CN113941169A - Preparation method and preparation device of electronic grade dimethyl carbonate - Google Patents
Preparation method and preparation device of electronic grade dimethyl carbonate Download PDFInfo
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Abstract
The invention relates to the field of lithium battery electrolyte, in particular to a preparation method and a preparation device of electronic grade dimethyl carbonate, which comprise a suspension crystallizer, a solid-liquid separator, a static crystallizer and a dehydration tower; the suspension crystallizer is connected with the dehydration tower through the solid-liquid separator and the static crystallizer in sequence; the electronic grade DMC is obtained by the DMC crude product through the steps of suspension crystallization, solid-liquid separation, static crystallization and dehydration. Compared with the prior art, the method combines suspension crystallization and static crystallization to purify the DMC crude product, fully utilizes the process characteristics of two crystallization modes aiming at the physical property of dimethyl carbonate, realizes the production of electronic grade DMC, and ensures that the methanol content in the product is lower than 20ppm, the water content is lower than 20ppm, and the dimethyl carbonate content is not lower than 99.99 wt%; and a plurality of material circulations are arranged in the process, so that the yield of the final electronic grade DMC dimethyl carbonate reaches more than 80%.
Description
Technical Field
The invention relates to the field of lithium battery electrolyte, in particular to a preparation method and a preparation device of electronic grade dimethyl carbonate.
Background
The rise of green chemistry in the later 90 s of the 20 th century provides effective means for solving the problem of environmental pollution caused by chemical industry. From the viewpoint of green chemistry, the pollution control is started from the beginning of production, namely, nontoxic or low-toxic raw materials are adopted from the beginning of raw materials, and a production process which does not generate pollutants as much as possible is adopted in the production process. Against this background, Dimethyl carbonate (DMC) is regenerated in the form of a "green intermediate". DMC is very toxic and Europe listed it as a non-toxic chemical in 1992. As a new green chemical, DMC itself has been produced greenly by oxidative carbonylation of methanol. The molecular structure of DMC is CH3O-CO-OCH3Since the structure contains a group such as methyl, carbonyl, or methoxy, the role of the compound as a reagent for carbonylation, methylation, or methyl esterification in organic synthesis has been attracting attention. After the 21 st century, with the rise of the electric automobile industry, the demand of high-quality electrolyte is also increased. DMC has strong dissolving power, stable property and low toxicity, and is one of excellent electrolyte formulas.
GB/T33107-2016 states that the content of dimethyl carbonate in electronic grade dimethyl carbonate needs to be more than 99.99 wt%, and the content of methanol needs to be less than 20ppm, and the content of moisture needs to be less than 30ppm, and some enterprises have required the content of moisture in electronic grade dimethyl carbonate to be less than 20 ppm.
At present, the processes for producing dimethyl carbonate include phosgene methanol process, methanol oxidative carbonylation process, ester exchange process, urea alcoholysis process and carbon dioxide methanol process, wherein the ester exchange process and the urea alcoholysis process enter into industrial application stages. In addition, about 2% of dimethyl carbonate is produced as a byproduct in the process of preparing ethylene glycol from coal, the yield of ethylene glycol from coal in China in 2019 reaches 449 ten thousand tons, and about 7-8 ten thousand tons of dimethyl carbonate are produced as a byproduct every year, so that the recovery and production of electronic grade dimethyl carbonate from the ethylene glycol process is one of the current research hotspots.
Chinese patent CN111454152A discloses a method and an apparatus for preparing electronic grade dimethyl carbonate, comprising: 1) mixing propylene carbonate and methanol, and carrying out ester exchange reaction under the catalytic action of sodium methoxide to obtain a dimethyl carbonate/methanol azeotrope; 2) separating dimethyl carbonate/methanol azeotrope by adopting a molecular sieve membrane to obtain methanol and a dimethyl carbonate crude product; 3) rectifying the crude dimethyl carbonate product to obtain industrial grade dimethyl carbonate with the purity of more than or equal to 99.7 percent; 4) and (3) sequentially cooling, crystallizing, heating, sweating and melting the industrial grade dimethyl carbonate with the purity of more than or equal to 99.7% to obtain the electronic grade dimethyl carbonate. However, the method has the advantages of complex flow, multiple process steps, high rectification energy consumption, generally small treatment capacity of the molecular sieve membrane, easy blockage, frequent replacement, further increased process cost and low economic benefit.
Chinese patent CN111704545A discloses a method for separating dimethyl carbonate methanol azeotrope by melt crystallization and application thereof, specifically, the method comprises the steps of introducing dimethyl carbonate methanol azeotrope with 25-35% of dimethyl carbonate into a melt crystallization device, separating out dimethyl carbonate in a crystallization form by cooling, heating to sweat to partially melt dimethyl carbonate crystals, removing impurities occluded in the crystallization process, further purifying dimethyl carbonate, and finally obtaining a high-purity dimethyl carbonate product and a low-concentration crystallization mother liquor. Wherein the crystallization temperature of the dimethyl carbonate in an azeotropic system is-20 to-40 ℃, and the operation equilibrium temperature of a crystallization section is-50 to-60 ℃; the purity of the dimethyl carbonate product is 99.9-99.999%, and the concentration of the crystallization mother liquor is 5-15%. However, the dimethyl carbonate product of the patent does not consider the limitation of the content of methanol and the content of water in electronic grade dimethyl carbonate, and the crystallization temperature in the production process is low, so that the equipment investment and the energy consumption of the process are high, and the safety of the process is reduced.
Chinese patent CN111704547A discloses a device and a method for producing dimethyl carbonate by heat pump rectification melt crystallization coupling, which comprises a reaction rectification tower, a melt crystallizer and a methanol recovery tower, wherein raw materials and a catalyst enter the reaction rectification tower to generate dimethyl carbonate and byproducts, the byproducts are extracted from the tower bottom for collection, a dimethyl carbonate and methanol azeotropic system is extracted from the tower top, the dimethyl carbonate and methanol azeotropic system enters the melt crystallizer to obtain a high-purity dimethyl carbonate product through melt crystallization separation, and a crystallization mother liquor enters the methanol recovery tower to separate and recover methanol. Wherein the reaction rectifying tower and the methanol recovery tower are both provided with a heat pump system to recover the vapor phase heat at the top of the tower for heating the reboiler at the bottom of the tower. Although the heat pump technology is adopted to reduce the energy consumption, the energy consumption of rectification is still high, in addition, the reaction rectification raw material adopted by the patent contains a large amount of methanol, although a methanol recovery tower is arranged, the requirement of electronic grade dimethyl carbonate is difficult to achieve, the water content in a dimethyl carbonate product is not limited, and the electronic grade dimethyl carbonate is difficult to obtain. The melting crystallization in the process needs a low-temperature cold source of-40 to-50 ℃, which causes higher equipment investment and energy consumption of the process and reduces the process safety.
Chinese patent CN109970565A discloses a process for refining battery liquid grade dimethyl carbonate by coupling a pressurization method with melt crystallization, which comprises the following steps (1) preheating materials: firstly, a coal glycol product is subjected to a normal pressure T1 light component removal tower, a light component such as methylal and methyl formate is removed from the top of the T1 light component removal tower, a part of dimethyl carbonate and dimethyl oxalate are removed from the bottom of the T1 light component removal tower, and methanol and DMC which are extracted from a side line close to the upper part of a feed inlet of the tower are mixed and enter a T2 pressurizing tower; (2) introducing DMC azeotrope extracted from the side line of the T1 tower into a T2 pressurized tower, obtaining DMC azeotrope with DMC content of about 15-18% through the top of the pressurized rectifying tower, and obtaining DMC over 99.5% in the tower bottom; (3)99.5 percent of dimethyl carbonate enters a subsequent falling film melting crystallization device, and is frozen, sweated and dissolved to obtain 99.99 percent of battery liquid level dimethyl carbonate. However, the T1 lightness-removing tower in the patent needs a reflux ratio of 30-50, and the energy consumption is high; the T2 pressurized column is operated at very high pressure, increasing equipment investment and decreasing process safety.
Disclosure of Invention
The invention aims to solve at least one of the problems, and provides a preparation method and a preparation device of electronic grade dimethyl carbonate, which realize the low-energy consumption and high-purity production of the electronic grade dimethyl carbonate meeting the requirements of GB/T33107-2016.
The purpose of the invention is realized by the following technical scheme:
the invention provides a preparation device of electronic grade dimethyl carbonate, which comprises a suspension crystallizer, a solid-liquid separator, a static crystallizer and a dehydration tower, wherein the suspension crystallizer is connected with the solid-liquid separator;
the suspension crystallizer is connected with the dehydration tower sequentially through the solid-liquid separator and the static crystallizer.
Further, the solid-liquid separator is a vacuum drum filter with a washing function, a horizontal multi-stage pusher centrifuge or a washing tower.
Further, the static crystallizer comprises a box body and an inner part; the other surfaces of the box body except the upper cover plate are formed by single-side pillow type plate corrugated heat exchange plates, wherein the pillow type surface faces to the material side; the inner part is composed of a pillow type plate corrugated heat exchange plate bundle.
The corrugated heat exchange plate structure of the unilateral pillow type plate is formed by 2 plates, one plate is a flat thick plate, and the other plate is a plate pair which is formed by spot welding and edge welding of a wavy plate, wherein one side of the plate pair is flat and the other side of the plate pair is provided with a curved surface.
The pillow type plate corrugated heat exchange plate bundle structure is a plate pair with 2 wavy edges formed by 2 plate sheets through spot welding and edge welding.
Furthermore, a dehydrating agent is filled in the dehydrating tower, the dehydrating agent is one or more of a 4A molecular sieve, a 5A molecular sieve, silica gel and activated alumina, and preferably, the dehydrating agent is a 4A molecular sieve or silica gel.
Furthermore, the preparation device also comprises a plurality of storage tanks which are respectively a raw material tank, a mother liquor tank, a melting tank, a finished product storage tank and a final finished product tank and are respectively used for storing DMC crude products, mother liquor, crystals, high-purity DMC and electronic grade DMC.
The second aspect of the invention provides a preparation method of electronic grade dimethyl carbonate, which comprises the following steps:
s1: introducing the DMC crude product into a suspension crystallizer, and performing suspension crystallization to obtain slurry;
s2: feeding the slurry obtained in the step S1 into a solid-liquid separator for solid-liquid separation to obtain mother liquor and crystals;
s3: the mother liquor obtained in the step S2 is divided into two parts, one part of the mother liquor is returned to the suspension crystallizer to improve the yield, and the other part of the mother liquor is discharged as waste liquor; melting the crystals obtained in the step S2 to obtain an initial crystallization material, and dividing the initial crystallization material into two parts, wherein one part of the initial crystallization material is taken as a washing liquid and conveyed to a solid-liquid separator, and the other part of the initial crystallization material enters a static crystallizer;
s4: after inputting the other part of the initial crystallization material obtained in the step S3 into a static crystallizer, crystallizing, sweating and completely melting to obtain high-purity DMC;
s5: the high-purity DMC obtained in the step S4 enters a dehydration tower for dehydration to obtain electronic grade DMC;
s6: the electronic grade DMC obtained in step S5 is divided into two parts, one part of the electronic grade DMC is used as circulating material to be mixed with the high-purity DMC obtained in step S4 and enters a dehydration tower, and the other part of the electronic grade DMC is used as discharging product to be discharged.
Further, the DMC content in the crude DMC product in the step S1 is 95-99.5 wt%.
Further, the temperature of the material in the suspension crystallizer in the step S1 is-5 to 3.5 ℃, preferably-4 to 3 ℃, and further preferably-3.5 to 2.8 ℃.
Further, the stirring speed of the suspension crystallizer in the step S1 is 10 to 30rpm, preferably 15 to 25rpm, and more preferably 18 to 25 rpm.
Further, the temperature difference between the refrigerant inlet temperature of the suspension crystallizer and the material temperature in the step S1 is 4-15 ℃, preferably 6-13 ℃, and further preferably 7-12 ℃.
Further, the temperature difference between the inlet and the outlet of the refrigerant of the suspension crystallizer in the step S1 is 0.3 to 1 ℃, preferably 0.4 to 0.8 ℃, and more preferably 0.4 to 0.7 ℃.
Further, the solid content of the slurry in the step S1 is 20 to 40 wt%, preferably 25 to 35 wt%, and more preferably 27 to 33 wt%.
Further, a part of the mother liquor returned to the suspension crystallizer in the step S3 accounts for 80 to 95 wt%, preferably 82 to 93 wt%, and more preferably 85 to 91 wt% of the mother liquor.
Further, a part of the initial crystallized material as the washing liquid in the step S3 is 5 to 20 wt%, preferably 7 to 15 wt%, and more preferably 8 to 12 wt% of the initial crystallized material.
Further, the temperature of the washing liquid in the step S3 is 3.5 to 5.5 ℃, preferably 3.7 to 5.0 ℃, and more preferably 3.8 to 4.9 ℃.
Further, step S4 includes the following steps:
s401: precooling to the initial crystallization temperature, maintaining for half an hour, and cooling to the crystallization end point temperature;
s402: after crystallization is finished, preheating to the initial sweating temperature and maintaining for half an hour, and mixing the discharged residual liquid with the initial crystallization material;
s403: in the first stage, the temperature is increased for sweating, and the sweat in the first stage is discharged and mixed with the DMC crude product;
s404: raising the temperature and sweating in the second stage, and discharging the sweat in the second stage to mix with the initial crystallization material;
s405: heating to the total melting temperature to obtain the high-purity DMC.
Further, the initial crystallization temperature in step S401 is 4.5 to 5.5 ℃, preferably 4.7 to 5.2 ℃, and more preferably 4.7 to 5.0 ℃.
Further, the cooling rate in step S401 is 0.008 to 0.03 ℃/min, preferably 0.01 to 0.025 ℃/min, and more preferably 0.01 to 0.02 ℃/min.
Further, the crystallization end point temperature in step S401 is-1.7 to 0 ℃, preferably-1.5 to-0.2 ℃, and more preferably-1.5 to-0.3 ℃.
Further, the initial sweating temperature in step S402 is 2.5 to 3.8 ℃, preferably 2.8 to 3.6 ℃, and more preferably 2.9 to 3.5 ℃.
Further, the residual liquid in the step S402 accounts for 5-20 wt%, preferably 7-18 wt%, and more preferably 8-15 wt% of the initial crystallization material.
Further, the temperature rise rate of the first-stage temperature rise and sweating in step S403 is 0.02 to 0.05 ℃/min, preferably 0.025 to 0.045 ℃/min, and more preferably 0.027 to 0.041 ℃/min.
Further, the first-stage sweat in step S403 accounts for 5 to 10 wt%, preferably 6 to 9 wt%, and more preferably 7 to 8.8 wt% of the initial crystallization material.
Further, the temperature rise rate of the second-stage temperature rise and sweating in the step S404 is 0.01 to 0.04 ℃/min, preferably 0.015 to 0.035 ℃/min, and more preferably 0.02 to 0.033 ℃/min.
Further, the second stage sweat in step S404 accounts for 5 to 10 wt%, preferably 6 to 9 wt%, and further preferably 6 to 8 wt% of the initial crystallization material.
Further, the total melting temperature in step S405 is 8 to 15 ℃, preferably 9 to 13 ℃, and more preferably 10 to 12 ℃.
Further, the mass flow ratio of the discharged product to the circulating material in the step S6 is 1: 2-1: 6, preferably 1: 3-1: 5, more preferably 1: 3.5-1: 4.5.
furthermore, the refrigerant used for preparation is ethylene glycol aqueous solution.
Compared with the prior art, the invention has the following beneficial effects:
1. the method combines suspension crystallization and static crystallization to purify the DMC crude product, fully utilizes the process characteristics of two crystallization modes aiming at the physical property of dimethyl carbonate, realizes the production of electronic grade DMC, and ensures that the content of methanol in the product is lower than 20ppm, the content of water is lower than 20ppm, and the content of dimethyl carbonate is not lower than 99.99 wt%; and a plurality of material circulations are arranged in the process, so that the yield of the final electronic grade DMC dimethyl carbonate reaches more than 80%.
Suspension crystallization is characterized in that crystal particles are suspended in mother liquor to grow, so that the crystal has a large specific surface area which reaches about 18000m2/m3Crystals, and generally layer crystals, having a specific surface area of about 10m2/m3In other words, relative to other forms of hierarchyFor crystallization (static crystallization, one type of layer crystallization), suspension crystallization has a greater overall crystal growth rate, i.e., increases the production efficiency of the reactor. In addition, the product content of the suspension crystallization is less influenced by the fluctuation of the raw materials, namely the product content of the suspension crystallization is more stable.
The suspension crystallizer is a movable device with stirring and solid-liquid separation, a solid-liquid mixture from the suspension crystallizer needs to be separated by the solid-liquid separation device, generally speaking, the solid-liquid separation device comprises a washing tower and a centrifuge, the washing tower has higher separation efficiency, but the single tower has smaller production capacity, high investment, large production capacity of the centrifuge, simple equipment and slightly lower separation efficiency than the washing tower.
The static crystallization has no other moving equipment except a pump, is fully automatically produced, is stable and reliable in operation, more importantly, is sequencing batch operation, has lower static crystallization production efficiency compared with suspension crystallization, is flexible in adjustment and stable and guaranteed in separation efficiency, and is not allowed for the qualification of products caused by any production fluctuation of electronic grade chemicals, so that the static crystallization can be used as a final purity guarantee means in the high-purity separation process.
The combination of the suspension crystallization and the static crystallization is based on the principle, and the production of the electronic grade DMC is effectively ensured by utilizing the characteristics that the production efficiency of the suspension crystallization in a lower content interval is high and the separation effect of the static crystallization in a high content area is ensured.
2. Compared with the prior art of rectification or other purification modes, the suspension crystallization is adopted as a primary purification process, the operation flexibility is high, the method is insensitive to raw material fluctuation, the product purity is high, the energy consumption of a unit product is low, and the energy consumption of the unit product can be reduced by more than 50% when 95-99.5 wt% of DMC crude product is purified to 99.9 wt%.
3. Because the static crystallization process has flexible operation, high stability and less moving equipment, the sequencing batch static crystallization process is adopted during further purification, so that the stability of the whole process can be ensured, and the production of electronic grade DMC can be ensured.
4. When the water content in the DMC crude product exceeds 500ppm, the water content in the crystal obtained by crystallization is difficult to reduce to below 20ppm and cannot be used as electronic grade DMC.
Drawings
FIG. 1 is a schematic flow diagram of a process for the preparation of electronic grade dimethyl carbonate according to the present invention;
in the figure: 1-a suspension crystallizer; 2-a solid-liquid separator; 3-a static crystallizer; 4-a dehydration column; 51-raw material tank; 52-mother liquor tank; 53-a melt channel; 54-a crystallization finished product tank; 55-final product tank.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
A method and a device for preparing electronic grade dimethyl carbonate are disclosed, as shown in figure 1, firstly DMC crude product containing 95-99.5 wt% DMC is stored in a raw material tank 51, and then pumped into a suspension crystallizer 1 for suspension crystallization. The suspension crystallization adopts glycol aqueous solution as a cooling medium (cooling medium), and the glycol aqueous solution enters a jacket of the suspension crystallizer 1 to control the temperature of the material in the suspension crystallizer 1. The temperature of the material in the suspension crystallizer 1 is set to be-5-3.5 ℃, preferably-4-3 ℃, and further preferably-3.5-2.8 ℃; the stirring speed is set to be 10-30 rpm, preferably 15-25 rpm, and more preferably 18-25 rpm; the temperature difference between the inlet temperature of the refrigerant and the temperature of the material in the suspension crystallizer 1 is 4-15 ℃, preferably 6-13 ℃, and further preferably 7-12 ℃; the temperature difference between the inlet and the outlet of the refrigerant is 0.3-1 ℃, preferably 0.4-0.8 ℃, and more preferably 0.4-0.7 ℃. After suspension crystallization is carried out on the DMC crude product, slurry with the solid content of 20-40 wt%, preferably 25-35 wt% and further preferably 27-33 wt% is obtained, and the slurry enters a solid-liquid separator 2 in an overflow mode to carry out solid-liquid separation.
The solid-liquid separator 2 can be a vacuum drum filter with washing function, a horizontal multi-stage material-pushing centrifuge or a washing tower, the separated mother liquor flows into a mother liquor tank 52 under the action of gravity, the solid crystals fall into a melting tank 53 under the action of gravity, and the crystals are melted in the melting tank 53. And pumping 80-95 wt%, preferably 82-93 wt% and more preferably 85-91 wt% of the mother liquor entering the mother liquor tank 52 into the suspension crystallizer 1, continuously crystallizing to improve the yield, and discharging the rest as waste liquor. Melting the crystals entering the melting tank 53 to obtain an initial crystallized material, wherein 5-20 wt%, preferably 7-15 wt%, and more preferably 8-12 wt% of the initial crystallized material is conveyed to the solid-liquid separator 2 to be used as a washing liquid to wash the crystals, and the temperature of the washing liquid conveyed to the solid-liquid separator 2 is 3.5-5.5 ℃, preferably 3.7-5.0 ℃, and more preferably 3.8-4.9 ℃; the remaining part of the initial charge is pumped in batches to the static crystallizer 3 as a feed for static crystallization, the DMC content of which is not less than 99.9% by weight.
The static crystallizer 3 is composed of a box body and an internal part, the other surfaces of the box body except the upper cover plate are composed of unilateral pillow type plate corrugated heat exchange plates, wherein the pillow type surfaces face the material side, and the internal part is composed of pillow type plate corrugated heat exchange plate bundles. The box body pillow type plate and the internal part pillow type plate bundle share the same temperature of ethylene glycol water solution as a cooling medium or a heat source so as to prevent the influence of the external environment on the internal crystallization process. When the ethylene glycol aqueous solution is used as a refrigerant, the ethylene glycol aqueous solution is directly introduced into the static crystallizer 3; when the ethylene glycol aqueous solution is used as a heat source, the ethylene glycol aqueous solution needs to exchange heat with hot water to raise the temperature, and then is introduced into the static crystallizer 3.
The initial crystallization material entering the static crystallizer 3 is firstly quickly pre-cooled to the initial crystallization temperature (4.5-5.5 ℃, preferably 4.7-5.2 ℃, and more preferably 4.7-5.0 ℃) and maintained for half an hour, and then is cooled to the crystallization end point temperature (-1.7-0 ℃, preferably-1.5-0.2 ℃, and more preferably-1.5-0.3 ℃) at a cooling rate of 0.008-0.03 ℃/min, preferably 0.01-0.025 ℃/min, and more preferably 0.01-0.02 ℃/min, and then the crystallization process is carried out. After the crystallization is completed, sweating is carried out, the liquid is quickly preheated to the initial sweating temperature (2.5-3.8 ℃, preferably 2.8-3.6 ℃, and more preferably 2.9-3.5 ℃) and maintained for half an hour, residual liquid is generated in the period, the mass of the partial residual liquid accounts for 5-20 wt%, preferably 7-18 wt%, and more preferably 8-15 wt% of the initial crystallization material, and the partial residual liquid is discharged into a melting tank 53 to be mixed with the initial crystallization material. After reaching the initial sweating temperature and maintaining for half an hour, starting the first-stage sweating, and performing temperature-rising sweating at a temperature-rising rate of 0.02-0.05 ℃/min, preferably 0.025-0.045 ℃/min, more preferably 0.027-0.041 ℃/min, during which first-stage sweat is generated, wherein the first-stage sweat accounts for 5-10 wt%, preferably 6-9 wt%, more preferably 7-8.8 wt% of the initial crystallization material, and the first-stage sweat (the purity of DMC is similar to that of DMC in the DMC crude product) is discharged into a raw material tank 51 to be mixed with the DMC crude product. After the first stage sweating is finished, the second stage sweating is started, the temperature rising sweating is carried out at the temperature rising rate of 0.01-0.04 ℃/min, preferably 0.015-0.035 ℃/min, further preferably 0.02-0.033 ℃/min, during which the second stage sweat is generated, the second stage sweat accounts for 5-10 wt% of the initial crystallization material, preferably 6-9 wt%, further preferably 6-8 wt%, and the second stage sweat (the purity of DMC is similar to that of DMC in the melting tank 53) is discharged into the melting tank 53 to be mixed with the initial crystallization material. After the second stage sweating is finished, the material in the static crystallizer 3 is rapidly heated to the whole melting temperature (8-15 ℃, preferably 9-13 ℃, further preferably 10-12 ℃) to obtain high-purity DMC, and the high-purity DMC is completely discharged into a crystallization finished product tank 54.
The high-purity DMC in the crystallization finished product tank 54 is pumped into a dehydration tower 4 for dehydration so as to ensure that the final product meets the content requirement of GB/T33107-2016. The dehydrating tower 4 is filled with dehydrating agent, which can be one or more of 4A molecular sieve, 5A molecular sieve, silica gel and activated alumina, preferably, the dehydrating agent is 4A molecular sieve or silica gel.
Dehydrating the high-purity DMC by a dehydrating tower 4 to obtain electronic grade DMC, wherein part of the electronic grade DMC is returned to a crystallization finished product groove 54 as a circulating material to be mixed with the high-purity DMC, the rest of the electronic grade DMC enters a final finished product groove 55 as a discharging product, and the mass flow ratio of the discharging product to the circulating material is 1: 2-1: 6, preferably 1: 3-1: 5, more preferably 1: 3.5-1: 4.5.
by the combined application of the suspension crystallizer 1, the solid-liquid separator 2, the static crystallizer 3 and the dehydration tower 4, the electronic grade DMC production with low energy consumption, high stability, high purity, low water content and low methanol content can be realized. In the preparation method, except that the static crystallizer 3 adopts a sequencing batch process for ensuring the stability of crystallization and sweating, other steps adopt a continuous process, and the high-stability continuous production of the electronic grade DMC can be realized.
Example 1
Dimethyl carbonate produced by a certain process is adopted as a raw material, wherein the content of the dimethyl carbonate is 99.5 wt%, the moisture content is 460ppm, the methanol content is 0.4 wt%, and the rest components are easily separated components which are not listed.
The raw materials firstly enter a suspension crystallizer 1 for cooling crystallization, the temperature of crystallization materials is-2 ℃, the stirring speed in the suspension crystallizer 1 is 22rpm, the temperature of an ethylene glycol aqueous solution inlet in a jacket of the suspension crystallizer 1 is-8.3 ℃, the temperature difference of the ethylene glycol aqueous solution entering and exiting the jacket of the suspension crystallizer 1 is 0.5 ℃, and the solid content in the suspension crystallizer 1 is 31 wt%. Performing solid-liquid separation on the slurry obtained from the suspension crystallizer 1 by using a vacuum drum filter (solid-liquid separator 2), returning 91 wt% of mother liquor obtained by separation into the suspension crystallizer 1 again for crystallization, melting 9 wt% of the solid obtained by separation and using the melted solid as a washing liquid of the vacuum drum filter (solid-liquid separator 2), wherein the temperature of the washing liquid is controlled at 4.0 DEG C
The initial crystallization temperature of the static crystallizer 3 is 4.8 ℃, the cooling rate is 0.015 ℃/min, the crystallization end point temperature is-1.5 ℃, the initial sweating temperature is 2.9 ℃, and the residual liquid accounts for 11 wt% of the initial material. The temperature rise rate of the first stage sweating is 0.027 ℃/min, the proportion of the first stage sweat mass to the initial crystallization material is 7 wt%, the second stage temperature rise rate is 0.02 ℃/min, and the second stage sweat mass is 6 wt% of the initial crystallization material. The total melting temperature was 11 ℃.
The dehydrating agent adopts a 4A molecular sieve, and the mass flow ratio of the discharged product to the circulating material is 1: 3.5.
after the purification by the process under the conditions, the content of dimethyl carbonate in the material of the crystallization finished product tank 54 is 99.996 wt%, the content of methanol is 7.8ppm, the content of moisture is 14ppm, wherein the comprehensive yield of dimethyl carbonate is 96.7%, and the cold consumption of a unit product is 278 MJ/t.
Example 2
Dimethyl carbonate produced by a certain process is adopted as a raw material, wherein the content of the dimethyl carbonate is 95.7 wt%, the moisture content is 0.7 wt%, the methanol content is 2.9 wt%, and the rest components are easily separated components which are not listed.
The raw materials firstly enter a suspension crystallizer 1 for cooling crystallization, the temperature of crystallization materials is-3 ℃, the stirring speed in the suspension crystallizer 1 is 20rpm, the temperature of an ethylene glycol aqueous solution inlet in a jacket of the suspension crystallizer 1 is-13 ℃, the temperature difference of the ethylene glycol aqueous solution entering and exiting the jacket of the suspension crystallizer 1 is 0.6 ℃, and the solid content in the suspension crystallizer 1 is 29.6 wt%. Performing solid-liquid separation on the slurry obtained from the suspension crystallizer 1 by using a horizontal multistage material-pushing centrifuge (solid-liquid separator 2), returning 86 wt% of mother liquor obtained by separation into the suspension crystallizer 1 again for crystallization, melting 8 wt% of the solid obtained by separation and using the melted solid as a washing liquid of the horizontal multistage material-pushing centrifuge (solid-liquid separator 2), controlling the temperature of the washing liquid at 4.1 DEG C
The initial crystallization temperature of the static crystallizer 3 is 4.6 ℃, the cooling rate is 0.02 ℃/min, the crystallization end point temperature is-1.7 ℃, the initial sweating temperature is 2.6 ℃, and the residual liquid accounts for 10 wt% of the initial material. The temperature rise rate of the first stage sweating is 0.03 ℃/min, the proportion of the first stage sweat mass to the initial crystallization material is 8 wt%, the second stage temperature rise rate is 0.025 ℃/min, and the second stage sweat mass is 9 wt% of the initial crystallization material. The total melting temperature was 12 deg.C
The dehydrating agent is a 5A molecular sieve, and the mass flow ratio of the discharged product to the circulating material is 1: 4.
after the purification by the process under the conditions, the content of dimethyl carbonate in the material of the crystallization finished product tank 54 is 99.991 wt%, the content of methanol is 17ppm, the content of water is 108ppm, the content of a dehydrated finished product is 99.992%, the content of methanol is 16.8ppm, and the content of water is 18ppm, wherein the comprehensive yield of dimethyl carbonate is 80.3%, and the unit product cold consumption is 284 MJ/t.
Example 3
Dimethyl carbonate produced by a certain process is adopted as a raw material, wherein the content of the dimethyl carbonate is 97.8 wt%, the moisture content is 0.2 wt%, the methanol content is 1.3 wt%, and the rest components are easily separated components, which are not listed.
The raw materials firstly enter a suspension crystallizer 1 for cooling crystallization, the temperature of crystallization materials is-2.3 ℃, the stirring speed in the suspension crystallizer 1 is 25rpm, the temperature of an ethylene glycol aqueous solution inlet in a jacket of the suspension crystallizer 1 is-10 ℃, the temperature difference of the ethylene glycol aqueous solution entering and exiting the jacket of the suspension crystallizer 1 is 0.4 ℃, and the solid content in the suspension crystallizer 1 is 28.6 wt%. Performing solid-liquid separation on the slurry obtained from the suspension crystallizer 1 by using a horizontal multistage material-pushing centrifuge (solid-liquid separator 2), returning 89 wt% of mother liquor obtained by separation into the suspension crystallizer 1 again for crystallization, melting 13 wt% of the solid obtained by separation and using the melted solid as a washing liquid of the horizontal multistage material-pushing centrifuge (solid-liquid separator 2), controlling the temperature of the washing liquid at 3.8 DEG C
The initial crystallization temperature of the static crystallizer 3 is 4.7 ℃, the cooling rate is 0.03 ℃/min, the crystallization end point temperature is-1.6 ℃, the initial sweating temperature is 3 ℃, and the residual liquid accounts for 7.6 wt% of the initial material. The temperature rise rate of the first stage sweating is 0.036 ℃/min, the proportion of the first stage sweat mass to the initial crystallization material is 5.6 wt%, the second stage temperature rise rate is 0.024 ℃/min, and the second stage sweat mass is 8.3 wt% of the initial crystallization material. The total melting temperature was 11.3 deg.C
The dehydrating agent is silica gel, and the mass flow ratio of the discharged product to the circulating material is 1: 4.5.
after the purification by the process under the conditions, the content of dimethyl carbonate in the material of the crystallization finished product tank 54 is 99.994 wt%, the content of methanol is 12ppm, the content of water is 41ppm, the content of a dehydrated finished product is 99.99%, the content of methanol is 14.3ppm, and the content of water is 11ppm, wherein the comprehensive yield of dimethyl carbonate is 86.9%, and the cold consumption of a unit product is 307 MJ/t.
Comparative example 1
The raw material in example 3 was purified only by the static crystallizer 3, and the purification process was divided into two purification steps and one recovery step, i.e. the raw material was first purified once to obtain a primary crystallized product and a primary raffinate, and then the primary crystallized product was purified once again, and the primary raffinate was purified once again to recover dimethyl carbonate therein.
After purification by the process, the content of dimethyl carbonate in a final finished product is 99.991 wt%, the content of methanol is 101ppm, the content of moisture is 201ppm, wherein the comprehensive yield of dimethyl carbonate is 76.3%, and the cold consumption of a unit product is 630 MJ/t. Compared with example 3, the unit cold consumption of the comparative example 1 is about 2 times that of example 3, the methanol content and the moisture content exceed the standard specification of electronic grade DMC, the electronic grade DMC cannot be used, and the comprehensive yield is lower than that of example 3.
Comparative example 2
The raw material in example 1 was purified by a falling film crystallizer, and the purification process was divided into two purification steps and one recovery step, i.e., the raw material was first purified once to obtain a primary crystallized product and a primary raffinate, and then the primary crystallized product was purified once again, and the primary raffinate was purified once again to recover dimethyl carbonate therein.
After the purification by the process, the content of dimethyl carbonate in a final finished product is 99.92 wt%, the content of methanol is 17ppm, the content of water is 46ppm, wherein the comprehensive yield of dimethyl carbonate is 91.6%, and the cold consumption of a unit product is 1060 MJ/t. Compared with example 1, the unit product of comparative example 2 consumes about 4 times of cold energy compared with example 1, the moisture content exceeds the standard specification of electronic grade DMC, the product can not be used as electronic grade DMC, and the comprehensive yield is lower than that of example 1.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (10)
1. The preparation device of the electronic grade dimethyl carbonate is characterized by comprising a suspension crystallizer (1), a solid-liquid separator (2), a static crystallizer (3) and a dehydration tower (4);
the suspension crystallizer (1) is connected with the dehydration tower (4) sequentially through the solid-liquid separator (2) and the static crystallizer (3).
2. The apparatus for preparing electronic grade dimethyl carbonate according to claim 1, wherein the solid-liquid separator (2) is a vacuum drum filter with washing function, a horizontal multistage pusher centrifuge or a washing tower.
3. The apparatus for preparing electronic grade dimethyl carbonate according to claim 1, wherein the static crystallizer (3) comprises a box body and internal parts; the other surfaces of the box body except the upper cover plate are formed by single-side pillow type plate corrugated heat exchange plates, wherein the pillow type surface faces to the material side; the inner part is composed of a pillow type plate corrugated heat exchange plate bundle.
4. The apparatus for preparing electronic grade dimethyl carbonate according to claim 1, wherein the dehydrating tower (4) is filled with dehydrating agent, and the dehydrating agent is one or more of 4A molecular sieve, 5A molecular sieve, silica gel and activated alumina.
5. A process for the preparation of electronic grade dimethyl carbonate using the apparatus according to any one of claims 1 to 4, comprising the steps of:
s1: introducing the DMC crude product into a suspension crystallizer (1) for suspension crystallization to obtain slurry;
s2: feeding the slurry obtained in the step S1 into a solid-liquid separator (2), and performing solid-liquid separation to obtain a mother solution and crystals;
s3: the mother liquor obtained in the step S2 is divided into two parts, one part of the mother liquor returns to the suspension crystallizer (1), and the other part of the mother liquor is discharged as waste liquor; melting the crystals obtained in the step S2 to obtain an initial crystallization material, and dividing the initial crystallization material into two parts, wherein one part of the initial crystallization material is taken as a washing liquid and conveyed to a solid-liquid separator (2), and the other part of the initial crystallization material enters a static crystallizer (3);
s4: after the other part of the initial crystallization material obtained in the step S3 is input into a static crystallizer (3), crystallization, sweating and complete melting are carried out to obtain high-purity DMC;
s5: the high-purity DMC obtained in the step S4 enters a dehydration tower (4) for dehydration to obtain electronic grade DMC;
s6: the electronic grade DMC obtained in step S5 is divided into two parts, one part of the electronic grade DMC is used as circulating material to be mixed with the high-purity DMC obtained in step S4 and enters a dehydration tower (4), and the other part of the electronic grade DMC is used as discharging product to be discharged.
6. The method of claim 5, wherein step S1 includes one or more of the following:
(i) the DMC crude product contains 95-99.5 wt% of DMC;
(ii) the temperature of the material in the suspension crystallizer (1) is-5 to 3.5 ℃;
(iii) the stirring speed of the suspension crystallizer (1) is 10-30 rpm;
(iv) the temperature difference between the refrigerant inlet temperature of the suspension crystallizer (1) and the material temperature is 4-15 ℃;
(v) the temperature difference between the refrigerant inlet and the refrigerant outlet of the suspension crystallizer (1) is 0.3-1 ℃;
(vi) the solid content of the slurry is 20-40 wt%.
7. The method of claim 5, wherein step S3 includes one or more of the following:
(i) a part of the mother liquor returned to the suspension crystallizer (1) accounts for 80-95 wt% of the mother liquor;
(ii) a part of initial crystallization materials as washing liquid accounts for 5-20 wt% of the initial crystallization materials;
(iii) the temperature of the washing liquid is 3.5-5.5 ℃.
8. The method for preparing electronic grade dimethyl carbonate according to claim 5, wherein the step S4 comprises the following steps:
s401: precooling to the initial crystallization temperature, maintaining for half an hour, and cooling to the crystallization end point temperature;
s402: after crystallization is finished, preheating to the initial sweating temperature and maintaining for half an hour, and mixing the discharged residual liquid with the initial crystallization material;
s403: heating and sweating in the first stage, and discharging sweat in the first stage to mix with the DMC crude product;
s404: raising the temperature and sweating through the second stage, discharging the sweat of the second stage and mixing the sweat with the initial crystallization material;
s405: after sweating is finished, the material is quickly heated to the full melting temperature to obtain the high-purity DMC.
9. The method of claim 8, wherein the method comprises one or more of the following:
(i) the initial crystallization temperature in the step S401 is 4.5-5.5 ℃;
(ii) the cooling rate in the step S401 is 0.008-0.03 ℃/min;
(iii) the crystallization end point temperature in the step S401 is-1.7-0 ℃;
(iv) the initial sweating temperature in the step S402 is 2.5-3.8 ℃;
(v) the residual liquid in the step S402 accounts for 5-20 wt% of the initial crystallization material;
(vi) the temperature rise rate of the first-stage temperature rise and sweating in the step S403 is 0.02-0.05 ℃/min;
(viii) the sweat in the first stage in the step S403 accounts for 5-10 wt% of the initial crystallization material;
(ix) the temperature rise rate of the second-stage temperature rise sweating in the step S404 is 0.01-0.04 ℃/min;
(xi) The second stage sweat in the step S404 accounts for 5-10 wt% of the initial crystallization material;
(xii) The total melting temperature in the step S405 is 8-15 ℃.
10. The method for preparing electronic grade dimethyl carbonate according to claim 5, wherein the mass flow ratio of the discharged product to the circulating material in the step S6 is 1: 2-1: 6.
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| CN115463444A (en) * | 2022-09-30 | 2022-12-13 | 东华工程科技股份有限公司 | Preparation system and preparation process for preparing ultrapure dimethyl carbonate |
| CN116983707A (en) * | 2023-09-27 | 2023-11-03 | 天津乐科节能科技有限公司 | Solid-liquid countercurrent heat-mass exchange purification tower and purification method |
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