CN1190405C - Energy saving separation technology of refining dimethyl ether and recovery carbon dioxide at the same time - Google Patents

Abstract

The present invention relates to an energy-saving separation technology for refining dimethyl ether and recovering carbon dioxide at the same time. Equipment for realizing the technology is composed of an adsorption and separation unit, a rectification and separation unit and an afterheat recovery and refrigeration unit. In the adsorption and separation unit, a proper solvent is adopted to recover DME and CO2 from the tail gas of reaction products. In the rectification and separation unit, highly purified CO2 is separated from a first rectifying tower, and highly purified DME is separated from a second rectifying tower. The afterheat recovery and refrigeration unit is composed of a recoverer for the afterheat of products at the bottom of the two rectifying towers and an adsorption type refrigeration unit, so that afterheat discharged by the system can be utilized to drive ammonium adsorption type refrigeration cycle to generate cooling capacity, and the cooling capacity is provided for the condensation load of the tower top of the first rectifying tower. By using the technology of the present invention, the recovery rate of DME of reaction product gas can reach more than 99%, and the purity can reach 99.9%; the concentration of CO2 can reach more than 96%, the utilization ratio is higher than 18%, and the rest is used as recycle gas to be mixed with the raw materials and enters a reactor for utilization again.

Description

Separation process for refining dimethyl ether while recovering carbon dioxide

technical field

The invention relates to a method for producing dimethyl ether (DME), in particular to a separation process for directly producing dimethyl ether from synthesis gas while recovering carbon dioxide (CO ₂ ).

Background technique

The US DOE/PC/90018-T7 proposed a process for methanol dehydration to DME. The process flow is shown in Figure 1. It consists of reactor R, methanol-water separator S1, non-condensable gas separator S2, and CO2-DME separation. Device S3 constitutes. After the reaction product gas containing DME leaves the reactor R, it is condensed by the first separator S1, methanol and water are separated from the bottom of S1 in the form of liquid phase; further condensed by the second separator S2, unreacted gas CO and _H Separation, DME and _CO2 enter the third separator S3 in the form of liquid phase; the separation of _CO2 and DME is finally completed in S3.

In the process for the preparation of DME disclosed in German Patent 4 222 655, in order to separate DME from the cycle gas of the high-pressure separator, the gas stream is scrubbed with methanol by means of a gas scrubber. Subsequently, the DME and _CO2 contained in the scrub bottom stream are recombined with the product stream from the high pressure liquid separator. In a second scrubber, the combined product streams are then washed with methanol or water in order to remove _CO2 from the product. Finally, the washed product, which contains substantially equal amounts of DME and methanol, is passed through several rectification steps to obtain a highly pure DME product.

Based on the synthesis method of DME, Japan Steel Tube Co., Ltd. (NKK) has patents in Japan: JP-10-182 532, JP-10-182 533, JP-10-182534, JP-10-182535 and JP-11-152 241, the preparation process of DME was proposed. Including the synthesis of DME, the recovery of _CO2 and unreacted gas, the use of liquefied natural gas cold energy utilization technology, etc. Its basic process is shown in Figure 2. R1 in the figure is a conversion reactor, and R2 is a DME synthesis reactor. It can be seen that its DME separation process is basically the same as the US DOE report in Figure 1 above. Its main part has applied for a Chinese patent (Patent No. CN 1 169 888).

Dalian Institute of Chemical Physics, Chinese Academy of Sciences disclosed the preparation and separation method of DME in Chinese patent CN 1 215 716A. The patent proposes that after the synthesis gas is reacted in the DME synthesis reactor, the product gas is exchanged with the feed gas synthesis gas through a heat exchanger, the liquid (mainly water) is separated in the gas-liquid separator, and methanol is removed in the absorption tower , the product DME in the reaction tail gas is extracted by the solution in the extraction tower, the unreacted raw synthesis gas is pressurized by the compressor and mixed with fresh synthesis gas before entering the reactor, and the extracted DME enters the desorption-fractionation tower with the solvent Desorb and further concentrate. The solvent from which DME has been removed is cooled and pumped back to the extraction tower for recycling. The concentrated DME product is condensed by the cooler and compressed by the compressor, and then sent to the cylinder.

Danish Holdo Topser (Topsoe) company respectively in the international patent WO 96/23 755 and Chinese patent CN 1 172 468A titled "Preparation Method of Fuel-grade DME", explained that from containing hydrogen and carbon oxides A method of preparing fuel-grade DME from syngas. In one or more catalytic reactors, the synthesis gas is converted into a mixed process gas of DME, methanol and water in the presence of a catalyst active in both methanol synthesis and methanol dehydration. The mixed process gas is cooled to obtain a liquid process phase comprising methanol, DME and water, and a gaseous process phase comprising unconverted synthesis gas and partly produced DME. The patented process includes the additional step of separating the gaseous and liquid phases, passing the liquid phase through a first distillation unit and distilling off an overhead product containing DME and methanol and discharging a bottoms stream containing methanol and water, passing the bottoms stream through a second A distillation unit and a stream containing methanol are distilled off, the methanol is transferred to a cleaning scrubber where the gaseous process phase is scrubbed with methanol and a scrubbing stream of DME and methanol is discharged from the unit. In the catalytic dehydration reaction, a portion of the methanol in the wash stream is converted to DME and water by contact with a dehydration catalyst. A product stream of DME, water and unconverted methanol is withdrawn from the dehydration reactor, and the overhead product from the first distillation unit is combined with the product stream from the dehydration reactor to obtain a combined product stream of fuel grade DME. This process can only recover about 73% of DME.

Contents of the invention

The object of the present invention is to provide a separation process for refining dimethyl ether and reclaiming carbon dioxide simultaneously, that is, a process for directly producing dimethyl ether and reclaiming carbon dioxide from synthesis gas. This process separates high-purity DME with a high recovery rate. At the same time, higher purity CO ₂ can be separated, and the whole process has higher energy utilization efficiency.

To achieve the above object, the process flow of the present invention consists of three parts: absorption separation unit, rectification separation unit and waste heat recovery refrigeration unit.

In the absorption separation unit, the reaction product is absorbed by the absorbent to separate the target product DME and the by-product CO ₂ , and then through the rectification separation unit to obtain DME with a purity higher than 99% and CO 2 with a purity higher than 96% CO ₂ .

Specifically, the reaction product gas from the DME synthesis reactor mainly contains H ₂ , CO, CO ₂ , N ₂ , CH ₄ and 11% to 15% (mass %) of DME, at 45t.h ^-1 to 55t The mass flow rate of .h ^-1 enters the absorption tower. Under the operating conditions of 20°C~50°C and 1.0MPa~3.0MPa, water, methanol or ethanol is used as the absorbent, and the H ₂ , CO, N ₂ in the reaction gas and CH ₄ and most of the CO ₂ are separated from the overhead stream in the gas phase. While DME, CO ₂ and a small amount of methanol, H ₂ , N ₂ and CO are absorbed by the solvent and sent to the rectification unit.

The rectification unit consists of two rectification columns. The concentration of CO ₂ separated at the top of the first rectification tower under the operating pressure of 1.0MPa ~ 3.0MPa, the temperature of the top of the tower -30°C ~ -20°C, the temperature of the bottom of the tower 160°C ~ 200°C, and the reflux ratio of 0.9 ~ 1.3 It can reach more than 96% (mass %), and the content of H ₂ , N ₂ and CO is about 5% (mass %). DME, H ₂ O and a small amount of methanol flow out from the tower kettle, and after being cooled by the first waste heat recovery device (or cooler), they enter the second rectification tower; the operating pressure is 0.4MPa ~ 1.5MPa, and the tower top temperature is 20 ℃～50℃, the temperature of the tower kettle is 140℃～180℃, the reflux ratio is 0.9～2.5, the liquid phase DME is separated from the top of the second rectification column, the mass concentration reaches 99.9%, and the recovery rate of DME reaches more than 99% . The absorbent containing a small amount of methanol flows out from the tower kettle, and after being cooled by the second waste heat recovery device (or cooler), it is recycled for the absorption tower. The heat obtained by the first waste heat recovery device and the second waste heat recovery device is sent to the ammonia absorption refrigeration unit to provide cooling capacity for the first rectification tower.

The above-mentioned absorbent can also be a mixture of water-methanol or water-ethanol.

The pressure of the first rectifying tower is 1.5MPa-2.0MPa, the temperature at the top of the tower is -30°C--24°C, and the temperature at the bottom of the tower is 180°C-200°C.

The pressure of the second rectifying tower is 0.5MPa-0.7MPa, the temperature at the top of the tower is 20°C-30°C, and the temperature at the bottom of the tower is 140°C-160°C.

The refrigeration unit is an ammonia absorption refrigeration unit.

Description of drawings

FIG. 1 is a schematic diagram of a process flow for preparing DME by methanol dehydration in the background technology.

Fig. 2 is a schematic diagram of the DME separation process of NKK in Japan in the background technology.

Fig. 3 is a schematic diagram of the process flow of the present invention.

Detailed ways

The content of the present invention will be further described in detail below through the embodiments and in conjunction with the accompanying drawings.

Embodiment 1: use water as the separation process of absorbent

Referring to the process flow description in Fig. 3, the product from the DME synthesis reactor (stream number 1) mainly contains H ₂ , CO, CO ₂ , N ₂ , CH ₄ and 14.4% (mass %) of DME, at 51.865t/ The mass flow rate of h enters the absorption tower of the absorption unit through the pressure reducing valve. Under the operating conditions of 25°C and 2.5MPa, water is used as the absorbent, and H ₂ , CO, N ₂ , CH ₄ and most of the CO ₂ in the reaction gas are separated from the top of the tower in gas phase (stream number 9). While DME, CO ₂ and a small amount of methanol are absorbed by water (stream number 2) and sent to the rectification unit.

The first rectifying tower is under operating pressure 18bar, tower top temperature-25.5 ℃, tower bottom temperature 191 ℃, reflux ratio is 1.1, separates CO from tower _top (stream number 4), concentration reaches 95.9% (mass %) , the total content of H ₂ , N ₂ , and CO was 4.1% (mass %). DME, H ₂ O and a small amount of methanol are extracted from the bottom of the tower (stream No. 3), and after being cooled by a cooler, enter the second rectification tower (stream No. 5). Under the conditions of operating pressure of 0.72MPa, tower top temperature of 21°C, tower bottom temperature of 153°C, and reflux ratio of 1.1, DME (stream number 6) is separated from the top of the second rectification tower, and the mass concentration reaches 99.9%. . The water containing a trace amount of methanol is extracted from the tower kettle (stream number 7), and after being cooled by a cooler, it is recycled for the absorption tower (stream number 8).

The two waste heat recoverers of the waste heat recovery refrigeration unit send the heat released by the first rectification tower and the second rectification tower bottom extract (energy flow number 10, 11) to the ammonia absorption refrigeration unit for refrigeration, which is used for the second rectification tower A rectification column provides cooling capacity (energy flow number 12).

The results are shown in Table 1 and Table 2. The DME recovery rate of this process is 99.79%, and the _CO2 recovery rate is 14.37%. The concentration of DME and _CO can reach 99.9% and 95.9% (mass %) respectively. In this process, the steam heating load of the two rectification towers is about 32.285MW, and the cooling capacity (temperature below -25°C) load at the top of the first rectification tower is about 0.520MW. Calculated according to the conversion coefficient of 0.18kg standard coal/h for 1kW steam and 0.19kg standard coal/h for 1kW cooling capacity, the separation unit consumption of DME per kg product is 0.788kg standard coal. Based on the carbon content in the feed gas, 72 mole percent is converted to the product DME, 18 mole percent is converted to by-product CO2, and 10 mole percent leaves the separation system into the recycle gas stream.

Table 1 Take water as the logistics balance of the separation process of absorbent (embodiment 1)

Logistics No. Raw Gas 1 2 2 3 4 6 7 9

Mass flow rate/t h ^-1 7.991 51.865 123.072 119.512 3.560 7.500 112.012 39.384

Composition/w%: H ₂ 13.2 21.7 0 0 0.7 0 0 28.5

N ₂ 3.1 10.1 0.1 0 2.2 0 0 13.1

CO 76.2 5.5 0.0 0 1.2 0 0 7.1

CO ₂ 7.4 45.3 2.8 0 95.9 0 0 50.9

A 0 0 0 0 0 0.0

Alcohol 0.1 0.0 0.0

H ₂ O 0 2.8 90.9 93.7 0.0 0.0 99.9 0.3

DME 0 14.5 6.1 6.3 0.0 99.5 0 0

Table 2 The energy consumption and waste heat recovery of the separation process using water as absorbent (embodiment 1) project Load MW public facilities steam load First distillation column kettle 23.132 The second distillation tower kettle 9.153 Low temperature cooling load The top of the first distillation column 0.520 cooling water load The top of the second distillation column 1.801 waste heat discharge First distillation column still distillate cooler 15.193 Second distillation column still distillate cooler 7.940 by-product 0

Example 2: Separation process with ethanol as absorbent and heat integration

Referring to the process flow description in Figure 1, the product from the DME synthesis reactor (stream number 1) mainly contains H ₂ , CO, CO ₂ , N ₂ , CH ₄ and 13.6% (mass %) of DME, at 51.865t/ The mass flow rate of h enters the absorption tower of the absorption unit. Under the operating conditions of 25°C and 2.5MPa, ethanol is used as the absorbent, and H ₂ , CO, N ₂ , CH ₄ and most of the CO ₂ in the reaction gas are separated from the top of the tower in gas phase. While DME, CO ₂ and a small amount of methanol are absorbed by the solvent (stream number 2) and sent to the rectification unit.

The first rectification tower is under operating pressure 20bar, tower top temperature-25.5 ℃, tower bottom temperature 170 ℃, reflux ratio is 1.3, separates CO from the tower _top (stream number 4), and the purity reaches 96.4% (mass %) , the total content of H ₂ , N ₂ , and CO was 3.9% (mass %). DME, H ₂ O and a small amount of methanol are extracted from the bottom of the tower (stream number 3), cooled by the first waste heat recovery device, and then enter the second rectification tower. Under the conditions of operating pressure of 0.52MPa, tower top temperature of 21°C, tower bottom temperature of 126°C, and reflux ratio of 2.5, DME (stream number 6) is separated from the top of the second rectification tower with a purity of 99.9%. (quality%). The water containing a trace amount of methanol is extracted from the tower kettle (stream number 7), and after being cooled by the second waste heat recovery device, it is recycled for the absorption tower (stream number 8).

The two waste heat recoverers of the waste heat recovery refrigeration unit send the heat released by the first rectification tower and the second rectification tower bottom extract (energy flow number 10, 11) to the ammonia absorption refrigeration unit for refrigeration, which is used for the second rectification tower A rectification column provides cooling capacity (energy flow number 12).

The results are shown in Table 3 and Table 4. The DME recovery rate of this process is 99.79%, and the _CO2 recovery rate is 12.3%. The concentration of DME and _CO can reach 99.9% and 96.4% (mass %) respectively. The steam load of the two rectification towers in this process is about 24.372MW. The two waste heat recoverers recover 3.697MW and 11.421MW of waste heat respectively, and generate about 3.780MW of cooling capacity at -33°C. In addition to satisfying the cooling load for separation of 0.403MW, it can also output about 3.377MW of cooling capacity at a temperature of about -33°C. Conditions such as the production scale of this embodiment are substantially the same as embodiment 1, and by the conversion factor of embodiment 1, the separation unit consumption of every kgDME of this embodiment is 0.499kg standard coal, saving 36.7% than embodiment 1. Based on the carbon content in the feed gas, 72 mole percent is converted to the product DME, 18 mole percent is converted to by-product CO2, and 10 mole percent leaves the separation system into the recycle gas stream.

Table 3 Take ethanol as absorbent and have the material flow balance of heat-integrated separation process (embodiment 2)

Logistics No. Raw Gas 1 2 2 3 4 6 7 9

Mass flow rate/t h ^-1 7.991 51.865 123.072 119.512 3.560 7.500 112.012 39.384

Composition/w%: H ₂ 13.2 20.5 0 0 0.5 0 0 26.2

N ₂ 3.1 9.7 0 0 2.0 0 0 12.3

CO 76.2 5.1 0 0 1.1 0 0 6.5

CO ₂ 7.4 47.3 2.2 0 96.4 0 0 53.1

Methanol 0 0.1 0 0 0 0 0 0 0

H ₂ O 0 2.4 0 0.9 0 0 1.0 0

DME 0 13.6 5.1 5.2 0 99.9 0 0

ETOH 0 1.3 91.7 93.8 0.0 0.0 99.0 1.8

Table 4 Energy consumption and waste heat recovery of separation process with ethanol as absorbent and heat integration

(Example 2) project Load MW public facilities steam load First distillation column kettle 18.257 The second distillation tower kettle 6.115 Low temperature cooling load The top of the first distillation column 0.403 cooling water load The top of the second distillation column 2.995 waste heat recovery First distillation column still distillate cooler 11.421 Second distillation column still distillate cooler 3.697 By-product cooling capacity (-33°C) 3.780

Claims (5)

1, a kind of refining dimethyl ether reclaims the separating technology of carbonic acid gas simultaneously, is made up of absorption extraction unit, rectifying separation unit and three parts of waste heat recovery refrigeration unit; Reaction product gas is with 45～55t.h ^-1Mass flow rate enter the absorption tower, under 20～50 ℃, the condition of 1.0～3.0MPa, make absorption agent with water, methyl alcohol or ethanol, absorption extraction goes out dme and carbonic acid gas from reaction product, is sent to rectification cell;

Rectification cell is two rectifying tower, and wherein first rectifying tower is at 1.0～3.0MPa, tower top temperature-30～-20 ℃, and 160～200 ℃ of tower still temperature, reflux ratio is 0.9～1.3 time, cat head is isolated carbonic acid gas;

Dme flows out from the tower still, through the cooling of first waste-heat recoverer, enters second rectifying tower, at 0.4～1.5MPa, and 20～50 ℃ of tower top temperatures, 140～180 ℃ of tower still temperature, reflux ratio are 0.9～2.5 time, cat head is isolated the liquid phase dme;

Absorption agent flows out from the tower still, returns the absorption tower and recycle after the cooling of second waste-heat recoverer;

The heat that first and second waste-heat recoverers are obtained is sent to the refrigeration unit refrigeration, for first rectifying tower provides cold.

2, separating technology as claimed in claim 1 is characterized in that, described absorption agent is the mixture of water-methanol or water-ethanol.

3, separating technology as claimed in claim 1 is characterized in that, the pressure of described first rectifying tower is 1.5～2.0MPa, tower top temperature-30～-24 ℃, 180～200 ℃ of tower still temperature.

4, separating technology as claimed in claim 1 is characterized in that, the pressure of described second rectifying tower is 0.5～0.8MPa, 20～30 ℃ of tower top temperatures, 140～160 ℃ of tower still temperature.

5, separating technology as claimed in claim 1 is characterized in that, described refrigeration unit is the ammonia absorption type refrigeration unit.

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