CN110449147B - Catalyst for phosgene synthesis and preparation method and application thereof - Google Patents
Catalyst for phosgene synthesis and preparation method and application thereof Download PDFInfo
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- CN110449147B CN110449147B CN201910732986.4A CN201910732986A CN110449147B CN 110449147 B CN110449147 B CN 110449147B CN 201910732986 A CN201910732986 A CN 201910732986A CN 110449147 B CN110449147 B CN 110449147B
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Abstract
The invention relates to a phosgene synthesis catalyst, a preparation method and application thereof. The active components of the catalyst comprise active carbon and carbon nano tubes, the graphitization degree of the active carbon has the strength ratio of a D band to a G band in Raman spectrum analysis of 0.6-1.0, and the specific surface area is more than 800m 2 (ii)/g; the thermal conductivity coefficient of the catalyst is more than 1W.m ‑1 ·K ‑1 . The preparation method of the catalyst is simple, the carbon nano tube and the activated carbon which are connected in a chemical bonding mode are obtained by treating the activated carbon and the carbon nano tube by using the nitric acid solution of bismuth nitrate, and the catalyst has the advantages of high activity, high thermal conductivity, long service life and the like. The phosgene synthesis method adopting the catalyst has the advantages that the temperature distribution of the reactor bed layer is more uniform, the heat release of the phosgene synthesis reaction is favorably utilized, the high-quality phosgene is obtained, the safe and stable operation period of the device can be effectively prolonged, and the operation and maintenance cost is reduced.
Description
Technical Field
The invention relates to the technical field of phosgene preparation through reaction of carbon monoxide and chlorine, and particularly relates to a catalyst for preparing phosgene, and a preparation method and application thereof.
Background
Phosgene, also known as phosgene or carbonyl dichloride, is an important organic intermediate and has found wide application in organic compounds, monomers and polymers, such as isocyanates, urea derivatives, carbamoyl chlorides, carbonates, benzophenones, polyurethanes and polycarbonates, among others. High-quality phosgene is mostly used for high-end products, for example, the preparation of polycarbonate plastics needs to contain 50ppm of free chlorine at most, otherwise, the washing effect is influenced, the serious corrosion of equipment is caused, and the like; and contains at most 50ppm of carbon tetrachloride impurities, which would otherwise deteriorate the color tone of the polycarbonate resin and deteriorate the corrosion resistance of the mold.
It is known in industry to synthesize phosgene, usually starting from carbon monoxide and chlorine, using activated carbon as catalyst, the reaction being strongly exothermic and usually being carried out, for example, in a reactor similar to a tubular reactor designed as a conventional shell-and-tube heat exchanger.
The heat conductivity of common active carbon is very poor, so that the radial temperature difference of a catalyst bed layer is very large in the phosgene synthesis process, and the radial temperature difference can reach 300-400 ℃ in a reaction tube with the inner diameter of 50 mm. Therefore, if the control of feeding, heat removal and the like fails in the reaction process, the temperature of a catalyst bed layer is easily increased sharply (the highest hot spot temperature can reach 550-700 ℃), and the axial temperature gradient is changed greatly, so that catalyst pulverization and temperature unevenness of a heat transfer medium in the axial direction of a shell side are caused. Too high hot spot temperature will also promote the formation of by-product carbon tetrachloride, causing irreversible loss of catalyst and also presenting a difficult problem in the separation of carbon tetrachloride from the product.
Aiming at reducing the hot spot temperature of an activated carbon catalyst bed layer used in the phosgene synthesis process, more researches are carried out on documents. CN200510093948.7 mentions cooling of the reaction tubes from the outside by means of a coolant space cooled by water evaporation; CN201310375888.2 proposes an active carbon coating/foam silicon carbide structure catalyst modified by alkali metal salt, and a segmented filling process is adopted to realize the control of reaction temperature; CN201480041464.5 introduces a high thermal conductivity material in contact with the catalyst in the reactor, and adopts a segmented filling process to reduce the temperature of a hot spot; CN201811273312.4 proposes a catalyst loading method, which mentions that this allows sufficient reaction residence time and the heat of reaction is removed in time.
At present, in a phosgene synthesis industrial device, water with medium and low boiling points, saltless water and the like are mainly used as heat exchange media, and a large amount of reaction heat is circularly removed from the shell side of a fixed bed reactor. However, the traditional active carbon catalyst has high thermal resistance, so that the whole temperature of a reaction bed layer is high and the temperature cannot be removed. Therefore, if the problem of high temperature gradient of the catalyst bed, especially the problem of high radial temperature gradient, cannot be solved, the heat generated by the reaction is difficult to be comprehensively and effectively utilized, and the reaction load cannot be maintained at a high level.
Meanwhile, phosgene is extremely toxic and is easily adsorbed by activated carbon, the flow equalizing process is complex in the catalyst replacement process and certain potential safety hazards exist in the parking process, so that frequent parking and catalyst replacement operation caused by reduction of catalyst activity and activated carbon pulverization are not expected, and higher requirements on the catalyst and catalyst filling are provided.
In summary, the existing process for preparing phosgene by catalytic reaction of carbon monoxide and chlorine mainly has the following problems: the prior active carbon catalyst has the defects of poor heat conductivity, serious pulverization, low activity, short service life, large temperature difference between the radial direction and the axial direction of a reactor, low quality of phosgene and byproduct steam, incapability of stably operating for a long time, high maintenance cost, poor safety and the like. Therefore, there is a need for improvements in catalysts and a need to find a new process to replace the existing process.
Disclosure of Invention
The invention aims to solve the problems of the catalyst in the prior art and provide a phosgene synthesis catalyst with high activity, high thermal conductivity and long service life.
Another object of the present invention is to provide a process for preparing the catalyst.
The invention also aims to provide a method for preparing phosgene by using the catalyst, which can effectively reduce the temperature difference between the radial direction and the axial direction of a reactor, reduce the carbonization and pulverization conditions of the catalyst under high-temperature operation and prolong the service life of the catalyst. Meanwhile, high-quality phosgene and byproduct steam are produced, and the method has the advantages of reducing the stable operation and maintenance cost of the device and increasing the safe operation period of the device.
In order to achieve the purpose, the invention adopts the following technical scheme:
the first aspect of the invention provides a catalyst for phosgene synthesis, the active components of the catalyst comprise active carbon and carbon nano tubes, wherein the mass ratio of the carbon nano tubes to the active carbon is (0.01-0.1): 1, preferably 0.02 to 0.08:1;
the graphitization degree of the active carbon has the strength ratio of a D band to a G band in Raman spectrum analysis of 0.6-1.0, preferably 0.7-0.95; the specific surface area of the activated carbon is more than 800m 2 A/g, preferably greater than 1000m 2 /g。
The catalyst of the invention has a thermal conductivity greater than 1W.m -1 ·K -1 Preferably greater than 3W.m -1 ·K -1 。
In the catalyst of the invention, the carbon nanotube is preferably a multi-wall carbon nanotube, the outer tube diameter of the carbon nanotube is 10-60 nm, and the inner tube diameter is 2-7 nm.
In the catalyst of the invention, the carbon content of the carbon nano tube is more than 95wt%, and preferably, the content of graphite-like carbon is more than or equal to 85wt%.
In the catalyst of the invention, the specific surface area of the carbon nano tube is more than 100m 2 A/g, preferably greater than 200m 2 /g。
The catalyst of the invention can also comprise other auxiliary components except the active component, the auxiliary components are derived from solid products remained after roasting of auxiliary raw materials added in the preparation process, the auxiliary raw materials comprise all raw materials except the active component raw materials, and the adopted preparation method is different from other auxiliary components. According to different preparation methods, the auxiliary component can be one or more of carbon, silicon oxide, aluminum oxide, silicon carbide, silicon nitride, silicon-aluminum composite, boron nitride, boron carbide and the like in chemical composition, and the auxiliary component accounts for 0.1-50% of the total weight of the catalyst, preferably 0.5-25%, and more preferably 1-5%. The auxiliary components are present in the catalyst according to the invention in admixture with the active components (activated carbon and carbon nanotubes), which are relatively inert in the phosgene synthesis reaction and mainly act as a linking, diluting or heat-conducting component.
The auxiliary component is preferably carbon, and the source of the auxiliary component is preferably a solid product obtained by roasting an organic binder (such as polyvinyl alcohol, glutaraldehyde and the like) at high temperature in the preparation process of the catalyst; and the carbon is physically or chemically distinguished from the active components (activated carbon and carbon nanotubes) depending on the preparation conditions, including amorphous carbon and/or graphitic carbon and/or microcrystalline carbon, and is characterized by a low degree of graphitization, a low specific surface area, no significant channels and thus is relatively inert in the phosgene synthesis reaction.
In the catalyst, the activated carbon and the carbon nano tube are connected through chemical bonds, and the chemical bonds are C-C bonds and/or C-O-C bonds and the like. The carbon nano tube and the activated carbon are chemically connected by a C-C bond, a C-O-C bond or the like instead of simple physical doping, and the carbon nano tube and the activated carbon connected in such a way are in contact with Cl 2 The activation of (b) has a promoting effect, which gives rise to a sudden and dramatic increase in the catalyst activity.
The activity of the pure carbon nano tube for catalyzing phosgene synthesis is very low, and the common active carbon catalyst is difficult to give consideration to the comprehensive indexes of activity, thermal conductivity, high-temperature stability and the like. The inventor finds in the experimental process that on the basis of keeping the high specific surface area of the activated carbon material, the graphitization degree of the activated carbon material is limited, and the combined use of the carbon nano tubes is combined, so that the finally obtained catalyst has the comprehensive advantages of high activity, high thermal conductivity, high-temperature stability and the like, and is particularly suitable for industrial phosgene synthesis.
In the catalyst of the invention, the activated carbon has higher graphitization degree and passes through a D band (about 1350 cm) in Raman spectrum widely used in the field -1 Department) and G band (about 1550 cm) -1 At) is determined. The proper graphitization degree is also beneficial to improving the thermal conductivity of the catalyst, and the thermal conductivity data of the common activated carbon is only reported in the literature of 0.17-0.28 W.m -1 ·K -1 The thermal conductivity coefficient of the catalyst is more than 1W.m -1 ·K -1 And is therefore also extremely advantageous for the removal of heat during the phosgene synthesis. Controlling the degree of graphitization of the carbon material within the scope of the present invention also helps to inhibit C and Cl at high temperatures 2 Reaction to generate CCl 4 And thus is also advantageous for improving the quality of the phosgene synthesis product.
A second aspect of the present invention provides a method for preparing the catalyst for phosgene synthesis as described above, comprising the steps of:
(1) Treating the activated carbon and the carbon nano tube in a nitric acid solution of bismuth nitrate, taking out, washing and drying to obtain mixed powder of the activated carbon and the carbon nano tube;
(2) The mixed powder is evenly mixed with hydrochloric acid solution of polyvinyl alcohol and glutaraldehyde and kneaded into a plastic blank, extruded into strips for molding, and then cured, dried and roasted to obtain the catalyst for phosgene synthesis.
In the step (1) of the preparation method of the present invention, the activated carbon is a commercial activated carbon directly purchased, or a product modified based on the commercial activated carbon, and the modification method is not limited, as long as the graphitization degree and the specific surface area of the activated carbon can meet the requirements of the present invention through modification. According to literature reports, modification methods which can be used include physical methods (e.g. air, water vapor, CO) 2 High temperature treatment with gas, inert gas, etc.), chemical methods (such as zinc chloride, phosphoric acid, KOH treatment, etc.), or physical and chemical mixed treatment. For example, in some embodiments of the present invention, the activated carbon modification method employed is: the high specific surface area activated carbon with different graphitization degrees is obtained by heat treatment for 0.5-2 h at 1500-2000 ℃, preferably 1700 ℃ under Ar atmosphere, and then treatment for 1-3 h at 300-500 ℃, preferably 400 ℃ under Ar atmosphere containing 1-10 percent of oxygen, preferably 5 percent of oxygen.
In the step (1) of the preparation method of the present invention, the carbon nanotubes are directly purchased commercial products, the sources and the preparation method thereof are not limited, as long as the properties of the products meet the requirements of the present invention, and carbon nanotube products prepared by widely used arc discharge methods, laser ablation methods, chemical vapor deposition methods, etc. can be adopted, and preferably, carbon nanotube products prepared by chemical vapor deposition methods, which have high yield, are already industrially produced, and have excellent quality, are used.
In the preparation method of the invention, in the step (1), a mixture of the carbon nano tube and the activated carbon is treated by adopting a nitric acid solution of bismuth nitrate. The inventor finds in experiments that compared with the traditional acid treatment method, the nitric acid solution with bismuth nitrate introduced has an unexpected synergistic effect, can etch the surface of the carbon material more deeply, further improves the specific surface area of the activated carbon and the carbon nanotube, and can generate more oxygen-containing groups such as carboxyl, phenolic hydroxyl, carbonyl and the like on the graphitized carbon surface, so that the carbon nanotube and the activated carbon can be connected in a chemically bonded manner after subsequent high-temperature treatment.
In the step (1), the treatment method is not particularly limited, and conventional heating and stirring may be employed, or a hydrothermal treatment method may be employed. The heating and stirring method is to heat the activated carbon and the carbon nano tube in a nitric acid solution of bismuth nitrate, preferably to heat, stir and reflux;
the heating temperature is 60-90 ℃, and preferably 80-90 ℃; the heating time is 1 to 12 hours, preferably 3 to 8 hours.
The concentration of the nitric acid solution of the bismuth nitrate is 0.1-1 mol/L, and preferably 0.3-0.7 mol/L.
The mass ratio of the carbon nano tube to the active carbon is 0.01-0.1: 1, preferably 0.02 to 0.08:1.
the mass concentration of the active carbon and the carbon nano tube dispersed in the nitric acid solution of the bismuth nitrate is 5 to 50wt percent, and preferably 10 to 40wt percent.
In the preparation method of the present invention, in step (1), the washing, preferably water washing; the drying temperature is 80-150 ℃, preferably 100-130 ℃; the drying time is 1 to 24 hours, preferably 2 to 18 hours; in some embodiments of the present invention, the washing and drying methods used are specifically: filtering the treated slurry, collecting the upper filter cake, washing with water to neutrality, and drying at 120 deg.C;
in the step (2) of the preparation method, the composition of the polyvinyl alcohol and the glutaraldehyde has multiple functions of a binder, an extrusion aid and the like. Polyvinyl alcohol and glutaraldehyde are subjected to a cross-linking reaction under acid catalysis, so that the activated carbon, the carbon nano tube and the polyvinyl alcohol and glutaraldehyde which are subjected to the cross-linking reaction are mutually and tightly interwoven together, a combined body with better structural strength is formed under the action of strong external force of kneading and extruding strips, and the final catalyst product has better strength and high-temperature structural stability after subsequent drying and roasting high-temperature treatment steps.
The mass ratio of the polyvinyl alcohol to the glutaraldehyde is 10-50: 1, preferably 15 to 40:1.
the polyvinyl alcohol is preferably an aqueous solution of polyvinyl alcohol, and the mass concentration of the polyvinyl alcohol is 2-20%, preferably 5-10%;
preferably, the molecular weight of the polyvinyl alcohol is 20000 to 150000, more preferably 50000 to 120000.
Preferably, the mass concentration of the hydrochloric acid solution of the glutaraldehyde is 0.5-20 wt%, and more preferably 1-5 wt% of the hydrochloric acid solution of the glutaraldehyde is adopted; further, the hydrochloric acid solution of glutaraldehyde has a pH of 0 to 2, preferably 1 to 2.
Preferably, in the step (2), the mixed powder is mixed with the polyvinyl alcohol and the hydrochloric acid solution of glutaraldehyde in the order of adding the polyvinyl alcohol aqueous solution and the hydrochloric acid solution of glutaraldehyde to the mixed powder in sequence.
In the step (2) of the preparation method, the strip is extruded to form, preferably, a strip with the diameter of 1-5 mm and the length of 1-10 mm.
In the preparation method of the invention, in the step (2), the curing is carried out at room temperature, preferably at 20-30 ℃; the curing time is 1 to 5 hours, preferably 2 to 4 hours. The catalyst is cured after being formed and then dried, so that the strength and the activity of the obtained catalyst are better.
In the step (2) of the preparation method, the drying is carried out at the drying temperature of 80-150 ℃, preferably 100-130 ℃; the drying time is 1 to 24 hours, preferably 2 to 18 hours; the roasting is carried out in an argon atmosphere, and the roasting temperature is 700-1000 ℃, preferably 750-900 ℃; the calcination time is 1 to 5 hours, preferably 2 to 5 hours. The method obtains the required catalyst after drying and heat treatment in the argon atmosphere, the existing roasting method is usually carried out in the nitrogen environment, and the nitrogen and the carbon material have the possibility of reaction at high temperature, which can cause the reduction of the graphitization degree of the catalyst, thus being unfavorable, and the invention selects the argon environment to effectively solve the problems. After high-temperature heat treatment, the activated carbon and oxygen-containing groups on the surface of the carbon nano tube are subjected to reactions such as dehydration, decarboxylation, dehydroxylation and the like, and chemical bond connection is carried out in the forms of C-C or C-O-C bonds and the like; meanwhile, the polyvinyl alcohol and the glutaraldehyde which have cross-linking effect are carbonized, so that the physical and chemical structures of the catalyst are stable.
In a third aspect of the present invention, there is provided a method for synthesizing phosgene by catalyzing carbon monoxide and chlorine, wherein the method uses a catalyst for phosgene synthesis as described above or a catalyst prepared by the above preparation method, and comprises the steps of:
reacting carbon monoxide and chlorine in a fixed bed tubular reactor filled with a catalyst;
in the fixed bed tubular reactor, the catalyst is filled in a sectional mode, and porous inert ceramic balls are filled at the downstream of the catalyst.
In the method, the steps also comprise the step of removing reaction heat by using boiling water or high boiling point organic matters to generate high-pressure steam through gasification.
In the method, a phosgene product is directly obtained from an outlet of a fixed bed tubular reactor, wherein the content of free chlorine in the phosgene product is less than 20ppm, and the content of carbon tetrachloride in the phosgene product is less than 10ppm.
In the method, the volume ratio of the carbon monoxide to the chlorine is 1-1.05: 1.
in the method of the invention, the reaction pressure in the fixed bed tubular reactor is 0-0.4 Mpa (gauge pressure), preferably 0-0.35 Mpa (gauge pressure).
In the method, the catalyst is filled in a segmented mode in the reactor, and the activity of the catalyst along the direction of the gas flow is gradually increased. The increase of the catalyst activity can be achieved by adjusting the graphitization degree, the specific surface area, the ratio of the activated carbon to the carbon nanotubes and the like of the activated carbon, and can also be achieved by adjusting the size of the catalyst, and the methods are not limited as long as the properties of each section of the catalyst are within the range of the invention.
In the method, in the reactor, a porous inert ceramic ball is filled at the downstream of a catalyst, the surface of the porous inert ceramic ball is rough and porous, pore channels with the diameter of 50-500 mu m exist in the reactor, the pore channels in the reactor are communicated with each other, and each pore channel is communicated with the surface of the reactor; the average pore diameter of the porous inert ceramic ball is 50-500 mu m, the porosity is 1-30%, wherein the pore volume of the pore canal with the diameter of 50-500 mu m accounts for 20-70% of the total pore volume.
By adopting the filling mode of the catalyst in the reactor, the activity of the catalyst is gradually improved along with the direction of the air flow, so that the phosgene synthesis reaction can be distributed in each stage of a catalyst bed layer, the reaction heat release can be effectively controlled, and the hot spot temperature in the bed layer is reduced. The porous inert ceramic balls can gradually absorb active components which are gradually pulverized and shed off after the catalyst is used for a long time along with the airflow direction and can be used as the catalyst for secondary use by matching with the filling of the porous inert ceramic ball carrier at the downstream of the catalyst, and even under the condition that the performance of the upstream catalyst is reduced, the porous inert ceramic balls can also maintain the reaction balance in the whole reactor, so that the device can stably run for a long period under high load.
The heat transfer medium comprises boiling water or high boiling point organic matters, wherein the high boiling point organic matters comprise carbon tetrachloride, chlorobenzene, o-dichlorobenzene, toluene and the like, and the boiling water is preferred. The shell side of the fixed bed tubular reactor uses superheated boiling water or phase change of other boiling organic matters to generate steam, the heat energy absorbed by gasification is generally much higher than that absorbed by liquid heating, the reduction of radial temperature difference of the bed layer ensures that the heat emitted in the reaction process is quickly removed, and meanwhile, the gasification of bubbles on the tube wall of the shell side further strengthens heat conduction generated by the reaction and eliminates hot spots in the bed layer.
By adopting the method for synthesizing phosgene, the radial upper temperature difference in the tube array of the fixed bed tubular reactor is less than 200 ℃, the hot spot temperature is less than 450 ℃, and the outlet temperature of the reactor is less than 100 ℃.
Compared with the prior art, the invention has the beneficial effects that: the catalyst has the advantages of high activity, high heat conductivity and high structural stability, and the preparation method has simple flow. By adopting the method for synthesizing phosgene by using the catalyst, the temperature of a catalyst bed layer is lower in the reaction process, the reaction of the activated carbon and chlorine is prevented from generating carbon tetrachloride, and the content of carbon tetrachloride in tail gas is reduced; meanwhile, due to the higher activity of the catalyst, the reaction heat is fully utilized under the action of strong heat transfer, the outlet temperature of the reactor is lower, and the content of free chlorine in the tail gas is effectively reduced; the free chlorine content in the final product composition at the outlet of the reactor is less than 20ppm, and the carbon tetrachloride content is less than 10ppm, so that the method can be used in the synthesis fields of high-end polyurethane, polycarbonate and the like.
Drawings
FIG. 1 is a Raman spectrum of activated carbon;
FIG. 2 is a schematic view of catalyst loading;
FIG. 3 is a schematic view showing the temperature change in the fixed bed tube array shown in example 9;
FIG. 4 is a schematic view showing the temperature change in the fixed bed tube array shown in comparative example 1.
Detailed Description
Embodiments of the present invention are further illustrated in the following examples and figures. The invention is not limited to the embodiments listed but also comprises any other known variations within the scope of the invention as claimed.
1. The method for testing the content of phosgene free chlorine comprises the following steps:
(1) Principle of detection
Cl 2 +2KI＝2KCl+I 2
I 2 +2Na 2 S 2 O 3 ＝2NaI+Na 2 S 4 O 6
(2) 0.1mol/L of Na 2 S 2 O 3 Solution preparation and calibration
About 6.2g of N is weigheda 2 S 2 O 3 ·5H 2 Dissolving in appropriate amount of freshly boiled and freshly cooled distilled water (removing O from water) 2 And CO 2 ) In the mixture, 0.05 to 0.1g of Na is added 2 CO 3 (microbial inhibition) 250ml of solution was prepared and placed in a brown bottle. Standing for 1-2 weeks, calibrating, and storing in dark place;
accurately weighing 0.15gK 2 Cr 2 O 7 (drying for 2H at 110 ℃) in an iodine measuring flask, adding 10 to 20ml of water for dissolving, and adding 2gKI and 10ml of H 2 SO 4 Shaking and standing for 5 min, then adding 50ml water for dilution, and adding Na 2 S 2 O 3 Titrating the solution until the solution turns to light yellow-green, adding 2ml of starch indicator, and adding Na 2 S 2 O 3 The solution was titrated continuously until the solution turned from blue to light (bright) green (end point Cr 3+ A very light green color). Parallel calibration 3 times take the average.
(3) Analyzing the detection process
Pressure equalizing: rapidly rotating the cock on the sampling bottle for a week in a ventilation kitchen;
freezing: slowly putting the sample bottle after pressure equalization into a freezer for freezing for 20min;
absorption: preparing enough KI solution, connecting the frozen sampling bottle with a glass funnel by using a soft rubber tube, adding the KI solution into the funnel, opening a piston of the sampling bottle at the position of the soft rubber tube, enabling the KI solution to naturally flow into the sampling bottle until the KI solution cannot flow into the sampling bottle, properly rotating the sampling bottle in a ventilation kitchen to fully absorb the KI solution, and then putting the solution in a conical bottle;
titration: with prepared Na 2 S 2 O 3 Titrating the solution in the conical flask by using the standard solution until the purple red color is colorless;
(4) Formula for calculating free chlorine content in phosgene
Wherein:
cl-free chlorine content, mg/L;
V 1 the volume of sodium thiosulfate standard solution consumed in titrating the sample, ml;
V 2 -volume of gas sampling bottle, L;
C—Na 2 S 2 O 3 actual concentration of standard solution, mol/L;
2. the method for testing the content of carbon tetrachloride in phosgene comprises the following steps:
the content of carbon tetrachloride in phosgene is detected on line by a gas chromatograph. The gas chromatograph was a Hewlett Packard model HP 5890, the column was Restak TMRTX-1Crossbond 100% dimethylpolysiloxane, 0.25mm internal diameter, 105 m length. The gas chromatographic conditions were 50 ℃ for 10 minutes followed by a 15 ℃/minute rate programmed temperature up to 200 ℃.
3. Method for measuring specific surface area and pore structure information
BET specific surface area, BJH desorption pore volume and pore diameter of activated carbon and carbon nano tube are measured by N 2 The sample is obtained by physical adsorption method, and the model of the test instrument is Micrometics ASAP 2460.
4. Method for measuring Raman spectrum
The raman spectrum of activated carbon was measured using a 500 μm slit and 60s exposure using an Ar laser at 514.5nm as excitation light and a CCD (charge coupled device) as detector.
5. Reaction evaluation device
The fixed bed tubular reactors used in the examples and comparative examples were 7 tubular arrays each having a size of Φ 60.3 × 5mm and a length of 3500mm. Chlorine and carbon monoxide are fully mixed and then enter a phosgene synthesis fixed bed tubular reactor, and the tubular column and the cylindrical body of the fixed bed reactor are made of 316 stainless steel. Boiling water is introduced at 2750mm from the shell side of the reactor along the gas feeding direction, and no refrigerant or heating medium is introduced at the rear 750 mm. The flow rate of the boiling water is obtained by calculating the exothermic amount of the reaction according to the feeding amount of the reaction, and the boiling water gasifies the phase change at the shell side of the fixed bed to produce the byproduct steam, so that the exothermic reaction conducted to the wall surface of the tube array is absorbed, the heat released in the reaction process is quickly removed, the radial temperature difference of the bed layer is reduced, and the hot spot in the bed layer is eliminated. And the tail gas at the outlet of the fixed bed tubular reactor is the final phosgene product of the reaction.
6. Carbon nanotube
The multi-walled carbon nanotube adopted in the embodiment of the invention is purchased from Xiamen university, the outer tube diameter of the carbon nanotube is 10-60 nm, the inner tube diameter is 2-7 nm, the carbon content is more than or equal to 95wt%, the graphitic carbon content is more than or equal to 85wt%, and the specific surface area is about 158m 2 /g。
7. Porous inert ceramic ball
Porous inert ceramic balls manufactured according to patent number CN201510283433.7 are used as the source of the porous inert ceramic balls used in the invention.
The preparation method comprises the following steps: weighing 31g of wood fiber with the fiber length of 300-800 μm and the length-diameter ratio of 4-7, treating the wood fiber with 150ml of 1wt% dilute sulfuric acid at 200 ℃ for 6h, washing and drying the wood fiber, mechanically mixing the wood fiber with 35g of polypropylene (with the particle size of 150-600 μ 0) at 130 ℃ in a container rotating at high speed, and cooling the wood fiber to room temperature after 0.5 h. The mixture of wood fiber and polypropylene is mechanically mixed evenly with 290g of corundum particles (alumina content > 99 wt%), 290g of bauxite (alumina content 85wt%, silica content 13wt%, and other oxides of calcium and iron), 125g of kaolin (alumina content 40wt%, silica content 46wt%, and the balance mainly water), 25g of sesbania powder, 10g of potassium carbonate, 7g of sodium carbonate, and 5g of magnesium oxide. Adding 400g of nitric acid aqueous solution (the mass fraction of nitric acid is 3 wt%) into the mixture, and transferring the mixture into a kneader to be fully kneaded to obtain pug. The pug is made into pellets with the diameter of 4mm by a pelleting machine, 17g of 20-mesh sawdust which is highly crushed is inlaid on the surfaces of the pellets by a coating machine under the condition that 80g of sodium lignosulfonate aqueous solution (the mass fraction of the sodium lignosulfonate is 2 wt%) is used as a binder, and the pellets are subjected to microwave drying at 70 ℃ for 1h, oven drying at 110 ℃ for 4h and roasting at 1450 ℃ for 3h to obtain about 705g of porous inert porcelain pellets.
According to weight fraction, al in the porous inert ceramic ball 2 O 3 82.9% of SiO 2 Accounting for 13.9 percent, and the balance of oxides of elements such as Na, K, ca, mg, fe and the like; the porosity is 25.7%, and the pore volume of 50-500 μm pore channels in the pore diameter accounts for the total pores61.1% of the total volume, the average pore diameter being 122 μm; the diameter of the porcelain ball is 4.02mm.
8. Graphitization treatment of activated carbon
The commercial activated carbon (AC-1) used in the examples of the present invention was obtained from Fujian Xinsen activated carbon, inc. and had a specific surface area of 1284.7m 2 /g，I D /I G ＝1.05。
The graphitization treatment method comprises the following steps: carrying out heat treatment on the activated carbon under the protection of Ar atmosphere, wherein the heat treatment temperature is 1700 ℃, the treatment time is 0.5-2 h, and the volume fraction of the treated activated carbon is 5%O 2 95 percent of activated carbon AC-2, AC-3 and AC-4 required by the embodiment of the invention can be obtained by processing at 400 ℃ for 1 to 3 hours in Ar atmosphere, the Raman spectrum curves of the activated carbon are shown in figure 1, and the preparation conditions and the physical properties are summarized in the following table 1.
TABLE 1 preparation conditions and physical property data of different activated carbons
Other main sources of raw materials used in the examples or comparative examples of the present invention:
bismuth nitrate was purchased from Shenyang new photochemical plant;
polyvinyl alcohol and pentanediol were purchased from Shanghai Aladdin Biotechnology Ltd;
hydrochloric acid and nitric acid were purchased from Xiong chemical Co., ltd;
other raw materials are all commercially available materials unless otherwise specified.
Example 1
Preparation of catalyst # 1 for phosgene synthesis,
(1) 100g of AC-2 activated carbon and 5g of carbon nanotubes are weighed, dispersed in 500mL of 0.4mol/L nitric acid solution of bismuth nitrate (wherein the dosage of 68 percent nitric acid is 40.1 g), and heated, stirred and refluxed for 5 hours at 85 ℃;
filtering the slurry, washing the slurry with deionized water until the filtrate is neutral, collecting the upper filter cake, and drying the upper filter cake at 120 ℃ for 2 hours to obtain mixed powder of activated carbon and carbon nano tubes;
(2) Adding 10.4g of 10wt% polyvinyl alcohol aqueous solution with the molecular weight of 50000 and 2.08g of 2.5wt% glutaraldehyde hydrochloric acid solution with the pH value of 1.23 into 105g of the mixed powder of the activated carbon and the carbon nano tubes in sequence, kneading into a plastic blank, extruding to obtain a strip with the diameter of 3mm and the length of 3-6 mm;
curing the strip-shaped object at room temperature for 2h, and then drying the cured strip-shaped object at 120 ℃ for 2h to obtain a dried sample;
and roasting the dried sample for 2 hours at 850 ℃ in an argon atmosphere to obtain a catalyst 1#.
In catalyst 1#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde.
The thermal conductivity of the catalyst No. 1 is tested to obtain the normal temperature thermal conductivity of 2.81 W.m -1 ·K -1 。
Example 2
In catalyst 2#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity of the catalyst No. 2 is tested to obtain the normal temperature thermal conductivity of 3.04 W.m -1 ·K -1 。
Example 3
Referring to example 1 for preparing catalyst # 3, except that AC-4 activated carbon was used as a raw material, and 13g of a 15wt% aqueous solution of polyvinyl alcohol having a molecular weight of 100000 and 1.58g of a 9.6wt% aqueous solution of glutaraldehyde having a pH of 1.69 were sequentially added to a mixed powder of activated carbon and carbon nanotubes.
In catalyst 3#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 1.2wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity of the catalyst No. 3 is tested to obtain the normal temperature thermal conductivity of 1.87 W.m -1 ·K -1 。
Example 4
In catalyst 4#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity test is carried out on the catalyst No. 4 to obtain the normal-temperature thermal conductivity coefficient of 2.28 W.m -1 ·K -1 。
Example 5
With reference to preparation of catalyst # 5 in example 1, except that the die was changed at the time of extrusion of the catalyst to obtain a catalyst having a diameter of 1.5mm and a length of 3 to 6mm, and the obtained strand was calcined at 100 ℃ for 1 hour under an argon atmosphere to obtain a catalyst.
In catalyst 5#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity test is carried out on the catalyst No. 5 to obtain the normal-temperature thermal conductivity coefficient of 3.35 W.m -1 ·K -1 。
Example 6
Catalyst # 6 was prepared according to example 1, except that the die was changed during extrusion of the catalyst to obtain a catalyst having a diameter of 4mm and a length of 3 to 6mm.
In catalyst 6#, the mass ratio of carbon nanotubes to activated carbon was 0.05: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity of the catalyst No. 6 is tested to obtain the normal temperature thermal conductivity of 2.69 W.m -1 ·K -1 。
Example 7
Referring to example 1 for preparation of catalyst # 7, except that the amount of carbon nanotubes was increased to 10g, and 15g of 5.5wt% aqueous polyvinyl alcohol solution having a molecular weight of 75000, 0.25g of 17wt% glutaraldehyde hydrochloride solution having a pH of 0.86 was sequentially added to the mixed powder of activated carbon and carbon nanotubes.
Catalyst No. 7, carbon nanotubes and activated carbonThe amount ratio is 0.1: the catalyst also contains about 0.45wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity of the catalyst No. 7 was measured to obtain a thermal conductivity of 4.74 W.m at room temperature -1 ·K -1 。
Example 8
Catalyst # 8 was prepared according to example 1 except that the amount of carbon nanotubes was reduced to 2g and the aging time of the extrudate was extended to 5 hours.
In catalyst 8#, the mass ratio of carbon nanotubes to activated carbon was 0.02: the catalyst also contains about 0.6wt% of polyvinyl alcohol and residual carbon after high-temperature roasting of glutaraldehyde. The thermal conductivity test is carried out on the catalyst No. 7 to obtain the normal-temperature thermal conductivity coefficient of 1.94 W.m -1 ·K -1 。
Example 9
Catalyst No. 6, catalyst No. 1, catalyst No. 5 and porous inert ceramic balls are respectively filled in the fixed bed tubular reactor from 1 to 4 sections as shown in figure 2, and the lengths of the catalyst No. 6, the catalyst No. 1, the catalyst No. 5 and the porous inert ceramic balls respectively account for 10 percent, 20 percent, 48 percent and 22 percent of the total length of the tubular reactor.
The volume ratio of the raw materials of carbon monoxide and chlorine is 1.05 3 The time is/hr. The pressure in the reaction system was 0.3MPa (gauge pressure). 215 ℃ superheated boiling water is introduced into the shell side of the fixed bed reactor, and high-pressure steam of 2.0MPa (gauge pressure) is generated through gasification to remove reaction heat. The schematic diagram of the temperature change in the fixed bed layer tube at the beginning of the reaction and after 8000h of reaction is shown in FIG. 3, and the obtained reaction temperature conditions, the content of free chlorine and carbon tetrachloride in the product composition and the long-period operation of the device are shown in Table 2.
Example 10
Catalyst No. 8, catalyst No. 1, catalyst No. 7, catalyst No. 4 and porous inert ceramic balls are respectively filled in the fixed bed tubular reactor from 1 to 5 sections as shown in figure 2, and the lengths of the catalyst No. 8, the catalyst No. 1, the catalyst No. 7, the catalyst No. 4 and the porous inert ceramic balls respectively account for 10 percent, 20 percent, 28 percent and 22 percent of the total length of the tubular reactor.
The volume ratio of the raw materials of carbon monoxide and chlorine is 1.05 3 And/hr. The pressure in the reaction system was 0.3MPa (gauge pressure). Superheated boiling water at 234 ℃ is introduced into the shell side of the fixed bed reactor, and high-pressure steam of 3.0MPa is generated through gasification to remove reaction heat. Obtained by reaction ofThe temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
Example 11
Catalyst No. 2, catalyst No. 3, catalyst No. 1, catalyst No. 5 and porous inert ceramic balls are respectively filled in the fixed bed tubular reactor from 1 to 5 sections as shown in figure 2, and the lengths of the porous inert ceramic balls respectively account for 13%,17%,21%,25% and 24% of the total length of the tubular reactor.
The volume ratio of the raw materials of carbon monoxide and chlorine is 1.05 3 And/hr. The pressure in the reaction system was 0.35MPa. The shell side of the fixed bed reactor is filled with superheated boiling water of 180 ℃, and high-pressure steam of 1.0MPa is generated through gasification of the boiling water to remove reaction heat. The obtained reaction temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
Comparative example 1
Catalyst # 9 was prepared with reference to example 1, except that AC-1 activated carbon was used as the starting material. The thermal conductivity of the catalyst No. 9 was measured to obtain a constant temperature thermal conductivity of 0.33 W.m -1 ·K -1 。
Similarly, catalyst # 10 was prepared with reference to example # 6;
catalyst # 11 was prepared by reference to example # 5.
Catalyst No. 10, catalyst No. 9, catalyst No. 11 and porous inert ceramic balls were packed in the fixed bed tubular reactor from stages 1 to 4 as shown in FIG. 2, and the lengths thereof were 10%,20%,48% and 22% of the total length of the tubular reactor, respectively, and the reaction was carried out under the process conditions shown in example 9. A schematic diagram of the temperature change in the fixed bed tube array shown in FIG. 4 was obtained, and the obtained reaction temperature conditions, the free chlorine and carbon tetrachloride content in the product composition and the long-term operation of the apparatus are shown in Table 2.
Comparative example 2:
catalyst # 12 was prepared with reference to example 1, except that no carbon nanotubes were added. The thermal conductivity of the catalyst No. 12 was measured to obtain a normal temperature thermal conductivity of 2.62 W.m -1 ·K -1 。
Similarly, catalyst # 13 was prepared with reference to example # 6;
catalyst # 14 was prepared by reference to example # 5.
Catalyst No. 13, catalyst No. 12, catalyst No. 14 and porous inert ceramic balls were packed in the fixed bed tubular reactor from stages 1 to 4 as shown in FIG. 2, and the lengths thereof were 10%,20%,48% and 22% of the total length of the tubular reactor, respectively, and the reaction was carried out under the process conditions shown in example 9. The obtained reaction temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
Comparative example 3:
the catalyst loading conditions and reaction process were the same as in example 10 except that the porous inert ceramic balls were replaced with inert coke. The obtained reaction temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
Comparative example 4:
the method of filling inert agent coke of 30cm + columnar active carbon granular catalyst of 290cm + inert agent coke of 30cm in the fixed bed layer tubular column by stages is carried out according to the process conditions shown in the example 9; warm water with the temperature of 40-50 ℃ is introduced into the shell side of the reactor, and the heat generated by the reaction is removed. The obtained reaction temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
Comparative example 5:
catalyst # 15 was prepared with reference to example 1, except that the activated carbon and carbon nanotubes were not treated with a nitric acid solution of bismuth nitrate. The thermal conductivity of the catalyst No. 15 was measured to obtain a normal temperature thermal conductivity of 4.51 W.m -1 ·K -1 。
Similarly, catalyst # 16 was prepared with reference to example # 6;
catalyst # 17 was prepared by reference to example # 5.
Catalyst No. 16, catalyst No. 15, catalyst No. 17 and porous inert ceramic balls were packed in the fixed bed tubular reactor from stages 1 to 4 as shown in FIG. 2, and the lengths thereof were 10%,20%,48% and 22% of the total length of the tubular reactor, respectively, and the reaction was carried out under the process conditions shown in example 9. The obtained reaction temperature conditions, the contents of free chlorine and carbon tetrachloride in the product composition and the long-term operation of the apparatus are shown in Table 2.
TABLE 2 Experimental data for the examples and comparative examples
As can be seen from Table 2, the radial and axial temperature differences of the catalyst bed and the hot spot temperature of the bed can be significantly reduced when the phosgene synthesis reaction is carried out by the method of the invention. Meanwhile, by obtaining higher wall temperature on a longer pipe diameter, the exothermic heat of the phosgene synthesis reaction can be effectively utilized, stable and higher-quality steam is obtained, high-quality phosgene is obtained, the phenomena of pulverization and powder removal of various catalysts are reduced, the service life of the catalysts is prolonged, the safe and stable operation period of the device is prolonged, and the operation and maintenance cost is reduced.
Claims (25)
1. A catalyst for phosgene synthesis characterized by: the active components of the catalyst comprise active carbon and carbon nano tubes, wherein the mass ratio of the carbon nano tubes to the active carbon is (0.01-0.1): 1; the activated carbon and the carbon nano tube are connected through chemical bonds, and the chemical bonds are C-C bonds and/or C-O-C bonds;
the graphitization degree of the active carbon is that the intensity ratio of a D band to a G band in Raman spectrum analysis is 0.6-1.0; the specific surface area of the activated carbon is more than 800m <2 >/g;
the preparation method of the catalyst comprises the following steps:
(1) Treating the activated carbon and the carbon nano tube in a nitric acid solution of bismuth nitrate, taking out, washing and drying to obtain mixed powder of the activated carbon and the carbon nano tube;
(2) The mixed powder is evenly mixed with hydrochloric acid solution of polyvinyl alcohol and glutaraldehyde and kneaded into a plastic blank, extruded into strips for molding, and then cured, dried and roasted to obtain the catalyst for phosgene synthesis.
2. The catalyst according to claim 1, wherein the mass ratio of the carbon nanotubes to the activated carbon is 0.02 to 0.08:1.
3. the catalyst according to claim 1, wherein the degree of graphitization of the activated carbon is such that the intensity ratio of D band to G band in raman spectroscopic analysis is between 0.7 and 0.95.
4. The catalyst according to claim 1, wherein the activated carbon has a specific surface area of more than 1000m 2 /g。
5. The catalyst of claim 1 having a thermal conductivity greater than 1w.m -1 •K -1 。
6. The catalyst of claim 5 wherein the thermal conductivity is greater than 3W.m-1.K -1 。
7. The catalyst according to claim 1, wherein the carbon nanotubes are multi-walled carbon nanotubes, the outer diameter of the carbon nanotubes is 10 to 60nm, and the inner diameter of the carbon nanotubes is 2 to 7nm; and/or
The carbon content of the carbon nano tube is more than 95wt%; and/or
The specific surface area of the carbon nano tube is more than 100m 2 /g。
8. The catalyst of claim 7, wherein the graphitic carbon content of the carbon nanotubes is greater than or equal to 85wt%; and/or
The specific surface area of the carbon nano tube is more than 200m 2 /g。
9. The catalyst of claim 1, further comprising a promoter component selected from one or more combinations of carbon, silicon oxide, aluminum oxide, silicon carbide, silicon nitride, silicon aluminum composite, boron nitride, and boron carbide.
10. The catalyst of claim 9 wherein the promoter component is carbon derived from the solid product of the high temperature calcination of the organic binder used in the catalyst preparation process.
11. The catalyst of claim 9 wherein the adjunct component comprises from 0.1 to 50% by weight of the total catalyst.
12. The catalyst of claim 11 wherein the adjunct component is present in an amount of from 0.5 to 25% by weight based on the total weight of the catalyst.
13. The catalyst of claim 12 wherein the adjunct component is present in an amount of 1 to 5% by weight based on the total weight of the catalyst.
14. A method for preparing a catalyst according to any one of claims 1 to 13, comprising the steps of:
(1) Treating the activated carbon and the carbon nano tube in a nitric acid solution of bismuth nitrate, taking out, washing and drying to obtain mixed powder of the activated carbon and the carbon nano tube;
(2) The mixed powder is evenly mixed with hydrochloric acid solution of polyvinyl alcohol and glutaraldehyde and kneaded into a plastic blank, extruded into strips for molding, and then cured, dried and roasted to obtain the catalyst for phosgene synthesis.
15. The method according to claim 14, wherein when the activated carbon and the carbon nanotubes are treated in a nitric acid solution of bismuth nitrate, the treatment method is heating and stirring; and/or
The concentration of the nitric acid solution of the bismuth nitrate is 0.1-1 mol/L; and/or
The mass ratio of the carbon nano tube to the active carbon is 0.01-0.1: 1; and/or
The mass concentration of the active carbon and the carbon nano tube dispersed in the nitric acid solution of the bismuth nitrate is 5-50%; and/or
The heating temperature is 60-90 ℃, and the heating time is 1-12 h.
16. The method according to claim 15, wherein the treatment method is heating, stirring and refluxing; and/or
The concentration of the nitric acid solution of the bismuth nitrate is 0.3-0.7 mol/L; and/or
The mass ratio of the carbon nano tube to the active carbon is 0.02-0.08: 1; and/or
The mass concentration of the active carbon and the carbon nano tube dispersed in the nitric acid solution of the bismuth nitrate is 10-40%; and/or
The heating temperature is 80-90 ℃, and the heating time is 3-8 h.
17. The method according to claim 14, wherein in the step (2), the mass ratio of the polyvinyl alcohol to the glutaraldehyde is 10 to 50:1; and/or
The molecular weight of the polyvinyl alcohol is 20000-150000; and/or
The mass concentration of the hydrochloric acid solution of the glutaraldehyde is 0.5-20%.
18. The preparation method according to claim 17, wherein the mass ratio of the polyvinyl alcohol to the glutaraldehyde is 15-40: 1; and/or
The molecular weight of the polyvinyl alcohol is 50000-120000; and/or
The mass concentration of the hydrochloric acid solution of the glutaraldehyde is 1-5%.
19. The method according to claim 14, wherein in the step (2), the extrusion molding is performed by selecting a bar having a diameter of 1 to 5mm and a length of 1 to 10 mm; and/or
The curing is carried out at room temperature for 1-5 h; and/or
Drying at 80-150 deg.c for 1-24 hr; and/or
The roasting is carried out in argon atmosphere, the roasting temperature is 700-1000 ℃, and the roasting time is 1-5 h.
20. The method of claim 19, wherein the aging is performed at 20 to 30 ℃ for 2 to 4 hours; and/or
The drying temperature is 100-130 ℃, and the drying time is 2-18 h; and/or
The roasting temperature is 750-900 ℃, and the roasting time is 2-5 h.
21. A method for synthesizing phosgene by catalyzing carbon monoxide and chlorine, which is characterized in that the catalyst prepared by the method of any one of claims 1 to 13 or 14 to 20 is adopted, and the method comprises the following steps:
reacting carbon monoxide and chlorine in a fixed bed tubular reactor filled with a catalyst;
in the fixed bed tubular reactor, the catalyst is filled in a sectional mode, and porous inert ceramic balls are filled at the downstream of the catalyst.
22. The method of claim 21, further comprising the steps of using boiling water or high boiling point organics to remove heat of reaction by generating high pressure steam through gasification; the high boiling point organic matter comprises carbon tetrachloride, chlorobenzene, o-dichlorobenzene or toluene.
23. The process of claim 21, wherein the volume ratio of carbon monoxide to chlorine is from 1 to 1.05:1; and/or
The reaction pressure is 0-0.4 Mpa gage pressure; and/or
The activity of the catalyst in the reactor along the direction of gas flow is gradually increased; and/or
The average pore diameter of the porous inert ceramic ball is 50-500 mu m, the porosity is 1-30%, wherein the pore volume of the pore canal with the diameter of 50-500 mu m accounts for 20-70% of the total pore volume.
24. The method of claim 21, wherein the reaction pressure is 0 to 0.35Mpa gauge.
25. The process of claim 21, wherein the temperature difference in the fixed bed shell and tube reactor is <200 ℃, the hot spot temperature is <450 ℃, and the reactor outlet temperature is < 100 ℃; and/or
The free chlorine content in the product at the outlet of the reactor is less than 20ppm, and the carbon tetrachloride content is less than 10ppm.
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