-LSX granules are tested for nitrogen gas adsorption capacity and it showed an adsorption capacity of 20.3 ml N2 per gram of zeolite.

[0066] Example 2

[0067] 200 gm of commercial Na-LSX zeolite, mentioned in example 1, was taken and a similar Li-exchange process is followed with 2 molar LiCl solution. The LiCl solution was circulated for 5 hours at 95°C. Same protocol as mentioned in the example 1 was followed for washing, drying and calcination of Li-LSX zeolite granules. Adsorption capacity for nitrogen gas in this case was around 20.8 ml N2 per gram of zeolite.

[0068] Example 3

[0069] 200 gm of commercial Na-LSX mentioned in example 1 was taken as Li-exchange process was done in recirculation mode i.e. fixed quantity of solution was kept on circulating. 3.25 kg of 2 molar LiCl solution was prepared with pH adjusted to 8.5 using LiOH solution. The solution was kept circulating for 16 hours through the column at 95°C. Following the Li- exchange process, a similar protocol as mentioned in example 1 was followed for washing, drying and calcination. In this process, nitrogen gas adsorption capacity of 16.3 mL / gm was achieved.

[0070] Example 4 - Procedure for LiCl salt solution recovery and recycle The spent LiCl solution obtained in example 1 after the Li-exchange process is taken for LiCl recovery and reuse. The complete solution was fed to an evaporator to evaporate complete water from the salt solution. The 50 gm of dry solid salts obtained from evaporation were taken and added in a mixing vessel. 780 gm of isoamyl alcohol was added to the mixing vessel and was stirred for around 1 hour. The undissolved fraction of salt, which are mainly sodium and potassium salts, was filtered out. The filtrate was then extracted with an equal amount of DM water. LiCl in the organic layer gets extracted in DM water to form aqueous LiCl solution. Organic layer obtained after liquid-liquid extraction which is almost pure isoamyl alcohol can be reused for the next round of recovery of LiCl salt. The aqueous LiCl solution obtained was then adjusted for pH to 8.5 using LiOH solution and then used for Li-exchange experiment at 6 gm scale of Na-LSX zeolite. Operating parameters were the same as those mentioned in example 1. The flow of solution in this case was 0.9 gm / min and duration of Li-exchange was 5 hours. The same protocol for washing, drying and calcination was followed after the Li-exchange process as mentioned in example 1. Li-LSX granules obtained showed N2 adsorption capacity of 21.3 ml / gm.

[0071] ADVANTAGES OF THE PRESENT INVENTION

[0072] 1. The present invention provides apparatus / reactor with specific design, interconnected tanks and flow of liquids / solutions / solvents for an effective and continuous preparation of cation-LSX zeolites within a shorter period of time (4 to5 hrs).

[0073] 2. The present invention provides a process for the synthesis of Li-LSX zeolites, wherein washing and purification is done in the apparatus itself.

[0074] 3. The present invention provides a process for the synthesis of Li-LSX zeolites, wherein handling of zeolites is easy as exchange, washing and drying is done in single equipment i.e., exchange column, and also reduces loss of material by breakage of the granules.

[0075] 4. The present invention provides a process for the synthesis of Li-LSX zeolites, in which spent wash water and spent salt solution is easily recoverable and reusable.

[0076] 5. The present invention provides a process for the synthesis of Li-LSX zeolites, with good adsorption capacity of the synthesized LSX zeolites.

Claims

We Claim:

1. A continuous process reactor (100) system for the production of cation-LSX zeolites, comprising: a) leaching vessel (112) connected with organic solvent tank (104) and crude / impure salt solution supply (126), to leach out salt from the crude / impure salt, obtaining a salt solution mixture in the vessel (112); b) liquid-liquid extraction (LLE) column (105) connected to said leaching vessel (112) via filter(s) (107), in order to perform liquid-liquid-extraction of the salt solution mixture to separate and obtain pure aqueous salt solution and organic solvent; c) aqueous salt solution tank (108) connected to said liquid-liquid extraction (LLE) column (105), to store said pure aqueous salt solution; d) plurality of cation exchange column(s) [(101) and (102)] connected to said aqueous salt solution tank (108), for cation exchange of LSX zeolites in presence of said aqueous salt solution; e) water tank (103) connected to the plurality of cation exchange column(s) [(101) and (102)] to supply water for washing of the cation exchanged LSX zeolites in said plurality of cation exchange column(s) [(101) and (102)]; f) spent wash water tanks [(109) and (110)] connected to the cation exchange columns [(101) and (102)], in order to store spent wash water received from the cation exchange columns [(101) and (102)] after washing; g) calcinator (116) connected to said plurality of cation exchange column(s) [(101) and (102)], to obtain calcined cation LSX zeolites; h) multiple effect evaporator with Agitated Thin Film Dryer (122) connected to said plurality of cation exchange column(s) [(101) and (102)] via spent salt solution supply line (128), to obtain water condensate and dry spent salt; i) one part of water condensate from said multiple effect evaporator with Agitated Thin Film Dryer (ATFD) [(122)] is fed back to liquid-liquid extraction (LLE)column (105) via condensate supply line (124), and second part of water condensate is fed back to said water tank (103) via supply line (123); and j) the dry spent salt obtained from multiple effect evaporator with Agitated Thin Film Dryer (ATFD) (122) is supplied to the leaching vessel (112) via a supply line (127) for re-use in the production of cation-LSX zeolites.

2. The continuous process reactor (100) system as claimed in claim 1, wherein a) the plurality of cation exchange column(s) [(101) and (102)] are cylindrical columns; b) the water tank (103) is also connected to a solution preparation tank (111) in order to supply water for the preparation of alkali solution; and c) said organic solvent tank (104) is connected to the leaching vessel (112) in order to supply organic solvent for leaching out impure salts and remove impurities via said filter(s) (107).

3. The continuous process reactor (100) system as claimed in claim 1, wherein the reactor system further comprises: a) a solution preparation tank (111) comprising alkali solution, connected to said aqueous salt solution tank (108), in order to adjust pH of the aqueous salt solution in the range of 7.5 to 9.5 before supplying to the cation exchange columns [(101) and (102)]; b) vacuum pump (125) connected to said plurality of cation exchange column(s) [(101) and (102)] for drying the cation exchanged LSX zeolites in the plurality of cation exchange column(s) [(101) and (102)] itself; c) one or more heating elements or preheaters (106) is / are placed between aqueous salt solution tank (108) and the plurality of cation exchange column(s) [(101) and (102)] in order to supply pre-heated aqueous salt solution; d) spent wash water from the spent wash water tanks [(109) and (110)] is fed back into the cation exchange columns [(102) and (103)], and / or to the liquid liquid extraction column (105); e) hold vessel (113) is provided to hold filtered cation exchange salt solution containing organic solvent and pure salt after passing through said filter(s) (107);f) the hold vessels (114 and 115) is provided to hold spent cation exchanged salt solution from the cation exchange columns [(102) and (103)]; g) decanter (117) connected to said liquid-liquid extraction column (105), to separate aqueous and organic layer coming from the top section of the liquid-liquid extraction column (105); h) jackets [(118) and (119)] onto said plurality of cation exchange column(s) [(101) and (102)] to maintain the temperature within the columns in the range of 75-95 °C; i) heat supply (120) to said jackets [(118) and (119)] to attain said temperature in the range of 75 -95 °C; j) LSX zeolite supply line (121) to said cation exchange columns [(102) and (103)]; and k) impurities of salt after filtration through the filter (107) is removed from supply line (129).

4. The continuous process reactor (100) as claimed in claim 1, wherein spent wash water from the spent wash water tanks (109) is recycled back for zeolite washing of the next batch, and spent wash water from the spent wash water tanks (110) is sent to liquidliquid extraction column (105) for liquid-liquid extraction of organic solvent.

5. A method for production of cation-LSX zeolites by cation exchange process comprising the steps of: a) preparing pure aqueous salt solution via leaching and liquid-liquid extraction of cation salt solution having Na and K as impurities; b) reacting continuously flowing freshly prepared salt solution with LSX zeolite in cation exchange column(s) at temperature in the range of 75-95°C and for time period in the range of 5-8 hrs to obtain cation zeolite granules; c) washing cation zeolite granules with DM water to obtain washed cation zeolite and spent wash water; d) recycling spent wash water back for zeolite washing of next batch and / or sent to liquid-liquid extraction column for extraction of organic solvent;e) drying the washed cation zeolite within the column itself by applying vacuum or passing hot dry air through the column; and f) calcining the dried zeolite granules at temperature in the range of 350 to 450°C for time period in the range of 4-5 hours to obtain pure cation zeolite granules.

6. The method as claimed in claim 5, wherein the cation in the cation-LSX zeolites is selected from Na+, Li+, Mg2+, Ca2+, Sr2+, Rb+, Cs+, Ag+, Ba2+, Zn2+, Co3+, Ni2+, Cd2+, Mn2+and K+; wherein the cation in the cation-LSX zeolites is Li2+; and wherein the LSX zeolite used in cation exchange column(s) in step b) is Na-LSX zeolite.

7. The method as claimed in claim 5, wherein the organic solvent in step d) is selected from isoamyl alcohol, n-hexanol and 2 -ethylhexanol; and wherein the calcination of step f) is done at a temperature in the range of 350 to 450 °C for time period in the range of 4-5 hours.

8. The method as claimed in claim 5, wherein the step a) comprising: a) adding a salt solution into leaching vessel (112), followed by leaching of cation salt using an organic solvent, which is added from organic solvent tank (104) through the pump (P-03), wherein said step effects a selective dissolving of cation salt in the leaching vessel (112) to obtain a salt slurry; b) pumping the slurry using pump P-14 through filter (107) to filter out undissolved sodium and potassium impurities, which produces an organic filtrate; c) collecting the organic filtrate in the hold vessel (113) and pumping the same to liquid-liquid extraction (LLE) column (105), followed by the extraction of cation salt from the organic filtrate using DM water initially and spent wash water from spent wash water tanks [(109) and (110)] to obtain an aqueous salt solution; d) sending the aqueous salt solution from LLE column (105) to aqueous salt solution tank (108), followed by adding aqueous alkali solution from solution preparation tank (111) for pH adjustment of around 7.5 to 9.5 to obtain pure aqueous salt solution; andspent organic solvent from top of liquid-liquid extraction (LLE) column is separated through decanter (117) and sent back to the organic solvent tank (104) for re-use.

9. The method as claimed in claim 6, wherein the step b) comprising: a) passing cation zeolites in plurality of cation exchange column(s) [(101) and (102)]; b) feeding the plurality of cation exchange column(s) [(101) and (102)] [(101) and (102)] filled with LSX zeolite granules, pre-heated pure aqueous salt solution from aqueous salt solution tank (108) through a preheater (106) in an upflow mode; c) maintaining a temperature within the plurality of cation exchange column(s) [(101) and (102)] at 95°C by supplying heating utility selected from low pressure steam (LPS) or hot oil circulation (120) through a jacket (118); d) passing aqueous salt solution continuously through the plurality of cation exchange column(s) [(101) and (102)] for time period in the range of 5-8 hours to obtain cation exchanged-LSX zeolite granules; e) washing the cation exchanged-LSX zeolite granules with DM water from the water tank (103) in downflow mode to remove adsorbed salts, followed by collecting the spent wash water in two parts in spent wash water tanks [(109) and (110)], wherein the spent wash water from spent wash water tank (109) is recycled back for zeolite washing of the next batch in the cation exchange columns (101 and 102), and the spent wash water from spent wash water tank (110) is sent to the LLE column (105) for LLE of organic solvent; f) drying the washed cation exchanged-LSX zeolite granules within the cation exchange column itself by applying a vacuum or by passing hot dry air through a supply line (125); and g) removing and sending the dried cation exchanged-LSX zeolite granules to the calcinator (116), where a hot dry air is passed for performing calcination at temperature of 400 °C for time period in the range of 4-5 hours, followed by cooling and packing the cation exchanged -LSX granules.

0. The method as claimed in claim 9, wherein the salt solution is circulated in a single pass mode or in a recirculation mode in step b) and step d); wherein the LSX zeolite is Na- LSX zeolite; and wherein the adsorbed salts removed during washing in the cation exchange columns (101 and 102) are NaCl and KC1.

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