WO2016109987A1 - 一种光气合成塔催化剂更换的方法 - Google Patents

一种光气合成塔催化剂更换的方法 Download PDF

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WO2016109987A1
WO2016109987A1 PCT/CN2015/070863 CN2015070863W WO2016109987A1 WO 2016109987 A1 WO2016109987 A1 WO 2016109987A1 CN 2015070863 W CN2015070863 W CN 2015070863W WO 2016109987 A1 WO2016109987 A1 WO 2016109987A1
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phosgene
synthesis tower
mpa
phosgene synthesis
tower
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French (fr)
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张宏科
姚雨
赵东科
曹官义
刘小高
曹友念
李翀
马亚波
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Wanhua Chemical Group Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/06—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds in tube reactors; the solid particles being arranged in tubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/20—Carbon compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/008—Details of the reactor or of the particulate material; Processes to increase or to retard the rate of reaction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/0278—Feeding reactive fluids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/0292—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds with stationary packing material in the bed, e.g. bricks, wire rings, baffles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/80—Phosgene
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
    • C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/06—Details of tube reactors containing solid particles

Definitions

  • the invention relates to a method for replacing a catalyst of a phosgene synthesis tower, in particular to a method for rapidly removing phosgene in a catalyst when a catalyst of a phosgene synthesis tower is replaced.
  • Phosgene is an important organic intermediate that has many uses in pesticides, pharmaceuticals, engineering plastics, polyurethane materials, and military applications. There are many preparation methods for phosgene. At present, the main method for industrially producing phosgene is to use carbon monoxide and chlorine as raw materials and activated carbon as catalyst to synthesize phosgene. The commonly used activated carbon is coconut shell carbon and coal-based carbon. At present, 80% of the phosgene produced in the industry is used for the production of isocyanate, and is mainly used for the production of MDI (diphenylmethane diisocyanate), TDI (toluene diisocyanate) and polycarbonate.
  • MDI diphenylmethane diisocyanate
  • TDI toluene diisocyanate
  • polycarbonate polycarbonate
  • the production of isocyanate has strict requirements on the quality of phosgene of raw materials.
  • the free chlorine content in phosgene is controlled within 200ppm.
  • the free chlorine content in synthetic phosgene is generally controlled by 5-10% of CO relative to chlorine.
  • the catalyst activated carbon powder and catalytic capacity decrease, the free chlorine content in the synthetic phosgene increases, and the catalyst of the phosgene synthesis tower needs to be replaced.
  • Phosgene is a highly toxic chemical with a maximum allowable concentration of 0.5 ppm in air. Before replacing the activated carbon of the phosgene synthesis tower, it is necessary to completely purify the phosgene remaining in the synthesis tower and the phosgene adsorbed in the activated carbon. Activated carbon has a large adsorption capacity for phosgene saturation, and it takes a long time to purify the phosgene in the activated carbon completely, which affects the catalyst replacement time of the phosgene synthesis tower, and also consumes a large amount of nitrogen.
  • Patent CN102502700A discloses a method of replacing a catalyst with an ammonia system.
  • the patent describes the synthesis system to release carbon dioxide gas into the synthesis system after pressure relief, and the gas replacement of the system by carbon dioxide gas, but the effect of removing trace phosgene in the activated carbon is poor, resulting in a longer final purge time.
  • Patent CN202199338U discloses a solid catalyst replacement device.
  • the patent describes the addition of a vacuum valve and a material inlet at the top of the catalyst storage tank.
  • the vacuum valve is connected to the vacuum pump through a vacuum tube, and the material inlet is connected to the column tube containing the catalyst in the reactor through the material tube.
  • the phosgene synthesis tower activated carbon has a large amount of phosgene adsorption, and the synthesis tower outlet has extremely low phosgene concentration requirements. It is difficult to completely remove the phosgene in the synthesis tower in a short time directly through the vacuum system.
  • Patent CN101829526A discloses a catalyst replacement system, a catalyst replacement method, and a rectification column having the same.
  • the patent describes that the catalyst is processed by a rectification system and then pumped to the reaction system.
  • the phosgene synthesis tower is a gas-solid reaction system, and the activated carbon cannot be regenerated after reaching the service life.
  • the method of replacing the catalyst of the synthesis column described in the above patent has a long phosgene purge time and a complicated catalyst replacement device.
  • the process of rapidly purifying the phosgene synthesis tower and improving the catalyst replacement rate of the phosgene synthesis tower has not been disclosed in the report. Therefore, in view of the characteristics of the phosgene synthesis tower system and the properties of phosgene, it is necessary to develop a method which can quickly remove phosgene in the phosgene synthesis tower and facilitate safe operation.
  • the object of the present invention is to provide a method for replacing a phosgene synthesis tower catalyst (for example, activated carbon), which can rapidly remove phosgene from a phosgene synthesis tower by nitrogen purge and ammonia purge and optional ammonia gas pressure. Up to 0.5ppm or less, the method can significantly reduce the catalyst replacement time of the phosgene synthesis tower, the process flow is simple, the nitrogen consumption is reduced, and the process operation safety is high.
  • a phosgene synthesis tower catalyst for example, activated carbon
  • a method for rapidly removing phosgene in a catalyst prior to replacement of a catalyst (e.g., activated carbon) of a phosgene synthesis column comprising:
  • A) Nitrogen purge step After the phosgene synthesis tower stops the carbon monoxide and chlorine gas feed, the nitrogen gas is purged from the bottom of the phosgene synthesis tower, and the phosgene in the phosgene synthesis tower is purged to the phosgene decomposition tower until the light is measured.
  • the phosgene concentration at the outlet of the gas synthesis column is less than a predetermined level, and the concentration of phosgene is 0.5% (v/v) or less, preferably 0.05-0.5% (v/v), more preferably the total gas volume. 0.1-0.45% (v/v);
  • Ammonia purging step purging is continuously carried out from the bottom of the phosgene synthesis tower.
  • the phosgene concentration in the phosgene synthesis tower cannot be reduced to less than 0.5 ppm by using only nitrogen purge phosgene, and at least 6 is required when the phosgene concentration at the outlet of the synthesis tower is reduced to 0.1% by nitrogen purge.
  • the phosgene concentration is further reduced, since the phosgene is all adsorbed in the pores of the activated carbon at this time, the adsorption force is strong, and then the nitrogen gas is purged.
  • the nitrogen gas purge phosgene removal rate is significantly reduced, and the purge time is greatly extended. For example, it takes up to 30 to 35 days to reduce the phosgene concentration to 8 to 10 ppm.
  • the outlet concentration of the phosgene synthesis column after nitrogen purge is controlled to be 0.05% to 0.5%, preferably 0.1 to 0.45%.
  • step B) is preferred, while doing so can also increase the utilization of ammonia.
  • the phosgene synthesis column apparatus of the present invention may employ any of the tubular reactors known to those skilled in the art.
  • the fresh catalyst filling method of the phosgene synthesis tower may employ a catalyst filling method well known to those skilled in the art.
  • the above method further comprises:
  • Catalyst replacement step The catalyst (for example, activated carbon) is taken out from the phosgene synthesis column, and a fresh catalyst (for example, activated carbon) is loaded into the phosgene synthesis column.
  • the catalyst for example, activated carbon
  • a fresh catalyst for example, activated carbon
  • the D) catalyst (eg, activated carbon) replacement step is carried out by withdrawing the catalyst from the tubes of the phosgene synthesis column (eg, by disassembling the phosgene synthesis column) Upper and lower heads, the catalyst is taken out from the tube), then the phosgene synthesis tower tube is rinsed with a water gun, the synthesis tower tube is dried with hot gas, and finally a fresh catalyst (such as activated carbon) is filled into the synthesis column tube. .
  • a fresh catalyst such as activated carbon
  • the purge nitrogen temperature is from 80 ° C to 160 ° C, preferably from 100 ° C to 150 ° C.
  • the moisture content in nitrogen is 500 ppm or less, preferably 30 to 500 ppm, more preferably 50 to 300 ppm.
  • the purge nitrogen flow rate is from 50 to 500 Nm 3 /h, preferably from 100 to 400 Nm 3 /h.
  • the nitrogen purge time is from 1 to 10 days, preferably from 2 to 6 days.
  • the purge nitrogen pressure is 0.05 to 1.0 MPa, preferably 0.102 to 0.3 MPa, more preferably 0.15 to 0.25 MPa.
  • step C) the ammonia gas is purged until the phosgene synthesis column outlet phosgene concentration is 1 ppm or less, preferably 0.1 to 1 ppm, more preferably 0.2 to 0.5 ppm.
  • step B) ammonia gas is introduced into the phosgene synthesis column for rolling so that the pressure in the phosgene synthesis column reaches between 0.1 and 1 MPa, more preferably between 0.2 and 4 MPa, more preferably Between 0.5-3MPa, more preferred Between 0.7 and 2 MPa, for example 1 MPa, or a pressure of 0.5 to 5 MPa, preferably 1-3 MPa.
  • the two operations including rolling and opening the outlet of the phosgene synthesis tower may be performed once or repeatedly (ie, opening the phosgene synthesis tower outlet after rolling, and then closing the outlet and then rolling), for example 3 -10 times, preferably 4-8 times, preferably, the time for each pressing is 1-10 h, preferably 2-8 h.
  • the function of rolling is to promote the entry of ammonia into the pores of the activated carbon, and fully react with the phosgene adsorbed in the pores of the activated carbon to achieve the purpose of removing phosgene.
  • the repeated rolling and pressure relief operations are also beneficial to the light adsorbed in the pores of the activated carbon. The gas is released and reacts with ammonia.
  • the ammonia gas flow rate of the purge phosgene synthesis column is 50-200 Nm 3 /h, preferably 80-150 Nm 3 /h.
  • the ammonia gas pressure is usually from 0.05 to 1.0 MPa, preferably from 0.102 to 0.3 MPa, more preferably from 0.15 to 0.25 MPa.
  • the temperature of the ammonia gas is generally from 30 to 100 ° C, preferably from 40 to 80 ° C.
  • the ammonia for purging is (substantially) free of moisture (i.e., less than 20 ppm) or contains traces of moisture, such as 500 ppm or less, or 20-500 ppm, preferably 50-300 ppm of moisture.
  • Phosgene is an acid gas
  • ammonia is an alkaline gas. The reaction between the two is rapid. If the alkali solution is reacted with phosgene, the reaction will be uneven, and local acidity will cause corrosion of the equipment.
  • ammonia reacts rapidly with phosgene, and the reaction product is solid, free of moisture, and does not cause corrosion to equipment. Compared with phosgene, ammonia is less toxic. Therefore, the nitrogen purge of the present invention is followed by purging with ammonia gas.
  • the ammonia purge time is from 1 to 10 days, preferably from 2 to 5 days.
  • the phosgene and the excess ammonia gas blown by the phosgene synthesis tower are sent to a phosgene decomposition tower, and are decomposed by the inorganic acid under the catalysis of activated carbon.
  • the inorganic acid is hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid, preferably hydrochloric acid or sulfuric acid, more preferably hydrochloric acid.
  • the concentration of the inorganic acid is from 0.5 to 10% by mass, preferably from 1 to 5% by mass.
  • the hot gas used in step D) is one of air, nitrogen, CO 2 , preferably air.
  • the temperature of the hot gas is from 100 to 200 ° C, preferably from 120 to 180 ° C.
  • the hot gas pressure is 0.05 to 1.0 MPa, preferably 0.102 to 0.3 MPa, preferably 0.15 to 0.25 MPa.
  • Flow rate of the hot gas is 200-1000Nm 3 / h, preferably 300-800Nm 3 / h.
  • the dew point in the phosgene synthesis column is measured to be less than -30 ° C, preferably less than -40 ° C.
  • the catalyst of the phosgene synthesis column or the catalyst filled in the phosgene synthesis column tube is preferably activated carbon, more preferably coke, coal-based carbon, coconut shell charcoal, and even more preferably coconut shell charcoal.
  • the phosgene synthesis tower is pressurized with ammonia gas
  • the ammonia gas is introduced into the phosgene synthesis tower for rolling
  • ammonia gas is introduced into the phosgene synthesis tower which closes or closes the outlet in order to maintain the pressure inside the phosgene synthesis tower above atmospheric pressure, for example between 0.11-5 MPa, more preferably between 0.2-4 MPa, more preferably at Between 0.5 and 3 MPa, more preferably between 0.7 and 2 MPa, for example 1 MPa.
  • the time of each rolling or the time of maintaining the pressure is generally from 30 min to 10 h, preferably from 1 h to 9 h, more preferably from 2 h to 8 h, still more preferably from 2.5 h to 6 h.
  • the outlet of the phosgene synthesis tower is opened to discharge the ammonia gas.
  • the two operations including rolling and opening the outlet of the phosgene synthesis tower may be performed once or repeatedly (ie, opening the phosgene synthesis tower outlet after rolling, and then closing the outlet and then rolling), for example 3 -10 times, preferably 4-8 times.
  • Figure 1 is a schematic view of a phosgene synthesis column apparatus used in Examples 1-4, wherein reference numeral 1 is a phosgene synthesis column.
  • the phosgene synthesis tower outlet phosgene concentration determination method can be determined by an iodometric method known to those skilled in the art.
  • the phosgene synthesis tower stops feeding, 100 Nm 3 /h of nitrogen gas is introduced from the bottom of the synthesis tower, the nitrogen temperature is 100 ° C, the moisture content in the nitrogen gas is 100 ppm, the nitrogen pressure is 0.15 MPa, and the nitrogen gas is continuously passed for 2 days, and the measurement is blown.
  • the phosgene concentration at the outlet of the phosgene synthesis tower after sweeping was 0.45% (v/v).
  • the ammonia gas is purged, firstly introduced into the ammonia gas for rolling, and the phosgene synthesis tower is pressed to 1 MPa, and the pressure is increased for 2 hours, and then the phosgene synthesis tower outlet is opened, and the pressure is repeatedly pressed 8 times.
  • the ammonia gas is continuously supplied, the ammonia gas flow rate is 80Nm 3 /h, the ammonia gas temperature is 40 ° C, the ammonia gas content is 50 ppm, the ammonia gas is purged for 5 days, and the phosgene synthesis tower outlet phosgene concentration is determined to be 0.5. Ppm.
  • the phosgene enters the phosgene decomposition column to decompose, the inorganic acid concentration is 1%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the tube is purged with hot air at 120 ° C.
  • the hot air pressure is 0.15 MPa
  • the hot air flow rate is 300 Nm 3 /h
  • the dew point of the synthesis tower is determined as - 40 ° C.
  • the phosgene concentration at the outlet of the phosgene synthesis tower and the total purge time are shown in Table 1.
  • the phosgene synthesis tower stops feeding, 200 Nm 3 /h of nitrogen gas is introduced from the bottom of the synthesis tower, the nitrogen temperature is 120 ° C, the moisture content in nitrogen is 300 ppm, the nitrogen pressure is 0.2 MPa, and the nitrogen gas is continuously passed for 3 days, and the measurement is blown.
  • the phosgene concentration at the exit of the phosgene synthesis tower was 0.3% (v/v).
  • ammonia gas was introduced for rolling, and the phosgene synthesis tower was pressed to 2 MPa, and pressed for 4 hours, and then the phosgene synthesis tower outlet was opened, and the pressure was repeatedly pressed 4 times.
  • the ammonia gas purge was continued, the ammonia gas flow rate was 100 Nm 3 /h, the ammonia gas temperature was 60 ° C, the ammonia gas was purged for 3 days, and the phosgene synthesis tower outlet phosgene concentration was determined to be 0.4 ppm.
  • the phosgene enters the phosgene decomposition tower to decompose, the inorganic acid concentration is 2%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the tube is purged with hot nitrogen at 150 ° C.
  • the hot nitrogen pressure is 0.25 MPa
  • the hot nitrogen flow rate is 500 Nm 3 /h
  • the dew point of the synthesis tower is determined as - 40 ° C.
  • the phosgene concentration at the outlet of the phosgene synthesis tower and the total purge time are shown in Table 1.
  • the phosgene synthesis tower stops feeding, 400 Nm 3 /h of nitrogen gas is introduced from the bottom of the synthesis tower, the nitrogen temperature is 150 ° C, the moisture content in the nitrogen is 200 ppm, the nitrogen pressure is 0.25 MPa, and the nitrogen gas is continuously passed for 6 days.
  • the phosgene concentration at the exit of the phosgene synthesis tower was 0.1% (v/v).
  • the ammonia gas is purged, firstly introduced into the ammonia gas for rolling, the phosgene synthesis tower is pressed to 3Mpa, the pressure is pressed for 5 hours, and then the phosgene synthesis tower outlet is opened, so that the rolling is repeated five times.
  • the ammonia gas purge was continued, the ammonia gas flow rate was 150 Nm 3 /h, the ammonia gas temperature was 80 ° C, the ammonia gas was purged for 1 day, and the phosgene synthesis tower outlet phosgene concentration was determined to be 0.2 ppm.
  • the phosgene enters the phosgene decomposition column to decompose, the inorganic acid concentration is 5%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the tube is purged with 150 ° C hot air.
  • the hot air pressure is 0.2 MPa
  • the hot air flow is 800 Nm 3 /h
  • the dew point of the synthesis tower is determined as - 40 ° C.
  • the phosgene concentration at the outlet of the phosgene synthesis tower and the total purge time are shown in Table 1.
  • the phosgene synthesis tower stops feeding, 100 Nm 3 /h of nitrogen gas is introduced from the bottom of the synthesis tower, the nitrogen temperature is 100 ° C, the moisture content in the nitrogen gas is 100 ppm, the nitrogen pressure is 0.15 MPa, and the nitrogen gas is continuously passed for 2 days, and the measurement is blown.
  • the phosgene concentration at the outlet of the phosgene synthesis tower after sweeping was 0.45% (v/v).
  • the ammonia gas is continuously supplied, the ammonia gas flow rate is 80Nm 3 /h, the ammonia gas temperature is 40 ° C, the ammonia gas content is 50 ppm, the ammonia gas is purged for 7 days, and the phosgene synthesis tower outlet phosgene concentration is determined to be 0.5 ppm. .
  • the phosgene enters the phosgene decomposition column to decompose, the inorganic acid concentration is 1%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the tube is purged with hot air at 120 ° C.
  • the hot air pressure is 0.15 MPa
  • the hot air flow is 300 Nm 3 /h
  • the dew point of the synthesis tower is determined as - 40 ° C.
  • the phosgene concentration at the outlet of the phosgene synthesis tower and the total purge time are shown in Table 1.
  • the phosgene synthesis tower stops feeding, 500 Nm 3 /h of nitrogen gas is introduced from the bottom of the phosgene synthesis tower, the nitrogen temperature is 120 ° C, the moisture content in nitrogen is 100 ppm, the nitrogen pressure is 0.5 MPa, and the nitrogen gas is continuously passed for 35 days.
  • the phosgene concentration at the outlet of the phosgene synthesis tower after the purge was measured to be 8.1 ppm.
  • the phosgene enters the phosgene decomposition tower to decompose, the inorganic acid concentration is 2%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the synthesis tower tube is purged with 150 ° C hot nitrogen gas, and the dew point of the synthesis tower outlet is determined to be -40 ° C, and the phosgene synthesis tower outlet phosgene concentration and total purge are measured.
  • the time is shown in Table 1.
  • the phosgene synthesis tower stops feeding, 500 Nm 3 /h of nitrogen gas is introduced from the bottom of the phosgene synthesis tower, the nitrogen temperature is 150 ° C, the moisture content in nitrogen is 100 ppm, the nitrogen pressure is 0.2 MPa, and the nitrogen gas is continuously passed for 30 days.
  • the phosgene concentration at the outlet of the phosgene synthesis tower after the purge was measured to be 10.2 ppm.
  • the phosgene enters the phosgene decomposition column to decompose, the inorganic acid concentration is 1%, and the inorganic acid is hydrochloric acid.
  • the phosgene synthesis tower tube is cleaned with a water gun, and the synthesis tower tube is purged with 150 ° C hot nitrogen gas, and the dew point of the synthesis tower outlet is determined to be -40 ° C, and the phosgene synthesis tower outlet phosgene concentration and total purge are measured.
  • the time is shown in Table 1.

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Abstract

一种光气合成塔催化剂更换时催化剂中光气快速脱除的方法。该方法采用先用氮气吹扫将吸附在光气合成塔催化剂活性炭中容易脱附的光气吹扫出来，再用氨气吹扫，氨气与光气合成塔催化剂中的较难脱附的光气反应除去。然后用水枪将光气合成塔冲洗后用热气体干燥。吹扫后光气合成塔出口光气含量低于0.5ppm，能够明显降低光气合成塔吹扫光气的时间，大大减少了氮气消耗量，并提高工艺操作的安全性。

Description

一种光气合成塔催化剂更换的方法 技术领域
本发明涉及一种光气合成塔催化剂更换的方法，特别涉及一种光气合成塔催化剂更换时催化剂中光气快速脱除的方法。
技术背景
光气是一种重要的有机中间体，在农药、医药、工程塑料、聚氨酯材料以及军事上都有许多用途。光气的制备方法很多，目前工业化制造光气的主要方法是用一氧化碳和氯气作原料，以活性炭为催化剂合成光气，常用的活性炭是椰壳炭和煤基炭。目前工业上生产的光气80％用于异氰酸酯的生产，主要用于MDI(二苯基甲烷二异氰酸酯)、TDI(甲苯二异氰酸酯)及聚碳酸脂的生产。生产异氰酸酯对原料光气质量要求很严格，其中光气中游离氯含量控制在200ppm以内，工业上一般采用CO相对于氯气过量5-10％来控制合成光气中游离氯含量。光气合成后期，随着催化剂活性炭粉化及催化能力下降，合成光气中游离氯含量升高，需要更换光气合成塔的催化剂。
光气作为一种剧毒化学品，空气中最高允许浓度为0.5ppm。更换光气合成塔活性炭前需要将合成塔中残留的光气及活性炭中吸附的光气完全吹扫出来。活性炭对光气饱和吸附量较大，需要很长时间吹扫才能将活性炭中光气完全脱除，影响光气合成塔催化剂更换时间，还需要消耗大量氮气。
专利CN102502700A公开了一种合成氨系统更换催化剂的方法。专利中描述合成系统泄压后向合成系统通入二氧化碳气体，利用二氧化碳气体对系统进行气体置换，但是对于脱除活性炭中的微量光气效果较差，导致最终吹扫时间较长。
专利CN202199338U公开了一种固体催化剂更换装置。专利中描述通过在催化剂储罐顶部增加抽真空阀及物料进口，抽真空阀通过真空管与真空泵连接，物料进口通过物料管与反应器内盛装催化剂的列管联通。但光气合成塔活性炭对光气吸附量较大，且合成塔出口对光气浓度要求极低，直接通过真空系统很难在较短时间将合成塔中光气完全脱除。
专利CN101829526A公开了一种催化剂更换系统、催化剂更换方法及具有该系统的精馏塔。专利描述催化剂通过精馏系统处理后再通过泵送至反应系统。但是光气合成塔为气-固反应系统，且活性炭到达使用寿命后不可再生。
上述专利中所描述的合成塔催化剂更换的方法存在光气吹扫时间较长、催化剂更换设备复杂。报道中尚未披露快速吹扫光气合成塔，提高光气合成塔催化剂更换速度的工艺方法。因此针对光气合成塔体系的特点及光气的性质，需要开发一种既能快速脱除光气合成塔中光气并且便于安全操作的方法。
现有技术中采用单纯氮气直接吹扫光气合成，对于吹扫后期光气浓度较低情况下需要消耗大量氮气，且吹扫速度很慢，合成塔中仍残留部分光气，更换合成塔催化剂时安全风险很大。
发明内容
本发明的目的是提供一种光气合成塔催化剂(例如活性炭)更换的方法，通过氮气吹扫及氨气吹扫和任选的氨气憋压能够快速将光气合成塔中光气脱除至0.5ppm以下，该方法能够显著降低光气合成塔催化剂更换时间，工艺流程简单，降低氮气消耗量且工艺操作安全性高。
为了达到以上目的，本发明采用如下技术方案：
根据本发明的第一个实施方案，提供在光气合成塔的催化剂(例如活性炭)更换之前快速脱除催化剂中光气的方法，该方法包括：
A)氮气吹扫步骤：光气合成塔停止一氧化碳及氯气进料后，从光气合成塔底部通入氮气吹扫，将光气合成塔中光气吹扫至光气分解塔，直至测定光气合成塔出口光气浓度低于规定的水平为止，相对于气体总体积量，光气的浓度为0.5％(v/v)以下，优选为0.05-0.5％(v/v)，更优选为0.1-0.45％(v/v)；
任选的B)憋压步骤：关闭光气合成塔的出口，从光气合成塔底部通入氨气，让光气合成塔憋压，然后打开光气合成塔的出口而排出光气合成塔内的气体，其中，包括憋压和打开光气合成塔的出口的这两个操作过程进行一次或重复进行多次；
和
C)氨气吹扫步骤：从光气合成塔底部持续通入氨气进行吹扫。
一般来说，仅采用氮气吹扫光气的方式无法将光气合成塔中光气浓度降低至0.5ppm以下，而且采用氮气吹扫将合成塔出口光气浓度降至0.1％时，至少需要6天时间，若进一步降低光气浓度，由于此时光气全部吸附在活性炭孔道内，吸附力较强，再用氮气吹扫， 氮气吹扫光气脱除速率显著下降，吹扫时间大大延长，例如将光气浓度降到8～10ppm需要长达30～35天时间。再者如果氮气吹扫后，光气浓度过高，则需要的氨气量也较多，此外，生成的氯化铵及尿素粉末较多，会堵塞合成塔列管，导致合成塔压降偏高，光气合成塔压力上升。因此氮气吹扫后光气合成塔出口浓度控制在0.05％-0.5％，优选0.1～0.45％。
在通入氨气的初期，光气合成塔中光气还是比较多，为防止初期氨气将光气带出合成塔在后续管道中反应生成的固体物堵塞管道，先憋压一定时间，使得光气与氨气反应，然后再持续通入氨气。因此，步骤B)是优选的，同时这样做还可以提高氨气的利用率。
本发明所述的光气合成塔装置可以采用本领域技术人员公知的任意列管式反应器。光气合成塔新鲜催化剂填充方式可以采用本领域技术人员公知的催化剂填充方法。
进一步优选的是，上述方法还包括：
D)催化剂更换步骤：从光气合成塔中取出催化剂(例如活性炭)，将新鲜的催化剂(例如活性炭)装载到光气合成塔中。
优选的是，对于使用列管式光气合成塔的情况，D)催化剂(例如活性炭)更换步骤是如下进行的：从光气合成塔的列管中取出催化剂(例如通过拆开光气合成塔上下封头，将催化剂从列管中捅出)，然后用水枪冲洗光气合成塔列管，再用热气体干燥合成塔列管，最后将新鲜催化剂(例如活性炭)填充到合成塔列管中。
优选的是，步骤A)中，吹扫氮气温度为80℃-160℃，优选100℃-150℃。氮气中水分含量为500ppm以下，优选30-500ppm，更优选50-300ppm。
优选的是，在步骤A)中，吹扫氮气流量为50-500Nm3/h，优选100-400Nm3/h。氮气吹扫时间为1-10天，优选2-6天。吹扫氮气压力为0.05～1.0MPa，优选0.102-0.3MPa，更优选0.15-0.25MPa。
优选的是，在步骤C)中，氨气吹扫直至光气合成塔出口光气浓度为1ppm以下，优选0.1-1ppm，更优选为0.2-0.5ppm。
优选的是，在步骤B)中，在光气合成塔中通入氨气进行憋压使得光气合成塔内的压力达到0.11-5MPa之间，更优选在0.2－4MPa之间，更优选在0.5－3MPa之间，更优选 在0.7-2MPa之间，例如1MPa,或达到0.5-5MPa，优选为1-3MPa的压力。包括憋压和打开光气合成塔的出口的这两个操作过程可进行一次或可重复进行多次(即，憋压后打开光气合成塔出口，然后关闭该出口再憋压)，例如3-10次，优选为4-8次，优选的是，每次憋压的时间为1-10h，优选为2-8h。一般而言，每次憋压的时间越短，憋压的反复次数越多，反之，每次憋压的时间越长，憋压的反复次数越少。憋压的作用在于促进氨气进入活性炭孔道，使其与吸附在活性炭孔道中的光气充分反应达到去除光气的目的，反复憋压及泄压的操作还有利于吸附在活性炭孔道中的光气释放出来，与氨气反应。
优选是，在C)氨气吹扫步骤中，吹扫光气合成塔的氨气流量为50-200Nm3/h，优选80-150Nm3/h。氨气压力通常为0.05～1.0MPa，优选0.102-0.3MPa，更优选0.15-0.25MPa。氨气的温度一般为30-100℃，优选40-80℃。优选的是，吹扫用的氨气(基本上)不含水分(即低于20ppm)或含有微量水分，例如500ppm以下，或20-500ppm，优选50-300ppm的水分。光气属于酸性气体，氨气为碱性气体，二者反应迅速，如果选用碱液与光气反应的话会造成反应不均匀，局部酸性会造成设备腐蚀。此外，氨气与光气反应迅速，反应产物为固体，没有水分，不会对设备造成腐蚀。与光气相比，氨气毒害性小。因此本发明氮气吹扫后选用氨气进行吹扫。
一般，在C)氨气吹扫步骤中，氨气吹扫时间为1-10天，优选为2-5天。
通常，光气合成塔吹扫出的光气及过量氨气被送至光气分解塔中，采用无机酸在活性炭的催化下分解。优选，所述的无机酸为盐酸、硫酸、磷酸、硝酸，优选为盐酸或硫酸，更优选为盐酸。优选的是，无机酸的浓度为0.5-10质量％，优选为1-5质量％。
优选的是，在步骤D)中所使用的热气体为空气、氮气、CO2中的一种，优选为空气。热气体的温度为100-200℃，优选为120-180℃。热气体压力为0.05～1.0MPa，优选0.102-0.3MPa，优选为0.15-0.25MPa。热气体的流量为200-1000Nm3/h，优选为300-800Nm3/h。
优选的是，光气合成塔用热气体干燥后，测得光气合成塔内的露点为低于-30℃，优选为低于-40℃。
一般，光气合成塔的催化剂或填充到光气合成塔列管中的催化剂优选是活性炭，更优选为焦炭、煤基炭、椰壳炭，再更优选为椰壳炭。
在本申请中，“光气合成塔用氨气憋压”，或“在光气合成塔中通入氨气进行憋压” 是指在封闭或关闭出口的光气合成塔中通入氨气以便保持光气合成塔内部的压力高于大气压，例如在0.11-5MPa之间，更优选在0.2－4MPa之间，更优选在0.5－3MPa之间，更优选在0.7-2MPa之间，例如1MPa。每一次憋压的时间或每一次保持压力的时间一般是30min－10h，优选1h-9h，更优选2h-8h，更优选2.5h-6h。憋压之后打开光气合成塔的出口以排出氨气。包括憋压和打开光气合成塔的出口的这两个操作过程可进行一次或可重复进行多次(即，憋压后打开光气合成塔出口，然后关闭该出口再憋压)，例如3-10次，优选为4-8次。
在本申请中，“任选的”表示有或没有。“任选地”表示进行或不进行。
与现有的技术相比，本方法的优点如下：
(1)先用氮气将光气合成塔中大量容易脱除的光气吹扫出来，然后用氨气将剩余较难脱除的光气反应除去，保证光气合成塔出口光气浓度较低。
(2)氮气吹扫后用氨气吹扫，氨气能够与吸附在活性炭孔隙中较难脱除的光气直接反应除去，大大缩短了光气合成塔光气脱除时间，同时操作更加安全。
(3)解决了目前光气合成塔更换催化剂过程中光气脱除时间较长问题并降低了光气吹扫过程中光气泄露的风险，提高工艺安全性。
附图说明
图1是实施例1-4中使用的光气合成塔装置示意图，其中附图标记1为光气合成塔。
具体实施方式
下面用实施例进一步说明本发明，但本发明不受其限制。下列实施例中未注明具体条件的实验方法，通常按照常规条件。
光气合成塔出口光气浓度测定方法可通过本领域技术人员已知的碘量法测定。
实施例1
光气合成塔停止进料后，从合成塔底部通入100Nm3/h的氮气，氮气温度为100℃，氮气中水分含量为100ppm，氮气压力为0.15MPa，氮气持续通入2天，测定吹扫后光气合成塔出口光气浓度为0.45％(v/v)。然后通入氨气吹扫，先通入氨气进行憋压，光气合成塔憋压至1MPa，憋压2h，然后打开光气合成塔出口，如此反复憋压8次。然后再持续通入氨气，氨气流量为80Nm3/h，氨气温度为40℃，氨气中水分含量为50ppm，氨气吹扫5天，测定光气合成塔出口光气浓度为0.5ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为1％，无机酸为盐酸。氨气吹扫结束后，用水枪清理光气合成塔列管后，用 120℃热空气吹扫列管，热空气压力为0.15MPa，热空气流量为300Nm3/h，测定合成塔露点为-40℃。光气合成塔出口光气浓度及吹扫总时间如表1所示。
实施例2
光气合成塔停止进料后，从合成塔底部通入200Nm3/h的氮气，氮气温度为120℃，氮气中水分含量为300ppm，氮气压力为0.2MPa，氮气持续通入3天，测定吹扫后光气合成塔出口光气浓度为0.3％(v/v)。先通入氨气进行憋压，光气合成塔憋压至2MPa，憋压4h，然后打开光气合成塔出口，如此反复憋压4次。然后再持续通入氨气吹扫，氨气流量为100Nm3/h，氨气温度为60℃，氨气吹扫3天，测定光气合成塔出口光气浓度为0.4ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为2％，无机酸为盐酸。氨气吹扫结束后，用水枪清理光气合成塔列管后，用150℃热氮气吹扫列管，热氮气压力为0.25MPa，热氮气流量为500Nm3/h，测定合成塔露点为-40℃。光气合成塔出口光气浓度及吹扫总时间如表1所示。
实施例3
光气合成塔停止进料后，从合成塔底部通入400Nm3/h的氮气，氮气温度为150℃，氮气中水分含量为200ppm，氮气压力为0.25MPa，氮气持续通入6天，测定吹扫后光气合成塔出口光气浓度为0.1％(v/v)。然后通入氨气吹扫，先通入氨气进行憋压，光气合成塔憋压至3Mpa，憋压5h，然后打开光气合成塔出口，如此反复憋压5次。然后再持续通入氨气吹扫，氨气流量为150Nm3/h，氨气温度为80℃，氨气吹扫1天，测定光气合成塔出口光气浓度为0.2ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为5％，无机酸为盐酸。氨气吹扫结束后，用水枪清理光气合成塔列管后，用150℃热空气吹扫列管，热空气压力为0.2MPa，热空气流量为800Nm3/h，测定合成塔露点为-40℃。光气合成塔出口光气浓度及吹扫总时间如表1所示。
实施例4
光气合成塔停止进料后，从合成塔底部通入100Nm3/h的氮气，氮气温度为100℃，氮气中水分含量为100ppm，氮气压力为0.15MPa，氮气持续通入2天，测定吹扫后光气合成塔出口光气浓度为0.45％(v/v)。然后持续通入氨气，氨气流量为80Nm3/h，氨气温度为40℃，氨气中水分含量为50ppm，氨气吹扫7天，测定光气合成塔出口光气浓度为0.5ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为1％，无机酸为盐酸。氨气吹扫结束后，用水枪清理光气合成塔列管后，用120℃热空气吹扫列管，热空气压力为0.15 MPa，热空气流量为300Nm3/h，测定合成塔露点为-40℃。光气合成塔出口光气浓度及吹扫总时间如表1所示。
对比例1
光气合成塔停止进料后，从光气合成塔底部通入500Nm3/h的氮气，氮气温度为120℃，氮气中水分含量为100ppm，氮气压力为0.5MPa，氮气持续通入35天，测定吹扫后光气合成塔出口光气浓度为8.1ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为2％，无机酸为盐酸。氮气吹扫结束后，用水枪清理光气合成塔列管，用150℃热氮气吹扫合成塔列管，测定合成塔出口露点为-40℃，光气合成塔出口光气浓度及吹扫总时间如表1所示。
对比例2
光气合成塔停止进料后，从光气合成塔底部通入500Nm3/h的氮气，氮气温度为150℃，氮气中水分含量为100ppm，氮气压力为0.2MPa，氮气持续通入30天，测定吹扫后光气合成塔出口光气浓度为10.2ppm。吹扫后光气进入光气分解塔分解，无机酸浓度为1％，无机酸为盐酸。氮气吹扫结束后，用水枪清理光气合成塔列管，用150℃热氮气吹扫合成塔列管，测定合成塔出口露点为-40℃，光气合成塔出口光气浓度及吹扫总时间如表1所示。
表1分析结果
Figure PCTCN2015070863-appb-000001

Claims (14)

  1. 在光气合成塔的催化剂更换之前快速脱除催化剂中光气的方法，该方法包括：
    A)氮气吹扫步骤：光气合成塔停止一氧化碳及氯气进料后，从光气合成塔底部通入氮气吹扫，将光气合成塔中光气吹扫至光气分解塔，直至测定光气合成塔出口光气浓度为0.05-0.5％(v/v)，相对于气体总体积量，优选为0.1-0.45％(v/v)；
    任选的B)憋压步骤：关闭光气合成塔的出口，从光气合成塔底部通入氨气，让光气合成塔憋压，然后打开光气合成塔的出口而排出光气合成塔内的气体，其中，包括憋压和打开光气合成塔的出口的这两个操作过程进行一次或重复进行多次；
    和
    C)氨气吹扫步骤：从光气合成塔底部持续通入氨气进行吹扫。
  2. 根据权利要求1所述的方法，其进一步包括：
    D)催化剂更换步骤：
    从光气合成塔中取出催化剂，将新鲜的催化剂装载到光气合成塔中；或
    当使用列管式光气合成塔时，从光气合成塔的列管中取出催化剂，然后用水枪冲洗光气合成塔列管，再用热气体干燥合成塔列管，最后将新鲜催化剂填充到合成塔列管中。
  3. 根据权利要求1或2所述的方法，其特征在于，步骤A)中，吹扫氮气温度为80℃-160℃，优选100℃-150℃，和/或，氮气中水分含量为500ppm以下，优选30-500ppm，更优选50-300ppm。
  4. 根据权利要求1-3中任一项所述的方法，其特征在于，在步骤A)中，吹扫氮气流量为50-500Nm3/h，优选100-400Nm3/h，氮气吹扫时间为1-10天，优选2-6天，吹扫氮气压力为0.05～1.0MPa，优选0.102-0.3MPa，更优选0.15-0.25MPa。
  5. 根据权利要求1-4中任一项所述的方法，其特征在于，在步骤C)中，氨气吹扫直至光气合成塔出口光气浓度为1ppm以下，优选0.1-1ppm，更优选为0.2-0.5ppm。
  6. 根据权利要求1-5中任一项所述的方法，其特征在于，在步骤B)中，在光气合 成塔中通入氨气进行憋压使得光气合成塔内的压力达到0.11-5MPa之间，更优选在0.2－4MPa之间，更优选在0.5－3MPa之间，更优选在0.7-2MPa之间，例如1MPa，或达到0.5-5MPa，优选为1-3MPa；和/或，包括憋压和打开光气合成塔的出口的这两个操作过程重复进行3-10次，优选为4-8次，优选的是，每次憋压的时间为1-10h，优选为2-8h。
  7. 根据权利要求1-6中任一项所述的方法，其特征在于，在C)氨气吹扫步骤中，吹扫光气合成塔的氨气流量为50-200Nm3/h，优选80-150Nm3/h，和/或，氨气压力0.05～1.0MPa，优选0.10-0.3MPa，更优选0.15-0.25MPa，和/或，氨气温度为30-100℃，优选40-80℃；优选的是，吹扫用的氨气不含水分或含有微量水分，例如20-500ppm，优选50-300ppm的水分。
  8. 根据权利要求1-7的任一项所述的方法，其特征在于，在C)氨气吹扫步骤中，氨气吹扫时间为1-10天，优选为2-5天。
  9. 根据权利要求1-8的任一项所述的方法，其特征在于，光气合成塔吹扫出的光气及过量氨气被送至光气分解塔中，采用无机酸在活性炭的催化下分解。
  10. 根据权利要求8所述的方法，其特征在于无机酸为盐酸、硫酸、磷酸、硝酸，优选为盐酸或硫酸，更优选为盐酸。
  11. 根据权利要求9或10所述的方法，其特征在于，无机酸的浓度为0.5-10质量％，优选为1-5质量％。
  12. 根据权利要求2所述的方法，其特征在于，在步骤D)中所使用的热气体为空气、氮气、CO2中的一种，优选为空气，和/或，热气体的温度为100-200℃，优选为120-180℃，和/或，热气体压力为0.05～1.0MPa，优选0.102-0.3MPa，优选为0.15-0.25MPa，和/或，热气体的流量为200-1000Nm3/h，优选为300-800Nm3/h。
  13. 根据权利要求2－12中任何一项所述的方法，其特征在于，光气合成塔用热气体干燥后测得光气合成塔内的露点为低于-30℃，优选为低于-40℃。
  14. 根据权利要求1－13的中任一项所述的方法，其特征在于，光气合成塔的催化剂或填充到光气合成塔列管中的催化剂是活性炭，优选为焦炭、煤基炭、椰壳炭，更优选为椰壳炭。
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