CN114380305A - Method for recovering raw and auxiliary materials in production of lithium bis (fluorosulfonyl) imide - Google Patents
Method for recovering raw and auxiliary materials in production of lithium bis (fluorosulfonyl) imide Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 111
- VDVLPSWVDYJFRW-UHFFFAOYSA-N lithium;bis(fluorosulfonyl)azanide Chemical compound [Li+].FS(=O)(=O)[N-]S(F)(=O)=O VDVLPSWVDYJFRW-UHFFFAOYSA-N 0.000 title claims abstract description 75
- 239000000463 material Substances 0.000 title claims abstract description 51
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 38
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 claims abstract description 300
- 238000011084 recovery Methods 0.000 claims abstract description 108
- 230000008569 process Effects 0.000 claims abstract description 79
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 claims description 241
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 165
- 229910001868 water Inorganic materials 0.000 claims description 160
- 239000012071 phase Substances 0.000 claims description 124
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 89
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 71
- 239000007788 liquid Substances 0.000 claims description 65
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 claims description 54
- 230000018044 dehydration Effects 0.000 claims description 54
- 238000006297 dehydration reaction Methods 0.000 claims description 54
- 239000000243 solution Substances 0.000 claims description 51
- 238000001704 evaporation Methods 0.000 claims description 49
- 238000006243 chemical reaction Methods 0.000 claims description 46
- 230000008020 evaporation Effects 0.000 claims description 41
- 238000002425 crystallisation Methods 0.000 claims description 38
- 230000008025 crystallization Effects 0.000 claims description 38
- 238000000605 extraction Methods 0.000 claims description 31
- 239000000203 mixture Substances 0.000 claims description 31
- 239000012535 impurity Substances 0.000 claims description 28
- 229910006095 SO2F Inorganic materials 0.000 claims description 27
- 239000000047 product Substances 0.000 claims description 27
- 150000002500 ions Chemical class 0.000 claims description 23
- 239000012074 organic phase Substances 0.000 claims description 21
- 229910001515 alkali metal fluoride Inorganic materials 0.000 claims description 20
- 238000000926 separation method Methods 0.000 claims description 18
- 239000002912 waste gas Substances 0.000 claims description 18
- 239000008346 aqueous phase Substances 0.000 claims description 16
- 238000001179 sorption measurement Methods 0.000 claims description 16
- NTJBWZHVSJNKAD-UHFFFAOYSA-N triethylazanium;fluoride Chemical compound [F-].CC[NH+](CC)CC NTJBWZHVSJNKAD-UHFFFAOYSA-N 0.000 claims description 16
- 238000004064 recycling Methods 0.000 claims description 15
- 238000003860 storage Methods 0.000 claims description 15
- 238000009833 condensation Methods 0.000 claims description 13
- 230000005494 condensation Effects 0.000 claims description 13
- 238000002156 mixing Methods 0.000 claims description 13
- 238000003756 stirring Methods 0.000 claims description 12
- 238000005406 washing Methods 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 11
- 239000007789 gas Substances 0.000 claims description 11
- 229910052744 lithium Inorganic materials 0.000 claims description 11
- 230000003068 static effect Effects 0.000 claims description 11
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 9
- 239000002808 molecular sieve Substances 0.000 claims description 9
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 9
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 8
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- 239000012267 brine Substances 0.000 claims description 8
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 8
- 238000005191 phase separation Methods 0.000 claims description 8
- 239000010865 sewage Substances 0.000 claims description 8
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 8
- OBTWBSRJZRCYQV-UHFFFAOYSA-N sulfuryl difluoride Chemical compound FS(F)(=O)=O OBTWBSRJZRCYQV-UHFFFAOYSA-N 0.000 claims description 8
- 150000008044 alkali metal hydroxides Chemical class 0.000 claims description 7
- 239000011347 resin Substances 0.000 claims description 7
- 229920005989 resin Polymers 0.000 claims description 7
- 150000003839 salts Chemical class 0.000 claims description 6
- 239000005935 Sulfuryl fluoride Substances 0.000 claims description 5
- 238000004581 coalescence Methods 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 5
- 239000002351 wastewater Substances 0.000 claims description 5
- 239000007791 liquid phase Substances 0.000 claims description 4
- 238000013517 stratification Methods 0.000 claims description 4
- 229910052783 alkali metal Inorganic materials 0.000 claims description 3
- 150000001340 alkali metals Chemical class 0.000 claims description 3
- 229910000069 nitrogen hydride Inorganic materials 0.000 claims description 3
- 239000002244 precipitate Substances 0.000 claims description 3
- 229910052708 sodium Inorganic materials 0.000 claims description 3
- 239000003513 alkali Substances 0.000 claims description 2
- 239000007795 chemical reaction product Substances 0.000 claims description 2
- 229920006395 saturated elastomer Polymers 0.000 claims description 2
- 229910010941 LiFSI Inorganic materials 0.000 claims 1
- 230000000536 complexating effect Effects 0.000 claims 1
- 238000004065 wastewater treatment Methods 0.000 claims 1
- 230000007613 environmental effect Effects 0.000 abstract description 6
- -1 fluoride ions Chemical class 0.000 abstract description 4
- 239000003759 ester based solvent Substances 0.000 abstract description 3
- 239000011549 crystallization solution Substances 0.000 abstract 1
- 238000010626 work up procedure Methods 0.000 abstract 1
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 description 20
- 239000011698 potassium fluoride Substances 0.000 description 16
- 239000007864 aqueous solution Substances 0.000 description 12
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 10
- 230000015572 biosynthetic process Effects 0.000 description 10
- 238000001035 drying Methods 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 10
- 238000005086 pumping Methods 0.000 description 10
- 238000003786 synthesis reaction Methods 0.000 description 10
- 238000010586 diagram Methods 0.000 description 9
- 239000006227 byproduct Substances 0.000 description 8
- 229910001416 lithium ion Inorganic materials 0.000 description 8
- 239000011552 falling film Substances 0.000 description 7
- 239000000706 filtrate Substances 0.000 description 7
- 238000001914 filtration Methods 0.000 description 7
- 229910003002 lithium salt Inorganic materials 0.000 description 7
- 159000000002 lithium salts Chemical class 0.000 description 7
- 239000007787 solid Substances 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 239000008367 deionised water Substances 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- 238000000746 purification Methods 0.000 description 5
- 238000004445 quantitative analysis Methods 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- 239000002699 waste material Substances 0.000 description 5
- NROKBHXJSPEDAR-UHFFFAOYSA-M potassium fluoride Chemical group [F-].[K+] NROKBHXJSPEDAR-UHFFFAOYSA-M 0.000 description 4
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000004817 gas chromatography Methods 0.000 description 3
- 239000011344 liquid material Substances 0.000 description 3
- 238000006386 neutralization reaction Methods 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000011541 reaction mixture Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 239000012043 crude product Substances 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 238000004255 ion exchange chromatography Methods 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 235000003270 potassium fluoride Nutrition 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- 229940124530 sulfonamide Drugs 0.000 description 2
- 150000003456 sulfonamides Chemical class 0.000 description 2
- 239000006228 supernatant Substances 0.000 description 2
- 230000002194 synthesizing effect Effects 0.000 description 2
- 239000013076 target substance Substances 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- 239000006057 Non-nutritive feed additive Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 125000003368 amide group Chemical group 0.000 description 1
- 239000006286 aqueous extract Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000009924 canning Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 125000004093 cyano group Chemical group *C#N 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 208000028659 discharge Diseases 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 150000002642 lithium compounds Chemical class 0.000 description 1
- SAPIQCCFEBULSH-UHFFFAOYSA-M lithium;sulfamate Chemical compound [Li+].NS([O-])(=O)=O SAPIQCCFEBULSH-UHFFFAOYSA-M 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000002910 solid waste Substances 0.000 description 1
- 238000010025 steaming Methods 0.000 description 1
- NVBFHJWHLNUMCV-UHFFFAOYSA-N sulfamide Chemical compound NS(N)(=O)=O NVBFHJWHLNUMCV-UHFFFAOYSA-N 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/02—Fluorides
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
- C07C209/82—Purification; Separation; Stabilisation; Use of additives
- C07C209/86—Separation
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The application relates to a method for recovering raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide. The process comprises one or more different recovery sections A, B, C, D and/or E, corresponding respectively to the recovery and work-up of the raw and auxiliary materials used in the production of lithium bis (fluorosulfonyl) imide, such as triethylamine, fluoride ions, ester solvents, crystallization solutions, etc. The method for recovering the raw and auxiliary materials enables the production of the lithium bis (fluorosulfonyl) imide to have obviously improved economical efficiency and environmental friendliness.
Description
Technical Field
The application relates to a method for recovering raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide, in particular to a method for recovering triethylamine, fluoride, ester solvents, crystallization liquid and/or dichloromethane waste gas in waste liquid generated in the production of lithium bis (fluorosulfonyl) imide through different recovery working sections.
Background
Lithium bis (fluorosulfonylimide) (chemical formula Li [ N (SO) ]2F)2]Acronym LiFSI) is an important new material containing fluorine. Due to its special molecular structure, Li+And FSI-Has lower binding energy between them, is beneficial to Li+Thereby, the higher conductivity can be obtained by adding LiFSI in the electrolyte. Meanwhile, LiFSI also has the characteristics of high thermal stability, wider electrochemical window and lower corrosion rate, and particularly in a power battery, the LiFSI can improve the cycle performance and the rate capability of the power battery and is expected to become a novel electrolyte lithium salt of a lithium ion battery. The japanese catalyst showed LiFSI for the first time in 2012, and the industrial production was realized in 2013. At present, LiFSI and LiPF are used in high-end occasions in Japanese and Korean battery enterprises6Mixing and using.
LiFSI cannot be used on a large scale at present, and the reason is mainly high production cost due to the limitation of synthesis process conditions. In the synthesis process, the defects of complex process, long flow, low product conversion rate, high energy consumption, environmental pollution and the like exist. In addition, as an electrolyte for a lithium ion secondary battery, it is required to satisfy severe requirements such as high purity and no water. Particularly, after the introduction of water, it is difficult to completely remove the water by heating the mixture to bring the water, drying the mixture to remove the water until the decomposition, and even if the water can be removed, a large yield is lost.
In addition, in the industrial synthesis and purification process of LiFSI, it is necessary to fully recycle the raw and auxiliary materials used and to reduce the generation of three wastes (waste water, waste gas, and solid waste) as much as possible.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for recovering raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide, which can improve the recovery rate of raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide and improve the economy and environmental friendliness of lithium bis (fluorosulfonyl) imide.
In order to achieve the above object, the present application provides, in a first aspect, a method for recovering raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide, which comprises a reaction 1 of reacting sulfuryl fluoride, triethylamine and ammonia gas and a subsequent reaction 2 of alkalifying the reaction product,
reaction 1: SO (SO)2F2+NH3+Et3N→(SO2F-NH-SO2F)·Et3N+Et3N·(HF)n(n＝1-12)，
Reaction 2: (SO)2F-NH-SO2F)·Et3N+LiOH→(SO2F-N-SO2F)-Li++Et3N+H2O，
The method comprises the following steps:
recovery section A. separation of the product mixture resulting from reaction 1 into a mixture comprising (SO)2F-NH-SO2F)·Et3An oil phase of N and an aqueous phase comprising triethylamine hydrogen fluoride and impurity ions; will contain (SO)2F-NH-SO2F)·Et3The oil phase of N is subjected to an alkalization process according to the reaction 2, a water phase containing triethylamine hydrogen fluoride and impurity ions is introduced into an alkalization kettle to be mixed with alkali metal hydroxide under stirring and react, and then a solution obtained after the reaction in the alkalization kettle is introduced into a layering tank for phase separation; the upper oil phase is an organic phase containing water and triethylamine, and the organic phase is separated out and stored in an oil phase secondary layering tank; and
a recovery section B: removing triethylamine and part of water from a product mixture obtained by performing an alkalization process according to the reaction 2 through an evaporator, introducing the evaporated triethylamine and water into a condenser for condensation, standing and separating liquid; transferring the upper triethylamine solution obtained after liquid separation into a triethylamine transferring tank, and separating into a water phase and an oil phase through a centrifugal machine, wherein the oil phase is an organic phase containing water and triethylamine; introducing the organic phase and the organic phase containing water and triethylamine obtained in the recovery working section A into a single-effect evaporation system together to obtain a water-containing triethylamine phase; and then removing residual water through dehydration in a dehydration tower and rectification in a rectification tower respectively to obtain the high-purity triethylamine.
In any embodiment, the recovery process is part of a complete process for the production and purification of lithium bis (fluorosulfonyl) imide, which includes multiple recovery stages, corresponding to the separation and recovery of different raw and auxiliary materials. There may also be material communication and merging between recovery sections.
In any embodiment, the purity of the high purity triethylamine obtained by the method is 95 wt% or more; optionally, the purity is 98 wt% or more, 99 wt% or more, or 99.5 wt% or more. In any embodiment, in the recovery section B, the product mixture obtained from the alkalization process is passed through an evaporator to distill off a mixture comprising triethylamine and water, the mixture is condensed in a condenser, heated to a temperature of 30-55 ℃ and left to separate layers. In any embodiment, the product mixture resulting from reaction 1 in recovery section a is separated by stratification in a static mixer or by extraction in an extraction column.
In any embodiment, the lower aqueous phase obtained by phase separation in the stratified tank of the recovery section a comprises mainly the alkali metal fluoride solution and a small amount of triethylamine; combining the obtained water phase with the lower water phase obtained in the single-effect evaporation system, the dehydration tower and the rectification tower in the recovery section B in a brine tank; introducing the liquid in the brine tank into a stripping tower for steam stripping, and returning the obtained light phase mainly containing triethylamine and water to the oil phase secondary layering tank of the recovery working section A; and (3) introducing the heavy component into a double-effect evaporator for evaporation to obtain a high-concentration alkali metal fluoride solution. In any embodiment, the alkali metal is Li, Na, or K.
In any embodiment, the production of lithium bis (fluorosulfonyl) imide further comprises a dehydration process using an ester solvent, the aqueous ester solvent distilled off by evaporation is recovered by a recovery section C: introducing the water-containing ester solvent into an ester solvent buffer tank, mixing the water-containing ester solvent with the lithium hydroxide solution in a pipeline mixer, and then separating the mixture by a coalescence separator; the separated oil phase is mainly an ester solvent and is introduced into an ester solvent storage tank. Further, adding a lithium hydroxide solution into the water phase obtained after separation by the coalescence separator to adjust the pH value, entering a stripping tower through a preheater for steam stripping, obtaining an oil phase which is a water-containing ester solvent, and returning the oil phase to the ester solvent buffer tank; and introducing the obtained water phase and residual liquid into a sewage treatment device for post-treatment.
In any embodiment, the ester solvent includes ethyl methyl carbonate EMC, diethyl carbonate DEC, and dimethyl carbonate DMC.
In any embodiment, the production of lithium bis (fluorosulfonyl) imide further comprises a crystallization process using a crystallization liquid to dissolve an ester solvent and precipitate a product LiFSI crystal, wherein the separated crystallization liquid water-washing oil phase comprises dichloromethane, an ester solvent, water, and a salt; the crystallization liquid is recycled through a recycling working section D, and the recycling working section D is as follows: putting the crystallized liquid washing oil phase into a dehydration tower, wherein the condensed liquid at the top of the tower contains dichloromethane and water, the upper layer of water phase after layering is put into a sewage collection tank for post-treatment, and the lower layer of dichloromethane is totally refluxed; and introducing the tower bottom liquid of the dehydration tower into a single-effect evaporation system, introducing the gas phase obtained by evaporation into a rectifying tower for rectification, obtaining dichloromethane from the condensed liquid at the top of the rectifying tower, collecting the dichloromethane to a dichloromethane blending tank, adding lithium hydroxide into the tank, adjusting the pH value through a pump circulation pipeline, carrying out phase splitting, separating the obtained water phase, and introducing the obtained oil phase into a dichloromethane storage tank.
In any embodiment, ethanol is obtained from the middle part of the rectifying tower and separated for post-treatment; obtaining an ester solvent from the condensate liquid at the middle lower part of the rectifying tower, and introducing the ester solvent into an ester solvent storage tank for recycling the dehydration process; and separating residual liquid obtained from the tower kettle of the rectifying tower for post-treatment.
In any embodiment, the liquid phase obtained from the single-effect evaporation system is subjected to vacuum concentration, and the obtained condensate containing dichloromethane and ester solvent is sent back to the dehydration tower; the concentrated solution after vacuum concentration is separated for post-treatment.
In any embodiment, the process further comprises a recovery section E to recover the off-gas comprising dichloromethane produced in each stage, recovery section E: cooling the waste gas containing dichloromethane generated in each stage, introducing the waste gas into three-stage adsorption resin for adsorption, desorbing the waste gas by using steam after the waste gas is saturated by adsorption, collecting the waste gas by condensation, standing and layering the collected liquid containing dichloromethane and water, and separating and post-treating the waste water containing trace dichloromethane in the upper water phase; the lower oil phase is dichloromethane containing trace water, and is introduced into a dehydration device for dehydration and then recycled.
In any embodiment, the water content in the methylene chloride containing a trace amount of water is 1000-2000ppm, and the dehydration is carried out until the water content is 50-200 ppm. In any embodiment, the dehydration is performed by 4A molecular sieves.
By the method for recovering raw and auxiliary materials as described above, at least one or more raw and auxiliary materials used in the production of lithium bis (fluorosulfonyl) imide can be recycled at a plurality of different recovery sections, and the generated three wastes are post-treated, thereby allowing the production of lithium bis (fluorosulfonyl) imide with significantly improved economy and environmental friendliness.
Drawings
In order to more clearly illustrate the technical solution of the present application, the drawings required to be used in the embodiments of the present application will be briefly described below. It is obvious that the drawings described below are only some embodiments of the application, and that for a person skilled in the art, other drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a schematic process flow diagram of section a of a process for producing lithium bis (fluorosulfonyl) imide in one embodiment of the present application.
FIG. 2 is a schematic process flow diagram of the beta stage of the process for producing lithium bis (fluorosulfonyl) imide in one embodiment of the present application.
FIG. 3 is a schematic process flow diagram of recovery section A (alpha water basification) in one embodiment of the present application.
FIG. 4 is a schematic process flow diagram of recovery section B (triethylamine recovery) in one embodiment of the present application.
FIG. 5 is a schematic process flow diagram of recovery section C (ester solvent recovery, for example DEC) in one embodiment of the present application.
FIG. 6 is a schematic process flow diagram of the recovery section D (recovery of the crystallized liquid) in one embodiment of the present application.
FIG. 7 is a schematic process flow diagram of the recovery section E (methylene chloride off-gas recovery) in one embodiment of the present application.
Detailed Description
For the sake of brevity, some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself, as a lower or upper limit, be combined with any other point or individual value or with other lower or upper limits to form ranges not explicitly recited.
Due to the special molecular structure of the lithium bis (fluorosulfonyl) imide (LiFSI), the electrolyte can obtain higher conductivity when LiFSI is added. Meanwhile, LiFSI also has the characteristics of high thermal stability, wider electrochemical window and lower corrosion rate, and particularly in a power battery, the cycle performance and the rate capability of the power battery can be improved, so that LiFSI is an excellent choice for electrolyte lithium salt of a lithium ion battery. In the prior art, many problems exist in the industrial large-scale production of LiFSI synthesis and purification, the synthesis process is complicated, the flow is long, the product conversion rate is low, the consumption of raw and auxiliary materials is high, and the raw and auxiliary materials are difficult to recover, so the economy is not high. The present invention aims to solve at least some of these problems and proposes a new process for the production of LiFSI and a method for the recovery of raw and auxiliary materials.
The process for producing LiFSI mainly comprises the following steps:
synthesizing: the sulfuryl fluoride, ammonia gas and triethylamine are fully mixed, the sulfuryl fluoride and the ammonia gas fully react, and the triethylamine is used as a solvent and participates in the reaction. Other organic solvents, such as acetonitrile, may also be used as a solvent for the reaction. The main reaction is SO2F2+NH3+Et3N→(SO2F-NH-SO2F)·Et3N+Et3N·(HF)n(n＝1-12)。
When the temperature in the reaction vessel is too high, the following side reactions occur to affect the yield: NH (NH)3+SO2F2+Et3N→NH2-SO2-NH2(sulfamide, solid) + Et3N·(HF)n(triethylamine hydrogen fluoride, dissolved in CH)3In CN, n is 1-12). After the reaction, the by-product sulfonamide solids can be filtered off using, for example, a 5 μm tetrafluoro filter bag.
After the synthesis process, the material composition mainly comprises (SO)2F-NH-SO2F)·Et3N, acetonitrile, triethylamine hydrogen fluoride, triethylamine (in small amounts), and impurity ions. The impurity ions mainly contain F-、SO4 2-、FSO3 -And Cl-。
And (3) evaporation: the product mixture (feed α 1) was evaporated in an evaporator and the acetonitrile solvent was separated off. The material can be heated by a falling film evaporator, the liquid and the steam are separated by a gas-liquid separator, and the steam acetonitrile (containing a small amount of triethylamine) is condensed by a condenser and is recycled for the first step of synthesis.
After the evaporation process, the material composition mainly comprises (SO)2F-NH-SO2F)·Et3N, triethylamine hydrogen fluoride, acetonitrile (trace), and impurity ions.
And (3) extraction: the concentrated solution (material alpha 2) obtained by evaporation is washed by water, and impurities (mainly triethylamine hydrogen fluoride) which are easy to dissolve in water are washed away. Two schemes can be used for this:
the first scheme is that the bottom of the extraction tower is filled with a light phase (with low density), the upper part of the extraction tower is filled with the light phase, the top of the extraction tower is filled with a heavy phase, the bottom of the extraction tower is filled with the heavy phase, and the middle of the extraction tower is stirred to be spiral; scheme two, a static mixer and a phase separation tank. The extract oil phase (material alpha 3) mainly comprises (SO)2F-NH-SO2F)·Et3N, while the aqueous extract phase (feed alpha water) contains predominantly triethylamine hydrogen fluoride and impurity ions (e.g. F)-、SO4 2-、FSO3 -、Cl-). In some embodiments, extraction with an extraction column can be achieved for impurity ions (e.g., F)-) Better separation. In some embodiments, the content of impurity ions in the oil phase obtained by the static mixer extraction is obtained by extraction in an extraction columnTo 5-30 times, optionally 10-20 times, the content of impurity ions in the oil phase. Optionally, the impurity ion is F-. The stage of synthesis-evaporation-extraction in the production of lithium bis (fluorosulfonyl) imide of the present application is referred to as the α -stage, and the specific flow scheme thereof can be referred to the process flow diagram of fig. 1 of the present application.
Alkalization: mixing the extracted oil phase (material alpha 3) obtained after extraction with the lithium hydroxide aqueous solution and fully reacting. The reaction is reaction 2: (SO)2F-NH-SO2F)·Et3N+LiOH→(SO2F-N-SO2F)-Li++Et3N+H2And O. The reaction principle is that strong base replaces weak base, and the alkalinity of LiOH is higher than (SO)2F-NH-SO2F)·Et3Triethylamine in N, so that triethylamine is displaced. Removal of triethylamine by falling film evaporation with simultaneous LiOH and (SO)2F-NH-SO2F)·Et3N reacts to form a lithium salt (lithium bis (fluorosulfonyl) imide, abbreviated to LiFSI).
And (3) dehydrating: the reaction mixture (feed β 1) obtained in reaction 2 was dehydrated using an evaporator. The ester solvent is adopted to carry water, and no chemical reaction is involved. Since lithium salts have very strong water absorption, it is not practical to reduce the water content to the target level simply by evaporation. The addition of a large amount of ester solvent can weaken the water adsorption of the lithium salt, and the water content can be reduced to the target requirement in the process of evaporating the ester solvent while adding the ester solvent. The ester solvent can be recycled after being purified by a recovery section. The ester solvent may include Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and the like. In the course of dehydration (SO)2F-N-SO2F)-Li+Also decomposing to generate LiF and Li as by-products2SO4Lithium sulfamate, and the like. The solid by-product is filtered or centrifuged (e.g., using centrifugal settling to remove solids, such as a scraper or disk centrifuge) prior to the subsequent desolventizing step.
Desolventizing: the evaporated and dehydrated material (material beta 2) is desolventized in an evaporator. The desolventization does not involve a reaction, but is only for evaporating the ester solvent out. Since the lithium salt is dissolved in the ester solvent, if the ester solvent is not evaporated to a certain extent (e.g., from 60% to 65% to 30%), the crystallization cannot be performed at a later stage or the crystallization rate is very low. The ester solvent can be recycled after being purified by a recovery section. After the desolventizing step, crude lithium bis (fluorosulfonyl) imide (material beta 3) with a low water content (e.g., less than 3000ppm) is obtained. The stage of alkalization-dehydration-desolventization in the production of lithium bis (fluorosulfonyl) imide of the present application is referred to as the β -stage, and the specific flow chart thereof can be referred to the process flow chart of fig. 2 of the present application.
And (3) crystallization: by crystallization is meant that when a substance is in a non-equilibrium state, additional phases are precipitated which precipitate in the form of crystals. The material beta 3 is introduced into a crystallization kettle, and dichloromethane is added. Methylene dichloride is used for dissolving the ester solvent but not the LiFSI, so that the LiFSI is supersaturated in the ester solvent to be separated out, and crystal nuclei grow. And introducing the obtained mixture into a two-in-one device with a filtering and washing function, and washing off other impurities attached to the surface of the LiFSI crystal. After the crystallization liquid is purified by a recovery section, the ester solvent and the dichloromethane can be recycled.
And (3) drying: and (4) introducing the washed materials into a drying kettle. After heating nitrogen, the mixture is introduced into a drying kettle. The material is fluidized under the action of stirring and airflow, and in the large-area gas-solid two-phase contact, the moisture of the material is quickly evaporated, and high-humidity nitrogen is discharged out of the kettle, so that the material meets the drying requirement.
In some embodiments, the material β 3 may be directly fed to the dissolution process without performing the above-described crystallization and drying steps.
Dissolving: in the dissolving process, the above dried crystals (for crystallization process) or crude product (for non-crystallization process) can be dissolved with an ester solvent such as Ethyl Methyl Carbonate (EMC) or dimethyl carbonate (DMC) as required, the acid is removed (if the HF content in the detected solution is excessive (such as standard HF is less than or equal to 50 μ g/g), the acid is removed with LiOH), the water is removed (if the water content in the detected solution is excessive (such as standard water is less than or equal to 20 μ g/g), the solution is passed through a molecular sieve, concentrated, filtered by a filter core and stored (such as barreling or tank loading).
The above is a general procedure for producing lithium bis (fluorosulfonyl) imide (LiFSI) in the present invention. In the process of LiFSI synthesis and purification, the use amount is largeRaw materials for the reaction and processing aids such as triethylamine as a reactant and a solvent, an ester solvent (e.g., diethyl carbonate, DEC) for a dehydration process, Dichloromethane (DCM) for a crystallization liquid, etc., and various byproducts and impurity ions, mainly F produced in the reaction 1, are also produced-And an alkali metal fluoride obtained subsequently after the alkalization process. These raw and auxiliary materials constitute a considerable part of the cost of the production of LiFSI in the present invention and therefore need to be recycled as much as possible, and the by-products and impurities produced need to be disposed of and recovered as much as possible due to environmental concerns. On the basis, the inventor proposes a method for recycling the raw and auxiliary materials used in the production process. The process comprises a plurality of different recovery sections which are closely integrated and integrated with the process flow for the production of LiFSI, enabling staged separation and recovery of the main raw and auxiliary materials. The method for recovering the raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide will be described in detail below with reference to the schematic process flow diagrams in the recovery sections a to E in the drawings.
Recovery section a (alpha water basification): separation of the product mixture resulting from reaction 1 in the alpha stage of LiFSI production into a mixture comprising predominantly (SO)2F-NH-SO2F)·Et3An oil phase of N and an aqueous phase comprising predominantly triethylamine hydrogen fluoride and impurity ions. The separation in this step can be carried out by layering with a layering tank by means of a static mixer or by extraction by means of an extraction column. Surprisingly, it was found that when the product mixture of reaction 1 was extracted by an extraction column, the resulting oil phase (feed α 3, mainly comprising (SO)2F-NH-SO2F)·Et3N) impurity ions (mainly F)-) Is significantly lower than the impurity ions in the oil phase obtained by layering with a layering tank by means of a static mixer. In some embodiments, the content of impurity ions in the oil phase obtained by stratification by the static mixer is 5 to 30 times, optionally 10 to 20 times, the content of impurity ions in the oil phase obtained by extraction by the extraction column. In some embodiments, F is in the oil phase obtained after extraction of the product mixture by the extraction column-The concentration of (B) is 100-200 ppm; optionally, 100-160 ppm. And itIn contrast, F in the oil phase obtained by layering a static mixer with a layering tank-The concentration of (A) can be as high as 1000-2000 ppm.
Will contain (SO)2F-NH-SO2F)·Et3The oil phase of N (material α 3) was subjected to an alkalization process according to reaction 2, while the aqueous phase (material α water) containing triethylamine hydrogen fluoride and impurity ions was passed into the alkalization kettle. Specifically, a certain amount of alkali metal hydroxide is added into an alkalization kettle, alpha water is pumped according to the pH value, stirring is started, and the alpha water and the alkali metal hydroxide are mixed and reacted under stirring at normal temperature and normal pressure. The pH range may be selected to be in the range of 8-14, for example 9-12. The reaction time may be from 0.5 to 6 hours, alternatively from 1 to 4 hours. The alkali metal hydroxide may be selected from LiOH, NaOH or KOH; optionally, the alkali metal hydroxide is KOH. And then introducing the solution obtained after the reaction in the alkalization kettle into a layering tank for phase separation. For example, in the case where the alkali metal hydroxide is KOH, the KF produced is readily soluble in water. The triethylamine and KF aqueous solution have different densities and are not compatible, so that the triethylamine and the KF aqueous solution can be separated by standing and layering. The oil phase at the upper layer is an organic phase containing triethylamine and part of water, the organic phase is separated out and stored in an oil phase secondary layering tank, and then the oil phase is combined with an oil phase material which is obtained in a recovery working section B and also contains triethylamine and part of water. The lower layer is an aqueous phase comprising predominantly alkali metal fluoride solution, which may also contain small amounts of triethylamine. The specific process flow of the recovery section a is shown in fig. 3 of the present application.
Recovery section B (triethylamine recovery): the product mixture obtained after the completion of the alkalization reaction 2 in the β stage of LiFSI production was passed through an evaporator to remove triethylamine and a part of water, and the triethylamine and water distilled out were passed through a condenser to be condensed and left to separate liquids. Triethylamine is readily miscible with water at temperatures less than 18.5 ℃ and is slightly soluble in water at temperatures between 30 ℃ and 55 ℃. By utilizing the characteristic, the mixed solution of triethylamine and water recovered by low-temperature condensation is heated to 30-55 ℃, optionally 40-45 ℃, and then is kept stand for layering, and the lower-layer water is removed, so that the purpose of primary water removal is achieved.
Transferring the upper triethylamine solution obtained after liquid separation into a triethylamine transferring tank, and separating into a water phase and an oil phase by a centrifugal machine. The centrifuge may be a disk centrifuge. The oil phase is an organic phase containing water and triethylamine; and (3) introducing the organic phase and the organic phase (stored in the oil phase secondary layering tank) containing water and triethylamine obtained in the recovery working section A into a single-effect evaporation system for evaporation. The single-effect evaporation system can select a single-effect evaporator, and the required heating steam consumption can be calculated according to the production flux and the operation parameters. The single-effect evaporator refers to a single evaporator, and secondary steam generated when solution evaporation is carried out is not used. Evaporating to obtain a water-containing triethylamine phase, and then dehydrating through a dehydration tower and further removing residual water through rectification of a rectification tower respectively to finally obtain the high-purity triethylamine. In some embodiments, the triethylamine obtained after rectification is introduced into a triethylamine blending tank for thorough stirring and then stored in a triethylamine storage tank. In some embodiments, the resulting high purity triethylamine is 95 wt% or more pure; optionally, the purity is 98 wt% or more, 99 wt% or more, or 99.5 wt% or more. The obtained triethylamine can be directly reused in the production of lithium bis (fluorosulfonyl) imide (LiFSI) of the invention, for example, added into a reaction kettle of the reaction 1, or conveyed to a special liquid material packaging barrel or a tank car for sale. By combining the recovery working section A and the recovery working section B, triethylamine used in the LiFSI production can be recovered and reused in a high proportion, and the purity of the recovered triethylamine product is high, so that the utilization rate and the economical efficiency of raw materials in the LiFSI production can be obviously improved.
In some embodiments, the water phase separated by the centrifuge in the recovery section B is passed to the alkalization process of reaction 2 for alkali preparation, or to the extraction process as water washing water, or to a sewage treatment plant for treatment. In the method of the invention, the substances used in each stage can be recycled or post-treated, and the environmental protection property can be obviously improved.
In some embodiments, the lower aqueous phase obtained by phase separation in the stratified tank of recovery section a comprises mainly alkali metal fluoride solution and a small amount of triethylamine; in the recovery section B, a lower aqueous phase is obtained by evaporation in a single-effect evaporation system, a dehydration column and a rectification column, which likewise contains predominantly alkali metal fluoride solution and a small amount of triethylamine. These two streams were combined in a brine tank and the liquid in the brine tank was then stripped by passing it to a stripper column. By stripping, the liquid feed can be separated into a light phase and a heavy phase. And the light phase mainly comprises triethylamine and water, is condensed and recovered, and returns to the oil phase secondary layering tank of the recovery working section A. The resulting recombinant fraction after stripping is a salt-containing aqueous phase, comprising mainly alkali metal fluoride solution. And (3) extracting the heavy component from the tower kettle of the stripping tower, introducing the heavy component into a double-effect evaporator for evaporation, and condensing the evaporated water to obtain a high-concentration alkali metal fluoride solution. The double-effect evaporator is characterized in that two single-effect evaporators are connected in series, secondary steam generated by a first-effect evaporator is used as a heating source, the other single-effect evaporator is introduced, and the secondary steam generated by the first-effect evaporator can be used for heating as long as the pressure and the solution boiling point in the evaporator are controlled to be properly reduced. In some embodiments, the concentration of the alkali metal fluoride solution can be increased from 25 wt% to over 50 wt%, and even over 55 wt%, by evaporation in a double effect evaporator. The obtained high-concentration alkali metal fluoride solution can be conveyed to a special liquid material packaging barrel or a tank car for sale.
In some embodiments, the alkali metal fluoride may be extracted by reducing the temperature of the crystallization kettle to crystallize out the alkali metal fluoride, and centrifuging the alkali metal fluoride to extract the alkali metal fluoride by utilizing the solubility difference of the alkali metal fluoride at different temperatures. The alkali metal can be Li, Na or K; correspondingly, the alkali metal fluoride is LiF, NaF or KF.
In some embodiments, the alkali metal fluoride is KF. By recovering the alkali metal fluoride, the economy and environmental protection of the LiFSI production can be further improved. The specific process flow of the recovery section B is shown in fig. 4 of the present application.
Recovery section C (ester solvent recovery): the beta section of the production of the lithium bis (fluorosulfonyl) imide comprises a dehydration step, in which an ester solvent is added into an evaporator and mixed with the alkalinized reaction mixture from reaction 2, water is taken away by evaporating the ester solvent, and new ester solvent is continuously supplemented at the same time, thereby realizing continuous dehydration. The ester solvent may include, for example, ethyl methyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, and the like. The recycling of the ester solvent is explained in detail below by taking diethyl carbonate DEC as an example; it will be appreciated that these descriptions apply to other suitable ester solvents. The aqueous DEC distilled from the evaporator is passed to a condenser for condensation and the resulting condensate is led to a condensate collection tank. Pumping the condensed aqueous DEC into a DEC buffer tank, mixing the aqueous DEC with a lithium hydroxide solution through a pipeline mixer, separating the aqueous DEC with a coalescence separator to obtain an oil phase DEC, and introducing the oil phase DEC into a DEC storage tank. The recovered DEC can be recycled for the dehydration process (beta section). And (3) introducing the water phase obtained after separation by the coalescence separator into a neutralization tank, and adding a lithium hydroxide solution into the tank to adjust the pH value. For example, the adjusted pH may be from 8 to 14, alternatively from 9 to 12. Then introducing the material in the neutralization tank into a stripping tower through a preheater for steam stripping to obtain aqueous DEC as an oil phase, and returning the aqueous DEC to a DEC buffer tank; and introducing the obtained water phase and residual liquid into a sewage treatment device for post-treatment. The lithium hydroxide solution introduced into the line mixer to be mixed with the aqueous DEC may be derived from the lithium hydroxide solution in the β -stage, may also be obtained by direct addition of deionized water and lithium hydroxide, or may be derived from a mixture of the two. The lithium hydroxide solution may be stored in a lithium hydroxide dosing tank and then mixed with the aqueous DEC by passing it through a line mixer. Alternatively, the pH of the aqueous phase obtained after separation in the coalescer may be adjusted by pumping the lithium hydroxide solution directly from the lithium hydroxide dosage tank into the neutralization tank. The purity of DEC in the liquid stream passed to the DEC holding tank can be up to 95 wt.% or more; alternatively, the purity may be 98 wt% or greater, or 99 wt% or greater. The specific process flow of the recovery section C is shown in fig. 5 of the present application, wherein DEC is specifically exemplified as the ester solvent.
Recovery section D (crystallization liquid recovery): in the process of producing lithium bis (fluorosulfonyl) imide by crystallization process, the crystallization liquid used needs to be recovered or reused. The main component of the crystallization liquid used was Dichloromethane (DCM). And (3) introducing the crude product of the lithium bis (fluorosulfonyl) imide (material flow beta 3) subjected to the desolventizing process into a crystallization kettle, and adding dichloromethane crystallization liquid into the crystallization kettle. And (3) dissolving DEC but not LiFSI by using dichloromethane, so that the LiFSI is supersaturated and precipitated in the DEC, and crystal nuclei grow. And introducing the obtained mixture into a two-in-one device with a filtering and washing function, and washing off other impurities attached to the surface of the LiFSI crystal. The water-washed oil phase containing the crystallization liquid separated from the two-in-one equipment comprises dichloromethane, water, an ester solvent and impurity salts such as LiF. And pumping the water-washing oil phase (dichloromethane, diethyl carbonate, water, salt and the like) into a dehydration tower for dehydration. And (3) performing liquid separation treatment on the tower top condensate mainly comprising dichloromethane and water, collecting the separated water to a sewage collecting tank, and refluxing all the separated dichloromethane to the tower. And introducing the tower bottom liquid of the dehydration tower into a single-effect evaporation system, introducing the gas phase obtained by evaporation into a rectifying tower for rectification, obtaining dichloromethane from the condensed liquid at the top of the rectifying tower, collecting the dichloromethane to a dichloromethane blending tank, adding lithium hydroxide into the tank, adjusting the pH value through a pump circulation pipeline, carrying out phase splitting, separating the obtained water phase, and introducing the obtained oil phase into a dichloromethane storage tank. The recycled dichloromethane can be recycled for the crystallization process.
In some embodiments, ethanol is separated from the middle of the rectification column for post-treatment; obtaining an ester solvent from the condensate liquid at the middle lower part of the rectifying tower, and introducing the ester solvent into an ester solvent storage tank for recycling the dehydration process; and separating residual liquid obtained from the tower kettle of the rectifying tower for post-treatment. In some embodiments, the liquid phase from the single-effect evaporation system is vacuum concentrated to obtain a condensate comprising methylene chloride and an ester solvent, which is fed back to the dehydration column; the concentrated solution after vacuum concentration is separated for post-treatment. The specific process flow of the recovery section D is shown in fig. 6 of the present application.
Recovery section E (dichloromethane off-gas recovery): dichloromethane is volatile liquid, and in the crystallization process and the subsequent crystallization liquid recovery process, a certain amount of dichloromethane is contained in the waste gas discharged from each stage due to the temperature rise. The methylene chloride discharged through the off-gas also needs to be centrally treated and recovered. Cooling waste gas with dichloromethane from each process flow (such as two-in-one equipment, a dehydration tower and a rectification tower in the crystallization process), introducing the cooled waste gas into three-stage adsorption resin for adsorption, desorbing by using steam after adsorption saturation, collecting by condensation, collecting the obtained liquid containing dichloromethane and water, standing and layering, wherein the upper water phase contains trace dichloromethane, and separating as waste water for post-treatment; the lower oil phase is dichloromethane containing trace water, and is introduced into a dehydration device for dehydration to a certain limit and then recycled. The waste gas with methylene chloride can be cooled by normal temperature water. The third-stage adsorption resin can be selected from polar adsorption resins, such as adsorption resins with polar functional groups, such as amide groups, cyano groups, phenolic hydroxyl groups, and the like.
In some embodiments, the dehydration is performed by 4A molecular sieves. The pore diameter of the 4A molecular sieve is 4A, and the molecular sieve can adsorb water molecules but not dichloromethane, so that dehydration of dichloromethane oil phase containing trace moisture is realized. In some embodiments, the water content in the methylene chloride oil phase containing a trace amount of water is 1000-2000ppm, and the dehydration is carried out to a water content of 50-200 ppm; optionally, the dehydration is carried out to a water content of 50-100 ppm. The specific process flow of the recovery section E is shown in fig. 7 of the present application.
The above is a process flow for recycling raw and auxiliary materials used in lithium bis (fluorosulfonyl) imide (LiFSI) production through the recycling section A, B, C, D and/or E and post-treating the three wastes generated. It will be appreciated that these different stations can be freely combined with each other to achieve the treatment of different target substances. In addition, the obtained target substances such as triethylamine or dichloromethane can be recycled in the production of LiFSI, and can also be prepared into products for sale.
The method for recovering the raw and auxiliary materials in the process of synthesizing and purifying the lithium bis (fluorosulfonyl) imide (LiFSI) reduces the production cost of LiFSI and reduces the generation of three wastes, the used raw materials are fully recycled, and the byproducts can generate additional economic benefits after purification, so that the method is suitable for industrial production. By recycling the raw and auxiliary materials, the consumption of the raw and auxiliary materials is reduced, the utilization rate of reaction raw materials is improved, the discharge treatment cost of compounds is reduced, the production cost is effectively reduced, and the economic benefit is improved.
Examples
Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1
1. Triethylamine recovery
Pump the mixed solution to a volume of 40m3Triethylamine 35m3Acetonitrile is pumped into 100m respectively3In the synthesis kettle. The temperature of the kettle is reduced to 15 ℃, then 120kg of ammonia gas is introduced, finally, the ammonia gas (2000kg) and the sulfuryl fluoride (26000kg) are introduced simultaneously, the pressure in the kettle is kept to be not higher than 0.4MPa, and the temperature in the kettle is kept to be not higher than 15 ℃. After the reaction is continued for 4 hours, the pressure in the kettle is reduced to 0.1MPa, and the stirring is stopped. The reaction mixture stream α 1 obtained, which comprises 40% by weight of (SO)2F-NH-SO2F)·Et3N, 18% by weight of triethylamine hydrogen fluoride and 6% by weight of triethylamine) was filtered through a tetrafluoro filter bag having a pore size of 5 μm, and a solid by-product sulfonamide was filtered out. Pumping the filtrate into a falling-film evaporator (hot water tank temperature of 75 deg.C), and evaporating the solvent in the filtrate under vacuum degree of-0.02 MPa (vacuum pump front stage is condensed with 0 deg.C water, and rear stage is condensed with-15 deg.C water) to obtain a filtrate containing (SO)2F-NH-SO2F)·Et3Stream α 2 of N and triethylamine hydrogen fluoride (which comprises 70% by weight of (SO)2F-NH-SO2F)·Et3N, 28% by weight triethylamine hydrogen fluoride) and a condensate containing acetonitrile. The condensate is recycled for use in the first step of the synthesis vessel. The stream α 2 was pumped to a rotating disk extraction column (stirring frequency 15 ± 1 HZ; flow control, deionized water: α 2 ═ 1.2 ± 0.1 (weight ratio)), and after thoroughly mixing with deionized water in the extraction column (mass ratio of deionized water to stream α 2 was controlled at 1.2:1 by means of a flow meter), a product was obtained asAqueous alpha water containing triethylamine hydrogen fluoride as a supernatant (which comprises 77% by weight of water and 22% by weight of triethylamine hydrogen fluoride), and (SO) as a underflow2F-NH-SO2F)·Et3N oil phase α 3 (which also contains 15 wt% water). The lower oil phase α 3 is sent to the alkalization step. The oil phase alpha 3 was also detected to contain 100ppm of F-。
The upper aqueous phase alpha water is sent to a recovery workshop for treatment (recovery section A). In the recovery section A, alpha water was pumped in to 100m3In the alkalization kettle, stirring is started. Adding potassium hydroxide solution (5mol/L) into the alkalization kettle, and adjusting the pH value of the liquid in the alkalization kettle to be kept in a range of 8-10. After reacting for 2h at normal temperature and pressure, pumping the alkalization kettle solution into a layering tank for phase splitting for 2 h. The water phase is potassium fluoride solution (containing a small amount of triethylamine), and the potassium fluoride solution is separated and pumped to a recovery working section B; the oil phase is an organic phase of water and triethylamine, and is separated and pumped to a recovery section B.
Containing (SO)2F-NH-SO2F)·Et3The oil phase alpha 3 of N is directly alkalized in an evaporator B (the steam heating temperature of a hot water bucket is 35 ℃), and the lithium hydroxide aqueous solution (the concentration is 5mol/L, wherein the volume ratio of the material flow alpha 3 to the lithium hydroxide aqueous solution is 1.1: 1) is added dropwise while continuously stirring. After 1 hour of reaction, a mixture stream β 1-1 (crude lithium salt) is obtained. Heat was applied using 35 ℃ hot water and the vacuum was turned on. The vacuum degree in the kettle is kept at-0.08 MPa, and the steaming time is about 6 h. And (3) respectively carrying out five-stage condensation on the front stage and the rear stage of the vacuum pump by using water at 25 ℃ and water at 0 ℃, and standing and separating the condensate. And recycling the condensed water of the lower layer liquid in an alkalization process to prepare the aqueous solution of the lithium hydroxide. In the evaporation process, partial products are decomposed, and a lithium hydroxide solution (with the concentration of 5mol/L) needs to be continuously added, so that the pH value is kept at about 8. The supernatant is triethylamine aqueous solution, and the triethylamine aqueous solution is pumped to a recovery workshop for recovery (recovery section B). In the recovery section B, the triethylamine aqueous solution is introduced into a triethylamine transfer tank and separated into a water phase and an oil phase by a disc centrifuge. The oil phase is an organic phase containing water and triethylamine; and (3) combining the organic phase with the organic phase containing water and triethylamine obtained in the recovery working section A, introducing the combined organic phase and the organic phase containing water and triethylamine into a single-effect evaporator for evaporation to obtain a triethylamine phase containing water. Then respectively pass through a dehydration tower for dehydrationAnd removing residual moisture through rectification of a rectifying tower to obtain the high-purity triethylamine. The recovery rate of the recovered triethylamine was calculated to be 93%, and the purity by gas chromatography quantitative analysis was 99.2% by weight. The chromatographic parameters were set as: the temperature of the column box is 40-260 ℃, the detector type is FID/TCD, the temperature of the detector is 300 ℃, the air pressure is 0.4MPa, the hydrogen flow is 30ml/min, and the air flow is 400 ml/min.
KF recovery
The lower aqueous phase obtained by phase separation in the layering tank of the recovery section a mainly contains KF solution and a small amount of triethylamine. It is combined with the lower aqueous phase obtained in the single-effect evaporation system, the dehydration tower and the rectification tower in the recovery section B in a brine tank. Introducing the liquid in the brine tank into a stripping tower for steam stripping, and returning the obtained light phase mainly containing triethylamine and water to the oil phase secondary layering tank of the recovery working section A; and (3) introducing the heavy component into a double-effect evaporator for evaporation to obtain a high-concentration KF solution. The recovery rate of KF in the recovered high-concentration KF solution was 88%, and the concentration was 56.8% by weight by quantitative analysis by ion chromatography. The chromatographic parameters were set as: the temperature of the chromatographic column is 30-45 ℃, the DS5 conductivity detector, the Shodex IC SI-904E analytical column is 4.6 gamma 250mm, the Shodex IC SI-90G protective column is 4.6 gamma 10mm, the flow rate of leacheate is 1.0mL/min, and the flow rate of regeneration liquid is 1.0 mL/min.
DEC recovery
The aqueous solution (beta 1-2 for short) of the product of the lithium bis (fluorosulfonyl) imide obtained after passing through the evaporator B is continuously evaporated in a falling-film evaporator C (the steam heating temperature of a hot water barrel is 50 ℃). Simultaneously, metering and pumping diethyl carbonate (DEC) (controlling a flow meter to ensure that the volume ratio of the DEC to the material flow beta 1-2 is 0.6:1), continuously heating and evaporating in vacuum (-0.08MPa), respectively carrying out five-stage condensation on the front stage and the rear stage of a vacuum pump by using normal-temperature water and water at 0 ℃, wherein the condensate is an aqueous solution containing the DEC. The aqueous solution containing DEC is stored in a collection tank and sent to a recovery plant for recovery (recovery section C).
After evaporation in a falling-film evaporator C, a stream β 2 comprising lithium bis-fluorosulfonylimide (which comprises 70% by weight of lithium bis-fluorosulfonylimide and 29% by weight of diethyl carbonate and 1% by weight of water) is obtained. During the evaporation in the falling-film evaporator C, an aqueous lithium hydroxide solution (concentration 5mol/L) is metered in, so that the pH of the stream β 2 is maintained at 8.
And (3) filtering the material flow obtained after evaporation by the falling-film evaporator C, and filtering out a byproduct lithium compound to obtain a filtrate beta 2-1 containing 1 wt% of water, 30 wt% of diethyl carbonate and 69 wt% of lithium bis (fluorosulfonyl) imide. Pumping the filtrate beta 2-1 into a scraper evaporator D (the steam heating temperature of a hot water barrel is 75 ℃), and heating, evaporating and dehydrating in vacuum (the vacuum degree is-0.08 MPa). The condensate, which mainly comprises DEC and a small amount of water, is sent to a recovery plant for recovery (recovery section C). After 6 hours of evaporation, lithium bis (fluorosulfonylimide) β 3 (which contains 85% by weight of lithium bis (fluorosulfonylimide) and 15% by weight of diethyl carbonate) was obtained with a water content of 3000 ppm.
In recovery section C, aqueous DEC is passed into a DEC buffer tank and mixed with a 50% strength by weight lithium hydroxide solution in a line mixer so that the pH is adjusted to 8 to 9. The combined liquid stream is then separated by a coalescer. The oil phase obtained after separation is mainly DEC and is introduced into a DEC storage tank. The purity of DEC in the liquid material obtained in the DEC storage tank was 98.6 wt% by gas chromatography quantitative analysis.
3. Recovery of crystallization liquid
Pumping beta 3 into a crystallization kettle, pumping dichloromethane into the crystallization kettle at the speed of 20L/h, stirring and mixing, pumping into a two-in-one device with a filtering and washing function, conveying dichloromethane (containing DEC) to a recovery workshop for recovery (recovery section D), allowing the rest lithium bis (fluorosulfonyl) imide crystals to fall into a drying kettle at the lower layer of the two-in-one device through gravity, and introducing nitrogen into a dryer to blow and sweep the crystals for drying, wherein the drying temperature is 60 ℃. After drying and condensation, the condensate contains 99.5 percent of dichloromethane and 0.5 percent of water, and the condensate is sent to a crystallization process for recycling. After the water content of the crystals is reduced to the target requirement (50ppm), the obtained powder product is sent to a dissolving section.
In the dissolution section, 70L of ethyl methyl carbonate and 0.1kg of lithium hydroxide were added to 30kg of lithium bis-fluorosulfonylimide β 3. Then a disc centrifuge is used for centrifugation (the rotating speed is 1500rpm) to remove solids, then the filtrate g-1(HF is less than or equal to 50 mu g/g) is sent to a dehydration kettle, 20kg of molecular sieve is added into the dehydration kettle, the stirring rotating speed is 800, and the processing time is 2 h. Then a filter is used for filtering out the molecular sieve, and the obtained filtrate g-2 (the water content is less than or equal to 20 mu g/g) is sent to a product blending kettle. Finally demagnetizing (passing through a demagnetizing filter, 8000 Gauss) and filtering (respectively passing through a 1 micron filter, a 0.5 micron filter and a 0.1 micron filter) to obtain a 28 wt% lithium bis (fluorosulfonyl) imide methyl ethyl carbonate solution, and finally canning.
In the recovery section D, the crystallization liquid water washing oil phase (dichloromethane, DEC, water, salt, etc.) is pumped into a dehydration tower for dehydration. And (3) performing liquid separation treatment on the tower top condensate mainly comprising dichloromethane and water, collecting the separated water to a sewage collecting tank, and refluxing all the separated dichloromethane to the tower. And introducing the tower bottom liquid of the dehydration tower into a single-effect evaporator, introducing the gas phase obtained by evaporation into a rectifying tower for rectification, obtaining dichloromethane from the tower top condensate of the rectifying tower, and collecting the dichloromethane to a dichloromethane preparation tank. A50% strength by weight lithium hydroxide solution is added to the tank, the pH is adjusted to 9-10 via a pump circulation line and the phases are separated. Separating the obtained water phase for post-treatment, and introducing the obtained oil phase into a dichloromethane storage tank. Ethanol extracted from the tower is barreled for treatment. DEC is extracted from the middle lower part of the tower and is pumped to a DEC storage tank for recycling in a dehydration procedure (beta section). Carrying out treatment on the kettle residues in a barrel; and (3) concentrating the liquid phase subjected to single-effect evaporation in vacuum, further recovering dichloromethane and diethyl carbonate (DEC), sending the obtained product back to a dehydration tower, and barreling the concentrated solution for treatment. The purity of methylene chloride in the oil phase passed into the methylene chloride storage tank was 99.2% by weight by gas chromatography quantitative analysis.
4. Recovery of methylene dichloride off-gas
And collecting volatilized gas mainly containing dichloromethane waste gas and evaporated water from the tops of the two-in-one equipment in the crystallization process, the dehydration tower and the rectification tower in the recovery section D by using a collecting pipe. And introducing the collected waste gas into a dichloromethane absorption and recovery device, and cooling with normal-temperature water. And (4) cooling, introducing into three-stage adsorption resin for adsorption, and desorbing by using steam after adsorption saturation. Condensing and collecting, and standing and layering the collected dichloromethane and water. The upper layer liquid water contains trace dichloromethane and is used as wastewater for post-treatment; the lower layer liquid dichloromethane contains about 1800ppm of water and is pumped into a 4A molecular sieve dehydration device for dehydration to below 150ppm for recycling.
Example 2
Example 2 was carried out in the same manner as in example 1, except that in the α stage for producing lithium bis (fluorosulfonyl) imide, the α 2 stream was pumped to a static mixer (length to tube diameter ratio L/D10; flow control, deionized water: α 2 ═ 1.2 ± 0.1 (weight ratio)) instead of the extraction column, and after thoroughly mixing with deionized water in the static mixer, it was sent to a layering tank, and left to stand for layering for 2 h.
And finally, evaporating the heavy components obtained in the stripping tower of the recovery section B by using a double-effect evaporator to obtain a KF solution, wherein the recovery rate of KF is 79%, and the concentration of KF in the KF solution is 42.8% by weight through ion chromatography quantitative analysis.
While the application has been described with reference to an embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the application. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. The present application is not intended to be limited to the particular embodiments disclosed herein but is to cover all embodiments that may fall within the scope of the appended claims.
Claims (19)
1. A method for recovering raw and auxiliary materials in the production of lithium bis (fluorosulfonyl) imide, which comprises a reaction 1 of reacting sulfuryl fluoride, triethylamine and ammonia gas and a subsequent reaction 2 of alkalifying the reaction product,
reaction 1: SO (SO)2F2+NH3+Et3N→(SO2F-NH-SO2F)·Et3N+Et3N·(HF)n(n＝1-12)，
Reaction 2: (SO)2F-NH-SO2F)·Et3N+LiOH→(SO2F-N-SO2F)-Li++Et3N+H2O，
The method comprises the following steps:
recovery section A. separation of the product mixture resulting from reaction 1 into a mixture comprising (SO)2F-NH-SO2F)·Et3An oil phase of N and an aqueous phase comprising triethylamine hydrogen fluoride and impurity ions; will contain (SO)2F-NH-SO2F)·Et3The oil phase of N is subjected to an alkalization process according to the reaction 2, a water phase containing triethylamine hydrogen fluoride and impurity ions is introduced into an alkalization kettle to be mixed with alkali metal hydroxide under stirring and react, and then a solution obtained after the reaction in the alkalization kettle is introduced into a layering tank for phase separation; the upper oil phase is an organic phase containing water and triethylamine, and the organic phase is separated out and stored in an oil phase secondary layering tank; and
a recovery section B: removing triethylamine and part of water from a product mixture obtained by performing an alkalization process according to the reaction 2 through an evaporator, introducing the evaporated triethylamine and water into a condenser for condensation, standing and separating liquid; transferring the upper triethylamine solution obtained after liquid separation into a triethylamine transferring tank, and separating into a water phase and an oil phase through a centrifugal machine, wherein the oil phase is an organic phase containing water and triethylamine; introducing the organic phase and the organic phase containing water and triethylamine obtained in the recovery working section A into a single-effect evaporation system together to obtain a water-containing triethylamine phase; and then removing residual water through dehydration in a dehydration tower and rectification in a rectification tower respectively to obtain the high-purity triethylamine.
2. The process according to claim 1, wherein the high purity triethylamine obtained by the process has a purity of 95% by weight or more; optionally, the triethylamine has a purity of 98 wt% or more, 99 wt% or more, or 99.5 wt% or more.
3. The method of claim 1 or 2, wherein the impurity ions comprise F-、SO4 2-、FSO3 -And Cl-。
4. A process according to any one of claims 1 to 3, wherein in the recovery section B the product mixture obtained from the basification process is distilled off by means of an evaporator to a mixture comprising triethylamine and water, the mixture is heated, after condensation in a condenser, to a temperature of 30-55 ℃, optionally 40-45 ℃ and left to layer.
5. Process according to any one of claims 1 to 4, in which the separation of the product mixture resulting from reaction 1 in the recovery section A is a stratification by means of a static mixer or an extraction by means of an extraction column.
6. The process of claim 5, wherein the content of impurity ions in the oil phase resulting from the stratification by the static mixer is 5-30 times, optionally 10-20 times, the content of impurity ions in the oil phase resulting from the extraction by the extraction column; optionally, the impurity ion is F-。
7. The method of any one of claims 1 to 6, wherein the centrifuge is a disk centrifuge.
8. A process as claimed in any one of claims 1 to 7, wherein the aqueous phase separated off in the recovery section B by the centrifuge is passed to an alkalization process for reaction 2 for the complexing of alkali, to an extraction process as wash water or to a waste water treatment plant for treatment.
9. A process according to any one of claims 1 to 8, wherein the lower aqueous phase obtained by phase separation in the stratified tank of the recovery section A comprises mainly alkali metal fluoride solution and a small amount of triethylamine; combining the obtained water phase with the lower water phase obtained in the single-effect evaporation system, the dehydration tower and the rectification tower in the recovery section B in a brine tank; introducing the liquid in the brine tank into a stripping tower for steam stripping, and returning the obtained light phase mainly containing triethylamine and water to the oil phase secondary layering tank of the recovery working section A; and (3) introducing the heavy component into a double-effect evaporator for evaporation to obtain a high-concentration alkali metal fluoride solution.
10. The method of any one of claims 1 to 9, wherein the alkali metal is Li, Na, or K.
11. The process according to any one of claims 1 to 10, wherein the production of lithium bis-fluorosulfonylimide further comprises a dehydration process using an ester solvent, the aqueous ester solvent obtained by evaporation and condensation being recovered by a recovery section C:
and (4) a recovery section C: and introducing the water-containing ester solvent into an ester solvent buffer tank, mixing the water-containing ester solvent with the lithium hydroxide solution in a pipeline mixer, separating the mixture by a coalescence separator to obtain an oil phase as the ester solvent, and introducing the oil phase into an ester solvent storage tank.
12. The method according to claim 11, wherein the aqueous phase obtained after separation by the coalescer is added with a lithium hydroxide solution to adjust the pH value, and then enters a stripping tower for stripping by a preheater to obtain an oil phase containing the aqueous ester solvent, and the oil phase is returned to the ester solvent buffer tank; and introducing the obtained water phase and residual liquid into a sewage treatment device for post-treatment.
13. The method according to claim 11 or 12, wherein the ester solvent includes ethyl methyl carbonate EMC, diethyl carbonate DEC, and dimethyl carbonate DMC.
14. The method according to any one of claims 1 to 13, wherein the production of lithium bis-fluorosulfonylimide further comprises a crystallization process using a crystallization liquid to dissolve an ester solvent and precipitate a product LiFSI crystal, the crystallization liquid obtained by evaporation and condensation washing an oil phase with water comprising dichloromethane, an ester solvent, water, and a salt; and the crystallization liquid is recycled through a recycling section D:
and (4) a recovery section D: putting the crystallized liquid washing oil phase into a dehydration tower, wherein the condensed liquid at the top of the tower contains dichloromethane and water, the upper layer of water phase after layering is put into a sewage collection tank for post-treatment, and the lower layer of dichloromethane is totally refluxed;
and introducing the tower bottom liquid of the dehydration tower into a single-effect evaporation system, introducing the gas phase obtained by evaporation into a rectifying tower for rectification, obtaining dichloromethane from the condensed liquid at the top of the rectifying tower, collecting the dichloromethane to a dichloromethane blending tank, adding lithium hydroxide into the tank, adjusting the pH value through a pump circulation pipeline, carrying out phase splitting, separating the obtained water phase, and introducing the obtained oil phase into a dichloromethane storage tank.
15. The method according to claim 14, wherein ethanol is separated from the middle part of the rectifying tower for post-treatment; obtaining an ester solvent from the condensate liquid at the middle lower part of the rectifying tower, and introducing the ester solvent into an ester solvent storage tank for recycling the dehydration process; and separating residual liquid obtained from the tower kettle of the rectifying tower for post-treatment.
16. The process of claim 14, wherein the liquid phase from the single-effect evaporation system is concentrated under vacuum to obtain a condensate comprising methylene chloride and the ester solvent, which is fed back to the dehydration column; the concentrated solution after vacuum concentration is separated for post-treatment.
17. A process according to any one of claims 1 to 16, wherein the process further comprises a recovery section E for recovering the off-gas comprising dichloromethane produced in each stage:
a recovery section E: cooling the waste gas containing dichloromethane generated in each stage, introducing the waste gas into three-stage adsorption resin for adsorption, desorbing the waste gas by using steam after the waste gas is saturated by adsorption, collecting the waste gas by condensation, standing and layering the collected liquid containing dichloromethane and water, and separating and post-treating the waste water containing trace dichloromethane in the upper water phase; the lower oil phase is dichloromethane containing trace water, and is introduced into a dehydration device for dehydration and then recycled.
18. The method as claimed in claim 17, wherein the water content in the methylene chloride containing a trace amount of water is 1000-2000ppm, and the dehydration is carried out to a water content of 50-200 ppm.
19. The method of claim 17, wherein the dehydrating is through a 4A molecular sieve.
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