CN112625746B

CN112625746B - Device and method for preparing high-quality wax

Info

Publication number: CN112625746B
Application number: CN201910908764.3A
Authority: CN
Inventors: 钱震; 周岩; 李俊诚; 苗恒; 菅青娥; 马国清; 郑会月; 郭良兰; 王海国; 高源�; 解利军; 秦艳
Original assignee: Inner Mongolia Yitai Coal Based New Materials Research Institute Co Ltd
Current assignee: Inner Mongolia Yitai Coal Based New Materials Research Institute Co Ltd
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2022-08-30
Anticipated expiration: 2039-09-24
Also published as: CN112625746A

Abstract

An apparatus and method for preparing high quality wax, the apparatus comprising: the device comprises a solvent deoiling unit, a solvent recovery unit, a fractional crystallization unit and a clay refining unit; the solvent deoiling unit comprises a deoiling raw material tank, a solvent tank, a deoiling tower and a solvent and wax oil collecting tank; the solvent recovery unit is used for separating the solvent and the undersea oil collected in the solvent and undersea oil collecting tank and recovering the solvent; the fractional crystallization unit comprises a plurality of crystallizers connected in series and is used for removing light components in the rectification fraction and obtaining a target crystallization component; the clay refining unit comprises a filter, and a filter screen is arranged in the filter. The method has the advantages of simple operation, low cost, wide adaptability, high solvent recovery rate and high deoiling efficiency.

Description

Device and method for preparing high-quality wax

Technical Field

The invention belongs to the technical field of chemical industry, and particularly relates to a device and a method for preparing high-quality wax.

Background

In the process of petroleum refining, after light fuel oil components such as gasoline, coal, diesel oil and the like are separated, high-wax distillate oil, residual oil and the like are obtained. Wherein the high wax fraction is such as to separate the paraffins and the base oil by solvent or refrigeration, and the resulting paraffins also contain 1% to 5% of "oils", these residual oils being contained in the paraffin waxes to lower the melting point of the latter, to soften them and to impart an oily odour to the wax. This gives the paraffin wax a very wide range of applications, with many negative properties, even affecting its use.

The existing solvent deoiling device has high cost, large volume and general deoiling effect. The classical deoiling process, which has been known in the industry for many years, is known as "sweating". The vertical sweating method has the advantages of no solvent, simple process, capability of producing various grades of paraffin simultaneously, lower processing cost and the like, and is an innovation compared with the disc sweating method. However, the method is still operated intermittently, the investment is high, the steel consumption is the most, the corrosion is serious (the storage tank is updated every 7 to 8 years), and the average oil content of the finished product is also high.

Large-scale circular sweating boxes and box-type sweating boxes have been designed in existing equipment. The conventional sweating apparatus is a room or oven in which 10 to 15 or more horizontal trays are stacked, each tray having a metal mesh and a drain tube at the bottom to control the paraffin to solidify on the metal mesh, and then the temperature of the whole sweating chamber is raised at a rate of 1 ℃ per hour, at which time oil droplets seep from the surface of the wax, run through the mesh and flow out through the drain tube, the temperature rises to 3-5 ℃ below the melting point of the paraffin, and sweating is stopped, typically to reduce the oil content to below 1%. The sweating equipment has simple structure but low efficiency, and the whole sweating equipment is heated by the heating pipes on the four walls of the oven, so the equipment has large size, occupies small space and has low unit volume output.

Technical terms:

deoiling wax: the wax obtained by cold pressing or solvent dewaxing has an oil content of about ten percent, and when commercial paraffin wax is manufactured, the oil needs to be removed, and the process is called wax deoiling.

Solvent deoiling:

the mixed solvent has different dissolving capacities on oil and wax in the raw materials, the solvent is added successively in the cooling process of the raw materials, the viscosity of the raw materials is reduced, the fluidity of the raw materials is improved, a proper condition is created for wax crystallization, the wax is formed into uniform and compact crystals, the oil and the wax are conveniently separated by a filtering method, and the wax is dissolved by the solvent, so that the oil content in the wax is further reduced. And respectively sending the filtrate, the wax liquid and the wax oil liquid which are separated by filtration to a recovery system, and recovering the solvent for recycling by utilizing the boiling point difference of the solvent and the oil, the wax and the wax oil to obtain the oil, the wax and the wax oil from which the solvent is removed.

Disclosure of Invention

In view of the above, the present invention provides an apparatus and a method for preparing high quality wax, which are used to improve the deoiling efficiency.

In order to achieve the above objects, in one aspect, the present invention provides an apparatus for preparing high quality wax, comprising: the device comprises a solvent deoiling unit, a solvent recovery unit, a fractional crystallization unit and a clay refining unit;

the solvent deoiling unit comprises a deoiling raw material tank, a solvent tank, a deoiling tower and a solvent and wax oil collecting tank, wherein the deoiling raw material tank and the solvent tank are respectively connected with an inlet of the deoiling tower, a filter screen is arranged at the bottom of the deoiling tower, an outlet of the deoiling tower is connected to the solvent and wax oil collecting tank, a heating and cooling jacket is arranged on the outer wall of the deoiling tower, and preferably, the number of the deoiling towers is multiple;

the solvent recovery unit is used for separating the solvent and the undersea oil collected in the solvent and undersea oil collecting tank and recovering the solvent;

the fractional crystallization unit comprises a plurality of crystallizers connected in series and is used for removing light components in the rectification fraction and obtaining a target crystallization component;

the clay refining unit comprises a filter, and a filter screen is arranged in the filter; optionally, qualitative filter paper is arranged on the filter screen.

In some embodiments, the solvent recovery unit comprises a rectification tower, a first heating kettle, a wax oil collecting tank and a solvent collecting tank, wherein the first heating kettle is located at the bottom of the rectification tower and is connected with the solvent and the wax oil collecting tank, and the outlet of the rectification tower is respectively connected with the wax oil collecting tank and the solvent collecting tank.

In some embodiments, the apparatus further comprises a molecular distillation unit comprising a thin film evaporator and a molecular evaporator, the thin film evaporator being provided with a feed inlet for introducing the base wax and a discharge outlet for withdrawing the light fraction; the molecular evaporator is connected with the thin film evaporator through a pipeline and is used for separating the residual fraction in the thin film evaporator into a heavy fraction and a middle fraction.

In some embodiments, the molecular distillation unit further comprises a cooler connected to the molecular evaporator and the first vacuum pump through pipes and provided with a pipe through which a refrigerant passes inside.

In some embodiments, the number of the coolers is two, the coolers are connected through a pipeline, and the lower ends of the coolers are connected with the first buffer tank.

In some embodiments, the solvent deoiling unit further comprises a second buffer tank and a second vacuum pump, the solvent and paraffin oil collecting tank is connected with one end of the second buffer tank, and the other end of the second buffer tank is connected with the second vacuum pump.

In some embodiments, the solvent deoiling unit further comprises a safety gas unit for providing safety gas to the deoiling tower and the deoiling feed tank.

In some embodiments, the fractional crystallization unit comprises a first crystallizer and a second crystallizer, the outlet of the first crystallizer being connected to the sweat container and the inlet of the second crystallizer, respectively, and the outlet of the second crystallizer being connected to the sweat container and the crystallized product container, respectively.

In some embodiments, the first crystallizer and the second crystallizer are respectively connected with a heat medium pipeline and a cold medium pipeline for heating and crystallizing materials in the first crystallizer and the second crystallizer.

In some embodiments, the clay refining unit comprises a second heating kettle, an outlet of the second heating kettle is connected with an inlet of the filter, the filter is connected with one end of a third buffer tank through a pipeline, and the other end of the third buffer tank is connected with a third vacuum pump.

In some embodiments, a hydrogenation unit is further disposed between the fractional crystallization unit and the clay refining unit.

In another aspect, the present invention provides a method for preparing high quality wax using the apparatus, comprising:

introducing the raw material wax and a solvent into a deoiling tower for mixing, heating to 60-200 ℃ to dissolve the raw material wax, uniformly stirring at-40-60 ℃, and then performing solvent deoiling treatment;

introducing the deoiled wax into a plurality of crystallizers connected in series for fractional crystallization to obtain wax products with different melting points;

and carrying out clay refining on the wax product to obtain a final product.

In some embodiments, the feedstock wax is pretreated by molecular distillation.

In some embodiments, the molecular distillation is operated at a temperature of 80 to 400 ℃ and at a pressure of 0.1PaA to atmospheric pressure.

In some embodiments, the solvent comprises one or more of methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene.

In some embodiments, the volume ratio of the feedstock wax to the solvent is 1: 6 to 10, such as 1:7, 1:8, or 1: 9.

In some embodiments, the method further comprises a solvent recovery step comprising rectifying the oil-containing solvent at 20 to 180 ℃.

In some embodiments, the fractional crystallization is performed at a temperature of-40 to 200 ℃ and at a pressure of atmospheric pressure.

In some embodiments, the clay refining is performed at an operating temperature of 30-200 ℃, a vacuum degree of 1-60 Kpa, and a filter screen is a 100-1500 mesh stainless steel filter screen.

In some embodiments, the method further comprises hydrotreating at an operating temperature of 100 to 350 ℃ and a pressure of 2 to 6Mpa prior to clay refining.

Compared with the prior art, the invention can solve the problems of complex operation, large occupied area, low deoiling rate and the like of the existing equipment. The device can reduce the floor area of equipment, improve the oil yield and yield of unit volume, has simple operation, low cost, wide adaptability, high solvent recovery rate which is more than 70 percent and high deoiling efficiency, can deoil the oil content to be less than 0.5 percent, and can process and produce high-quality wax products through subsequent working sections to meet the requirements of various industries.

Drawings

Fig. 1 is a schematic structural diagram of an apparatus according to an embodiment of the present invention.

Description of reference numerals:

1-a thin film evaporator; 2-a molecular evaporator; 3-a base wax sample tank; 4-a light fraction collection tank; 5-middle distillate collection tank; 6-heavy fraction collection tank; 7-a cooler; 8-a first vacuum pump; 9-a first buffer tank; 10-deoiling raw material tank; 11-a solvent tank; 12-a deoiling tower; 13-a temperature control device; 14-a filter screen; 15-solvent and wax oil collection tank; 16-a second buffer tank; 17-a second vacuum pump; 18-a safety gas unit; 19-a first heating kettle; 20-a wax oil collecting tank; 21-a solvent collection tank; 22-a wax collection tank; 23-a crystallization feed tank; 24-a first crystallizer; 25-a second crystallizer; 26-a refrigerant tank; 27-a heat medium tank; 28-a sweat tank; 29-crystallization finished product tank; 30-a second heating kettle; 31-a filter; 32-a third buffer tank; 33-a third vacuum pump; 34-a thermocouple; 35-rectifying tower.

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

As shown in fig. 1, an embodiment of the present invention provides an apparatus for preparing high-quality wax, which reduces the floor area of a unit deoiling apparatus by changing a conventional sweating room or oven room into a tubular deoiling tower, and includes a molecular distillation unit, a solvent deoiling unit, a solvent recovery unit, a fractional crystallization unit, and a clay refining unit.

The molecular distillation unit is used for carrying out primary separation on the base wax, and if the quality of the raw material is higher, the raw material can directly enter the solvent deoiling unit without passing through the molecular distillation unit.

The molecular distillation unit comprises a thin film evaporator 1 and a molecular evaporator 2, wherein the thin film evaporator 1 is provided with a feed inlet and a discharge outlet, the feed inlet is used for introducing the basic wax from a basic wax sample tank 3, and the discharge outlet is used for leading the light fraction to a light fraction collecting tank 4.

The molecular evaporator 2 is connected with the thin film evaporator 1 through a pipeline, and is used for separating the residual fraction in the thin film evaporator 1 into a middle fraction and a heavy fraction, and respectively leading out the middle fraction and the heavy fraction to a middle fraction collecting tank 5 and a heavy fraction collecting tank 6.

The molecular distillation unit further comprises a cooler 7, wherein the cooler 7 is connected with the molecular evaporator 2 and the first vacuum pump 8 through pipelines, and a pipeline for passing a refrigerant is arranged inside the cooler 7. The cooler 7 is used to cool the light components produced when the short path distillation apparatus cuts the sample fraction.

The number of coolers 7 is preferably a plurality, for example two, which are connected by a pipe. The cooler 7 is connected at its lower end to a first buffer tank 9. The first buffer tank 9 is used for collecting light components generated when the short-path distillation device cuts the sample fraction and preventing the light components from entering the first vacuum pump 8.

The solvent deoiling unit comprises a deoiling raw material tank 10, a solvent tank 11, a deoiling tower 12, a solvent and wax oil collecting tank 15, a second buffer tank 16, a second vacuum pump 17 and a safety gas unit 18.

The deoiling raw material tank 10 is used for accommodating a raw material to be deoiled, and may be provided with a heating unit, such as an electric heating unit or a heat transfer oil heating unit, the solvent tank 11 is used for accommodating a deoiling solvent, the deoiling raw material tank 10 and the solvent tank 11 are respectively connected to the deoiling tower 12, the safety gas unit 18 is used for supplying safety gas to the deoiling tower 12 and the deoiling raw material tank 10 for pressurization or purging, and the safety gas unit 18 may include an air pump or a gas steel cylinder.

The outer wall of the deoiling tower 12 is provided with a heating and cooling jacket, the heating and cooling jacket is connected with a temperature control device 13 and is used for heating or cooling the deoiling tower, the bottom of the deoiling tower 12 is provided with a filter screen 14 (the filter screens with various meshes can be freely matched), and an outlet of the deoiling tower 12 is connected to a solvent and wax oil collecting tank 15 and is used for collecting the solvent and wax oil in the deoiling process. The de-oiled wax is transferred to a wax collection tank 22. The solvent and wax oil collecting tank 15 is connected with a second buffer tank 16, the second buffer tank 16 is connected with a second vacuum pump 17, and the second buffer tank 16 is used for preventing the collected solvent and wax oil from entering the second vacuum pump 17.

An agitator may also be provided in the deoiling tower 12. The bottom of the deoiling tower 12 can also be provided with a blind plate, and the two filter screens and the blind plate are connected in a triangular manner and can be switched with each other. Wherein the screen is used to separate the wax crystals from the de-oiling solvent. The blind plate is used for sealing the bottom of the deoiling tower, so that the deoiling solvent can fully dissolve the oil in the wax. When the bottom of the deoiling tower is switched to the blind plate, the device is in the deoiling solvent for washing and dissolving the oil in the wax, and when the bottom of the deoiling tower is switched to the filter screen, the device is in the vacuum state, and the oil under the wax is separated from the deoiled wax.

The number of the deoiling towers 12 can be one or more according to production needs, for example, 3 deoiling towers connected in parallel are included in fig. 1.

The solvent recovery unit comprises a rectifying tower 35, a first heating kettle 19, a wax oil collecting tank 20 and a solvent collecting tank 21, wherein the first heating kettle 19 is positioned at the bottom of the rectifying tower 35 and is connected with the solvent and wax oil collecting tank 15 for heating the collected solvent and wax oil, and a stirrer can be arranged in the first heating kettle 19. The heated solvent and wax oil are separated by the rectifying tower 35 and are respectively conveyed into the wax oil collecting tank 20 and the solvent collecting tank 21.

The fractional crystallization unit comprises a wax collection tank 22, a crystallization raw material tank 23, a first crystallizer 24 and a second crystallizer 25, wherein the first crystallizer 24 and the second crystallizer 25 are respectively connected with a cooling medium tank 26 and a heating medium tank 27, the crystallization raw material in the crystallization raw material tank 23 is firstly conveyed to the first crystallizer 24 for heating and crystallization, a light component is conveyed to a sweat tank 28, the rest components are conveyed to the second crystallizer 25 for continuous heating and crystallization, the light component is conveyed to the sweat tank 28, and the rest components are conveyed to a crystallization finished product tank 29.

The clay refining unit comprises a second heating kettle 30 and a filter 31, wherein the inlet of the second heating kettle 30 is connected with the crystallization finished product tank 29, the outlet of the second heating kettle 30 is connected with the inlet of the filter 31, a filter screen is arranged in the filter 31, and optionally, qualitative filter paper can be arranged on the filter screen. The second heated kettle 30 may include an agitator. The wax is heated in the second heating kettle 30 and then mixed with the clay uniformly, and the wax product is obtained after the wax is filtered by the filter screen in the filter 31. And refining the crystallized finished product in a clay refining unit to obtain a final product.

The filter 31 is connected to a third buffer tank 32 through a pipe, and the third buffer tank 32 is connected to a third vacuum pump 33. The third buffer tank 32 is used to prevent the refined decolored sample from being pumped into the third vacuum pump 33 under negative pressure.

In some embodiments, a hydrogenation unit may be further disposed between the fractional crystallization unit and the clay refining unit, and if the crystallized product obtained in the fractional crystallization unit has a dark color and a strong odor, the hydrogenation unit may be turned on for refining, if not, the crystallized product may directly enter the clay refining unit.

Thermocouples 34 may be provided on the piping downstream of the deoiled feed tank 10, the wax holding tank 22, and the wax holding tank 22 for real-time monitoring of temperature. The piping downstream of the wax collection tank 22 is also preferably provided with heating tape and insulation.

The device can prepare the wide-fraction raw material into a narrow-fraction high-quality product: the raw material wax is firstly processed and prepared by a solvent deoiling unit (the raw material wax can be purchased in the market through a molecular distillation unit), the oil content of the raw material wax is deoiled to be less than or equal to 0.5 percent, the low-oil product wax is then subjected to a step crystallization unit, the low-oil product wax is recrystallized into products with different brands step by step according to the melting point difference, (if necessary, the products are subjected to hydrogenation decolorization and deodorization, for example, the products with odor number being more than or equal to 4 grade or the raw materials are subjected to hydrogenation treatment), and then the products are refined by a white clay refining unit to remove mechanical impurities to obtain high-quality wax products. The high-quality wax product can be used for different fields of product wax according to different purposes. For example: cosmetic waxes, candle waxes, phase change waxes, asphalt modified waxes, and the like. The solvent and the wax oil are subjected to solvent recovery and wax oil collection through a solvent recovery unit, wherein the wax oil can be used as other chemical raw materials such as high-quality lubricating oil base oil.

In one embodiment of the invention, Fischer-Tropsch wax is used for preparing the deoiled raw material wax through a molecular distillation unit, the operation temperature is 80-400 ℃, and the operation pressure is 0.1PaA (absolute pressure) to normal pressure.

The operating conditions of the solvent deoiling unit are as follows: mixing raw material wax and one or more deoiling solvents (butanone, MIBK (methyl isobutyl ketone), benzene, toluene and the like) according to a volume ratio of 1:8, heating to 60-200 ℃ for dissolving, mechanically stirring at a stirring speed of 80-160 r/min at-40-60 ℃, deoiling in a solvent deoiling tower after the mixture is in a uniform mixed state, and adding the deoiling solvent for washing for many times in the process.

The operating conditions of the solvent recovery unit were: adding the mixed solvent with oil into a solvent recovery tower, and rectifying at the set temperature of 20-180 ℃ in a tower kettle.

The operating conditions of the fractional crystallisation unit are: heating and melting the product after solvent deoiling at 30-160 ℃, and adding the product into a fractional crystallization unit. The operation temperature is-40 to 200 ℃, and the pressure is normal pressure.

The operating conditions of the hydrogenation unit were: and (3) hydrogenating the product after fractional crystallization, wherein the operation temperature is 100-350 ℃, and the pressure is 2-6 Mpa.

The operating conditions of the clay refining unit are as follows: and (3) performing clay refining on the product after fractional crystallization or the product after hydrogenation, uniformly mixing the wax and the clay, and filtering the mixture by using a filter screen to obtain a wax product, wherein the operation temperature is 30-200 ℃, the vacuum degree is 1-60 Kpa, the filter screen is a stainless steel filter screen of 100-1500 meshes, and qualitative filter paper is laid on the stainless steel filter screen.

By utilizing the device and the method, the deoiled wax can be used as a raw material to be subjected to fractional crystallization treatment, and high-purity wax products with different brands can be obtained.

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An apparatus for preparing high quality wax comprising: the device comprises a solvent deoiling unit, a solvent recovery unit, a fractional crystallization unit and a clay refining unit;

the solvent deoiling unit comprises a deoiling raw material tank, a solvent tank, a deoiling tower and a solvent and wax oil collecting tank, wherein the deoiling raw material tank and the solvent tank are respectively connected with an inlet of the deoiling tower;

the clay refining unit comprises a filter, and a filter screen is arranged in the filter;

the device also comprises a molecular distillation unit, wherein the molecular distillation unit comprises a thin film evaporator and a molecular evaporator, the thin film evaporator is provided with a feed inlet and a discharge outlet, the feed inlet is used for introducing the basic wax, and the discharge outlet is used for leading out light fraction; the molecular evaporator is connected with the thin film evaporator through a pipeline and is used for separating the residual fraction in the thin film evaporator into a heavy fraction and a middle fraction.

2. The apparatus of claim 1, wherein the number of the deoiling towers is plural.

3. The device of claim 1, wherein a qualitative filter paper is disposed on the filter web.

4. The apparatus of claim 1, wherein the solvent recovery unit comprises a rectification tower, a first heating kettle, a wax oil collecting tank and a solvent collecting tank, wherein the first heating kettle is located at the bottom of the rectification tower and is connected with the solvent and the wax oil collecting tank, and an outlet of the rectification tower is connected with the wax oil collecting tank and the solvent collecting tank respectively.

5. The apparatus of claim 1, wherein the molecular distillation unit further comprises a cooler connected to the molecular evaporator and the first vacuum pump through pipes and internally provided with pipes through which a refrigerant passes.

6. The apparatus of claim 5, wherein the number of the coolers is two, the coolers are connected through a pipe, and the lower ends of the coolers are connected with the first buffer tank.

7. The apparatus according to claim 1, wherein the solvent deoiling unit further comprises a second buffer tank and a second vacuum pump, the solvent and paraffin oil collecting tank is connected to one end of the second buffer tank, and the other end of the second buffer tank is connected to the second vacuum pump.

8. The apparatus of claim 1, wherein the solvent deoiling unit further comprises a safety gas unit for providing safety gas to the deoiling tower and the deoiling feed tank.

9. The device of claim 1, wherein the fractional crystallization unit comprises a first crystallizer and a second crystallizer, the outlet of the first crystallizer being connected to the sweat reservoir and the inlet of the second crystallizer, respectively, and the outlet of the second crystallizer being connected to the sweat reservoir and the crystallized product reservoir, respectively.

10. The apparatus according to claim 9, wherein the first crystallizer and the second crystallizer are connected to a heating medium line and a cooling medium line, respectively, for heating and crystallizing the materials in the first crystallizer and the second crystallizer.

11. The apparatus of claim 1, wherein the clay refining unit comprises a second heating kettle, an outlet of the second heating kettle is connected with an inlet of the filter, the filter is connected with one end of a third buffer tank through a pipeline, and the other end of the third buffer tank is connected with a third vacuum pump.

12. The apparatus of claim 1 wherein a hydrogenation unit is further disposed between the fractional crystallization unit and the clay refining unit.

13. A method of making high quality wax using the apparatus of any one of claims 1-12, comprising:

and carrying out clay refining on the wax product to obtain a final product.

14. The method of claim 13, wherein the feedstock wax is pretreated by molecular distillation.

15. The process of claim 14, wherein the molecular distillation is carried out at an operating temperature of 80 to 400 ℃ and an operating pressure of 0.1PaA to atmospheric pressure.

16. The method of claim 13, wherein the solvent comprises one or more of butanone, methyl isobutyl ketone, benzene, toluene.

17. The method according to claim 13, wherein the volume ratio of the raw wax to the solvent is 1 (6-10).

18. The method of claim 13, wherein the volume ratio of the feedstock wax to solvent is 1:7, 1:8, or 1: 9.

19. The method according to claim 13, wherein the method further comprises a solvent recovery step comprising rectifying the oil-containing solvent at 20-180 ℃.

20. The method according to claim 13, wherein the fractional crystallization is carried out at an operating temperature of-40 to 200 ℃ and at a pressure of atmospheric pressure.

21. The method according to claim 13, wherein the clay refining is performed at an operating temperature of 30 to 200 ℃, a vacuum degree of 1 to 60Kpa, and a filter screen is a 100 to 1500 mesh stainless steel filter screen.

22. The process of claim 13, further comprising hydrotreating prior to clay refining at an operating temperature of from 100 to 350 ℃ and a pressure of from 2 to 6 Mpa.