A method for synthesizing 3,4-dichloronitrile

Abstract

This invention relates to a method for synthesizing 3,4-dichlorobenzonitrile, belonging to the field of organic synthesis technology. This invention creatively uses tetramethyl silicate as a silicon source, aluminum chloride hexahydrate as an aluminum source, and yttrium chloride hexahydrate as a yttrium / rare earth source. Based on the sol-gel method, the timing of adding the aluminum and yttrium sources to the reaction solvent is controlled to prepare an aluminum-yttrium-doped silica sol. The aluminum and yttrium sources are added in two stages: the first addition is before the tetramethyl silicate is added dropwise to the reaction solvent, and the second addition is after all the tetramethyl silicate has been added dropwise to the reaction solvent. Then, based on the impregnation method, a vanadium-chromium catalyst is supported on the aluminum-yttrium-doped silica sol to obtain a supported catalyst. When applied to the ammoxidation reaction of 3,4-dichlorotoluene, it can effectively catalyze the synthesis of 3,4-dichlorobenzonitrile, exhibiting not only high conversion but also good selectivity, achieving remarkable technical results.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for synthesizing 3,4-dichlorobenzonitrile. Background Technology

[0002] 3,4-Dichlorobenzonitrile, as an important organic intermediate, is widely used in agriculture, medicine, pigments, and new materials. Currently, there are many methods for synthesizing 3,4-dichlorobenzonitrile, which can be broadly classified into four main routes: the reaction of 3,4-dichlorotrichloromethylbenzene with ammonium chloride, the dehydration synthesis of 3,4-dichlorobenzamide, the dehydration synthesis of 3,4-dichlorobenzaldehyde oxime, and the ammoxidation synthesis of 3,4-dichlorotoluene. Compared to the first three routes, the fourth route is more advantageous in both economic and environmental aspects. It has gradually become the mainstream method in industrial production. The key to the ammonia oxidation method (ammonia oxidation reaction) often lies in the selection of catalyst. How to develop a catalyst with high catalytic activity and high selectivity has been a long-standing topic for engineers. Although a large number of studies have shown that vanadium-chromium catalysts can effectively catalyze the one-step reaction of 3,4-dichlorotoluene to produce 3,4-dichlorobenzonitrile, existing vanadium-chromium catalysts still face the dilemma of low catalytic activity and selectivity. Even after being supported by a support such as silica, there is still a lot of room for improvement. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a method for synthesizing 3,4-dichlorobenzonitrile. This invention creatively uses tetramethyl silicate as the silicon source, aluminum chloride hexahydrate as the aluminum source, and yttrium chloride hexahydrate as the yttrium / rare earth source. Based on the sol-gel method, the timing of adding the aluminum and yttrium sources to the reaction solvent is controlled to prepare an aluminum-yttrium-doped silica sol. The aluminum and yttrium sources are added in two stages: the first addition is before the tetramethyl silicate is added dropwise to the reaction solvent, and the second addition is after all the tetramethyl silicate has been added dropwise to the reaction solvent. Then, based on the impregnation method, a vanadium-chromium catalyst is supported on the aluminum-yttrium-doped silica sol to obtain a supported catalyst. When applied to the ammoxidation reaction of 3,4-dichlorotoluene, it can effectively catalyze the synthesis of 3,4-dichlorobenzonitrile, exhibiting not only high conversion rate but also good selectivity, achieving remarkable technical results.

[0004] The objective of this invention can be achieved through the following technical solutions: A method for synthesizing 3,4-dichlorobenzonitrile, the method comprising the following steps: A supported catalyst is loaded into a reactor, and a raw material consisting of 3,4-dichlorotoluene, ammonia, and air is added to react. The product is then post-treated. The reaction temperature is 390-405℃, the reaction pressure is atmospheric pressure, and the reaction space rate is 600-1000 h⁻¹.-1 .

[0005] As a preferred embodiment of the present invention, the supported catalyst is prepared by the following steps: Step A: At room temperature, add hydrochloric acid solution to 100-110 parts by weight of ethanol aqueous solution until the pH is adjusted to 2.5-3. Then add 0.4-0.6 parts by weight of aluminum chloride hexahydrate and 0.2-0.3 parts by weight of yttrium chloride hexahydrate, stir for 5-10 minutes to mix. Then, while stirring, add 13-16 parts by weight of tetramethyl silicate dropwise. After all the addition is complete, continue stirring for 15-30 minutes to mix. Finally, add 0.3-0.4 parts by weight of aluminum chloride hexahydrate and 0.08-0.1 parts by weight of yttrium chloride hexahydrate, stir for 2-3 hours to mix, concentrate, and obtain aluminum yttrium doped silica sol. Step B: Add 40-45 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heat to 80-90℃, keep warm, and stir for 10-15 minutes to mix. Next, add vanadium pentoxide and chromium trioxide, stir until no bubbles are generated, and let it cool naturally to room temperature. Add 100-110 parts by weight of aluminum yttrium-doped silica sol, concentrate, let stand at room temperature, dry, calcine, and let it cool naturally to room temperature.

[0006] Furthermore, the mass fraction of the ethanol aqueous solution in step A is 30-35%.

[0007] Further, the concentration of the hydrochloric acid aqueous solution in step A is 0.1-0.2 mol / L.

[0008] Furthermore, the dropping rate described in step A is 3-4 s / drop.

[0009] Further, the concentration mentioned in step A refers to vacuum distillation at 40-45°C under a vacuum of 0.05 MPa until the solid content is 35-40 wt%.

[0010] Furthermore, the heating rate in step B is 3-6 °C / min.

[0011] Further, the mass ratio of oxalic acid to vanadium pentoxide in step B is 45:6-8.

[0012] Further, the mass ratio of oxalic acid to chromium trioxide in step B is 45:7-8.

[0013] Further, the concentration mentioned in step B refers to vacuum distillation at 40-45°C under a vacuum of 0.08 MPa until the volume is reduced to 30-40% of the original volume.

[0014] Furthermore, the settling time described in step B is 8-10 hours.

[0015] Furthermore, the drying described in step B refers to drying at 95-100°C to a constant weight.

[0016] Furthermore, the calcination mentioned in step B refers to heating to 520-570℃ at a heating rate of 5℃ / min and then holding at that temperature for 6-8 hours.

[0017] As a preferred embodiment of the present invention, the molar ratio of 3,4-dichlorotoluene, ammonia and oxygen in the air is 1:3-4:4.

[0018] The beneficial effects of this invention are as follows: (1) This invention creatively uses tetramethyl silicate as a silicon source, aluminum chloride hexahydrate as an aluminum source, and yttrium chloride hexahydrate as a yttrium / rare earth source. Then, based on the sol-gel method, the timing of adding the aluminum source and yttrium source to the reaction solvent is controlled to prepare an aluminum-yttrium-doped silica sol. The aluminum source and yttrium source are added in two parts. The first addition is before tetramethyl silicate is added to the reaction solvent, and the second addition is after all tetramethyl silicate is added to the reaction solvent. Then, based on the impregnation method, the aluminum-yttrium-doped silica sol is used to support the vanadium-chromium catalyst to obtain a supported catalyst. When it is applied to the ammoxidation reaction of 3,4-dichlorotoluene, it can effectively catalyze the synthesis of 3,4-dichlorobenzonitrile. It not only has a high conversion rate but also good selectivity, achieving remarkable technical results.

[0019] (2) Given that the catalytic activity and selectivity of existing vanadium-chromium catalysts still need improvement even after loading onto a support (silica sol), this invention creatively improves the silica sol by preparing an aluminum-yttrium-doped silica sol based on the sol-gel method. On one hand, aluminum-yttrium doping of the silica sol allows the subsequently prepared supported catalyst to form more Lewis acid sites, causing changes in acid-base properties, which to some extent helps improve catalytic activity and selectivity. On the other hand, aluminum-yttrium doping can also regulate the specific surface area, pore structure, and interfacial activity of the silica sol (particles), enhancing its interaction with the vanadium-chromium catalyst and achieving better loading effects, further enhancing catalytic activity and selectivity. This is noteworthy. It is important to note that the timing of adding the aluminum and yttrium sources to the aluminum-yttrium doped silica sol in this invention needs to be carefully controlled. Adding them in two stages greatly promotes the selectivity of the subsequently prepared supported catalyst. This is because the reaction process of tetramethyl silicate (during the preparation of silica sol) involves hydrolysis and polycondensation. Adding them in two stages allows the aluminum-yttrium to be more uniformly "fixed" in the silica framework, changing the electron density distribution, thereby regulating the redox reaction behavior, enhancing the stabilization effect on the intermediates generated by the ammoxidation reaction of 3,4-dichlorotoluene, and promoting selectivity. In addition, compared with single-element doping, the dual-element doping of aluminum and rare earth yttrium can form a good complementary advantage, exert excellent synergistic effect, and obtain better technical results.

[0020] (3) The present invention provides a method for synthesizing 3,4-dichlorobenzonitrile, which is based on technical improvements around the catalyst (support) and can obtain a high yield of 3,4-dichlorobenzonitrile, making it very suitable for large-scale industrial production. Detailed Implementation

[0021] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0022] The reactors used in the following examples and comparative examples all refer to φ38mm fluidized bed reactors with a length of 1800mm; the amount of supported catalyst used is 250g. Post-processing refers to first condensing the product in a condenser to obtain condensate, then sending the condensate to a separator, allowing it to stand for 20 minutes to separate the organic phase, and finally sending the organic phase to a distillation column for rectification. The condensation temperature is 75°C, the separator temperature is maintained at 80°C, and the rectification conditions are: vacuum degree controlled at 0.095 MPa, column top temperature controlled at 118°C, column bottom temperature controlled at 156°C, and reflux ratio controlled at 4.

[0023] Example 1 A method for synthesizing 3,4-dichlorobenzonitrile, the method comprising the following steps: A supported catalyst was loaded into a reactor, and a raw material consisting of 3,4-dichlorotoluene, ammonia, and air was added to react. The product was then post-treated. The reaction temperature was 390°C, the reaction pressure was atmospheric pressure, and the reaction space rate was 600 h⁻¹. -1 .

[0024] The supported catalyst is prepared through the following steps: Step A: At room temperature, add hydrochloric acid solution to 100 parts by weight of ethanol aqueous solution until the pH is adjusted to 2.5. Then add 0.4 parts by weight of aluminum chloride hexahydrate and 0.2 parts by weight of yttrium chloride hexahydrate, stir for 5 minutes to mix. Then, while stirring, add 13 parts by weight of tetramethyl silicate dropwise. After all the addition is complete, continue stirring for 15 minutes to mix. Finally, add 0.3 parts by weight of aluminum chloride hexahydrate and 0.08 parts by weight of yttrium chloride hexahydrate, stir for 2 hours to mix, concentrate, and obtain aluminum yttrium doped silica sol. Step B: Add 40 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heat to 80°C, keep warm, stir for 10 minutes to mix, then add vanadium pentoxide and chromium trioxide, stir until no bubbles are generated, cool naturally to room temperature, add 100 parts by weight of aluminum yttrium doped silica sol, concentrate, let stand at room temperature, dry, calcine, and cool naturally to room temperature.

[0025] The ethanol aqueous solution in step A has a mass fraction of 30%.

[0026] The concentration of the hydrochloric acid aqueous solution in step A is 0.1 mol / L.

[0027] The dropping rate described in step A is 3 drops per second.

[0028] The concentration mentioned in step A refers to vacuum distillation at 40°C under a vacuum of 0.05 MPa until the solid content is 35 wt%.

[0029] The heating rate described in step B is 3°C / min.

[0030] The mass ratio of oxalic acid to vanadium pentoxide in step B is 45:6.

[0031] The mass ratio of oxalic acid to chromium trioxide in step B is 45:7.

[0032] The concentration mentioned in step B refers to vacuum distillation at 40°C under a vacuum of 0.08 MPa until the volume is reduced to 30% of the original volume.

[0033] The settling time described in step B is 8 hours.

[0034] The drying described in step B refers to drying at 95°C to a constant weight.

[0035] The calcination mentioned in step B refers to heating to 520°C at a heating rate of 5°C / min and then holding at that temperature for 6 hours.

[0036] The molar ratio of the 3,4-dichlorotoluene, the ammonia, and the oxygen in the air is 1:3:4.

[0037] Example 2 A method for synthesizing 3,4-dichlorobenzonitrile, the method comprising the following steps: A supported catalyst was loaded into a reactor, and a raw material consisting of 3,4-dichlorotoluene, ammonia, and air was added to react. The product was then post-treated. The reaction temperature was 405°C, the reaction pressure was atmospheric pressure, and the reaction space rate was 1000 h⁻¹. -1 .

[0038] The supported catalyst is prepared through the following steps: Step A: At room temperature, add hydrochloric acid solution to 110 parts by weight of ethanol aqueous solution until the pH is adjusted to 3. Then add 0.6 parts by weight of aluminum chloride hexahydrate and 0.3 parts by weight of yttrium chloride hexahydrate, stir for 10 min to mix. Then, while stirring, add 16 parts by weight of tetramethyl silicate dropwise. After all the addition is complete, continue stirring for 30 min to mix. Finally, add 0.4 parts by weight of aluminum chloride hexahydrate and 0.1 parts by weight of yttrium chloride hexahydrate, stir for 3 h to mix, concentrate, and obtain aluminum yttrium doped silica sol. Step B: Add 45 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heat to 90°C, keep warm, stir for 15 minutes to mix, then add vanadium pentoxide and chromium trioxide, stir until no bubbles are generated, cool naturally to room temperature, add 110 parts by weight of aluminum yttrium doped silica sol, concentrate, let stand at room temperature, dry, calcine, and cool naturally to room temperature.

[0039] The ethanol aqueous solution in step A has a mass fraction of 35%.

[0040] The concentration of the hydrochloric acid aqueous solution in step A is 0.2 mol / L.

[0041] The dropping rate described in step A is 4 drops per second.

[0042] The concentration mentioned in step A refers to vacuum distillation at 45°C under a vacuum of 0.05 MPa until the solid content is 40 wt%.

[0043] The heating rate described in step B is 6°C / min.

[0044] The mass ratio of oxalic acid to vanadium pentoxide in step B is 45:8.

[0045] The mass ratio of oxalic acid to chromium trioxide in step B is 45:8.

[0046] The concentration mentioned in step B refers to vacuum distillation at 45°C under a vacuum of 0.08 MPa until the volume is reduced to 40% of the original volume.

[0047] The settling time described in step B is 10 hours.

[0048] The drying process described in step B refers to drying at 100°C to a constant weight.

[0049] The calcination mentioned in step B refers to heating to 570°C at a heating rate of 5°C / min and then holding at that temperature for 8 hours.

[0050] The molar ratio of the 3,4-dichlorotoluene, the ammonia, and the oxygen in the air is 1:4:4.

[0051] Example 3 A method for synthesizing 3,4-dichlorobenzonitrile, the method comprising the following steps: A supported catalyst was loaded into a reactor, and a raw material consisting of 3,4-dichlorotoluene, ammonia, and air was added to react. The product was then post-treated. The reaction temperature was 400°C, the reaction pressure was atmospheric pressure, and the reaction space rate was 800 h⁻¹. -1 .

[0052] The supported catalyst is prepared through the following steps: Step A: At room temperature, add hydrochloric acid solution to 105 parts by weight of ethanol aqueous solution until the pH is adjusted to 2.8. Then add 0.5 parts by weight of aluminum chloride hexahydrate and 0.25 parts by weight of yttrium chloride hexahydrate, stir for 8 minutes to mix. Then, while stirring, add 15 parts by weight of tetramethyl silicate dropwise. After all the addition is complete, continue stirring for 20 minutes to mix. Finally, add 0.35 parts by weight of aluminum chloride hexahydrate and 0.09 parts by weight of yttrium chloride hexahydrate, stir for 2.5 hours to mix, concentrate, and obtain aluminum yttrium doped silica sol. Step B: Add 44 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heat to 85°C, keep warm, stir for 12 minutes to mix, then add vanadium pentoxide and chromium trioxide, stir until no bubbles are generated, cool naturally to room temperature, add 105 parts by weight of aluminum yttrium doped silica sol, concentrate, let stand at room temperature, dry, calcine, and cool naturally to room temperature.

[0053] The ethanol aqueous solution in step A has a mass fraction of 33%.

[0054] The concentration of the hydrochloric acid aqueous solution in step A is 0.15 mol / L.

[0055] The dropping rate described in step A is 3.5 s / drop.

[0056] The concentration mentioned in step A refers to vacuum distillation at 42°C under a vacuum of 0.05 MPa until the solid content is 38 wt%.

[0057] The heating rate described in step B is 5°C / min.

[0058] The mass ratio of oxalic acid to vanadium pentoxide in step B is 45:7.

[0059] The mass ratio of oxalic acid to chromium trioxide in step B is 45:7.3.

[0060] The concentration mentioned in step B refers to vacuum distillation at 44°C under a vacuum of 0.08 MPa until the volume is reduced to 36% of the original volume.

[0061] The settling time described in step B is 9 hours.

[0062] The drying process described in step B refers to drying at 98°C to a constant weight.

[0063] The calcination mentioned in step B refers to heating to 550°C at a heating rate of 5°C / min and then holding at that temperature for 7 hours.

[0064] The molar ratio of the 3,4-dichlorotoluene, the ammonia, and the oxygen in the air is 1:3.5:4.

[0065] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that in step A, aluminum chloride hexahydrate was replaced with equimolar yttrium chloride hexahydrate, while the rest remained unchanged.

[0066] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that in step A, yttrium chloride hexahydrate was replaced with an equimolar amount of aluminum chloride hexahydrate, while the rest remained unchanged.

[0067] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that step A is changed to adding hydrochloric acid aqueous solution to 105 parts by weight of ethanol aqueous solution at room temperature until the pH is adjusted to 2.8, then adding 0.85 parts by weight of aluminum chloride hexahydrate and 0.34 parts by weight of yttrium chloride hexahydrate, stirring for 8 minutes to mix, then adding 15 parts by weight of tetramethyl silicate dropwise while stirring, and continuing to stir for 170 minutes after all the addition is completed, and then concentrating to obtain aluminum yttrium doped silica sol; the rest remains unchanged.

[0068] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that step A is changed to adding hydrochloric acid aqueous solution to 105 parts by weight of ethanol aqueous solution at room temperature until the pH is adjusted to 2.8, then adding 15 parts by weight of tetramethyl silicate dropwise while stirring. After all the addition is completed, stirring is continued for 20 minutes to mix. Finally, 0.85 parts by weight of aluminum chloride hexahydrate and 0.34 parts by weight of yttrium chloride hexahydrate are added, and the mixture is stirred for 2.5 hours to mix and then concentrated to obtain aluminum yttrium doped silica sol; all other steps remain unchanged.

[0069] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is as follows: Step A is changed to adding hydrochloric acid aqueous solution to 105 parts by weight of ethanol aqueous solution at room temperature until the pH is adjusted to 2.8, then adding 15 parts by weight of tetramethyl silicate dropwise while stirring. After all the addition is completed, stirring is continued for 170 minutes to mix, and then concentrated to obtain silica sol; Step B is changed to adding 44 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heating to 85°C, holding at that temperature, stirring for 12 minutes to mix, then adding vanadium pentoxide and chromium trioxide, stirring until no bubbles are generated, naturally cooling to room temperature, adding 105 parts by weight of silica sol, concentrating, standing at room temperature, drying, calcining, and naturally cooling to room temperature; the rest remains unchanged.

[0070] Conversion rate and yield evaluation: The conversion rates of 3,4-dichlorotoluene and the yields of 3,4-dichlorobenzonitrile in Examples 1-3 and Comparative Examples 1-5 were calculated respectively (GC-MASS qualitative analysis, gas chromatography quantitative analysis, and external standard method for quantification).

[0071] The conversion rate of 3,4-dichlorotoluene = (molar amount of 3,4-dichlorotoluene in the reaction / molar amount of 3,4-dichlorotoluene in the feed) × 100%, and the result is rounded to the nearest integer.

[0072] The yield of 3,4-dichlorobenzonitrile is calculated as follows: (molar amount of 3,4-dichlorobenzonitrile produced / molar amount of 3,4-dichlorobenzonitrile to be obtained) × 100%, and the result is rounded to the nearest integer.

[0073] Table 1. Evaluation Results of Conversion Rate and Yield ; As can be seen from Table 1, the synthesis method of the present invention can achieve higher conversion rates (3,4-dichlorotoluene) and yields (3,4-dichlorobenzonitrile), achieving remarkable technical results. The catalyst supports of Comparative Examples 1-2 were all doped with only a single element, resulting in varying degrees of reduction in conversion and yield. Comparative Examples 3-4 changed the timing of the addition of the aluminum source and yttrium source (all were added at once, not in two stages), resulting in a significant decrease in yield. However, the decrease in conversion was not significant, which indirectly indicates a decrease in selectivity. The catalyst support of Comparative Example 5 was not doped with any element, and its effect was not ideal.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for the synthesis of 3,4-dichloronitrile, characterized in that: The synthesis method includes the following steps: A supported catalyst is loaded into a reactor, and a raw material consisting of 3,4-dichlorotoluene, ammonia, and air is added to react. The product is then post-treated. The reaction temperature is 390-405℃, the reaction pressure is atmospheric pressure, and the reaction space rate is 600-1000 h⁻¹. -1 ; The supported catalyst is prepared through the following steps: Step A: At room temperature, add hydrochloric acid solution to 100-110 parts by weight of ethanol aqueous solution until the pH is adjusted to 2.5-3. Then add 0.4-0.6 parts by weight of aluminum chloride hexahydrate and 0.2-0.3 parts by weight of yttrium chloride hexahydrate, stir for 5-10 minutes to mix. Then, while stirring, add 13-16 parts by weight of tetramethyl silicate dropwise. After all the addition is complete, continue stirring for 15-30 minutes to mix. Finally, add 0.3-0.4 parts by weight of aluminum chloride hexahydrate and 0.08-0.1 parts by weight of yttrium chloride hexahydrate, stir for 2-3 hours to mix, concentrate, and obtain aluminum yttrium doped silica sol. Step B: Add 40-45 parts by weight of oxalic acid to 400 parts by weight of deionized water at room temperature, then heat to 80-90℃, keep warm, stir for 10-15 minutes to mix, then add vanadium pentoxide and chromium trioxide, stir until no bubbles are generated, cool naturally to room temperature, add 100-110 parts by weight of aluminum yttrium doped silica sol, concentrate, let stand at room temperature, dry, calcine, and cool naturally to room temperature; The molar ratio of the 3,4-dichlorotoluene, the ammonia, and the oxygen in the air is 1:3-4:

4.

2. The method for synthesizing 3,4-dichlorobenzonitrile according to claim 1, characterized in that: The ethanol aqueous solution in step A has a mass fraction of 30-35%.

3. The method for synthesizing 3,4-dichlorobenzonitrile according to claim 1, characterized in that: The dropping rate described in step A is 3-4 seconds per drop.

4. The method for synthesizing 3,4-dichlorobenzonitrile according to claim 1, characterized in that: The concentration mentioned in step A refers to vacuum distillation at 40-45°C under a vacuum of 0.05 MPa until the solid content is 35-40 wt%.

5. The method of claim 1, wherein: The mass ratio of oxalic acid to vanadium pentoxide in step B is 45:6-8.

6. The method of claim 1, wherein: The mass ratio of oxalic acid to chromium trioxide in step B is 45:7-8.

7. The method of claim 1, wherein: The concentration mentioned in step B refers to vacuum distillation at 40-45°C under a vacuum of 0.08 MPa until the volume is reduced to 30-40% of the original volume.