Dimethyl sulfate and preparation method thereof

Abstract

The invention relates to dimethyl sulfate and a preparation method thereof, and the method comprises the following steps: burning liquid sulfur and air, and carrying out at least three-stage conversion reaction to obtain sulfur trioxide; the sulfur trioxide is absorbed by at least three stages of absorption towers through fuming sulfuric acid, the first part of sulfur trioxide is absorbed by the fuming sulfuric acid, the second part of sulfur trioxide which is not absorbed circularly enters the first-stage absorption tower to be absorbed, SO2 which is absorbed by the first-stage absorption tower is subjected to four-stage conversion, and SO2 is subjected to secondary conversion. After conversion, entering a secondary absorption tower for absorption; desorbing the fuming sulfuric acid which absorbs the sulfur trioxide and is obtained in the step 102 in a negative pressure tower, spraying and absorbing the sulfur trioxide and dimethyl sulfate to generate dimethyl pyrosulfate with a first concentration, feeding the sulfur trioxide which is not absorbed into a pyroester tower for spraying and absorbing, and cooling to generate dimethyl pyrosulfate with a second concentration; the dimethyl pyrosulfate with the first concentration and the dimethyl pyrosulfate with the second concentration are subjected to esterification reaction with dimethyl ether to generate dimethyl sulfate.

Description

Technical Field

[0001] The present invention relates to the technical field of dimethyl sulfate preparation, and particularly to dimethyl sulfate and a preparation method thereof. Background Art

[0002] Dimethyl sulfate is an effective alkylating agent, used in the manufacture of dyes and as a methylating agent for amines and alcohols. Common reactions include two categories: O-methylation reaction and N-methylation reaction, which are widely used in organic synthesis industrial fields such as pharmaceuticals, pesticides, spices, and dyes. However, the traditional dimethyl sulfate production process faces many challenges. This method not only has high raw material requirements, but also generates a large amount of "recovered sulfuric acid" treatment problems during the production process, restricting production efficiency and scale, especially difficult to promote in small and medium-sized sulfuric acid plants. With the continuous development of the chemical industry, higher requirements are put forward for the dimethyl sulfate production process. On the one hand, it is necessary to reduce production costs and improve raw material utilization; on the other hand, it is necessary to solve environmental protection problems and reduce pollutant emissions during the production process. Therefore, the research and development of new processes has become an urgent need in the industry. Against the background of the increasing global environmental awareness, the environmental protection pressure in the chemical industry is constantly increasing.

[0003] Under industrial production conditions, methanol is dehydrated to produce dimethyl ether. The liquid material separated during the purification process of the crude dimethyl ether gas contains nearly 40% unreacted methanol, which must be recovered by distillation. Sulfur trioxide is mostly prepared by heating and evaporating fuming sulfuric acid, and its purity can reach about 99%. There are also manufacturers who use low-concentration sulfur trioxide to produce dimethyl sulfate. The low-concentration sulfur trioxide gas in the converter of the sulfuric acid production device is directly led out, absorbed by dimethyl sulfate in the absorption tower, and then reacts with dimethyl ether obtained by sulfuric acid-catalyzed methanol dehydration in the esterification tower, and then the finished product is obtained through a distillation kettle. The dimethyl ether content in the dimethyl sulfate synthesized from dimethyl ether-sulfur trioxide is between 5-9%, and the acidity is also relatively high. It needs to be rectified again to obtain dimethyl sulfate and dimethyl sulfate products with qualified acidity. Usually, the dimethyl ether content in the dimethyl sulfate produced by the dimethyl sulfate product in the synthesis tower after one distillation is about 2-5%, which is difficult to meet the special requirements of some manufacturers. Due to the high dimethyl ether content in dimethyl sulfate, it affects the next methylation reaction and at the same time increases the raw material consumption of dimethyl sulfate. Therefore, some manufacturers have clear requirements for the dimethyl ether content. Since the commercially available dimethyl sulfate is generally about 2-5%. Some synthesis reactions require the dimethyl ether content to be less than 0.5%. The dimethyl sulfate purchased by the manufacturer has to be rectified again to meet the methylation use requirements.

[0004] Related documents disclose a method for preparing dimethyl sulfate using sulfur as a raw material. The method includes: during the distillation of crude dimethyl sulfate, the dimethyl sulfate vapor coming out of the distillation kettle is cooled in two stages. The temperature of the first-stage condensed dimethyl sulfate is controlled at 95-105°C, and the vacuum degree of the distillate collection kettle is controlled to be lower than -0.08 MPa; the temperature of the second-stage dimethyl sulfate cooling is 30-40°C, and the vacuum degree of the distillate collection kettle is controlled to be lower than -0.09 MPa. The methyl ether in the high-temperature dimethyl sulfate collected in the first stage is less than 0.5%, and its output accounts for about 70% of the total output. The negative pressure system of the collection kettle is connected to the dimethyl sulfate synthesis tower, and the dimethyl ether desorbed at reduced pressure and high temperature is used as a raw material again in the synthesis tower to absorb and react with sulfur trioxide to synthesize dimethyl sulfate, thereby reducing raw material consumption.

[0005] However, the above method for the production process of dimethyl sulfate has a relatively large environmental pollution risk, such as the emission problems of waste gas and waste water.

[0006] Thus, it can be seen that in the above-mentioned existing preparation methods of dimethyl sulfate, there are obviously still inconveniences and defects, and it is urgent to be further improved. In order to solve the problems existing in dimethyl sulfate and its preparation method, relevant manufacturers have tried their best to seek solutions, but no applicable design has been developed and completed for a long time. This is obviously a problem that relevant industries are eager to solve.

[0007] In view of the above-mentioned defects existing in the existing dimethyl sulfate and its preparation method, based on the rich practical experience and professional knowledge in the design and manufacture of such products for many years, and in cooperation with the application of theory, the inventor actively conducts research and innovation in order to create a new dimethyl sulfate and its preparation method, which can improve the general existing dimethyl sulfate and its preparation method and make it more practical. After continuous research, design, repeated trial production and improvement, the present invention with practical value has finally been created. Summary of the Invention

[0008] The main object of the present invention is to overcome the defects existing in the existing dimethyl sulfate and its preparation method, and to provide a new dimethyl sulfate and its preparation method. The technical problem to be solved is that the production process of dimethyl sulfate has a relatively large environmental pollution risk, such as the emission problems of waste gas and waste water.

[0009] Compared with the prior art, the present invention has obvious advantages and beneficial effects. As can be seen from the above technical solutions, in order to achieve the aforementioned invention purpose, the main technical content of the present invention is as follows:

[0010] The present invention provides a method for preparing dimethyl sulfate, including:

[0011] Step 101, burning liquid sulfur with air to carry out at least three-stage conversion reaction to obtain sulfur trioxide;

[0012] Step 102: Absorb the sulfur trioxide with fuming sulfuric acid in at least three-stage absorption towers. Among them, the first part of the sulfur trioxide is absorbed by the nicotinic acid absorption tower in the three-stage absorption tower, and the unabsorbed second part of the sulfur trioxide is recycled into the first-stage sulfuric acid absorption tower in the three-stage absorption tower for absorption. The SO2 after being absorbed by the first-stage sulfuric acid absorption tower in the three-stage absorption tower undergoes four-stage conversion, and after conversion, it enters the second-stage absorption tower for absorption.

[0013] Step 103: After the fuming sulfuric acid that has absorbed sulfur trioxide obtained in Step 102 is desorbed in a negative pressure tower, the sulfur trioxide is spray-absorbed with dimethyl sulfate to generate dimethyl pyrosulfate with a first concentration. The unabsorbed sulfur trioxide enters the pyrosulfate tower for spray absorption and generates dimethyl pyrosulfate with a second concentration after cooling.

[0014] Step 104: Dimethyl pyrosulfate with the first concentration and dimethyl pyrosulfate with the second concentration undergo an esterification reaction with dimethyl ether to generate dimethyl sulfate.

[0015] In an optional embodiment, in Step 101, the air is dust-removed and dried and then mixed countercurrently with liquid sulfur at a temperature of 135°C to 145°C for combustion.

[0016] In an optional embodiment, in Step 101, the outlet temperature of each stage in the three-stage conversion decreases sequentially.

[0017] Among them, the reaction temperature of the first-stage conversion in the three-stage conversion is 400°C to 420°C, the reaction temperature of the second-stage conversion is 425°C to 430°C, and the reaction temperature of the third-stage conversion is 430°C to 450°C.

[0018] In an optional embodiment, in Step 102, the flue gas containing sulfur dioxide after being absorbed by the nicotinic acid absorption tower and the first-stage sulfuric acid absorption tower in the three-stage absorption tower undergoes heat exchange and then enters the four-stage conversion. The sulfur trioxide after conversion undergoes heat exchange and then enters the second-stage absorption tower for absorption.

[0019] In an optional embodiment, it further includes oxidizing the sulfur dioxide in Step 102 with hydrogen peroxide to generate sulfuric acid, and storing the generated sulfuric acid.

[0020] In an optional embodiment, Step 104 further includes: a step of preparing dimethyl ether, and the step of preparing dimethyl ether further includes: methanol undergoes a dehydration reaction at 220°C to 240°C, a reaction pressure of 0.6 MPa to 1.3 MPa, and under the action of a catalyst to generate a mixture of dimethyl ether and water vapor.

[0021] In an alternative embodiment, the step of preparing dimethyl ether further includes rectifying dimethyl ether at a pressure of 0.6 MPa to 1.2 MPa and a temperature of 100 °C to 115 °C.

[0022] In an alternative embodiment, the step of preparing dimethyl ether further includes recovering methanol generated during the rectification of dimethyl ether at a pressure of 0.05 MPa to 0.2 MPa.

[0023] In an alternative embodiment, it further includes separating dimethyl ether in dimethyl sulfate at 90 °C to 110 °C under a negative pressure condition to obtain crude dimethyl sulfate.

[0024] The first part of the crude dimethyl sulfate is sent to the upper part of the coke ester tower after condensation to spray and absorb sulfur trioxide that is not absorbed in the lower part of the coke ester tower, and the second part enters the rectification tower for rectification and purification under a negative pressure state. The rectification pressure is -0.085 MPa to -0.1 MPa, and the rectification temperature is 120 °C to 145 °C.

[0025] On the other hand, a dimethyl sulfate is provided, which is prepared by using the dimethyl sulfate preparation method described in any one of the above.

[0026] The method provided by the embodiments of the present invention has at least the following beneficial effects:

[0027] The method provided by the embodiments of the present invention burns liquid sulfur with air to obtain sulfur trioxide through a conversion reaction, absorbs sulfur trioxide with fuming sulfuric acid, and then separates high-concentration fuming sulfuric acid by evaporation and negative pressure extraction to obtain pure sulfur trioxide; sulfur trioxide is efficiently absorbed by dimethyl sulfate (chemical formula: (CH3O)2SO2) to obtain dimethyl pyrosulfate, and dimethyl pyrosulfate reacts with gaseous dimethyl ether to obtain dimethyl sulfate, and a dimethyl sulfate product with a purity of more than 99.5% is obtained through a negative pressure rectification process. The method provided by the embodiments of the present invention does not have the problem of recovering sulfuric acid during the production process, does not have the problem of wastewater discharge, and has few side reactions, a simple process, and low costs during the production process.

[0028] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following further details the preferred embodiments of the present invention in conjunction with the accompanying drawings.

[0029] The specific dimethyl sulfate preparation method of the present invention is given in detail by the following examples and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic flow chart of the dimethyl sulfate preparation method provided by the embodiments of the present invention. Detailed Implementation Modes

[0031] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation modes and effects of the method for preparing dimethyl sulfate according to the present invention as follows.

[0032] Please refer to Figure 1 , the method for preparing dimethyl sulfate in the preferred embodiment of the present invention mainly includes the following steps: Step 101: Burn liquid sulfur and air, and perform at least three-stage conversion reaction to obtain sulfur trioxide.

[0033] Step 102: Absorb sulfur trioxide with fuming sulfuric acid in at least three-stage absorption towers. Among them, the first part of sulfur trioxide is absorbed by the nicotinic acid absorption tower in the three-stage absorption tower, and the unabsorbed second part of sulfur trioxide is circulated into the first-stage sulfuric acid absorption tower in the three-stage absorption tower for absorption. The SO2 after being absorbed by the first-stage sulfuric acid absorption tower in the three-stage absorption tower undergoes four-stage conversion and then enters the second-stage absorption tower for absorption.

[0034] Step 103: After the fuming sulfuric acid absorbed with sulfur trioxide obtained in Step 102 is desorbed in a negative pressure tower, sulfur trioxide and dimethyl sulfate are sprayed and absorbed to generate dimethyl pyrosulfate with a first concentration, and the unabsorbed sulfur trioxide enters the pyrosulfate tower for spraying and absorption, and after cooling, generates dimethyl pyrosulfate with a second concentration.

[0035] Step 104: Dimethyl pyrosulfate with the first concentration and dimethyl pyrosulfate with the second concentration react with dimethyl ether to generate dimethyl sulfate.

[0036] The method provided by the embodiment of the present invention has at least the following beneficial effects:

[0037] The method provided by the embodiment of the present invention burns liquid sulfur and air, and through the conversion reaction, sulfur trioxide is obtained. Sulfur trioxide is absorbed by fuming sulfuric acid, and then pure sulfur trioxide is separated from the high-concentration fuming sulfuric acid by evaporation and negative pressure extraction methods; sulfur trioxide is efficiently absorbed by dimethyl sulfate (chemical formula: (CH3O)2SO2) to obtain dimethyl pyrosulfate, and dimethyl pyrosulfate reacts with gaseous dimethyl ether to obtain dimethyl sulfate. Through the process of negative pressure rectification, dimethyl sulfate finished products with a purity of more than 99.5% are obtained. The method provided by the embodiment of the present invention does not have the problem of recovering sulfuric acid during the production process, does not have the problem of wastewater discharge, and has few side reactions, simple process and low cost during the production process.

[0038] It should be noted that the fuming sulfuric acid in the embodiment of the present invention refers to the sulfuric acid solution of sulfur trioxide, and its chemical formula is H2SO4·xSO3.

[0039] In an alternative embodiment, in step 101, after the air is dust-removed and dried, it is mixed countercurrently with liquid sulfur at a temperature of 135°C to 145°C for combustion.

[0040] In an alternative embodiment, in step 101, the outlet temperature of each stage in the three-stage conversion decreases sequentially; among them, the reaction temperature of the first-stage conversion in the three-stage conversion is 400°C to 420°C, the reaction temperature of the second-stage conversion is 425°C to 430°C, and the reaction temperature of the third-stage conversion is 430°C to 450°C.

[0041] Exemplarily, in the embodiment of the present invention, liquid sulfur from the liquid sulfur storage tank in the tank farm can enter the pre-tank of the liquid sulfur furnace through a liquid sulfur feeding pump, and then be transported to the sulfur-burning furnace through a liquid sulfur feed pump; the air after being dust-removed by an air filter is sent into a drying tower by a main blower and contacts countercurrently with 94% concentrated sulfuric acid with a sprinkling temperature lower than 60°C to be dried. After the dried air removes the entrained acid mist through a fiber demister at the top of the tower, it enters the sulfur-burning furnace (the moisture entrained in the air is reduced to 0.1 g / Nm 3 as follows).

[0042] Exemplarily, in the embodiment of the present invention, liquid sulfur and air burn in a sulfur-burning furnace (the sulfur-burning furnace is heated to 500°C) to generate SO2. The high-temperature furnace gas of SO2 enters a steam generator for heat exchange and temperature reduction, and at the same time by-produces 2.5 MPa saturated steam. After the temperature of the SO2 flue gas drops from 1050°C to 400°C, it enters a converter for the first-stage conversion; the 610°C gas after the first-stage conversion in the converter enters a high-temperature superheater for heat exchange, and after the temperature drops to 450°C, it enters the converter for the second-stage conversion. The temperature of the gas after the second-stage conversion in the converter is 515°C; then the gas after the second-stage conversion enters a heat exchanger for heat exchange to 440°C and then enters the converter for the third-stage conversion. The temperature of the gas at the outlet of the third stage at 480°C is further reduced to about 250°C after heat exchange in a cold and hot exchanger; the cooled gas then enters a flue gas preheater and is heated by a part of the flue gas from the outlet of the first stage of the converter to above 300°C and then enters a sulfur trioxide evaporator. The reaction principle is: main reaction: S + O2 → SO2, side reaction: N2 + O2 → NO x ,

[0043] In step 102, fuming sulfuric acid is used to absorb sulfur trioxide in at least a three-stage absorption tower. Among them, the first part of sulfur trioxide is absorbed by fuming sulfuric acid, and the second part of sulfur trioxide that is not absorbed is recycled into the first-stage absorption tower for absorption. After the SO2 is absorbed in the first-stage absorption tower, it undergoes four-stage conversion and then enters the second-stage absorption tower for absorption.

[0044] In an alternative embodiment, in step 102, the flue gas containing sulfur dioxide after being absorbed by the nicotinic acid absorption tower and the primary sulfuric acid absorption tower in the three-stage absorption tower undergoes heat exchange and then enters the fourth stage for conversion. The sulfur trioxide after conversion undergoes heat exchange and then enters the secondary absorption tower for absorption.

[0045] In an alternative embodiment, it further includes oxidizing sulfur dioxide in step 102 with hydrogen peroxide to generate sulfuric acid, neutralizing the generated 25% sulfuric acid and 98% acid, and storing it after reaching a high concentration of acid.

[0046] Exemplarily, in the production startup of the embodiment of the present invention, 22% nicotinic acid (SO3) is transported from the sulfuric acid underground tank to the primary nicotinic acid absorption tower, secondary nicotinic acid absorption tower, and tertiary nicotinic acid absorption tower via a sulfuric acid extraction pump. The flue gas in section III from the sulfur trioxide evaporator is successively spray-absorbed by the primary nicotinic acid absorption tower, secondary nicotinic acid absorption tower, and tertiary nicotinic acid absorption tower (the SO3 absorption rate of each nicotinic acid absorption tower is 75%); the 35% nicotinic acid after spray absorption exits the primary nicotinic acid absorption tower and enters the sulfur trioxide evaporator after being heated successively by an acid-acid heat exchanger and a nicotinic acid heater; the unabsorbed flue gas in section III enters the primary absorption tower from the tertiary nicotinic acid absorption tower and is spray-absorbed with concentrated sulfuric acid for the remaining SO3 (SO3 absorption rate ≥ 99.99%).

[0047] The 50°C flue gas in section III containing SO2 after being absorbed by the primary absorption tower successively enters a cold-hot heat exchanger and a hot-hot heat exchanger, is heated to 425°C, and then enters the fourth section of the converter for conversion; the 445°C flue gas at the outlet of section IV after conversion successively enters a low-temperature superheater and a feed water preheater to recover energy; after the temperature drops to about 160°C, it enters the secondary sulfuric acid absorption tower for flue gas absorption after heat exchange with the nicotinic acid heater, and the unabsorbed flue gas enters the desulfurization tower for desulfurization. The reaction principle is: SO3 + H2SO4 → H2SO4·SO3 (nicotinic acid)

[0048] As an example, the third-stage conversion flue gas (i.e., the generated sulfur trioxide gas) from step 101 heats 35% niacin to evaporate SO3 after heat exchange in the niacin absorption tower. The sulfur trioxide gas coming out from the top of the sulfur trioxide evaporator is cooled to 50°C by a primary sulfur trioxide cooler and then directly enters the production section of dimethyl sulfate, that is, it can be directly used to produce dimethyl sulfate; the 26% niacin after evaporation in the upper part of the sulfur trioxide evaporator is absorbed by the fuming sulfuric acid buffer tank and then enters the degassing tower. The SO3 coming out from the top of the degassing tower is cooled to 50°C by a secondary sulfur trioxide cooler and directly enters the production section of dimethyl sulfate; the 22% niacin coming out from the bottom of the degassing tower is cooled by an acid-acid heat exchanger and then enters the third-stage niacin absorption tower. In step 103, the fuming sulfuric acid that has absorbed sulfur trioxide obtained in step 102 is desorbed in a negative pressure tower, and then sulfur trioxide and dimethyl sulfate are spray-absorbed to form dimethyl pyrosulfate of the first concentration. The unabsorbed sulfur trioxide enters the pyrosulfate tower for spray absorption and after cooling, dimethyl pyrosulfate of the second concentration is formed.

[0049] It should be noted that in the embodiment of the present invention, it is not desorbed first and then spray-absorbed with dimethyl sulfate. Instead, the reaction is directly carried out while desorbing in the desorption tower, that is, sulfur trioxide and dimethyl sulfate are spray-absorbed to form dimethyl pyrosulfate of the first concentration after desorption in the negative pressure tower.

[0050] As an example, the flue gas at the outlet of the secondary absorption tower in step 103 sequentially enters the primary desulfurization tower and the secondary desulfurization tower, is desulfurized with 27.5% hydrogen peroxide, then enters an electrostatic demister for demisting, and is discharged through a 30m high chimney. The 25% dilute sulfuric acid generated in the desulfurization tower enters the drying tower, is mixed with concentrated sulfuric acid after drying air, and the by-produced 92.5% sulfuric acid is sent to a sulfuric acid storage tank for external sale as a by-product. The hydrogen peroxide for tail gas desulfurization is in excess, and the desulfurization efficiency is 99%. The reaction principle is as follows: SO2 + H2O2 → H2SO4.

[0051] In step 104, dimethyl pyrosulfate of the first concentration and dimethyl pyrosulfate of the second concentration react with dimethyl ether to form dimethyl sulfate.

[0052] In an alternative embodiment, step 104 further includes: a step of preparing dimethyl ether, and the step of preparing dimethyl ether further includes: methanol undergoes a dehydration reaction to generate a mixture of dimethyl ether and water vapor at 220°C to 240°C, a reaction pressure of 0.6MPa to 1.3MPa, and under the action of a catalyst.

[0053] Exemplarily, methanol undergoes a dehydration reaction to generate a mixture of dimethyl ether and water vapor at 220°C, 230°C, 240°C, a reaction pressure of 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, 1.2MPa or 1.3MPa, and under the action of a catalyst.

[0054] In an alternative embodiment, the step of preparing dimethyl ether further includes rectifying dimethyl ether at a pressure of 0.6 MPa to 1.2 MPa and a temperature of 100 °C to 115 °C.

[0055] In an alternative embodiment, the step of preparing dimethyl ether further includes recovering methanol generated during the rectification of dimethyl ether at a pressure of 0.05 MPa to 0.2 MPa.

[0056] In an alternative embodiment, it further includes separating dimethyl ether from dimethyl sulfate under the conditions of 90 °C to 110 °C and a negative pressure controlled for dimethyl sulfate to obtain crude dimethyl sulfate.

[0057] The first part of the crude dimethyl sulfate is sent to the upper part of the coke ester tower after condensation to spray and absorb sulfur trioxide that has not been absorbed in the lower part of the coke ester tower. The second part enters the rectification tower for rectification and purification under a negative pressure state. The rectification pressure is -0.085 MPa to -0.1 MPa, and the rectification temperature is 120 °C to 145 °C.

[0058] As an example, in the method provided by the embodiments of the present invention, the crude dimethyl sulfate at the bottom of the esterification reaction tower enters the degassing tower under its own pressure. The temperature in the degassing tower is controlled at 90 to 110 °C, and the pressure is controlled to be negative. The dimethyl ether in the crude dimethyl sulfate is separated from the crude product by heating with steam using the reboiler of the degassing tower. The light components of dimethyl sulfate after condensation of the gas separated from the top of the degassing tower enter the light component intermediate tank, and the uncondensed gas phase is absorbed after entering the absorption tower.

[0059] The crude dimethyl sulfate after degassing in the degassing tower, a part of which is condensed by the condenser at the outlet of the degassing tower and then sent to the upper part of the coke ester tower to spray and absorb the unabsorbed SO3 at the lower part of the coke ester tower, and a part of it enters the rectification tower for rectification and purification under negative pressure. The pressure in the rectification tower is controlled at -0.085 MPa to -0.1 MPa by the rectification tower vacuum pump. The material in the rectification tower is heated by steam using the rectification tower reboiler, and the temperature at the bottom of the rectification tower is controlled at 120 °C to 145 °C for rectification. The gas-phase components at the top of the rectification tower are condensed by the light-component condenser of the rectification tower and enter the light-component intermediate tank. The material in the light-component intermediate tank is transported to the dimethyl sulfate storage tank in the tank area by the light-component feeding pump for external sales as low-end products; after the liquid phase part at the upper part of the rectification tower is condensed by the rectification tower condenser, a part of it is pressurized by the rectification tower reflux pump, and the reflux flow rate is controlled by the regulating valve to be used as reflux liquid at the top and in the middle of the tower. The temperature at the top of the rectification tower is controlled at 90 - 100 °C. Another part is further condensed by the condenser at the outlet of the rectification tower and then enters the refined dimethyl sulfate intermediate tank, and then is transported to the dimethyl sulfate storage tank in the tank area by the refined dimethyl sulfate feeding pump for external sales as high-end products; the heavy components at the bottom of the rectification tower enter the heavy-component tower for further distillation. The dimethyl sulfate gas distilled from the top of the heavy-component tower returns to the rectification tower for rectification, and the distillation residue at the bottom enters the heavy-component discharge buffer tank, and then is transported to the waste liquid sulfuric acid tank in the tank area by the rectification tower bottom residue pump for external commissioning and disposal as hazardous waste. The reaction principle of the above reaction is: (CH3)2SO3 + H2O → CH3HSO4·SO3 + CH3OH;

[0060] (CH3)2SO3 + CH3OH → CH3HSO4 + CH3OCH3

[0061] CH3HSO4 + CH3OH → H2SO4 + CH3OCH3

[0062] In an alternative embodiment, the method provided by the embodiment of the present invention further includes a method for preparing methanol. As an example, methanol from the methanol storage tank in the tank area is sent into the methanol raw material tank by the methanol feeding pump, and is sequentially transported to the first-stage methanol heat exchanger and the second-stage methanol heat exchanger through the methanol feeding pump to exchange heat with the dimethyl ether mixed gas produced by the synthesis reactor. The heated methanol enters the methanol pre-distillation tower for further gasification and temperature increase. The gasified methanol gas sequentially enters the reaction pre-heater, and continues to exchange heat with the dimethyl ether mixed gas produced by the synthesis reactor in the reaction pre-heater to reach the temperature required for the synthesis reaction.

[0063] Steps for synthesizing dimethyl ether. The synthesis reactor is heated by heat transfer oil heated by a heat transfer oil heater (organic heat carrier boiler) to a temperature above 280°C. After the reaction is normal, the heat transfer oil heater (organic heat carrier boiler) is stopped, and the heat transfer oil is used as a heat removal medium to control the synthesis reactor between 280 and 300°C. Methanol from the methanol pre-fractionating column is heated to 220 - 240°C in the reaction pre-heater and then enters the synthesis reactor, where a gas-phase catalytic dehydration reaction of methanol occurs in the catalyst bed to produce a mixture of dimethyl ether and water. The pressure in the synthesis reactor is 0.6 - 1.3 MPa. The reaction principle is as follows: 2CH3OH → CH3OCH3 + H2O.

[0064] Steps for dimethyl ether rectification. Since the temperature of the dimethyl ether mixed gas produced by the synthesis reactor is relatively high, in order to improve the rectification purity of dimethyl ether, it is necessary to reduce the temperature of the mixed gas, and at the same time, the heat of the mixed gas is recovered using a heat exchanger: The high-temperature dimethyl ether mixed gas produced by the synthesis reaction comes out from the bottom of the synthesis reactor and successively enters the reaction pre-heater to exchange heat with methanol, and then enters the reboiler of the first rectification column to exchange heat with the bottom liquid of the dimethyl ether rectification column for temperature reduction. The cooled dimethyl ether mixed gas enters the reboiler of the 1# recovery column to exchange heat with the bottom liquid of the methanol recovery column for temperature reduction. The heat-exchanged dimethyl ether mixed gas successively enters the secondary methanol heat exchanger and the primary methanol heat exchanger to pre-heat methanol. The gas-liquid mixture after heat exchange and temperature reduction enters the middle of the dimethyl ether rectification column for rectification and purification. The dimethyl ether rectification and purification process is carried out under high pressure (0.6 - 1.2 MPa). The heating at the bottom of the rectification column is controlled by the heat of the dimethyl ether mixed gas in the reboiler of the first rectification column and the steam heat in the reboiler of the second rectification column. The bottom temperature is 100 - 115°C. The dimethyl ether gas coming out from the top of the dimethyl ether rectification column is condensed by the rectification column condenser and then enters the dimethyl ether reflux tank. The dimethyl ether in the dimethyl ether reflux tank is pressurized by the dimethyl ether reflux pump, and the reflux flow rate is controlled by a regulating valve and returned to the top of the column as reflux liquid. The top temperature is about 40°C; part of the uncondensed dimethyl ether gas directly enters the esterification rectification process through a regulating valve to control the pressure behind the valve. The bottom liquid of the dimethyl ether rectification column containing substances such as water and methanol is pressurized by the methanol extraction pump and then transported to the methanol pre-fractionating column for methanol recovery.

[0065] Methanol recovery step. The methanol mixture flowing out from the bottom of the methanol pre-distillation column enters the methanol recovery column for rectification and purification by using the pressure difference. The gasification of methanol in the methanol recovery column is controlled by the heat of the dimethyl ether mixed gas in the first reboiler of the recovery column and the heat of the steam in the second reboiler of the recovery column. The pressure in the methanol recovery column is controlled at 0.05 - 0.2 MPa. The methanol vapor fractionated from the top of the methanol recovery column is condensed by the recovery column condenser and then flows by gravity to the methanol reflux drum. Part of the methanol liquid in the methanol reflux drum is pressurized by the methanol reflux pump, and the reflux flow rate is controlled by the regulating valve and sent back to the top of the column as the reflux liquid. The reflux ratio of the materials in the column is controlled at 1:2.5. The excess methanol liquid in the methanol reflux drum is pressurized by the methanol circulation pump and sent back to the methanol pre-distillation column for reuse; the waste water at the bottom of the methanol recovery column is sent to the on-site sewage treatment area for treatment to meet the standards and then discharged into the park sewage treatment plant.

[0066] Example 1

[0067] Step 1: The liquid sulfur from the liquid sulfur storage tank in the tank farm enters the pre-tank before the liquid sulfur furnace through the liquid sulfur charging pump, and then is transported to the sulfur-burning furnace through the liquid sulfur feeding pump; the air after dust removal by the air filter is sent into the drying tower by the main blower and contacts countercurrently with 94% concentrated sulfuric acid with a sprinkling temperature lower than 60°C and is dried. After drying, the air enters the sulfur-burning furnace after the entrained acid mist is removed by the fiber demister at the top of the tower (the moisture entrained in the air is reduced to less than 0.1 g / Nm3).

[0068] Step 2: The liquid sulfur and air burn in the sulfur-burning furnace (the sulfur-burning furnace is heated to 500°C) to generate SO2. The high-temperature furnace gas of SO2 enters the steam generator for heat exchange and temperature reduction, and at the same time, 2.5 MPa saturated steam is by-produced. After the temperature of the SO2 flue gas drops from 1050°C to 400°C, it enters the converter for the first-stage conversion; the gas at 610°C after the first-stage conversion in the converter enters the high-temperature superheater for heat exchange, and after the temperature drops to 450°C, it enters the converter for the second-stage conversion. The temperature of the gas after the second-stage conversion in the converter is 515°C; then the gas after the second-stage conversion enters the heat exchanger for heat exchange to 440°C and then enters the converter for the third-stage conversion. The temperature of the gas at the outlet of the third stage at 480°C is further reduced to about 250°C after heat exchange in the cold and hot exchanger; the cooled gas then enters the flue gas preheater and is heated to above 300°C by a part of the flue gas from the outlet of the first stage of the converter and then enters the sulfur trioxide evaporator.

[0069] Step 3: During production startup, 22% niacin (SO3) is transported from the sulfuric acid underground tank to the first-stage niacin absorption tower, the second-stage niacin absorption tower, and the third-stage niacin absorption tower through a sulfuric acid extraction pump. The flue gas in Section III from the sulfur trioxide evaporator is successively spray-absorbed in the first-stage niacin absorption tower, the second-stage niacin absorption tower, and the third-stage niacin absorption tower (the SO3 absorption rate in each niacin absorption tower is 75%); the 35% niacin after spray absorption exits the first-stage niacin absorption tower and is successively heated by an acid-acid heat exchanger and a niacin heater and then enters the sulfur trioxide evaporator; the unabsorbed flue gas in Section III enters the first-stage absorption tower from the third-stage niacin absorption tower and is spray-absorbed with concentrated sulfuric acid for the remaining SO3 (SO3 absorption rate ≥ 99.99%).

[0070] Step 4: The crude dimethyl sulfate after degassing in the degassing tower, a part of which is condensed by the degassing tower discharge condenser and sent to the upper part of the coke ester tower to spray-absorb the unabsorbed SO3 in the lower part of the coke ester tower, and a part enters the rectification tower for rectification and purification under a negative pressure state. The pressure in the rectification tower is controlled at -0.085 MPa to -0.1 MPa by the rectification tower vacuum pump. The material in the rectification tower is heated by steam using the rectification tower reboiler, and the temperature at the bottom of the rectification tower is controlled at 120°C to 145°C for rectification. The gas-phase components at the top of the rectification tower are condensed by the rectification tower light component condenser and enter the light component intermediate tank. The material in the light component intermediate tank is transported to the dimethyl sulfate storage tank in the tank farm as low-end products for external sales through the light component feeding pump; a part of the liquid phase in the upper part of the rectification tower is condensed by the rectification tower condenser. After a part is pressurized by the rectification tower reflux pump, the reflux flow rate is controlled by a regulating valve to be used as reflux liquid at the top and in the middle of the tower. The temperature at the top of the rectification tower is controlled at 90 - 100°C. Another part is re-condensed by the rectification tower discharge condenser and enters the refined dimethyl sulfate intermediate tank, and then is transported to the dimethyl sulfate storage tank in the tank farm as high-end products for external sales through the refined dimethyl sulfate feeding pump; the heavy components at the bottom of the rectification tower enter the heavy component tower for further distillation. The dimethyl sulfate gas evaporated from the top of the heavy component tower returns to the rectification tower for rectification. The distillation residue at the bottom enters the heavy component discharge buffer tank and is then transported to the waste liquid sulfuric acid tank in the tank farm as hazardous waste for external commission disposal through the rectification tower bottom residue pump.

[0071] On the other hand, a dimethyl sulfate is provided, which is prepared by using the dimethyl sulfate preparation method of any one of the above.

[0072] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications within the scope of the technical solution of the present invention to obtain equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing dimethyl sulfate, characterized in that, Including: Step 101: Burn liquid sulfur with air and conduct at least three-stage conversion reactions to obtain sulfur trioxide; Step 102: Absorb the sulfur trioxide with fuming sulfuric acid in at least three-stage absorption towers. Among them, the first part of the sulfur trioxide is absorbed by the nicotinic acid absorption tower in the three-stage absorption tower, and the unabsorbed second part of the sulfur trioxide is recycled into the first-stage sulfuric acid absorption tower in the three-stage absorption tower for absorption. The SO2 after being absorbed by the first-stage sulfuric acid absorption tower in the three-stage absorption tower undergoes four-stage conversion, and after conversion, it enters the second-stage absorption tower for absorption; Step 103: After the fuming sulfuric acid that has absorbed sulfur trioxide obtained in Step 102 is desorbed in a negative pressure tower, the sulfur trioxide is spray-absorbed with dimethyl sulfate to generate dimethyl pyrosulfate with a first concentration. The unabsorbed sulfur trioxide enters the coke ester tower for spray absorption and generates dimethyl pyrosulfate with a second concentration after cooling; Step 104: Dimethyl pyrosulfate with the first concentration and dimethyl pyrosulfate with the second concentration undergo an esterification reaction with dimethyl ether to generate dimethyl sulfate.

2. The method for preparing dimethyl sulfate according to claim 1, wherein In Step 101, the air is dust-removed and dried and then mixed countercurrently with liquid sulfur at a temperature of 135°C to 145°C for combustion.

3. The method for preparing dimethyl sulfate according to claim 1, characterized in that, In Step 101, the outlet temperature of each stage in the three-stage conversion decreases sequentially; Among them, the reaction temperature of the first-stage conversion in the three-stage conversion is 400°C to 420°C, the reaction temperature of the second-stage conversion is 425°C to 430°C, and the reaction temperature of the third-stage conversion is 430°C to 450°C.

4. The method for preparing dimethyl sulfate according to claim 1, characterized in that, In Step 102, the flue gas containing sulfur dioxide after being absorbed by the nicotinic acid absorption tower and the first-stage sulfuric acid absorption tower in the three-stage absorption tower undergoes heat exchange and then enters the four-stage conversion. The sulfur trioxide after conversion undergoes heat exchange and then enters the second-stage absorption tower for absorption.

5. The method for preparing dimethyl sulfate according to claim 1, characterized in that, It also includes oxidizing sulfur dioxide in Step 102 with hydrogen peroxide to generate sulfuric acid, and storing the generated sulfuric acid.

6. The method for preparing dimethyl sulfate according to claim 1, characterized in that, Step 104 also includes: the step of preparing dimethyl ether, and the step of preparing dimethyl ether also includes: methanol undergoes a dehydration reaction to generate a dimethyl ether and water mixture at 220°C to 240°C and a reaction pressure of 0.6 MPa to 1.3 MPa under the action of a catalyst.

7. The method for preparing dimethyl sulfate according to claim 6, wherein The step of preparing dimethyl ether also includes rectifying dimethyl ether at a pressure of 0.6 MPa to 1.2 Mpa and a temperature of 100°C to 115°C.

8. The method for preparing dimethyl sulfate according to claim 7, characterized in that, The step of preparing dimethyl ether also includes recovering methanol generated during the rectification of dimethyl ether at a pressure of 0.05 MPa to 0.2 Mpa.

9. The method for preparing dimethyl sulfate according to claim 1, wherein It also includes separating dimethyl ether in dimethyl sulfate at 90°C to 110°C under the condition that the pressure is controlled to be negative pressure to obtain crude dimethyl sulfate; 10. A dimethyl sulfate, characterized in that, The first part of the crude dimethyl sulfate is sent to the upper part of the coke ester tower after condensation for spray absorption of the unabsorbed sulfur trioxide in the lower part of the coke ester tower, and the second part enters the rectification tower for rectification and purification under a negative pressure state. The rectification pressure is -0.085 MPa to -0.1 MPa, and the rectification temperature is 120°C to 145°C. Prepared by using the dimethyl sulfate preparation method described in any one of claims 1-9.

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