A method and device for self-heating distillation of dimethyl carbonate

Abstract

The present invention discloses a method for self-heating distillation of dimethyl carbonate, which is characterized by comprising: adding methanol, propylene carbonate and a catalyst into a distillation tower, and after distillation, the top steam flows out from the top of the tower, a part of which enters a condenser for condensation, and then refluxes to the top of the tower through a reflux tank; another part of the top steam is compressed and heated by a compressor and used to heat the bottom liquid of the tower, and this part of the top steam is further cooled by a cooler after releasing heat, and then refluxes to the top of the tower through a reflux tank. The present invention uses clean electric energy to drive the compressor, and compresses and heats the top steam of the tower in a mechanical compression manner as a heat source for the bottom of the tower, saving a large amount of steam and circulating water. Compared with the prior art, the annual operating cost of the method of the present invention can be saved by about 71%.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production, and in particular relates to a method and a device for self-heat recovery distillation of dimethyl carbonate. Background Art

[0002] Dimethyl carbonate is a new type of green chemical product that has developed rapidly in recent years. It is a widely used organic synthesis intermediate and a gasoline additive with excellent performance. In recent years, the transesterification reaction distillation process has become the mainstream production process, with the advantages of mild reaction conditions, small investment, quick effect, and no three wastes.

[0003] However, this process has high energy consumption. With the gradual elimination of coal-fired boilers in my country, the price of steam continues to rise. It is urgent to find a production method with less steam consumption and lower operating costs. Summary of the invention

[0004] The object of the present invention is to overcome the deficiencies of the prior art and provide an energy-saving method for self-heat regeneration distillation of dimethyl carbonate.

[0005] Another object of the present invention is to provide a special device for the above method.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for self-heat recovery distillation of dimethyl carbonate is characterized in that it comprises: adding methanol, propylene carbonate and a catalyst into a distillation tower, and after distillation, the tower top steam flows out from the tower top, a part of which enters a condenser for condensation, and then refluxes to the tower top through a reflux tank; another part of the tower top steam is compressed and heated by a compressor and used to heat the tower bottom liquid, and this part of the tower top steam releases heat and is further cooled by a cooler, and then refluxes to the tower top through a reflux tank.

[0008] In the above technical solution, the mass ratio of the part of the tower top steam entering the condenser to the other part is 1:(1-5).

[0009] In the above technical solution, the heat of the other part of the tower top steam used to heat the tower bottom liquid is the phase change heat of the tower top steam.

[0010] In the above technical solution, the heat exchange temperature difference between the tower top steam and the tower bottom liquid is 6 to 8°C.

[0011] In the above technical solution, the pressure ratio of the compressor is 1.5-3.

[0012] In the above technical solution, the compressor is a screw compressor, a Roots compressor or a centrifugal compressor, the inlet steam temperature of the compressor is 50-65°C, and the outlet temperature is 65-80°C.

[0013] In the above technical solution, the outlet temperature of the cooler is 40-50°C.

[0014] In the above technical solution, the reflux ratio of the distillation tower is 0.5-3, the top temperature is 50-65°C, the pressure is 75-90 kPa, and the bottom temperature is 60-75°C.

[0015] A device for self-heat recovery distillation of dimethyl carbonate, characterized in that it comprises: a distillation tower, a condenser, a reflux tank, a cooler, a compressor and a reboiler, wherein the distillation tower is provided with a feed inlet, the tower top is provided with a gas phase outlet and a reflux port, and the tower bottom is provided with a discharge port and a tower bottom liquid inlet; the gas phase outlet at the tower top of the distillation tower is connected to two pipelines, one of which is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is connected to the reflux port, and the other is connected to the compressor, the outlet of the compressor is connected to the heat source inlet of the reboiler, the heat source outlet of the compressor is connected to the cooler and the reflux tank in sequence, and the outlet of the reflux tank is connected to the reflux port of the distillation tower; the discharge port is connected to the material inlet of the reboiler, and the material outlet of the reboiler is connected to the tower bottom liquid inlet.

[0016] In the above technical solution, the reboiler is a horizontal tube falling film reboiler.

[0017] The advantages and beneficial effects of the present invention are:

[0018] 1. The present invention uses clean electric energy to drive the compressor, and compresses and heats the top steam in a mechanical compression manner as the heat source of the bottom of the tower, saving a large amount of steam and circulating water;

[0019] 2. A horizontal tube falling film reboiler is used to realize heat exchange between the top steam and the bottom liquid, making full use of the phase change heat of the top steam from saturated steam to condensate, with high thermal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a simplified flow chart of the distillation device of Example 1 of the present invention.

[0021] Among them, 1 is a distillation tower, 2 is a condenser, 3 is a compressor, 4 is a reboiler, 5 is a cooler, 6 is a reflux tank, 7 is a reflux pump, 8 is a spray pump, 9 is a circulating pump, CWS is a circulating water inlet, and CWR is a circulating water outlet. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] A method for self-heating distillation of dimethyl carbonate comprises: adding 19662 kg / h methanol, 1808 kg / h propylene oxide, 2350 kg / h propylene carbonate and 125 kg / h sodium methoxide catalyst at 70°C into a distillation tower 1, with a reflux ratio of 1. After distillation, the tower bottom temperature is 72°C, the tower top temperature is 60°C and the pressure is 85 kPa. The tower top steam flows out from the tower top, a part of which enters the condenser 2 for condensation, and then refluxes to the tower top through the reflux tank 6; the other part of the tower top steam is compressed by the compressor 3 and heated to 78°C, and the pressure is 200 kPa, wherein the pressure ratio of the compressor is 2.3. Then the tower top steam exchanges heat with the tower bottom liquid, and the phase change heat of the tower top steam condensation is used as the heat source of the tower bottom liquid. The heat exchange temperature difference between the tower top steam and the tower bottom liquid is 6°C. After releasing heat, the part of the tower top steam is further cooled to 50°C through the cooler 5, and then refluxes to the tower top through the reflux tank. The mass ratio of the part of the tower top steam entering the condenser to the other part is 1:3. In the above distillation tower, the composition of the tower top material is (mass fraction): methanol 70%, dimethyl carbonate 20%, propylene oxide 10%; the composition of the tower bottom material is: sodium methoxide 66%, methanol 30%, dimethyl carbonate 0.2%, propylene glycol 2.8%, propylene carbonate 1%.

[0025] A special device for a dimethyl carbonate self-regenerative distillation method comprises: a distillation tower, a condenser, a reflux tank, a cooler, a compressor and a reboiler. The distillation tower is provided with a feed inlet, a gas phase outlet and a reflux port are provided at the tower top, and a discharge port and a tower bottom liquid inlet are provided at the tower bottom; the gas phase outlet at the tower top of the distillation tower is connected to two pipelines (two branches), one of which is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is connected to the reflux port, and the other is connected to the compressor, the outlet of the compressor is connected to the heat source inlet of the reboiler, the heat source outlet is connected to the cooler and the reflux tank in sequence, and the outlet of the reflux tank is connected to the reflux port of the distillation tower; the discharge port is connected to the material inlet of the reboiler 4, and the material outlet of the reboiler is connected to the tower bottom liquid inlet. The device is also provided with a circulation pump 9, a reflux pump 7 and a spray pump 8. The circulation pump is used to send the bottom liquid to the reboiler, the reflux pump is used to send part of the liquid in the reflux tank to the top of the tower for extraction, and the spray pump is used to send the liquid in the reflux tank to the inlet and outlet of the compressor to convert the superheated gas therein into saturated gas.

[0026] The method and device of the present invention can be used to recover the excess heat at the top of the dimethyl carbonate distillation tower for heating the bottom liquid. Since the heat provided by the top of the tower is greater than the heat load of the bottom liquid, the top steam is divided into two parts, one part is used to heat the bottom liquid, and the other part is cooled by circulating water. The method of the present invention can save a lot of circulating water and does not require additional steam consumption, thereby greatly saving operating costs.

[0027] Example 2

[0028] A method for self-heating distillation of dimethyl carbonate comprises: adding 18330kg / h methanol, 1200kg / h propylene oxide, 2200kg / h propylene carbonate and 100kg / h sodium methoxide catalyst at 70°C into a distillation tower, with a reflux ratio of 1.5. After distillation, the tower bottom temperature is 66°C, the tower top temperature is 58°C and the pressure is 83kPa. The tower top steam flows out from the tower top, a part of which enters the condenser for condensation and then refluxes to the tower top through the reflux tank; the other part of the tower top steam is compressed by the compressor and heated to 74°C and the pressure is 180kPa, wherein the pressure ratio of the compressor is 2.2. Then the tower top steam exchanges heat with the tower bottom liquid, and the phase change heat of the tower top steam after condensation is used as the heat source of the tower bottom liquid. The heat exchange temperature difference between the tower top steam and the tower bottom liquid is 8°C. After releasing heat, the part of the tower top steam is further cooled to 40°C through the cooler and then refluxes to the tower top through the reflux tank. The mass ratio of the part of the tower top steam entering the condenser to the other part is 1:3.5. In the above distillation tower, the composition of the tower top material is (mass fraction): methanol 74%, dimethyl carbonate 18%, propylene oxide 8%; the composition of the tower bottom material is: sodium methoxide 68%, methanol 30%, dimethyl carbonate 0.3%, propylene glycol 0.7%, propylene carbonate 1%.

[0029] A special device for a dimethyl carbonate self-regenerative distillation method comprises: a distillation tower, a condenser, a reflux tank, a cooler, a compressor and a reboiler. The distillation tower is provided with a feed inlet, a gas phase outlet and a reflux port are provided at the tower top, and a discharge port and a tower bottom liquid inlet are provided at the tower bottom. The gas phase outlet at the tower top of the distillation tower is connected to two pipelines, one of which is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is connected to the reflux port, and the other pipeline is connected to the compressor, the outlet of the compressor is connected to the heat source inlet of the reboiler, the heat source outlet is connected to the cooler and the reflux tank in sequence, and the outlet of the reflux tank is connected to the reflux port of the distillation tower; the discharge port is connected to the material inlet of the reboiler, and the material outlet of the reboiler is connected to the tower bottom liquid inlet. The device is also equipped with a circulating pump, a reflux pump and a spray pump. The circulating pump is used to send the bottom liquid to the reboiler, the reflux pump is used to send part of the liquid in the reflux tank to the top of the tower for extraction, and the spray pump is used to send the liquid in the reflux tank to the inlet and outlet of the compressor to convert the superheated gas therein into saturated gas.

[0030] Example 3

[0031] A method for self-heating distillation of dimethyl carbonate comprises: adding 21030kg / h methanol, 1100kg / h propylene oxide, 2130kg / h propylene carbonate and 110kg / h sodium methoxide catalyst at 70°C into a distillation tower, with a reflux ratio of 1.5, and after distillation, the tower bottom temperature is 63°C, the pressure is 350kPa, and the tower top temperature is 57°C, the pressure is 79kPa. The tower top steam flows out from the tower top, a part of which enters the condenser for condensation, and then refluxes to the tower top through the reflux tank; the other part of the tower top steam is compressed by the compressor and heated to 70°C, and the pressure is 160kPa, wherein the pressure ratio of the compressor is 2. Then the tower top steam exchanges heat with the tower bottom liquid, and the phase change heat of the tower top steam after condensation is used as the heat source of the tower bottom liquid, and the heat exchange temperature difference between the tower top steam and the tower bottom liquid is 7°C, and the part of the tower top steam is further cooled to 40°C through the cooler after releasing heat, and then refluxes to the tower top through the reflux tank. The mass ratio of the part of the tower top steam entering the condenser to the other part is 1:4.2. In the above distillation tower, the composition of the tower top material is (mass fraction): methanol 67%, dimethyl carbonate 18%, propylene oxide 15%; the composition of the tower bottom material is: sodium methoxide 70%, methanol 28%, dimethyl carbonate 0.5%, propylene glycol 0.5%, propylene carbonate 1%.

[0032] A special device for a dimethyl carbonate self-regenerative distillation method comprises: a distillation tower, a condenser, a reflux tank, a cooler, a compressor and a reboiler. The distillation tower is provided with a feed inlet, a gas phase outlet and a reflux port are provided at the tower top, and a discharge port and a tower bottom liquid inlet are provided at the tower bottom. The gas phase outlet at the tower top of the distillation tower is connected to two pipelines, one of which is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is connected to the reflux port, and the other pipeline is connected to the compressor, the outlet of the compressor is connected to the heat source inlet of the reboiler, the heat source outlet is connected to the cooler and the reflux tank in sequence, and the outlet of the reflux tank is connected to the reflux port of the distillation tower; the discharge port is connected to the material inlet of the reboiler, and the material outlet of the reboiler is connected to the tower bottom liquid inlet. The device is also equipped with a circulating pump, a reflux pump and a spray pump. The circulating pump is used to send the bottom liquid to the reboiler, the reflux pump is used to send part of the liquid in the reflux tank to the top of the tower for extraction, and the spray pump is used to send the liquid in the reflux tank to the inlet and outlet of the compressor to convert the superheated gas therein into saturated gas.

[0033] The operating costs of Example 1 and the prior art device under the same tower kettle heat load are compared as follows:

[0034]

[0035]

[0036] (Depending on the specific conditions of the location of the device, the steam price is 172 yuan / ton, the electricity price is 0.65 yuan / kWh, and the cooling water price is 0.2 yuan / m 3, calculated based on 8,000 hours of operation per year)

[0037] By comparison, it can be seen that, compared with the prior art, the method of the present invention can save about 71% of the annual operating cost.

[0038] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A method for self-heating distillation of dimethyl carbonate, characterized in that: include: Methanol, propylene carbonate and a catalyst are added to a distillation tower. After distillation, top steam flows out from the top of the tower. A part of the top steam enters a condenser for condensation and then refluxes to the top of the tower through a reflux tank. Another part of the top steam is compressed and heated by a compressor and used to heat the bottom liquid. This part of the top steam releases heat and is further cooled by a cooler and then refluxes to the top of the tower through a reflux tank. The mass ratio of the part of the top steam entering the condenser to the other part is 1:(1-5). The heat exchange temperature difference between the top steam and the bottom liquid is 6-8°C. The pressure ratio of the compressor is 1.5-3. The compressor is a screw compressor, a Roots compressor or a centrifugal compressor. The inlet steam temperature of the compressor is 50-65°C and the outlet temperature is 65-80°C.

2. The method according to claim 1, characterized in that The heat of the other part of the tower top steam used to heat the tower bottom liquid is the phase change heat of the tower top steam.

3. The method according to claim 1, characterized in that The outlet temperature of the cooler is 40-50°C.

4. The method according to claim 1, characterized in that: The reflux ratio of the distillation tower is 0.5-3, the top temperature is 50-65°C, the pressure is 75-90 kPa, and the bottom temperature is 60-75°C.

5. A device for self-heat regeneration distillation of dimethyl carbonate, characterized in that: include: A distillation tower, a condenser, a reflux tank, a cooler, a compressor and a reboiler, wherein the distillation tower is provided with a feed inlet, a gas phase outlet and a reflux port are provided at the top of the tower, and a discharge port and a tower bottom liquid inlet are provided at the bottom of the tower; the gas phase outlet at the top of the distillation tower is connected to two pipelines, one of which is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is connected to the reflux port, and the other is connected to the compressor, the outlet of the compressor is connected to the heat source inlet of the reboiler, the heat source outlet is connected to the cooler and the reflux tank in sequence, and the outlet of the reflux tank is connected to the reflux port of the distillation tower; the discharge port is connected to the material inlet of the reboiler, and the material outlet of the reboiler is connected to the tower bottom liquid inlet, the pressure ratio of the compressor is 1.5-3, and the compressor is a screw compressor, a Roots compressor or a centrifugal compressor.

6. The device according to claim 5, characterized in that The reboiler is a horizontal tube falling film reboiler.

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