KR20040061866A - Method to manufacture hydrodesulfurization catalyst using microwave drying - Google Patents

Abstract

PURPOSE: A method for manufacturing hydrodesulfurization catalyst using microwave drying is provided to reduce time and cost required in the drying process by preparing a mixed slurry in which cobalt and molybdenum salts are supported onto pseudoboehmite gel and drying the mixed slurry by microwave drying. CONSTITUTION: In a method for preparing a pseudoboehmite gel plastic paste for extrusion molding, the method comprises a step (b) of positioning the drying container in a microwave oven and drying the pseudoboehmite mixed slurry using microwave after putting a pseudoboehmite mixed slurry onto which conventionally prepared active metal constituent is supported into a drying container; and a step (b) of preparing the pseudoboehmite gel plastic paste for extrusion molding using a pseudoboehmite mixed paste partially dried using microwave of the step (a) or a pseudoboehmite mixed paste to which ceramic plastic body manufacturing plasticizer including methylcellulose is added so that the ceramic plastic body manufacturing plasticizer is mixed with the pseudoboehmite mixed paste. The method for manufacturing hydrodesulfurization catalyst using microwave drying comprises a step (a) of manufacturing a hydrodesulfurization catalyst compression molded body using the pseudoboehmite gel plastic paste for extrusion molding; a step (b) of positioning the drying container in a microwave oven and drying the compression molded body using microwave after putting the compression molded body of the step (a) into a drying container; and a step (c) of manufacturing the hydrodesulfurization catalyst by firing the hydrodesulfurization catalyst compression molded body dried in the step (b).

Description

Method for manufacture hydrodesulfurization catalyst using microwave drying

The present invention is to remove the sulfur components contained in various oil fractions, such as naphtha, kerosene, light oil, atmospheric residue oil, vacuum residue oil, etc., fractionated and distilled in a distillation column, in a refinery refinery. The present invention relates to a method for producing a highly active hydrodesulfurization catalyst which can be applied to a hydrodesulfuriztion with high economic efficiency. More specifically, the present invention by preparing a mixed slurry in which cobalt and molybdenum salts are supported on a pseudoboehmite gel prepared using pseudoboehmite as a raw material of the catalyst carrier, and dried by microwave drying, The present invention relates to a pseudoboehmite gel plastic paste manufacturing method for extrusion molding using a microwave drying method, which can reduce the time and cost required for the drying process.

In addition, the present invention by extruding the plastic paste, and then dried by microwave drying method, it is possible to minimize the drying time of the extruded body, to reduce the manufacturing cost, to maximize the reaction activity of the catalyst, microwave drying method It relates to a hydrogenation desulfurization catalyst production method using.

Recently, due to the deepening of environmental problems, regulations on sulfur content in fuel oil are becoming more and more strict, and accordingly, development of a high activity hydrogen desulfurization catalyst that can satisfy the regulation value is required. In general, the catalyst is composed of an active metal component acting as an active point of the reaction with the carrier, and the catalyst mainly used in the desulfurization process is molybdenum, tungsten, or cobalt, It is composed of active metal components such as) and nickel and alumina as a carrier, and is usually Co-Mo / Al ₂ O ₃ , Ni-Mo / Al ₂ O ₃ , Ni-W / Al ₂ O ₃ , Co-Ni-Mo / Al ₂ O ₃ .

As a prior art for producing a hydrogenation desulfurization catalyst, U.S. Patent No. 4,306,965 impregnates an activated metal inorganic acid salt such as molybdenum of group VIA or cobalt or nickel of tungsten and group VIII in a molded alumina carrier and calcinates the active metal. A method of converting an inorganic acid salt into an active metal oxide to prepare a hydrodesulfurization catalyst containing an active metal component is disclosed. However, in this method, when the content of the active metal component is low, the active metal component may be uniformly dispersed in the carrier, but as the impregnation amount of the active metal component increases, it is difficult to uniformly disperse the active metal component in the carrier.

In order to solve this problem, in US Patent No. 4,839,028 and Korean Patent No. 10-291472, instead of impregnating an active metal component in a molded alumina carrier, an active metal inorganic acid salt is mixed with an alumina hydrogel or pseudoboehmite gel. Afterwards, a method of preparing a catalyst having excellent dispersibility of the active metal component even when the active metal component loading of the catalyst is low as well as high by drying by firing by a general heating method has been proposed. However, in the present invention, in order to prepare an extruded body from a slurry of alumina hydrogel or pseudoboehmite gel mixed with a catalyst material containing 95 wt% or more of water, it is a plastic material having a moisture content of 30-50 wt% by partial drying. There is a need for a process for preparing a paste. To this end, in Korean Patent No. 10-291472, the mixed slurry is dehydrated and washed with a filter or a centrifugal separator to obtain pseudoboehmite hydrogel containing 50-80 wt% of an active metal component, and at a temperature of 50 to 150 ° C. It was proposed to prepare a final hydrogenated desulfurization catalyst of the final form by adjusting the solid content to 25-50wt% by drying, extrusion molding, drying and calcining at a constant temperature. However, in this case, a long time of 12-48 hours or more is required to dry the alumina hydrogel or pseudoboehmite gel mixed slurry on which the active metal component is supported, which acts as a factor of increasing the cost of preparing the catalyst.

As described above, in the preparation of the hydrodesulfurization catalyst according to the above patents, a drying step is required before producing the extruded body from the alumina hydrogel or pseudoboehmite gel mixed slurry carrying the active metal component, and even before the sintering process after the extrusion body is manufactured. Drying process is required. However, the above patents do not provide any specific details on the effect of the drying process on the reaction activity of the hydrodesulfurization catalyst.

In the catalyst prepared by the impregnation method and the precipitation method, the process of drying the catalyst compact on which the catalyst material is supported has been reported to directly affect the catalytic activity (Chemical Engineering, July 7, pp. 59-63, 1986). In general, a molded article carrying a catalyst active material is dried by forcibly blowing high temperature wet air at a high speed to heat the outer surface of the catalyst, and a catalyst which is slowly dried under a low temperature and high humidity atmosphere has a high reaction activity. It is proposed to have. Chemical Engineering, July 7, 1986; Preparation of Catalysts, Vol II, pp. 59-63, Elsevier Scientific Pub. Co. 1976>. As such, in order to manufacture a catalyst having an optimum reaction activity, an increase in drying process time and equipment investment are required, and as a result, manufacturing cost increases. Therefore, in the drying process for preparing a commercial catalyst, the catalyst is manufactured by setting an optimal drying temperature and humidity in consideration of the catalyst manufacturing cost. However, the catalyst prepared by using the existing drying method has a lower reaction activity than the optimum catalyst activity of a catalyst of the same composition, so it is necessary to develop a new concept of drying process to optimize catalyst activity and cost. do.

Recently, the application of the microwave process has been made over a wide range, and the most advanced and successful application so far is the drying process of the water-carrying material. The drying process using microwaves can be dried in a short time due to the high thermal efficiency and the small change in moisture content depending on the position in the water-supported material when drying the material supported by the high moisture content in comparison with the general drying method. In addition, the energy absorption occurs homogeneously and quickly throughout the material to be dried, enabling uniform heating, thereby minimizing non-homogeneous drying and overheating on the surface of the material to be dried <The Encyclopedia od Admanced Materials edited by David Bloor , Richard J. Brook, Merton C. Flemings, Subhash Mahajan, Vol. 3, 1620-1623, 1994>. The microwave drying process has been applied to the slip casting process of ceramics, and the introduction of the microwave drying process has been shown to improve the slip casting rate using alumina by 150-300%. Examples of microwave drying processes used in ceramic gel drying include US Pat. Nos. 4,829,031, 6,047,568, and 5,938,805, wherein the sol-gel process is used to produce silicate glass monolithic and ceramic Dense crystalline oxide ceramics were fabricated at low temperatures using oxide dispasic xerogels, but these methods simply applied energy sources to microwaves when drying gels to produce solid powders. Is nothing. That is, as in the present invention, there is no application example in which the pseudoboehmite gel plastic paste for extrusion molding is prepared by a drying process using microwaves, and the extruded body manufactured therefrom is dried using microwaves.

The present invention is to solve the problems of the prior art as described above, an object of the present invention, in the preparation of a plastic paste for the hydrodesulfurization catalyst production, alumina hydrogel or pseudo boehmite gel mixed slurry loaded with an active metal component By using microwave drying instead of the wet hot air drying process and the radiant heat drying method under the wet atmosphere, which is generally used, it is possible to reduce the time and cost required for the drying process. The present invention provides a method for preparing a mite gel plastic paste.

In addition, another object of the present invention by extruding the plastic paste, and then dried using a microwave drying method, it is possible to minimize the drying time of the extrudate, lower the manufacturing cost, and maximize the reaction activity of the catalyst It is to provide a hydrogenation desulfurization catalyst production method using a microwave drying method.

In order to achieve the object as described above, the method for producing an extruded pseudoboehmite gel plastic paste using the microwave drying method according to the present invention is a method for producing an extruded pseudoboehmite gel plastic paste, (A) placing the prepared pseudoboehmite mixed slurry on which the prepared active metal component is placed in a drying container, and then placed in a microwave oven and drying using microwaves; And Pseudoboehm for extrusion molding using Pseudoboehmite mixture paste which is partially dried using Pseudoboehmite mixture paste of step (a) or plasticizer for preparing ceramic plastic body including methylcellulose It characterized in that it comprises a step (b) to prepare a mite gel plastic paste.

In the manufacturing method of pseudoboehmite gel plastic paste for extrusion molding using microwave drying method according to the present invention, the microwave oven which is an energy source for drying the pseudoboehmite mixed slurry of step (a) has a microwave frequency of 0.896-10 GHz, The magnetron output is characterized by 0.5-1.5MW.

In the manufacturing method of the pseudoboehmite gel plastic paste for extrusion molding using the microwave drying method according to the present invention, the temperature of the water in the drying vessel located in the microwave oven during drying of the pseudoboehmite mixed slurry of step (a) is 80-99 ℃ , The humidity in the drying vessel is characterized in that 60-98% range.

Hydrogenation desulfurization catalyst production method using a microwave drying method according to the present invention is a method for producing a hydrodesulfurization catalyst, the step of preparing a hydrodesulfurization catalyst extrusion molded body using the above pseudoboehmite gel plastic paste for extrusion (a ); (B) placing the extruded article of step (a) in a drying vessel and placing it in a microwave oven and drying using microwaves; And calcining the dried hydrogenated desulfurization catalyst extruded body of step (b) to produce a hydrogenation desulfurization catalyst.

In the hydrogenation desulfurization catalyst production method using the microwave drying method according to the invention, the microwave oven which is the energy source for drying the extruded body of the step (b) has a microwave frequency of 0.896-10GHz, the maximum magnetron output is 0.5-1.5MW It features.

In the hydrogenation desulfurization catalyst production method using the microwave drying method according to the present invention, the temperature of the water in the drying vessel located in the microwave oven during drying of the extrudate of step (b) is 80-99 ℃, the humidity in the drying vessel is 60-98 And% range.

The microwave oven drying vessel according to the present invention is a vessel used for drying the pseudoboehmite mixed slurry described above or drying an extruded body, wherein the inside of the vessel is treated with a woven fabric having a pore structure of 100-500 mesh size. It is done.

Hereinafter, the present invention will be described in detail by taking a process for preparing a cobalt-molybdenum-alumina catalyst as an example.

Pseudoboehmite gel mixed slurry carrying active metal components for hydrogenation desulfurization catalyst preparation was prepared using the method disclosed in Korean Patent No. 10-291472.

Specifically, ammonium heptamolybdate as the main catalyst component such that molybdenum oxide (MoO ₃ ) is 15 to 40 wt% and cobalt oxide (CoO) is 2 to 12 wt% in the final composite oxide catalyst. And the water content of 85-95wt% by dehydrating a pseudoboehmite gel mixed slurry loaded with cobalt nitrate as a promoter as a dehydrator made of nonwoven fabric having a pore size of 200-300 mesh in the air for 12-60 hours. A phosphorus pseudoboehmite mixed slurry is prepared.

Pseudoboehmite gel mixed slurry dehydrated with water content of 85-95wt% is made of material that does not absorb microwave energy, and each side except the bottom side is exposed to the atmosphere, the inside of which is 100-500 mesh It is put into the drying container for microwave ovens which has the structure enclosed with the woven fabric which has a pore structure. As an energy source for drying pseudoboehmite slurry, a microwave oven with a microwave frequency of 0.896-10 GHz and a maximum magnetron output of 0.5-1.5 MW was used, and the drying vessel containing the pseudoboehmite gel mixture slurry was microwaved. After placing in the oven, the pseudoboehmite gel mixture slurry is dried with rotation per minute.

At this time, the operating time or output of the microwave oven is adjusted so that the temperature of the water in the drying vessel located in the microwave oven is maintained at 80-99 ° C. In addition, the humidity in the drying vessel during drying with microwaves is maintained in the 60-98% range. To this end, the slurry drying process using a microwave oven may be made in a continuous mode.

The drying time required in the slurry drying process using microwaves depends on the frequency and magnetron output of the microwaves used, the amount and moisture content of the dehydrated pseudoboehmite mixed slurry to be dried.

Added and mixed with pseudoboehmite mixed paste with 30-50% moisture content partially dried using microwave or plasticizer (0-8wt%) for manufacturing ceramic plastic body such as methylcellulose The pseudoboehmite gel plastic paste for extrusion molding is prepared using the pseudoboehmite mixed paste. The amount of plasticizer is controlled according to the water content in the pseudoboehmite mixed paste, and when the water content is high, the amount of the plasticizer is increased to increase the critical water content required for extrusion.

The hydrodesulfurized catalyst extrusion molded body is prepared using the pseudoboehmite gel plastic paste for extrusion molding, and then dried by microwave drying using the same drying vessel as used for drying the pseudoboehmite gel mixed slurry. The specification of the microwave oven used at this time is the same as that of the microwave oven used at the drying process of the pseudoboehmite gel mixing slurry. The drying temperature and humidity range in the drying process of the hydrodesulfurized catalyst extrusion molded body are also the same as in the pseudoboehmite gel mixed slurry drying process. The drying time of the hydrogenated desulfurization catalyst extruded body is controlled according to the moisture content in the extruded body and the micro oven specifications used.

The hydrogenated desulfurization catalyst extruded body dried with a moisture content of 1% or less using microwaves is calcined at a temperature of 300 to 900 ° C, preferably 400 to 700 ° C to finally prepare a hydrogenated desulfurization catalyst in the form of a complex oxide.

The specific surface area of the catalyst prepared by the present invention is 200 ~ 400m ² / g, the pore amount is 0.3 ~ 1.2cc / g, the average pore size is in the range of 6 ~ 15nm.

Hereinafter, the configuration and the effects of the present invention will be described in more detail with reference to Examples. The following examples illustrate the content of the invention, but the content of the invention is not limited thereto.

<Example 1>

Using the method disclosed in Korean Patent No. 10-291472, a pseudoboehmite gel mixed slurry loaded with an active metal component for producing a hydrodesulfurization catalyst was prepared. Details are as follows.

First, pseudoboehmite sol containing phosphorus was added by adding 1667 g of pseudoboehmite to a nitric acid / phosphate solution prepared by mixing 65 g of 62% nitric acid solution and 3459 g of 85% phosphoric acid solution in 4000 ml of ion-exchanged water. Make. Thereafter, 10% aqueous ammonia was added to initiate the gelation reaction, and the mixture was pulverized by vigorous stirring at pH 6.0 and 60 ° C. for 30 minutes. Then, the pH was adjusted to 8.0 by adding 10% aqueous ammonia solution. After washing with water by adding exchanged water, partial dehydration using a nonwoven fabric was performed to prepare a pseudoboehmite gel slurry.

Next, 59.16 g of ammonium heptamolybdate and 29.1 g of cobalt nitrate were added to 900 ml of ion-exchanged water, 1122 g of hydrogen peroxide, 629 g of monoethanolamine, and 900 ml of methanol were added to prepare an aqueous active metal salt solution. The prepared active metal component-supported pseudoboehmite gel mixed slurry was prepared by uniformly mixing 885 g of the prepared pseudoboehmite hydrogel (solid content 12.43g) at 80 ° C. for 2 hours.

The prepared active metal component-supported pseudoboehmite gel mixed slurry is a container in which each surface is exposed to the air except for the bottom surface made of a material that does not absorb microwave energy, and a woven fabric having a pore structure of 200 mesh inside thereof. Pseudoboehmite gel mixture paste for extrusion was prepared by drying 20 times per minute using a microwave oven with a microwave frequency of 2.45 GHz and a maximum magnetron output of 1.5 MW in a drying vessel made to be cut off from the outside. . In this case, the operating time of the microwave oven was adjusted to maintain the temperature of the water in the drying vessel located in the microwave oven at 98 ° C. and the humidity at 90%. For this purpose, the drying process using the microwave oven may be performed in a discontinuous manner.

2 wt% methyl cellulose was added to the prepared paste and mixed with a kneader for 2 hours to prepare an extruded pseudoboehmite mixed plastic paste, and a catalyst extruded body was prepared by an extrusion method using a piston.

The hydrodesulfurized catalyst extrusion molded body was produced using the pseudoboehmite gel plastic paste for extrusion molding, and then dried in a humid atmosphere using an electric furnace for 20 hours.

The dried hydrodesulfurized catalyst extruded body was calcined at 500 ° C. for 6 hours to prepare a hydrodesulfurized catalyst.

<Example 2>

Example 2 is to prepare a pseudo boehmite gel mixed slurry carrying an active metal component, and drying it using a micro oven and extrusion molding the same as in Example 1, but the drying process of the hydrogenated desulfurization catalyst extrusion molded body as follows Performed differently together.

The drying process of the hydrogenated desulfurization catalyst molded body was dried by the microwave drying method using the same drying container as used for drying the pseudoboehmite gel mixed slurry described in Example 1. The specifications and drying conditions (temperature and humidity) of the microwave oven used were the same as those of the microwave oven used for drying the pseudoboehmite gel mixed slurry, and the drying time was 0.5 hours.

The hydrogenated desulfurization catalyst extruded body dried with a moisture content of 1% or less using a microwave was calcined at 500 ° C. for 6 hours to prepare a hydrogenation desulfurization catalyst.

Comparative Example 1

Using the method disclosed in Korean Patent No. 10-291472, a pseudoboehmite gel mixed slurry carrying active metal components was prepared and dried, a molded body was calcined, and a calcined desulfurization catalyst was prepared.

Experimental Example 1: Performance Evaluation of Hydrogen Desulfurization Catalyst

In order to determine the desulfurization performance of the hydrogenated desulfurization catalyst prepared according to the present invention, a high-pressure desulfurization reactor was used, and the catalyst performance was evaluated in the following manner.

The reactant crude oil is a direct diesel diesel fraction of Arabian light crude oil. The API Petroleum Institute (API) degree is about 33 to 34, and the sulfur content is about 1.29 wt%. The reactor used is a downflow reactor with a microreactor with a maximum allowable volume of less than 10 cc. The material is made of stainless steel, and a thermocouple is attached to the reactor to control the reaction temperature. When the catalyst was charged, the catalyst was pulverized to a size of 20-40 mesh, dried, and then mixed with 3 g of inert silicon carbide (SiC) of the same size so as to have a total volume of 5.3 cc. At the time of filling the catalyst, inert silicon carbide was filled in the upper and lower portions of the reactor to improve contact between the raw material oil and the catalyst, and a glass wool was charged in the catalyst layer to prevent the outflow of the pulverized catalyst. After the reactor was mounted in a reaction apparatus, the catalyst was sulfided at atmospheric pressure using a 10% hydrogen sulfide gas mixture diluted with hydrogen in order to transform the catalyst in the form of oxide into the activated sulfide form. The flow rate of the crude oil was constantly injected into the reactor by a diaphragm pump, and the total pressure of the reactor was controlled by a pressure regulator. The liquid product after the reaction was used to remove hydrogen sulfide dissolved in the product using nitrogen, and then undigested sulfur compound. Was analyzed by sulfur analyzer to measure the degree of reaction. The sulfidation and reaction conditions are as follows.

The specific reaction sequence is as follows.

1. After mounting the reactor filled with catalyst, introduce a 10% hydrogen sulfide / hydrogen mixed gas into the reactor at atmospheric pressure.

2. The reactor temperature is raised from room temperature to 400 ° C. and then maintained at this temperature for 2 hours.

3. After cooling the reactor temperature to 200 ° C., pressurize to the reaction pressure by replacing 10% hydrogen sulfide / hydrogen mixed gas with hydrogen gas.

4. After the reaction pressure is reached, the feedstock oil is started and the feedstock oil is supplied so that the catalyst layer is sufficiently wetted.

5. When it is confirmed that the catalyst bed is sufficiently wetted with raw material oil, gradually increase the reactor temperature to the reaction temperature.

6. After reaching the reaction temperature, hold for 8 hours, and then collect the liquid reaction product to measure the reaction.

Physical properties and performance evaluation results of the hydrodesulfurization catalysts prepared by Examples 1 and 2 and Comparative Example 1 are shown in Table 2 below.

* Specific surface area, total pore volume and average pore size are measured by nitrogen adsorption and desorption method.

* The relative reaction activity is the ratio of the desulfurization rate constant obtained from the desulfurization rate equation with temperature, which is a relative value of 100 for the desulfurization rate constant of the comparative example.

Comparing Examples 1 and 2 with Comparative Examples having the same active ingredient content, as shown in Table 1 above, the hydrogenation of the hydrodesulfurization catalyst was performed only by introducing a microwave drying step of the pseudoboehmite hydrogel mixed slurry loaded with the active metal component. Hydrodesulfurization activity is 30% higher, it can be seen that the hydrodesulfurization activity of the catalyst prepared using the microwave drying method presented in the present invention is about 30-70% higher than the catalyst prepared by the wet drying method using an external heat source. This can minimize the movement of active metal components due to non-uniformity of moisture and temperature distribution in the drying target, which can be minimized by microwave drying in a wet atmosphere. It seems to be because there is.

As described above, in the present invention, a pseudo-boehmite gel mixed slurry is dried using a microwave oven in a humid atmosphere to prepare a plastic paste for extrusion molding, and the extrusion molded body is dried to increase the activity of the hydrogenation desulfurization catalyst. In addition, the catalyst preparation time can be reduced to less than 1/10. This is because microwave energy efficiency in the drying process is higher than that of the conventional radiant heating method, and the temperature gradient and moisture content gradient in the material to be dried are minimized. Therefore, the reaction activity of the hydrogenated desulfurization catalysts prepared by the method presented in the present invention and the efficiency of the production process are much better than those of the catalyst prepared using the existing drying process.

The method for preparing a catalyst using the microwave drying method according to the present invention enables the preparation of a catalyst having a high active metal content because the dispersion degree of the active metal components can be maintained high even in a catalyst having a high active metal content.

Claims (7)

As a method for producing a pseudoboehmite gel plastic paste for extrusion molding, (A) placing the pseudoboehmite mixed slurry loaded with the active metal component prepared by a conventional method in a drying container, and then placing the same in a microwave oven and drying using microwaves; And Pseudoboehmite for extrusion molding using the pseudoboehmite mixed paste partially dried using the microwave of step (a) or the pseudoboehmite mixed paste containing and mixed with a plasticizer for preparing a ceramic plastic body including methylcellulose Pseudoboehmite gel plastic paste manufacturing method for extrusion molding using a microwave drying method comprising the step of preparing a gel plastic paste (b). The method of claim 1, Microwave oven, which is an energy source for drying pseudoboehmite slurry in step (a), has a microwave frequency of 0.896-10 GHz and a maximum magnetron output of 0.5-1.5 MW. Method for preparing gel plastic paste. The method of claim 1, When drying the pseudoboehmite mixed slurry of step (a), the temperature of the water in the drying vessel located in the microwave oven is 80-99 ° C., and the humidity in the drying vessel is in the range of 60-98%. Pseudoboehmite gel plastic paste for manufacturing method. As a method for producing a hydrogenation desulfurization catalyst, (A) preparing a hydrodesulfurized catalyst extrusion molded body using the pseudoboehmite gel plastic paste for extrusion molding according to claim 1; (B) placing the extruded article of step (a) in a drying vessel and placing it in a microwave oven and drying using microwaves; And Hydrogen desulfurization catalyst production method using a microwave drying method comprising the step (c) of firing the dried hydrodesulfurization catalyst extrusion molded product of the step (b) to produce a hydrodesulfurization catalyst. The method of claim 4, wherein The microwave oven, which is an energy source for drying the extruded article of step (b), has a microwave frequency of 0.896-10 GHz and a maximum magnetron output of 0.5-1.5 MW. The method of claim 4, wherein Temperature of the water in the drying vessel located in the microwave oven during drying of the extruded product of step (b) is 80-99 ℃, humidity in the drying vessel range of 60-98% hydrogenated desulfurization catalyst production method using a microwave drying method . A container for use in drying the pseudoboehmite mixed slurry according to claim 1 or drying an extruded body, A drying vessel for a microwave oven, characterized in that the interior of the vessel is treated with a woven fabric having a pore structure of 100-500 mesh size.