Method for dechlorination of waste plastic pyrolysis oil

Abstract

The application discloses a method for removing chlorine from waste plastic cracking oil, which comprises the following steps: S1, after removing mechanical impurities in the waste plastic cracking oil, inorganic chlorides are removed through water washing, then oil-water separation is performed, the obtained oil phase is subjected to drying treatment, and first-stage dechlorination waste plastic cracking oil is obtained; S2, after the first-stage dechlorination waste plastic cracking oil is mixed with hydrogen, pre-hydrogenation is performed in a pre-hydrogenation catalytic distillation column, diene is converted into mono-olefin, chlorine-rich light cracking oil is obtained at the top of the column, chlorine-poor heavy cracking oil is obtained at the bottom of the column, and the chlorine-poor heavy cracking oil is rich in sulfur, nitrogen and metal impurities; S3, the chlorine-rich light cracking oil is reacted with hydrogen under the action of a hydrogen dechlorination catalyst to remove organic chlorides, and a hydrogen dechlorination cracking oil is obtained through gas-liquid separation of a reaction product; and S4, the chlorine-poor heavy cracking oil is contacted with an adsorbent to obtain adsorption dechlorination cracking oil. The method has high chlorine removal rate for waste plastic cracking oil, is not prone to coking, and has slow catalyst deactivation.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic chemical recycling technology, specifically relating to a method for dechlorination of waste plastic pyrolysis oil. Background Technology

[0002] Since its inception, plastic has brought about tremendous changes to human production and life, becoming an indispensable part of modern society. However, plastics generally have a short lifespan, and the generation and improper disposal of large quantities of waste plastics have caused serious harm to human health and the ecological environment. To address plastic pollution, countries around the world have successively introduced a series of policies and regulations to encourage and support the recycling and reuse of plastics. Currently, the recycling of waste plastics is mainly based on physical methods, primarily treating relatively clean waste plastics with a single material composition. For low-value mixed waste plastics that cannot be disposed of through physical recycling, chemical recycling is not only an effective way to realize the resource utilization of plastic waste, but also an important means to solve plastic pollution, and it has a significantly better carbon emission reduction effect compared to incineration. Among the many chemical recycling technologies for waste plastics, "waste plastic pyrolysis + refining and chemical processing of pyrolysis oil" is a technical route commonly adopted by domestic and foreign companies. However, due to the complexity of waste plastic composition and the shortcomings of existing sorting technologies in terms of precision and efficiency, the properties of plastic pyrolysis oil are generally poor, with impurity content far exceeding that of crude oil and its distillate oils, making it unsuitable as a raw material for existing refining and chemical plants. Pretreatment of waste plastic pyrolysis oil has become an essential step in realizing the industrialization of this technical route. The removal of chlorine from waste plastic pyrolysis oil is the most critical aspect. This chlorine primarily originates from chlorinated plastics such as PVC and halogenated plastic additives, existing mainly in the form of organochlorine compounds in the pyrolysis oil. The concentration is generally between several hundred and several thousand ppm, far exceeding the design limits of existing refining units. If this un-dechlorinated pyrolysis oil directly enters the refinery, it can easily cause equipment corrosion and catalyst poisoning, posing a significant threat to the safe and stable operation of existing refining units. Among existing oil dechlorination technologies, adsorption is simple, but due to the extremely high chlorine content in the pyrolysis oil, the adsorbent easily reaches saturation and is difficult to regenerate, with frequent replacements increasing dechlorination costs. Hydrotreating has higher dechlorination efficiency, but impurities such as metals, sulfur, and nitrogen compete with chlorides on the catalyst surface, hindering chloride removal. The large amount of sulfides in the pyrolysis products restricts the use of high-efficiency precious metal catalysts. Furthermore, waste plastic pyrolysis oil has a high degree of unsaturation, and the large amount of dienes in the pyrolysis oil easily causes severe coking in equipment such as heaters and heat exchangers, significantly affecting the activity and lifespan of the catalyst. Summary of the Invention

[0003] The purpose of this invention is to provide a method for dechlorinating waste plastic pyrolysis oil. The method of this invention has a high chlorine removal rate, low investment and operating costs, and effectively avoids the shortcomings of direct hydrodechlorination of waste plastic pyrolysis oil, such as easy coking, rapid catalyst deactivation, and high dechlorination costs.

[0004] To achieve the above objectives, the present invention provides a method for dechlorinating waste plastic pyrolysis oil, characterized by comprising the following steps:

[0005] S1, after removing mechanical impurities from the waste plastic pyrolysis oil, it is washed with water to remove inorganic chlorides, and then separated by oil and water. The resulting oil phase is dried to obtain first-grade dechlorinated waste plastic pyrolysis oil.

[0006] S2, after mixing the primary dechlorinated waste plastic pyrolysis oil with hydrogen, pre-hydrogenation is carried out in a pre-hydrogenation catalytic distillation tower to convert dienes into monoolefins. Chlorine-rich light pyrolysis oil is obtained at the top of the tower, and chlorine-lean heavy pyrolysis oil is obtained at the bottom of the tower. The chlorine-lean heavy pyrolysis oil is rich in sulfur, nitrogen and metal impurities.

[0007] S3 involves reacting chlorine-rich light cracked oil with hydrogen under the action of a hydrodechlorination catalyst to remove organochlorides, and the reaction product is separated by gas-liquid separation to obtain hydrodechlorinated cracked oil.

[0008] S4, chlorine-poor heavy pyrolysis oil is contacted with an adsorbent to obtain adsorbed dechlorination pyrolysis oil.

[0009] The method for dechlorinating waste plastic pyrolysis oil according to the present invention wherein the total chlorine content of the waste plastic pyrolysis oil is not less than 100 ppm.

[0010] The method for dechlorinating waste plastic pyrolysis oil according to the present invention wherein the inorganic chlorine content in the first-stage dechlorinated waste plastic pyrolysis oil is not greater than 5 ppm and the water content is not greater than 500 ppm.

[0011] The method for dechlorinating waste plastic pyrolysis oil described in this invention involves packing pre-hydrogenation catalysts with decreasing reactivity from top to bottom into a pre-hydrogenation catalytic distillation column to match the temperature gradient within the distillation column.

[0012] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises a pre-hydrogenation catalyst composed of alumina and one or more oxides of Co, Mo, Ni, and W.

[0013] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises a pre-hydrogenation catalyst with an alumina content of 70% to 90% by mass and a content of one or more oxides of Co, Mo, Ni, and W of 10% to 30%.

[0014] The method for dechlorinating waste plastic pyrolysis oil according to the present invention uses a pre-hydrogenation catalyst with a structured catalyst.

[0015] The method for dechlorinating waste plastic pyrolysis oil according to the present invention uses a pre-hydrogenation catalytic distillation tower with a reaction temperature of 90–230°C, a pressure of 0.5–5 MPa, and a volume hourly space velocity of 2–5 h⁻¹. -1 The hydrogen-to-oil volume ratio is 5-100:1.

[0016] The method for dechlorinating waste plastic pyrolysis oil according to the present invention includes alumina, magnesium or phosphorus modified alumina, molecular sieve, nickel oxide or cobalt oxide, molybdenum oxide or tungsten oxide, zinc oxide or calcium oxide as the hydrodechlorination catalyst.

[0017] The method for dechlorinating waste plastic pyrolysis oil according to the present invention uses one or more of modified Y molecular sieve, modified ZSM-5 molecular sieve, and modified 13X molecular sieve. The modification described in this invention is acid modification or hydrothermal modification, etc., which are commonly used modification methods in the field of hydrodechlorination catalyst technology. This invention does not impose specific limitations, and those skilled in the art can choose according to the actual situation.

[0018] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises the following mass composition of the hydrodechlorination catalyst: 20-30% alumina, 10-30% magnesium or phosphorus modified alumina, 0.5-8% molecular sieve, 2-5% nickel oxide or cobalt oxide, 5-20% molybdenum oxide or tungsten oxide, and 7-65% zinc oxide or calcium oxide.

[0019] The method for dechlorinating waste plastic pyrolysis oil according to the present invention wherein the Na2O content in the molecular sieve is less than 0.5%.

[0020] The dechlorination method for waste plastic pyrolysis oil described in this invention includes the following hydrodechlorination reaction conditions in step S3: reaction temperature 200–360°C, hydrogen partial pressure 3.5–9 MPa, and volume hourly space velocity 0.5–2.5 h⁻¹. -1 The hydrogen-to-oil volume ratio is 300–700:1.

[0021] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises an adsorbent consisting of a support composed of one or more of modified 13X molecular sieve, NaY molecular sieve, alumina, and activated carbon, as well as a metal oxide supported on the support. The modification described in this invention is acid modification or hydrothermal modification, etc., both of which are commonly used modification methods in the field of adsorption dechlorination catalyst technology. This invention does not impose specific limitations, and those skilled in the art can choose according to the actual situation.

[0022] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises, in which the metal oxide in the adsorbent includes one or more of copper oxide, ferric oxide, magnesium oxide, nickel oxide, cobalt oxide, zinc oxide, and calcium oxide.

[0023] The method for dechlorinating waste plastic pyrolysis oil according to the present invention comprises an adsorbent with a carrier mass content of 75-90% and a metal oxide mass content of 10-25%.

[0024] The method for dechlorinating waste plastic pyrolysis oil according to the present invention has a reaction temperature of 50–200°C and a volume hourly space velocity of 0.5–1.0 h⁻¹ in step S4. -1The reaction pressure is 0.1–0.8 MPa.

[0025] In the method for dechlorinating waste plastic pyrolysis oil of the present invention, the hydrodechlorinated pyrolysis oil obtained is used as a feedstock for steam cracking or catalytic reforming after deep hydrorefining; the adsorbed dechlorinated pyrolysis oil obtained is used as a feedstock for atmospheric and vacuum distillation, hydrocracking, catalytic cracking or delayed coking in refineries.

[0026] Beneficial effects of this invention:

[0027] Because organochlorines in waste plastic pyrolysis oil are mainly concentrated in the light fraction, while the heavy fraction contains very little organochlorine, and metallic impurities such as iron and calcium are mainly enriched in the heavy fraction. Furthermore, the heavy fraction also contains higher levels of impurities such as sulfur and nitrogen than the light fraction. If the entire fraction of waste plastic pyrolysis oil is directly subjected to hydrodechlorination, the large molecular hydrocarbons and sulfur and nitrogen compounds in the medium and heavy fractions will compete with small molecular chlorides for adsorption, affecting the removal efficiency of organochlorines. Simultaneously, polycyclic aromatic hydrocarbons and metallic impurities in the heavy fraction can easily cover or poison the active sites of the hydrodechlorination catalyst, reducing catalyst activity. This invention, before organochlorine removal, cuts the waste plastic pyrolysis oil into light and heavy fractions based on the distribution of chlorine in the pyrolysis oil. For the light fraction with high organochlorine content, hydrodechlorination is used; for the heavy fraction with lower organochlorine content, adsorption dechlorination is used. Therefore, the application of the technical solution of this invention can, on the one hand, avoid the influence of heavy distillate oil molecules on the catalyst activity and service life when hydrodechlorinating the whole fraction, and on the other hand, only hydrodechlorinate the light distillate, and use adsorption dechlorination for the heavy distillate oil with relatively low organic chlorine content, which can improve the overall removal efficiency of organic chlorine and reduce operating costs.

[0028] During fractionation, the pre-hydrogenation catalytic distillation column can selectively remove dienes from light components by matching pre-hydrogenation catalysts with different activities according to the temperature gradient within the column. This reduces the diene content in chlorine-rich light cracked oil, effectively preventing diene condensation, reducing carbon buildup, and minimizing carbon deposition. This also helps reduce the coverage of catalyst active sites by carbon deposits during hydrodechlorination, extending the catalyst's lifespan. Furthermore, it helps reduce the coking rate in the heater and heat exchanger. In addition, integrating the pre-hydrogenation reactor and fractionation column into a single pre-hydrogenation catalytic distillation column effectively saves on equipment investment. Detailed Implementation

[0029] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0030] The properties of the waste plastic pyrolysis oil raw material in this embodiment of the invention are shown in Table 1.

[0031] Table 1 Properties of cracked oil feedstock

[0032]

[0033]

[0034] After filtering to remove mechanical impurities, the waste plastic pyrolysis oil feedstock is washed with water to remove inorganic chlorides. It then undergoes oil-water separation in a separator. The separated oil is then subjected to adsorption drying in a drying tower to obtain primary dechlorinated waste plastic pyrolysis oil. This primary dechlorinated waste plastic pyrolysis oil is mixed with hydrogen and fed into a pre-hydrogenation catalytic distillation tower. Under the action of a pre-hydrogenation catalyst, it reacts with hydrogen. The cutting temperature is determined based on the chlorine distribution of the waste plastic pyrolysis oil feedstock to obtain chlorine-rich light pyrolysis oil and chlorine-poor heavy pyrolysis oil. The chlorine-rich light pyrolysis oil is further reacted with hydrogen under the action of a hydrodechlorination catalyst to remove organic chlorides, yielding hydrodechlorinated pyrolysis oil. The chlorine-poor heavy pyrolysis oil is further contacted with an adsorbent to obtain adsorbed dechlorinated pyrolysis oil.

[0035] Example 1:

[0036] Pre-hydrogenation catalyst A is packed in the upper part of the catalytic distillation column, accounting for 45% of the volume, and its catalyst composition is: 80% alumina, 14% nickel oxide, and 6% molybdenum oxide. Pre-hydrogenation catalyst B is packed in the lower part of the catalytic distillation column, accounting for 45% of the volume, and its catalyst composition is: 88% alumina, 8% nickel oxide, and 4% molybdenum oxide. Both pre-hydrogenation catalyst A and pre-hydrogenation catalyst B are honeycomb-structured catalysts.

[0037] Pre-hydrogenation reaction process conditions: reaction temperature 180-195℃, pressure 2.5MPa, volume hourly space velocity 2.0h⁻¹ -1 The hydrogen-to-oil ratio is 100:1 (V:V).

[0038] The cut point for both light and heavy pyrolysis oils is 160℃.

[0039] The hydrodechlorination catalyst has the following composition by mass: 28% alumina, 30% phosphorus-modified alumina, 4% hydrothermally modified ZSM-5 molecular sieve (containing 0.4% Na2O), 4.5% cobalt oxide, 15.5% molybdenum oxide, and 18% zinc oxide.

[0040] Hydrodechlorination reaction process conditions: reaction temperature 290℃, hydrogen partial pressure 7MPa, volume hourly space velocity 1h. -1 The hydrogen-to-oil ratio is 500:1 (V:V).

[0041] The mass composition of the adsorption dechlorination catalyst is: 75% acid-modified 13X molecular sieve, 15% alumina, 5% magnesium oxide, and 5% ferric oxide.

[0042] The adsorption dechlorination reaction process conditions are: reaction temperature 60℃, volume hourly space velocity 0.6 h⁻¹. -1 The reaction pressure is 0.8 MPa.

[0043] Example 2:

[0044] The pre-hydrogenation catalyst consists of 80% alumina, 16% nickel oxide, and 4% cobalt oxide, and is a honeycomb-structured catalyst.

[0045] Pre-hydrogenation reaction process conditions: reaction temperature 145-155℃, pressure 0.8MPa, volume hourly space velocity 5.0h⁻¹ -1 The hydrogen-to-oil ratio is 10:1 (V:V).

[0046] The cut point for both light and heavy pyrolysis oils is 117°C.

[0047] The hydrodechlorination catalyst has the following composition by mass: 20% alumina, 10% phosphorus-modified alumina, 0.5% acid-modified Y molecular sieve, 3% cobalt oxide, 5% molybdenum oxide, and 61.5% zinc oxide.

[0048] Hydrodechlorination reaction process conditions: reaction temperature 210℃, hydrogen partial pressure 4MPa, volume hourly space velocity 2.5h⁻¹ -1 The hydrogen-to-oil ratio is 350:1 (V:V).

[0049] The adsorption dechlorination catalyst has the following composition by mass: 88% activated carbon, 2% copper oxide, and 10% calcium oxide.

[0050] The adsorption dechlorination reaction process conditions are: reaction temperature 150℃, volume hourly space velocity 0.8 h⁻¹. -1 The reaction pressure is 0.5 MPa.

[0051] Example 3:

[0052] The pre-hydrogenation catalyst composition is: 70% alumina, 16% nickel oxide, and 14% molybdenum oxide.

[0053] Pre-hydrogenation reaction process conditions: reaction temperature 215-228℃, pressure 4.8MPa, volume hourly space velocity 3.0h⁻¹ -1 The hydrogen-to-oil ratio is 50:1 (V:V).

[0054] The cut point for both light and heavy pyrolysis oils is 210℃.

[0055] The hydrodechlorination catalyst has the following composition by mass: 30% alumina, 15% magnesium-modified alumina, 8% hydrothermally modified 13X molecular sieve, 5% nickel oxide, 20% tungsten oxide, and 22% calcium oxide.

[0056] Hydrodechlorination reaction process conditions: reaction temperature 360℃, hydrogen partial pressure 9MPa, volume hourly space velocity 0.5h⁻¹-1 The hydrogen-to-oil ratio is 700:1 (V:V).

[0057] The adsorption dechlorination catalyst has the following composition by mass: 90% alumina, 5% nickel oxide, and 5% cobalt oxide.

[0058] The adsorption dechlorination reaction process conditions are: reaction temperature 200℃, volume hourly space velocity 1 h⁻¹. -1 The reaction pressure is 0.3 MPa.

[0059] The properties of light chlorine-rich cracked oil, heavy chlorine-poor cracked oil, and dechlorinated cracked oil are shown in Table 2.

[0060] Table 2 Properties of Primary Dechlorination Waste Plastic Pyrolysis Oil, Light Chlorine-Rich Pyrolysis Oil, Heavy Chlorine-Lean Pyrolysis Oil, and Dechlorination Pyrolysis Oil

[0061]

[0062]

[0063] Comparative Example 1:

[0064] Waste plastic pyrolysis oil raw material 1 was subjected to the same water washing, separation and drying process as in Example 1 to obtain waste plastic pyrolysis oil with inorganic chlorine removed; the obtained waste plastic pyrolysis oil was directly subjected to hydrodechlorination without pre-hydrogenation reaction and fractionation, and the hydrodechlorination conditions were the same as in Example 1 to obtain waste plastic pyrolysis oil with organic chlorine removed, the properties of which are shown in Table 3.

[0065] Comparative Example 2:

[0066] Waste plastic pyrolysis oil raw material 2 was subjected to the same water washing, separation and drying process as in Example 2 to obtain waste plastic pyrolysis oil with inorganic chlorine removed; the obtained waste plastic pyrolysis oil was directly subjected to adsorption dechlorination without pre-hydrogenation reaction and fractionation, and the adsorption dechlorination conditions were the same as in Example 2 to obtain waste plastic pyrolysis oil with organic chlorine removed, the properties of which are shown in Table 3.

[0067] Comparative Example 3:

[0068] Waste plastic pyrolysis oil raw material 3 was subjected to the same water washing, separation, and drying process as in Example 3 to obtain waste plastic pyrolysis oil with inorganic chlorine removed. The obtained waste plastic pyrolysis oil was not subjected to pre-hydrogenation reaction, but was cut into light and heavy components in the same proportion as in Example 3. The light and heavy components were subjected to hydrodechlorination and adsorption dechlorination processes, respectively, under the same conditions as in Example 3, to obtain light and heavy waste plastic pyrolysis oils with organic chlorine removed, the properties of which are shown in Table 3.

[0069] Table 3 Properties of the comparative dechlorination cracking oils of this invention

[0070] project Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 3 Full fraction Full fraction Light fractions Heavy fraction Total chlorine, mg / kg 128 97 23 9

[0071] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for dechlorinating waste plastic pyrolysis oil, characterized in that, Includes the following steps: S1, after removing mechanical impurities from the waste plastic pyrolysis oil, it is washed with water to remove inorganic chlorides, and then separated by oil and water. The resulting oil phase is dried to obtain first-grade dechlorinated waste plastic pyrolysis oil. S2, after mixing the primary dechlorinated waste plastic pyrolysis oil with hydrogen, pre-hydrogenation is carried out in a pre-hydrogenation catalytic distillation tower under the action of a pre-hydrogenation catalyst to convert dienes into monoolefins. Chlorine-rich light pyrolysis oil is obtained at the top of the tower, and chlorine-lean heavy pyrolysis oil is obtained at the bottom of the tower. The chlorine-lean heavy pyrolysis oil is rich in sulfur, nitrogen and metal impurities. S3 involves reacting chlorine-rich light cracked oil with hydrogen under the action of a hydrodechlorination catalyst to remove organochlorides, and the reaction product is separated by gas-liquid separation to obtain hydrodechlorinated cracked oil. S4, chlorine-poor heavy cracked oil is contacted with an adsorbent to obtain adsorbed dechlorinated cracked oil; The pre-hydrogenation catalyst is composed of alumina and one or more oxides selected from Co, Mo, Ni, and W; the mass content of alumina in the pre-hydrogenation catalyst is 70% to 90%, and the content of one or more oxides selected from Co, Mo, Ni, and W is 10% to 30%. The reaction temperature of the pre-hydrogenation catalytic distillation column is 90-230℃, the pressure is 0.5-5MPa, the volume space velocity is 2-5h -1 , and the volume ratio of hydrogen to oil is 5-100:

1. The hydrodechlorination catalyst has the following mass composition: 20-30% alumina, 10-30% magnesium or phosphorus modified alumina, 0.5-8% molecular sieve, 2-5% nickel oxide or cobalt oxide, 5-20% molybdenum oxide or tungsten oxide, and 7-65% zinc oxide or calcium oxide. The hydrogenochlorination reaction condition in step S3 is: reaction temperature 200-360℃, hydrogen partial pressure 3.5-9MPa, volume space velocity 0.5-2.5h -1 , hydrogen / oil volume ratio 300-700:

1.

2. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The total chlorine content of the waste plastic pyrolysis oil is not less than 100 ppm.

3. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The inorganic chlorine content in the primary dechlorinated waste plastic pyrolysis oil is no more than 5 ppm, and the water content is no more than 500 ppm.

4. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The pre-hydrogenated catalytic distillation column is filled with pre-hydrogenated catalysts of decreasing reactivity from top to bottom to match the temperature gradient within the distillation column.

5. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The pre-hydrogenation catalyst is a regular structure catalyst.

6. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The molecular sieve is one or more of modified Y molecular sieve, modified ZSM-5 molecular sieve, and modified 13X molecular sieve.

7. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The Na2O content in the molecular sieve is less than 0.5%.

8. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The adsorbent comprises a support consisting of one or more of modified 13X molecular sieve, NaY molecular sieve, alumina and activated carbon, and a metal oxide supported on the support.

9. The method for dechlorinating waste plastic pyrolysis oil according to claim 8, characterized in that, The metal oxides in the adsorbent include one or more of copper oxide, ferric oxide, magnesium oxide, nickel oxide, cobalt oxide, zinc oxide, and calcium oxide.

10. The method for dechlorinating waste plastic pyrolysis oil according to claim 8, characterized in that, The adsorbent contains 75-90% carrier by mass and 10-25% metal oxide by mass.

11. The method for dechlorinating waste plastic pyrolysis oil according to claim 1, characterized in that, The reaction temperature in step S4 is 50-200°C, the volume space velocity is 0.5-1.0h -1 , and the reaction pressure is 0.1-0.8 MPa.

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