CN111285755B - Separation method of reaction product for preparing dimethyl ether by methanol dehydration - Google Patents
Separation method of reaction product for preparing dimethyl ether by methanol dehydration Download PDFInfo
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Abstract
The invention relates to a separation method of reaction products of preparing dimethyl ether by dehydrating methanol, wherein the reaction products discharged from a methanol dehydration reactor are cooled and enter a gas-liquid separation tank, liquid-phase materials enter a dimethyl ether refining tower, the dimethyl ether refining tower is provided with a top pulling section, a refining section, a washing impurity removal section and a stripping section from top to bottom, and a solution containing ethanol and ester impurities is extracted from the side line of the washing impurity removal section and is sent to an ethanol refining unit; the dimethyl ether refining tower topping gas, the flash gas of the gas-liquid separation tank and the purge gas of the carbonylation unit are converged and enter a tail gas washing tower, and the tail gas after removing the oxide can be sent to a PSA unit to recycle the synthesis gas after being washed by the lower alcohol-water solution and the upper washing water. Compared with the prior art, the invention solves the problem that impurities brought by the raw material methanol are accumulated in the system and the problem that organic matters in the tail gas are recovered to meet the requirement of downstream PSA treatment, is beneficial to reducing energy consumption and material loss, reduces the requirement and size of pipeline materials of related equipment such as a reactor, a rectifying tower and the like, and saves investment.
Description
Technical Field
The invention relates to the field of chemical separation, in particular to a separation method of a reaction product for preparing dimethyl ether by methanol dehydration.
Background
Ethanol is an important basic chemical raw material, and can be used for synthesizing intermediates of various chemical products, such as paint, spice, dye, medicine and the like. Meanwhile, in the fuel field, gasoline and diesel containing ethanol are actively popularized and applied by various countries in the world, and the fuel ethanol becomes an important part of the international fuel energy industry.
At present, the domestic fuel ethanol production mainly takes grains such as corn and rice as raw materials, but as the grain price rises and the ethanol price rises continuously, the production of absolute ethanol by adopting a non-grain process route is a good supplement.
The methanol is used as a raw material, the methanol is dehydrated to generate dimethyl ether, the dimethyl ether and CO generate carbonylation reaction to produce methyl acetate, and the hydrogenation of the methyl acetate to generate the ethanol is a good technical route with prospect.
At present, the process for preparing dimethyl ether by gas-phase dehydration of methanol in China is mature, a plurality of sets of running devices are provided, and domestic units with the technology also have a plurality of companies such as Shanghai Petroleum chemical research institute, southwest chemical design institute Co., ltd., new Olympic New Energy (Beijing) science and technology Co., ltd., and the like; shanghai institute of petrochemical engineering patent CN101941891B discloses a method for preparing dimethyl ether by methanol dehydration, wherein a dimethyl ether rectifying tower is not provided with an impurity extraction outlet, and a methanol solution in a tower kettle directly returns to a stripping tower; meanwhile, the tail gas washing tower is only provided with a section of washing by adopting the kettle liquid of the dimethyl ether rectifying tower kettle as the washing liquid. The southwest chemical design institute CN10705688A discloses a production system and a production process for preparing dimethyl ether from methanol, wherein a dimethyl ether rectifying tower is not provided with an impurity extraction port, and a methanol solution at a tower kettle directly returns to a stripping tower; meanwhile, the tail gas washing tower does not adopt the tower bottom liquid of the dimethyl ether rectification tower, but uses the raw material methanol as an absorbent, and is not provided with a water washing section. The existing dimethyl ether device has no subsequent process for producing ethanol by reaction of dimethyl ether and synthesis gas, and does not need to consider the coupling with subsequent process units, for example, methanol is produced while producing ethanol after methyl acetate hydrogenation, so the methanol needs to be recycled to a unit for preparing dimethyl ether by methanol dehydration, and dimethyl ether in purge gas of a carbonylation unit also needs to be recovered, and the like.
The technical problem reports and related literature patents related to the rectification process in the reaction for synthesizing dimethyl ether from methanol in the complete process for preparing ethanol from dimethyl ether by methanol are not considered completely. In the practical application process, when the methanol and the synthesis gas are used as raw materials for producing the ethanol, because the circulating methanol returned from the ethanol refining unit contains some impurities, the impurities are circularly accumulated in the dimethyl ether preparation unit by methanol dehydration, so that the quality indexes of a methanol dehydration reaction and a dimethyl ether product are influenced, and the impurities contained in the dimethyl ether can cause the selectivity of dimethyl ether carbonylation reaction to be reduced, thereby causing chain adverse reactions.
The invention solves the technical problems that: methanol-to-dimethyl ether, dimethyl ether carbonylation, methyl acetate hydrogenation and ethanol refining are taken as a complete process system, impurities brought by circulating materials are considered, and the problem of accumulation of the impurities in the system is solved; and the effective components in the tail gas of the whole device are recovered under the premise of not adding new equipment by combining the characteristics of the upstream and downstream processes, and the washed tail gas can directly enter a PSA unit for synthesis gas recovery.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a separation method of a reaction product for preparing dimethyl ether by methanol dehydration.
The purpose of the invention can be realized by the following technical scheme:
a separation method of reaction products of dimethyl ether prepared by methanol dehydration comprises the following steps:
1) Raw material methanol and circulating methanol from an ethanol refining unit are used as reaction raw materials and enter a methanol dehydration reactor for reaction, the obtained reaction product is condensed and then enters a gas-liquid separation tank for gas-liquid separation, the separated gas-phase material enters a tail gas washing tower, and the liquid-phase material enters the dimethyl ether refining tower;
2) The dimethyl ether refining tower comprises a top-drawing section, a rectifying section, a washing impurity-removing section and a stripping section, wherein condensed liquid of gas phase materials at the top of the dimethyl ether refining tower is totally refluxed into the tower after being condensed, and the produced top-drawing gas of the dimethyl ether refining tower enters the tail gas washing tower; a dimethyl ether product is collected from the lateral line at the lower part of the topping section of the dimethyl ether refining tower; extracting impurity solution containing ethanol and esters from the lower side line of the impurity removal section of the dimethyl ether refining tower; tower bottom liquid containing methanol and water is extracted from a tower bottom of the dimethyl ether refining tower, the tower bottom liquid is sent to a methanol stripping tower for vaporization and separation, a gas phase material containing the methanol from the top of the methanol stripping tower is sent to a methanol dehydration reactor, and process wastewater is continuously discharged from the tower bottom of the methanol stripping tower;
3) And washing the gas-phase material and the dimethyl ether refining tower topping gas generated by the gas-liquid separation tank by using washing water or washing water and tower bottom liquid of the dimethyl ether refining tower in the tail gas washing tower, discharging tail gas from the tower top of the tail gas washing tower, and allowing the tower bottom liquid of the tail gas washing tower to enter the dimethyl ether refining tower from the washing impurity removal section.
The methanol entering the methanol dehydration reactor comprises raw material methanol and circulating methanol from an ethanol refining unit, and the total mass content of ethanol and esters in the methanol entering the methanol dehydration reactor is less than or equal to 3%. The circulating methanol contains methyl acetate, ethyl acetate and ethanol, wherein the total content of the methyl acetate and the ethyl acetate is 500-2000ppm, and the content of the ethanol is 600-1500ppm.
The impurity solution extracted from the side line at the lower part of the washing and impurity removing section of the dimethyl ether refining tower is sent to the ethanol refining unit; the circulating methanol generated by the ethanol refining unit enters from the top of the methanol stripping tower.
Gas-phase materials and the topping gas of the dimethyl ether refining tower, which are generated by the gas-liquid separation tank in the tail gas washing tower, are washed by the tower bottom liquid of the dimethyl ether refining tower and then washed by washing water; the washing water of the tail gas washing tower comes from the process wastewater of the methanol stripping tower kettle or fresh water outside the device.
The tail gas washing tower washes purge gas containing CO from a dimethyl ether carbonylation unit, wherein the mass content of dimethyl ether in the purge gas is 6-10%, the mass content of methyl acetate is 4-6%, and the mass content of CO is 68-80%;
and the gas-phase material produced by the gas-liquid separation tank, the topping gas of the dimethyl ether refining tower and the purge gas form mixed gas, the mixed gas enters a tail gas washing tower, and tail gas produced at the top of the tail gas washing tower is used for recovering CO by a PSA process.
The number of theoretical plates of the tail gas washing tower is 10-20, and the mass ratio of the tower bottom liquid of the dimethyl ether refining tower to the mixed gas is 3-6; the mass ratio of the washing water consumption to the mixed gas is 0.1-0.3.
The content of methyl acetate, dimethyl ether and methanol in the tail gas at the top of the tail gas washing tower is less than or equal to 1000ppm, 600ppm and 10ppm respectively.
The number of theoretical plates of the dimethyl ether refining tower is 20-30, and an impurity side draw-out port is arranged at the 18 th to 25 th theoretical plates counted from the top of the dimethyl ether refining tower to draw out the impurity solution; the mass ratio of the produced amount of the impurity solution to the produced amount of the dimethyl ether product is 0.0075-0.0225; the mass content of esters in the impurity solution is 15-30%, and the mass content of ethanol is 1.5-5%.
The dimethyl ether product is extracted from the 2 nd to 5 th theoretical plate side lines counted from the top of the dimethyl ether refining tower, the mass content of the dimethyl ether in the dimethyl ether product is more than or equal to 99.5 percent, and the contents of methanol and water are less than or equal to 500ppm.
The separation method can be applied to a method for preparing absolute ethyl alcohol from methanol by dimethyl ether, specifically, the dimethyl ether is prepared by methanol dehydration, carbonylation reaction is carried out on the dimethyl ether and CO to generate methyl acetate, the methyl acetate is hydrogenated to produce methanol and ethanol, the absolute ethyl alcohol and the methanol are obtained after the reaction products are rectified and separated by the ethanol, and the methanol is recycled; specifically, the process method comprises a dimethyl ether preparation unit by methanol dehydration, a dimethyl ether carbonylation unit, a methyl acetate hydrogenation unit and an ethanol refining unit; raw material methanol is subjected to dimethyl ether preparation through the methanol dehydration dimethyl ether preparation unit to obtain dimethyl ether, the dimethyl ether and synthesis gas react in the dimethyl ether carbonylation unit to obtain methyl acetate, the methyl acetate and the synthesis gas react in the methyl acetate hydrogenation unit to obtain reaction liquid containing ethanol, and the reaction liquid enters an ethanol refining unit to be separated to obtain refined ethanol, circulating methanol and esters.
The method comprises the steps of arranging 4 sections on a dimethyl ether refining tower, sequentially arranging a top drawing section, a refining section, a washing impurity removal section and a stripping section from top to bottom, extracting an ethanol and ester impurity-containing solution from the side line of the washing impurity removal section, sending the ethanol and ester impurity-containing solution to an ethanol refining unit, and returning the ester after rectification separation to a hydrogenation reactor; two sections of a tail gas washing tower are arranged, the lower section is washed by alcohol water solution, the upper section is washed by water, the topping gas of the dimethyl ether refining tower, the flash evaporation gas of the gas-liquid separation tank and the purge gas of the carbonylation unit are converged and enter the tail gas washing tower, and the tail gas after washing and removing the oxide can be sent to a PSA unit to recycle the synthesis gas. The method organically combines all units of the device for synthesizing the ethanol from the methanol by the dimethyl ether, solves the problem that impurities brought by the methanol as the raw material are accumulated in a system and the problem that organic matters in tail gas are recovered to meet the requirement of downstream PSA treatment, is favorable for reducing energy consumption and material loss, reduces the requirements on the material and the size of pipelines of related equipment such as a reactor and a rectifying tower, and saves investment.
Compared with the prior art, the invention has the advantages that:
1) Because the raw material methanol contains trace impurities such as ethanol, methyl acetate, ethyl acetate and the like, the impurities are easy to accumulate in a system in a unit for preparing dimethyl ether by dehydrating methanol, a washing impurity removal section is arranged on the existing dimethyl ether rectifying tower, a material with the highest impurity content in the tower is extracted from the lower part of the washing impurity removal section and is used as an outlet of system impurities, and the discharged impurities are sent to an ethanol refining unit for recovery, so that the accumulation of the impurities in a dimethyl ether synthesis and rectification system is avoided, the COD value of discharged wastewater can be effectively controlled, and the energy consumption and equipment investment are saved;
2) The existing mature process for preparing dimethyl ether by methanol gas phase dehydration is utilized, the tail gas washing tower is divided into two sections for absorption by utilizing the existing equipment, the lower section uses alcohol aqueous solution to absorb ester and dimethyl ether in the tail gas, the upper section uses water to absorb alcohol and the like carried in the tail gas, so that the ester, dimethyl ether and alcohol are all recovered, the product loss is reduced, the raw material consumption of unit products is reduced, and the washed tail gas can directly enter a PSA unit to recover CO raw material gas.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a block diagram of a process for preparing an absolute ethanol product from methanol via dimethyl ether;
in the figure, 1 is a reaction product of dimethyl ether prepared by methanol dehydration, 2 is a gas-liquid separation tank, 3 is a gas-phase material of the gas-liquid separation tank, 4 is a liquid-phase material of the gas-liquid separation tank, 5 is a dimethyl ether refining tower, 6 is an impurity solution, 7 is a material of a dimethyl ether refining tower bottom entering a methanol stripping tower, 8 is a material of a washing tower entering the dimethyl ether refining tower bottom, 9 is a dimethyl ether product, 10 is a dimethyl ether refining tower topping gas, 11 is a purge gas, 12 is process wastewater, 13 is a mixed gas, 14 is a tail gas washing tower, 15 is a washing tower bottom, 16 is a tail gas, 17 is a methanol stripping tower, and 18 is a methanol stripping tower bottom.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the concept of the invention. All falling within the scope of the present invention.
Example 1
A separation method for preparing dimethyl ether reaction product by methanol dehydration, the separation process is shown as the flow chart of figure 1, the separation method can be applied to the method for preparing absolute ethyl alcohol product by dimethyl ether from methanol, the specific process flow chart is shown as figure 2, the raw material methanol is prepared into dimethyl ether by a methanol dehydration dimethyl ether unit from a boundary region, the methanol dehydration dimethyl ether unit can also process carbonylation unit purge gas from a dimethyl ether carbonylation unit, generate tail gas to remove PSA and recover CO, the methanol dehydration dimethyl ether unit generates process wastewater to be discharged from the boundary region, and the generated ethanol, ester and other impurity produced liquid is sent to an ethanol refining unit; dimethyl ether and synthesis gas react in a dimethyl ether carbonylation unit to obtain methyl acetate, methyl acetate and synthesis gas react in a methyl acetate hydrogenation unit to obtain ethanol, methanol and the like, reaction liquid of the ethanol, the methanol and the like is sent to an ethanol refining unit to be separated to obtain an absolute ethanol product, circulating methanol and esters, the circulating methanol is returned to a methanol dehydration dimethyl ether preparation unit to continue to react, and the esters are returned to a methyl acetate hydrogenation unit to continue to react.
The specific process is that the raw material methanol from a battery limits is 9400t/h, and the mass composition is as follows: 99.5% of methanol, 0.5% of water and 9090kg/h of circulating methanol from an ethanol refining unit, wherein the mass composition of the circulating methanol is as follows: 99.76 percent of methanol, 0.11 percent of ethyl acetate, 0.05 percent of methyl acetate and 0.08 percent of ethanol; the two materials are gasified and mixed and then enter a reactor through heat to generate dehydration reaction, a reaction product 1 for preparing dimethyl ether by methanol dehydration enters a gas-liquid separation tank 2 after being cooled, a liquid-phase material 4 of the gas-liquid separation tank enters a dimethyl ether refining tower 5, the number of theoretical plates of the dimethyl ether refining tower 5 is 25, a tower bottom liquid 15 of a tail gas washing tower enters from the 17 th theoretical plate from the number of the top of the dimethyl ether refining tower 5, an impurity extraction port is arranged at the 21 st theoretical plate from the number of the top of the tower, and a methanol water solution containing impurities such as ester and ethanol with the flow rate of 210kg/h, namely an impurity solution 6, wherein the mass composition of the impurity solution 6 is as follows: dimethyl ether 7.2%, methyl acetate 14.2%, methanol 36.1%, ethyl acetate 6.1%, ethanol 2.6%, and water 33.8%; the impurity solution 6 is sent into an ethanol refining unit, a rectifying tower is not required to be added to separate the solution, and the separated methyl acetate and ethyl acetate are returned to a hydrogenation unit to be used as intermediate raw materials and further converted into alcohol. The dimethyl ether product 9 is extracted from the 4 th theoretical plate counted from the top of the dimethyl ether refining tower 5, and the flow rate of the dimethyl ether product 9 is as follows: 13205kg/h; the composition by mass is as follows: 99.87 percent of dimethyl ether, 350ppm of methyl acetate and 150ppm of methanol; and a part of the bottom liquid of the tower bottom is dimethyl ether refining tower bottom liquid, the dimethyl ether refining tower bottom liquid enters a methanol stripping tower material 7, and the material returns to a methanol stripping tower 17.
Gas phase material 3 of the gas-liquid separation tank, dimethyl ether refining overhead gas 10 and purge gas 11 from the carbonylation unit are converged to form mixed gas 13, the mixed gas enters a tail gas washing tower 14, wherein the flow of the purge gas 11 of the carbonylation unit is 550kg/h, and the mass composition is as follows: 5.5% of nitrogen, 69% of carbon monoxide, 11% of argon, 6.5% of dimethyl ether, 5.8% of methyl acetate and 2.2% of carbon dioxide; the flow rate of the mixed gas 13 is 1033kg/h, and the mass composition is as follows: 2.9 percent of nitrogen, 40 percent of carbon monoxide, 6 percent of argon, 44 percent of dimethyl ether, 3.8 percent of methyl acetate and 3.2 percent of carbon dioxide. The number of theoretical plates of a tail gas washing tower 14 is 15, the tower bottom liquid of the dimethyl ether refining tower enters a tail gas washing tower material 8, the material is cooled to 40 ℃ and then enters from a 10 th theoretical plate counted from the top of the tail gas washing tower 14, the use amount of the material 8 of the dimethyl ether refining tower bottom liquid entering the tail gas washing tower is 3500kg/h, the material is used as an absorbent methanol solution to absorb ester and dimethyl ether in tail gas, the process wastewater 12 from a methanol stripping tower bottom liquid 18 is used as an absorbent at the top of the tail gas washing tower 14, the use amount of the process wastewater 12 is 300kg/h, and the methanol solution and the washed tail gas are returned to a dimethyl ether refining tower 5 as the tower bottom liquid 15 of the tail gas washing tower; the flow rate of the tail gas 16 after being washed by the methanol solution and water is 500kg/h, and the tail gas comprises the following components in percentage by mass: 5.7 percent of nitrogen, 77.5 percent of CO, 12.5 percent of argon, 3 percent of carbon dioxide, 900ppm of methyl acetate and 300ppm of dimethyl ether, has no methanol and ethanol, basically recovers all the oxides, and can be sent into a PSA unit to recover CO raw material gas.
By adopting the separation process, the content of ester and ethanol in a dimethyl ether synthesis and rectification system is reduced, the accumulation of impurities is avoided, and the feed quality of the methanol dehydration reactor comprises the following components: 97.2% of methanol, 1.3% of water, 1.0% of ethanol, 0.3% of methyl acetate and 0.1% of ethyl acetate, and the content of impurities such as ester, ethanol and the like is lower than 2%, so that the energy consumption of products is saved. The specific product energy consumption (steam, recycled water, electricity) and the ton of dimethyl ether methanol consumption and the dimethyl ether dehydration reactor feed flow in this example are listed in table 1.
In the embodiment, the impurity solution extracted from the side line at the lower part of the impurity removal section of the dimethyl ether refining tower is sent to the ethanol refining unit, ethanol and ester substances in the impurities are recovered, the utilization rate of raw materials is improved, and organic matters such as esters in the tower kettle of the dimethyl ether refining tower are reduced, so that the organic matters in the process wastewater discharged from the tower kettle of the methanol stripping tower are reduced, and the COD value of the discharged wastewater can be effectively controlled; the circulating methanol generated by the ethanol refining unit enters from the top of the methanol stripping tower, so that the methanol in the ethanol refining unit is recycled under the condition of not increasing equipment; the dimethyl ether carbonylation unit generates purge gas containing CO, the purge gas is washed by a tail gas washing tower, and oxide in the purge gas is basically and completely recovered; and the tail gas at the top of the tower meets the requirement of entering a PSA unit, and the CO feed gas is recovered.
Example 2
The process flow diagram of the embodiment is the same as that of the embodiment 1, and the specific process flow is as follows:
the circulating methanol comprises the following components in percentage by mass: 99.76% of methanol, 0.15% of ethyl acetate, 0.03% of methyl acetate and 0.06% of ethanol; the number of theoretical plates of the dimethyl ether refining tower 5 is 28, washing water enters from the 20 th theoretical plate counted from the top of the tower, an impurity extraction port is arranged at the 24 th theoretical plate counted from the top of the tower 5 in the dimethyl ether tower, and methanol aqueous solution containing impurities such as ester, ethanol and the like with the flow rate of 200kg/h is extracted, and the methanol aqueous solution comprises the following components by mass: 2.6% of dimethyl ether, 9.9% of methyl acetate, 41% of methanol, 7.8% of ethyl acetate, 3.0% of ethanol and 36.3% of water; the methanol solution is sent to an ethanol refining unit, a rectifying tower is not required to be added to separate the solution, and the separated methyl acetate and ethyl acetate are returned to a hydrogenation unit to be used as intermediate raw materials and further converted into alcohol. The dimethyl ether product is extracted from the 5 th theoretical plate counted from the top of the tower, and the flow rate of the dimethyl ether product is as follows: 13210kg/h, mass composition: 99.9 percent, 300ppm of methyl acetate and 150ppm of methanol; and returning the bottom kettle liquid to the methanol stripping tower.
The carbonylation unit purge gas 11 comprises the following components by mass: 5.2% of nitrogen, 70% of carbon monoxide, 10.8% of argon, 7% of dimethyl ether, 5% of methyl acetate and 2% of carbon dioxide; the flow rate of the mixed gas is 1033kg/h, and the mass composition is as follows: 2.8% of nitrogen, 38.6% of carbon monoxide, 5.8% of argon, 45.3% of dimethyl ether, 2.5% of methyl acetate and 4.1% of carbon dioxide. The number of theoretical plates of a tail gas washing tower 14 is 12, dimethyl ether refining tower bottom liquid enters a tail gas washing tower material 8 from the top of the tail gas washing tower to the 8 th theoretical plate, the material is mainly methanol solution, the amount of the dimethyl ether refining tower bottom liquid entering the tail gas washing tower material 8 is 3500kg/h, boiler water used outside a boundary area is adopted as an absorbent at the top of the tail gas washing tower 14, the amount of water is 250kg/h, and the washing water of the tail gas after the methanol solution and the water are absorbed is returned to a dimethyl ether refining tower 5 as tail gas washing tower bottom liquid 15; the flow rate of tail gas 16 after methanol solution and water washing is 507kg/h, and the mass composition is as follows: 5.6 percent of nitrogen, 76.9 percent of CO, 11.6 percent of argon, 3.9 percent of carbon dioxide, 1000ppm of methyl acetate and 350ppm of dimethyl ether, has no methanol and ethanol, basically recycles all the oxygenates, and can be sent into a PSA unit to recycle CO raw material gas.
By adopting the separation process, the content of ester and ethanol in a dimethyl ether synthesis and rectification system is reduced, the accumulation of impurities is avoided, and the feed quality of the dehydration reactor comprises the following components: 96.7% of methanol, 1.2% of water, 1.3% of ethanol, 0.4% of methyl acetate and 0.2% of ethyl acetate, and the content of impurities such as ester, ethanol and the like is lower than 2%, so that the energy consumption of products is saved. The specific product energy consumption (steam, recycled water, electricity) and the ton of dimethyl ether methanol consumption and dimethyl ether dehydration reactor feed flow for this example 2 are listed in table 1.
Example 3
The process flow diagram of the embodiment is the same as that of the embodiment 1, the raw material methanol from the battery limits is 9400t/h, and the mass composition is as follows: 99.5% of methanol, 0.5% of water and 9090kg/h of circulating methanol from an ethanol refining unit, wherein the mass composition of the methanol is as follows: 99.76 percent of methanol, 0.11 percent of ethyl acetate, 0.05 percent of methyl acetate and 0.08 percent of ethanol; the two materials are gasified and mixed, then enter a reactor through heat to carry out dehydration reaction, a reaction product 1 for preparing dimethyl ether by methanol dehydration enters a gas-liquid separation tank 2 after being cooled, a liquid-phase material 4 of the gas-liquid separation tank enters a dimethyl ether refining tower 5, the dimethyl ether refining tower 5 is provided with 30 theoretical plates, the 5 th theoretical plate counted from the top of the tower is provided with a dimethyl ether product side-draw outlet, the product mass flow is 13188kg/h, and the mass content of dimethyl ether is 99.9%; the 25 th theoretical plate counted from the top of the tower is provided with an impurity extraction port, and the extracted methanol water solution containing impurities such as ester, ethanol and the like with the flow rate of 250kg/h, namely the impurity solution 6, comprises the following components by mass: dimethyl ether 7.4%, methyl acetate 12.2%, methanol 37.5%, ethyl acetate 5.5%, ethanol 2.4%, and water 35%;
the carbonylation unit purge gas 11 comprises the following components by mass: 5.2% of nitrogen, 70% of carbon monoxide, 10.8% of argon, 7% of dimethyl ether, 5% of methyl acetate and 2% of carbon dioxide; the flow rate of the mixed gas is 1033kg/h, and the mass composition is as follows: 2.8% of nitrogen, 38.6% of carbon monoxide, 5.8% of argon, 45.3% of dimethyl ether, 2.5% of methyl acetate and 4.1% of carbon dioxide. 20 theoretical plates are arranged on a tail gas washing tower 14, methanol aqueous solution from the bottom of a dimethyl ether rectification tower enters from the 13 th theoretical plate counted from the top of the tower, the amount of a methanol solution absorbent is 4000kg/h, process wastewater from the dimethyl ether stripping tower is adopted as an absorbent on the top of the tower, the flow is 300kg/h, and after two-stage washing of tail gas at the top of the tower, the mass flow is 499.5kg/h and the mass composition is as follows: 5.7 percent of nitrogen, 77.5 percent of CO, 12.5 percent of argon, 3 percent of carbon dioxide, 890ppm of methyl acetate and 160ppm of dimethyl ether, and no methanol or ethanol exists. Feed flow to the dehydration reactor: 23731kg/h, its mass composition is: 97.43% of methanol, 1.05% of water, 1.05% of ethanol, 0.38% of methyl acetate and 0.09% of ethyl acetate, the content of impurities such as ester, ethanol and the like is lower than 2%, and the impurities are not accumulated in the system, so that the energy consumption of the product is saved. Energy consumption per unit product (steam, recycled water, electricity) and ton dimethyl ether methanol consumption and dimethyl ether dehydration reactor feed flow in table 1 of this example 3.
Example 4
A separation method of dimethyl ether reaction products by methanol dehydration is disclosed, the separation process is shown as a flow chart in figure 1, the separation method can be applied to a method for preparing absolute ethanol products by methanol through dimethyl ether, a specific process flow chart is shown in figure 2, raw material methanol is prepared into dimethyl ether through a dimethyl ether unit by methanol dehydration, dimethyl ether and synthetic gas are reacted in a dimethyl ether carbonylation unit to obtain methyl acetate, the methyl acetate and the synthetic gas are reacted in a methyl acetate hydrogenation unit to obtain reaction liquid containing ethanol, and the reaction liquid enters an ethanol refining unit to be separated to obtain refined ethanol, circulating methanol and esters.
The specific process is that the raw material methanol from a battery limits is 9400t/h, and the mass composition is as follows: 99.5% of methanol, 0.5% of water and 9090kg/h of circulating methanol from an ethanol refining unit, wherein the mass composition of the circulating methanol is as follows: 99.74 percent of methanol, 0.11 percent of ethyl acetate, 0.09 percent of methyl acetate and 0.06 percent of ethanol; the two materials are gasified and mixed and then enter a reactor through heat to generate dehydration reaction, a reaction product 1 for preparing dimethyl ether by methanol dehydration enters a gas-liquid separation tank 2 after being cooled, a liquid-phase material 4 of the gas-liquid separation tank enters a dimethyl ether refining tower 5, the number of theoretical plates of the dimethyl ether refining tower 5 is 20, a tower bottom liquid 15 of a tail gas washing tower enters from 14 th theoretical plates from the top of the dimethyl ether refining tower 5, an impurity extraction port is arranged at the 18 th theoretical plate from the top of the tower, and a methanol water solution containing impurities such as ester and ethanol with the flow rate of 99.5kg/h, namely an impurity solution 6, is extracted, and the mass composition of the impurity solution 6 is as follows: dimethyl ether 4.7%, methyl acetate 17.8%, methanol 30.1%, ethyl acetate 12.2%, ethanol 4.5%, and water 30.5%; the impurity solution 6 is sent to an ethanol refining unit, a rectifying tower is not required to be additionally arranged to separate the solution, and the separated methyl acetate and ethyl acetate are returned to a hydrogenation unit to be used as intermediate raw materials to be further converted into alcohol. The dimethyl ether product 9 is extracted from the 2 nd theoretical plate counted from the top of the dimethyl ether refining tower 5, and the flow rate of the dimethyl ether product 9 is as follows: 13264kg/h; the composition by mass is as follows: 99.67% of dimethyl ether, 700ppm of methyl acetate and 400ppm of methanol; and a part of the bottom liquid of the tower bottom is dimethyl ether refining tower bottom liquid, the dimethyl ether refining tower bottom liquid enters a methanol stripping tower material 7, and the material returns to a methanol stripping tower 17.
Gas phase material 3 of the gas-liquid separation tank, dimethyl ether refining tower topping gas 10 and purge gas 11 from the carbonylation unit are converged to form mixed gas 13 which enters a tail gas washing tower 14, wherein the flow of the purge gas 11 of the carbonylation unit is 550kg/h, and the mass composition is as follows: 4% of nitrogen, 80% of carbon monoxide, 3% of argon, 6% of dimethyl ether, 6% of methyl acetate and 1% of carbon dioxide; the flow rate of the mixed gas 13 is 991.8kg/h, and the mass composition is as follows: 2.3% of nitrogen, 47.4% of carbon monoxide, 1.8% of argon, 42% of dimethyl ether, 3.4% of methyl acetate and 2.3% of carbon dioxide. The number of theoretical plates of a tail gas washing tower 14 is 10, the tower bottom liquid of the dimethyl ether refining tower enters a tail gas washing tower material 8, the material is cooled to 40 ℃ and then enters from a 5 th theoretical plate counted from the top of the tail gas washing tower 14, the use amount of the material 8 of the dimethyl ether refining tower entering the tail gas washing tower is 2975.4kg/h, the material is used as an absorbent methanol solution to absorb ester and dimethyl ether in tail gas, the process wastewater 12 from a methanol stripping tower bottom liquid 18 is used as an absorbent at the top of the tail gas washing tower 14, the use amount of the process wastewater 12 is 298kg/h, and the methanol solution and the water-washed tail gas are returned to a dimethyl ether refining tower 5 as a tail gas washing tower bottom liquid 15; the flow rate of the tail gas 16 after being washed by the methanol solution and water is 516kg/h, and the tail gas comprises the following components in percentage by mass: 4.3 percent of nitrogen, 86.8 percent of CO, 3.2 percent of argon, 2.2 percent of carbon dioxide, 1000ppm of methyl acetate, 540ppm of dimethyl ether, 10ppm of methanol, no ethanol and basically all oxides are recovered, and the oxygen-containing compounds can be sent into a PSA unit to recover CO feed gas.
By adopting the separation process, the content of ester and ethanol in a dimethyl ether synthesis and rectification system is reduced, the accumulation of impurities is avoided, and the feed quality of the methanol dehydration reactor comprises the following components: 95% of methanol, 1.6% of water, 1.5% of ethanol, 0.8% of methyl acetate and 0.5% of ethyl acetate, and the content of impurities such as ester, ethanol and the like is lower than 3%, so that the energy consumption of products is saved.
Example 5
A separation method of a reaction product of dimethyl ether prepared by methanol dehydration is disclosed, the separation process is shown as a flow chart in figure 1, the separation method can be applied to a method for preparing an absolute ethyl alcohol product by dimethyl ether from methanol, a specific process flow chart is shown in figure 2, dimethyl ether is prepared by a dimethyl ether preparation unit through methanol dehydration of raw material methanol, methyl acetate is obtained by reaction of dimethyl ether and synthetic gas in a dimethyl ether carbonylation unit, reaction liquid containing ethanol is obtained by reaction of methyl acetate and synthetic gas in a methyl acetate hydrogenation unit, and the reaction liquid enters an ethanol refining unit to be separated to obtain refined ethanol, recycled methanol and esters.
The specific process is that the raw material methanol from a battery limits is 9400t/h, and the mass composition is as follows: 99.5% of methanol, 0.5% of water and 9090kg/h of circulating methanol from an ethanol refining unit, wherein the mass composition of the circulating methanol is as follows: 99.8% of methanol, 0.03% of ethyl acetate, 0.02% of methyl acetate and 0.15% of ethanol; the two streams of materials are gasified and mixed and then enter a reactor through heat to generate dehydration reaction, a reaction product 1 for preparing dimethyl ether by methanol dehydration enters a gas-liquid separation tank 2 after being cooled, a liquid-phase material 4 of the gas-liquid separation tank enters a dimethyl ether refining tower 5, the number of theoretical plates of the dimethyl ether refining tower 5 is 30, a tail gas washing tower bottom liquid 15 enters from the 17 th theoretical plate from the top of the dimethyl ether refining tower 5, an impurity extraction port is arranged at the 25 th theoretical plate from the top of the tower, and a methanol water solution containing impurities such as ester and ethanol with the flow rate of 297kg/h is extracted, namely an impurity solution 6, wherein the mass composition of the impurity solution 6 is as follows: 2.5% of dimethyl ether, 14.5% of methyl acetate, 40% of methanol, 5.1% of ethyl acetate, 1.9% of ethanol and 35.7% of water; the impurity solution 6 is sent into an ethanol refining unit, a rectifying tower is not required to be added to separate the solution, and the separated methyl acetate and ethyl acetate are returned to a hydrogenation unit to be used as intermediate raw materials and further converted into alcohol. The dimethyl ether product 9 is extracted from the 5 th theoretical plate counted from the top of the dimethyl ether refining tower 5, and the flow rate of the dimethyl ether product 9 is as follows: 13203kg/h; the composition by mass is as follows: 99.9 percent of dimethyl ether, 280ppm of methyl acetate and 120ppm of methanol; and a part of the bottom liquid of the tower bottom is dimethyl ether refining tower bottom liquid, the dimethyl ether refining tower bottom liquid enters a methanol stripping tower material 7, and the material returns to a methanol stripping tower 17.
Gas phase material 3 of the gas-liquid separation tank, dimethyl ether refining overhead gas 10 and purge gas 11 from the carbonylation unit are converged to form mixed gas 13, the mixed gas enters a tail gas washing tower 14, wherein the flow of the purge gas 11 of the carbonylation unit is 550kg/h, and the mass composition is as follows: 7% of nitrogen, 68% of carbon monoxide, 8% of argon, 10% of dimethyl ether, 4% of methyl acetate and 3% of carbon dioxide; the flow rate of the mixed gas 13 is 1085kg/h, and the mass composition is as follows: 3.7% of nitrogen, 37% of carbon monoxide, 4.3% of argon, 47.4% of dimethyl ether, 2% of methyl acetate and 4.9% of carbon dioxide. The number of theoretical plates of a tail gas washing tower 14 is 20, the tower bottom liquid of the dimethyl ether refining tower enters a tail gas washing tower material 8, after being cooled to 40 ℃, the tower bottom liquid of the tail gas washing tower enters from a 12 th theoretical plate counted from the top of the tail gas washing tower 14, the use amount of the material 8 of the dimethyl ether refining tower entering the tail gas washing tower is 6510kg/h, the material is used as an absorbent methanol solution to absorb ester and dimethyl ether in tail gas, the process wastewater 12 from a methanol stripping tower bottom liquid 18 is used as an absorbent at the top of the tail gas washing tower 14, the use amount of the process wastewater 12 is 109kg/h, and the methanol solution and the water after washing the tail gas return to a dimethyl ether refining tower 5 as a tail gas washing tower bottom liquid 15; the flow rate of the tail gas 16 after being washed by the methanol solution and water is 497kg/h, and the mass composition is as follows: 7.7 percent of nitrogen, 76.8 percent of CO, 8.8 percent of argon, 4.9 percent of carbon dioxide, 750ppm of methyl acetate, 600ppm of dimethyl ether, 10ppm of methanol, no ethanol and basically all oxides are recovered, and the oxygen-containing compounds can be sent into a PSA unit to recover CO feed gas.
By adopting the separation process, the content of ester and ethanol in a dimethyl ether synthesis and rectification system is reduced, the accumulation of impurities is avoided, and the feeding quality of the methanol dehydration reactor comprises the following components: 97.6% of methanol, 0.9% of water, 0.6% of ethanol, 0.24% of methyl acetate and 0.15% of ethyl acetate, and the content of impurities such as ester, ethanol and the like is lower than 1%, so that the energy consumption of the product is saved.
Comparative example
The process flow diagram of the comparative example is the same as that of the figures 1 and 2, but the lower part of the dimethyl ether tower is not provided with an impurity extraction outlet; the tail gas washing tower does not add water as an absorbent, the tail gas at the top of the tail gas washing tower enters the washing tower for washing the material 8 only through a methanol solution, namely the dimethyl ether refining tower bottom liquid, and the other feeding conditions and the parameters of the rectifying tower are the same as those in the embodiment 1.
The calculation result is as follows: the lower part of the dimethyl ether tower is not provided with an impurity extraction outlet, so that the flow of the dimethyl ether product is obtained: 13265kg/h, mass composition: 99.82 percent, 800ppm of methyl acetate and 200ppm of methanol; the tail gas washing tower does not increase water as an absorbent, the tail gas at the top of the tail gas washing tower is only washed by a methanol solution, the flow rate is 570kg/h, and the mass composition is as follows: 5% of nitrogen, 68.9% of CO, 11% of argon, 3% of carbon dioxide, 3.7% of methanol, 4.3% of methyl acetate, 1.9% of ethyl acetate, 0.2% of dimethyl ether and 1% of ethanol, wherein the tail gas contains more oxygenates, a plurality of raw materials of methanol and ethanol are carried out by the tail gas, the material loss is more, and the raw material can be sent to a PSA unit to recover the CO raw material gas after being reprocessed.
The comparative example does not adopt the separation process of the invention, the content of ester and ethanol in the dimethyl ether synthesis and rectification system is higher, and the feed quality of the methanol dehydration reactor comprises the following components: 80% of methanol, 2.8% of water, 7.1% of ethanol, 4.5% of methyl acetate and 5.5% of ethyl acetate, wherein the total content of impurities such as ester, ethanol and the like is up to 17.1%, and the impurities are accumulated in a dimethyl ether synthesis and rectification system, so that the energy consumption of products is greatly increased. The specific product energy consumption (steam, circulating water, electricity) and the ton dimethyl ether methanol consumption and dimethyl ether dehydration reactor feed flow of the comparative example are listed in table 1.
TABLE 1 Unit product energy consumption, material consumption and dimethyl ether dehydration reactor feed flow
| Item | Steam unit consumption | Unit consumption of circulating water | Unit consumption of electricity | Ton dimethyl ether methanol consumption | Raw material flow of dimethyl ether feeding reactor |
| Unit of | t/t dimethyl ether | t/t dimethyl ether | kwh/t dimethyl ether | t/t dimethyl ether | kg/h |
| Example 1 | 0.813 | 49.4 | 7.1 | 1.393 | 23726 |
| Example 2 | 0.815 | 51.5 | 7.18 | 1.394 | 23736 |
| Example 3 | 0.814 | 49.4 | 7.1 | 1.393 | 23731 |
| Example 4 | 0.811 | 50.1 | 7.2 | 1.41 | 24541 |
| Example 5 | 0.818 | 49.2 | 7.0 | 1.39 | 23396 |
| Comparative example | 1.05 | 61 | 8.4 | 1.4015 | 28688 |
As can be seen from comparison between example 1 and a comparative example in Table 1, by adopting the separation process of the invention, the consumption of dimethyl ether steam per ton is saved by 0.24t, the consumption of dimethyl ether steam is saved by 24000 tons in one year, and the consumption of steam can be saved by nearly 300 ten thousand yuan; the methanol is saved by 850 tons each year, and the raw material cost can be saved by 280 ten thousand yuan. Meanwhile, the difference of the feeding amount of the reactor is close to 5t per hour, and the volume flow is reduced by 20 percent, so that the size of the reactor, the dimethyl ether rectifying tower and pipelines thereof can be reduced, and the total investment can be saved by 5-8 percent; and the problem that impurities are brought into the methanol dehydration reaction process to generate acid to corrode equipment can be avoided.
The invention clears the obstacles for the technical problems existing in the connection of the dimethyl ether unit prepared by methanol dehydration and the front and rear units in the complete technology of preparing ethanol from methanol, and simultaneously further perfects the separation process for preparing dimethyl ether from methanol by gas phase dehydration.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (9)
1. A separation method of reaction products of dimethyl ether prepared by methanol dehydration is characterized by comprising the following steps:
1) Raw material methanol and circulating methanol from an ethanol refining unit are used as reaction raw materials and enter a methanol dehydration reactor for reaction, the obtained reaction product is condensed and then enters a gas-liquid separation tank (2) for gas-liquid separation, the separated gas-phase material enters a tail gas washing tower (14), and the liquid-phase material enters a dimethyl ether refining tower (5);
2) The dimethyl ether refining tower (5) comprises a washing impurity removal section, wherein an impurity solution containing ethanol and esters is extracted from the lower side of the washing impurity removal section, and the impurity solution is sent to an ethanol refining unit for separation; condensing the gas phase material at the top of the dimethyl ether refining tower (5), then refluxing all the condensed liquid into the tower, and feeding the condensed produced dimethyl ether refining tower topping gas into the tail gas washing tower (14); a dimethyl ether product is collected from the side line of the dimethyl ether refining tower (5); the tower bottom liquid of the dimethyl ether refining tower (5) is sent to a methanol stripping tower (17) for separating and recovering methanol;
3) Washing gas-phase materials and dimethyl ether refining tower topping gas generated by a gas-liquid separation tank by using washing water or washing water and tower bottom liquid of a dimethyl ether refining tower (5) in the tail gas washing tower (14), discharging tail gas from the tower top of the tail gas washing tower (14), and enabling the tower bottom liquid of the tail gas washing tower (14) to enter the dimethyl ether refining tower (5) from the washing impurity removal section;
the total mass content of ethanol and esters in the reaction raw materials entering the methanol dehydration reactor is less than or equal to 3 percent; the circulating methanol contains methyl acetate, ethyl acetate and ethanol, wherein the total content of the methyl acetate and the ethyl acetate is 500-2000ppm, and the content of the ethanol is 600-1500ppm.
2. The method for separating the reaction product of dimethyl ether prepared by methanol dehydration according to claim 1, characterized in that the dimethyl ether refining tower (5) comprises a top-drawing section, a rectifying section, a washing and impurity removing section and a stripping section, and the dimethyl ether product is extracted from the lower side line of the top-drawing section of the dimethyl ether refining tower (5).
3. The separation method of the reaction product of dimethyl ether from methanol dehydration according to claim 1, characterized in that the recycled methanol produced by the ethanol refining unit enters from the top of the methanol stripping tower (17).
4. The method for separating the reaction product of dimethyl ether from methanol by dehydration according to claim 1, wherein the gas phase material produced by the gas-liquid separation tank in the tail gas washing tower (14) and the topping gas of the dimethyl ether refining tower are washed by the tower bottom liquid of the dimethyl ether refining tower (5) and then by the washing water; the washing water of the tail gas washing tower (14) comes from the process wastewater at the tower bottom of the methanol stripping tower (17) or fresh water outside the device.
5. The separation method of the reaction product of dimethyl ether prepared by methanol dehydration according to claim 4, characterized in that the tail gas washing tower (14) washes purge gas containing CO from a dimethyl ether carbonylation unit, wherein the purge gas contains 6-10% by mass of dimethyl ether, 4-6% by mass of methyl acetate and 68-80% by mass of CO;
and gas-phase materials generated by the gas-liquid separation tank, the topping gas of the dimethyl ether refining tower and the purge gas form mixed gas, the mixed gas enters a tail gas washing tower (14), and tail gas generated at the tower top of the tail gas washing tower (14) is subjected to a PSA (pressure swing adsorption) process to recover CO.
6. The separation method for the reaction product of dimethyl ether preparation through methanol dehydration according to claim 5, characterized in that the number of theoretical plates of the tail gas washing tower (14) is 10-20, and the mass ratio of the tower bottom liquid of the dimethyl ether refining tower (5) to the mixed gas is 3-6; the mass ratio of the washing water consumption to the mixed gas is 0.1-0.3.
7. The method for separating the reaction product of dimethyl ether through methanol dehydration according to claim 1, wherein the content of methyl acetate, dimethyl ether and methanol in the tail gas at the top of the tail gas washing tower (14) is less than or equal to 1000ppm, 600ppm and 10ppm.
8. The method for separating the reaction product of dimethyl ether through methanol dehydration according to claim 1, characterized in that the number of theoretical plates of the dimethyl ether refining column (5) is 20-30, and an impurity side draw-out port is arranged at the 18 th to 25 th theoretical plates from the top of the dimethyl ether refining column (5) to draw out the impurity solution; the mass ratio of the produced amount of the impurity solution to the produced amount of the dimethyl ether product is 0.0075-0.0225; the mass content of esters in the impurity solution is 15-30%, and the mass content of ethanol is 1.5-5%.
9. The method for separating the reaction product of dimethyl ether through methanol dehydration according to claim 1, wherein the dimethyl ether product is taken out from the side line of 2 th to 5 th theoretical plates from the top of the dimethyl ether refining tower (5), the mass content of dimethyl ether in the dimethyl ether product is more than or equal to 99.5 percent, and the contents of methanol and water are both less than or equal to 500ppm.
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