Process for preparing polymer-grade propylene by separating liquefied gas

Abstract

The invention discloses a process for preparing polymer-grade propylene by separating liquefied gas, which comprises the following steps: after the raw material liquefied gas is separated by a depropanizing tower, the tower bottom is a mixed C4 product, the tower top C3 and ethane gas are sent to a first-stage hydrolysis unit to remove COS and CS2, and the first-stage hydrolysis unit is usually a container or tower filled with a hydrolytic agent; the method comprises the following steps: (1) feeding C3 and ethane gas without COS and CS2 into a propylene tower, feeding the C3 and ethane gas without COS and CS2 into a deethanization tower, and removing the ethane gas which contains hydrocarbons such as carbon I, carbon II and carbon III generated by a normal gas fractionation device and also contains most H2S generated in the hydrolysis process in the step (1), and automatically pressing the C3 in a tower kettle into the propylene tower; deethanization tower bottoms enter a propylene tower to be separated, the tower bottom is a propane product, and the tower top is propylene; the propylene at the top of the tower is sent to a primary H2S removal unit to remove H2S; the propylene liquid continues to be sent to the second-stage hydrolysis unit and the second-stage H2S removal unit to further remove COS, CS2 and H2S, the number of zinc oxide bed layers or the switching frequency of zinc oxide desulfurization bed layers is greatly reduced, and investment is reduced.

Description

Technical Field

[0001] The invention relates to the field of petrochemical industry, and relates to a process for preparing polymerization-grade propylene, and in particular to a process for preparing polymerization-grade propylene by separating liquefied gas. Background Art

[0002] Liquefied gas in refineries usually comes from catalytic cracking, coking and other units. After passing through the liquefied gas refining unit, the total sulfur is usually controlled at 20ppmw, and COS is controlled within 10ppmw. The sulfur content in the propylene product separated by the distillation process of this type of liquefied gas is difficult to meet the requirements of polymerization-grade propylene, especially carbonyl sulfide (COS) and carbon disulfide (CS2), which can cause the termination of the polypropylene reaction chain. COS will also be enriched in the propylene product in the gas fractionation unit. In addition, with the widespread application of high-efficiency propylene polymerization catalysts, there are higher requirements for the sulfur content in polymerization-grade propylene. The total sulfur volume fraction must be less than 1ppm, and the COS volume fraction must be less than 0.1ppm, or even less than 0.02ppm. Therefore, it is necessary to set up a propylene refining process for the crude propylene product distilled out to further desulfurize and dehydrate the propylene to meet the requirements of polymerization-grade propylene.

[0003] In industry, a propylene refining unit is often installed in a polypropylene plant to separately treat sulfur and other impurities in propylene, and an organic sulfur hydrolysis catalyst is connected in series with a zinc oxide desulfurizer to remove the total sulfur in propylene, such as a propylene refining system disclosed in Application No. 202122060275.2. In this method, the principle of organic sulfur hydrolysis is: COS+H2O=H2S+CO2; CS2+2H2O=2H2S+CO2. The reaction principle of the zinc oxide desulfurizer is: ZnO+H2S=ZnS+H2O. Among them, the hydrolysis of organic sulfur is a catalytic equilibrium reaction, and the conversion rate of COS and CS2 is 90-95%; the H2S treated by the zinc oxide desulfurizer is mainly derived from the organic sulfur hydrolysis reaction. The main performance parameters of the zinc oxide desulfurizer are sulfur capacity and penetration sulfur capacity. The sulfur capacity is about 10%, and its penetration sulfur capacity is about 5%. Due to the enrichment effect, the COS of crude propylene obtained by liquefied gas separation is usually within 20ppmw, and the H2S in propylene treated by zinc oxide desulfurization is usually within 30ppmw. Therefore, in industry, the propylene refining unit needs to be equipped with a larger zinc oxide desulfurization bed or use two parallel and mutually switched zinc oxide desulfurization beds to achieve the purpose of long-term operation of the device.

[0004] Patent application number 201510130926.7 discloses a method for deep desulfurization of liquefied petroleum gas. The invention uses the depropanizer of the liquefied gas separation process to concentrate the desulfurization process in the C3 fraction and (or) C4 fraction, reducing the processing volume of liquefied petroleum gas in each (or part of) desulfurization unit. However, this cannot reduce the amount of H2S removed, that is, it cannot reduce the amount of H2S desulfurizer (zinc oxide desulfurizer) used. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a process for preparing polymerization-grade propylene by separating liquefied gas. The present invention utilizes a deethanizer for separating liquefied gas to remove H2S, thereby greatly reducing the loading amount of zinc oxide desulfurizer, thereby achieving the purpose of reducing the number of zinc oxide beds or the switching frequency of zinc oxide desulfurization beds, thereby reducing investment.

[0006] The present invention provides a process for separating liquefied gas to produce polymerization-grade propylene, comprising the following steps:

[0007] 1) After the raw liquefied gas is separated by the depropanizer, the bottom of the tower is a mixed C4 product, and the top of the tower is C3 and ethane gas sent to the primary hydrolysis unit to remove COS and CS2. The primary hydrolysis unit is usually a container or tower filled with a hydrolyzing agent;

[0008] 2) The C3 and ethane gas from the removal of COS and CS2 in step 1) are sent to a deethanizer to remove ethane gas. The ethane gas contains not only C1, C2, C3 and other hydrocarbons produced by a normal gas fractionation device, but also most of the H2S generated in the hydrolysis process in step 1). The C3 in the bottom of the tower is automatically compressed to the propylene tower;

[0009] 3) The deethanizer bottom liquid from step 2) enters a propylene tower for separation, the bottom of the tower is the propane product, and the top of the tower is propylene;

[0010] 4) The propylene from the top of the tower in step 3) is sent to a primary H2S removal unit to remove H2S;

[0011] 5) The propylene liquid from step 4) is continuously sent to a secondary hydrolysis unit and a secondary H2S removal unit to further remove COS, CS2 and H2S. The secondary hydrolysis unit is usually a container or a tower filled with a hydrolyzing agent, and the secondary H2S removal unit is usually a container or a tower filled with a H2S desulfurizing agent.

[0012] The raw liquefied gas contains 1 to 50 ppmvol of total sulfur and 1 to 50 ppmvol of carbonyl sulfide.

[0013] The primary hydrolysis unit is arranged before the deethanizer of the gas fractionation, and includes not only being arranged between the depropanizer and the deethanizer, but also being arranged before the depropanizer.

[0014] The reaction mechanism of the hydrolysis unit includes COS+H2O=H2S+CO2; CS2+2H2O=2H2S+CO2. Of course, it can also be a desulfurization reaction that generates H2S substances in other reaction processes.

[0015] The process of the primary H2S removal unit and the secondary H2S removal unit includes zinc oxide desulfurization, and of course, it can also be other processes for removing H2S.

[0016] The secondary hydrolysis unit and the secondary H2S removal unit can be set according to the sulfur content requirements in the propylene product, or the secondary hydrolysis unit and the secondary H2S removal unit can be omitted according to the requirements of the propylene sulfur content. At the same time, a tertiary hydrolysis unit and a tertiary H2S removal unit can also be set according to needs, and so on.

[0017] The operating pressure of the hydrolysis process is 0.5-4.0 MPaG, and the operating temperature is 0-150°C.

[0018] The operating pressure of the H2S removal process is 0.5-4.0 MPaG, and the operating temperature is 0-150°C.

[0019] The H2S desulfurizer is a zinc oxide desulfurizer or other non-renewable H2S desulfurizer.

[0020] The present invention has the following beneficial effects:

[0021] 1) After being refined in the refinery, the liquefied gas usually needs to be re-equipped with a propylene refining system to meet the sulfur content requirements of polymerization-grade propylene. The present invention combines the liquefied gas separation and propylene refining systems, and utilizes the separation effect of the deethanizer tower of the gas fractionation device to remove the H2S generated during the hydrolysis and desulfurization process of the liquefied gas, thereby greatly reducing the H2S processing capacity of the H2S removal unit, and the reduction in the H2S processing capacity is large, reaching more than 90%;

[0022] 2) Greatly reduce the required loading amount of desulfurizer in the H2S removal unit, reduce the number of H2S removal beds in the H2S removal unit or the switching frequency of the H2S removal beds in the H2S removal unit, thereby reducing investment;

[0023] 3) The H2S removal unit usually generates a large amount of solid waste, which needs to be recycled or landfilled by qualified manufacturers. The present invention can greatly reduce the generation of related solid waste, thereby protecting the ecological environment and promoting sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0025] In the figure: 1-liquefied petroleum gas raw material, 2-C3 and ethane gas, 3-mixed C4 product, 4-hydrolysis product, 5-ethane gas, 6-C3, 7-propylene, 8-propane product, 9-propylene, 10-propylene, 11-propylene product, 101-depropanizer, 102-primary hydrolysis unit, 103-deethanizer, 104-propylene tower, 105-primary H2S removal unit, 106-secondary hydrolysis unit, 107-secondary H2S removal unit. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings.

[0027] The present invention provides a process for separating liquefied gas to produce polymerization-grade propylene, comprising the following steps:

[0028] 1) After the raw liquefied gas is separated by the depropanizer 101, the bottom of the tower is a mixed C4 product 3, and the top of the tower is C3 and ethane gas 2, which are sent to the primary hydrolysis unit 102 to remove COS and CS2. The primary hydrolysis unit 102 is usually a container or a tower filled with a hydrolysis agent;

[0029] 2) The C3 and ethane gas 2 from the removal of COS and CS2 in step 1) are hydrolyzed products 4, which are sent to the deethanizer 103 to remove ethane gas. The ethane gas contains not only C1, C2, C3 and other hydrocarbons produced by a normal gas fractionation device, but also most of the H2S generated in the hydrolysis process of step 1). The C3 6 in the bottom of the tower is automatically compressed to the propylene tower 104;

[0030] 3) The deethanizer bottom liquid C3 6 from step 2) enters the propylene tower 104 for separation, the bottom of the tower is the propane product 8, and the top of the tower is propylene 7;

[0031] 4) Propylene 7 from the top of the tower in step 3) is sent to a primary H2S removal unit to remove H2S;

[0032] 5) Propylene 9 from step 4) is continuously sent to a secondary hydrolysis unit 106 and a secondary H2S removal unit 107 to further remove COS, CS2 and H2S. The secondary hydrolysis unit 106 is usually a container or a tower filled with a hydrolyzing agent, and the secondary H2S removal unit 107 is usually a container or a tower filled with a H2S desulfurizing agent.

[0033] The raw liquefied gas contains 1 to 50 ppmvol of total sulfur and 1 to 50 ppmvol of carbonyl sulfide.

[0034] The primary hydrolysis unit 102 is arranged before the deethanizer of the gas fractionation, and includes not only being arranged between the depropanizer and the deethanizer, but also being arranged before the depropanizer.

[0035] The reaction mechanism of the hydrolysis unit includes COS+H2O=H2S+CO2; CS2+2H2O=2H2S+CO2. Of course, it can also be a desulfurization reaction that generates H2S substances in other reaction processes.

[0036] The process of the H2S removal unit includes zinc oxide desulfurization, and of course, it can also be other processes for removing H2S.

[0037] The secondary hydrolysis unit 106 and the secondary H2S removal unit 107 can be set according to the sulfur content requirement in the propylene product, or can be set without the secondary hydrolysis unit 106 and the secondary H2S removal unit 107 according to the requirement of the propylene sulfur content. At the same time, a tertiary hydrolysis unit and a tertiary H2S removal unit can also be set according to the need, and so on.

[0038] The operating pressure of the hydrolysis process is 0.5-4.0 MPaG, and the operating temperature is 0-150°C.

[0039] The operating pressure of the H2S removal process is 0.5-4.0 MPaG and the operating temperature is 0-150°C.

[0040] The H2S desulfurizer is a zinc oxide desulfurizer or other non-renewable H2S desulfurizer.

[0041] like Figure 1 As shown, the liquefied petroleum gas feedstock 1 enters the depropanizer 101 to separate C3 and ethane gas 2 and a mixed C4 product 3. The C3 and ethane gas 2 at the top of the depropanizer 101 are sent to the (primary) hydrolysis unit 102 for hydrolysis reaction. The hydrolysis product 4 enters the deethanizer 103 to separate ethane gas 5 and C3 6. The ethane gas 5 at the top of the deethanizer 103 includes ethane gas from a conventional gas fractionation device, and also includes H2S produced by hydrolysis in the (primary) hydrolysis unit 102 due to the low boiling point of H2S. The C3 6 in the bottom of the deethanizer 103 is sent to the propylene tower 104 to separate propylene 7 and propane product 8. The propylene 7 at the top of the propylene tower 104 is sent to the (primary) H2S removal unit 105 to remove a small amount of H2S balanced in the C3 after separation in the deethanizer 103. The propylene 9 from which H2S has been removed is then successively sent to the (secondary) hydrolysis tower 106 and the (secondary) H2S removal tower 107 for further desulfurization, and the propylene product 11 is sent downstream.

[0042] The above description is only a typical embodiment of the present invention, and does not impose any form of limitation on the present invention. Any changes or modifications made by any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above content should be regarded as equivalent examples of equivalent changes. Any equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A process for separating liquefied gas to produce polymerization-grade propylene, characterized in that: The process includes the following steps: 1) After the raw liquefied gas is separated by the depropanizer, the bottom of the tower is a mixed C4 product, and the top of the tower is C3 and ethane gas sent to the primary hydrolysis unit to remove COS and CS2. The primary hydrolysis unit is usually a container or tower filled with a hydrolyzing agent; 2) The C3 and ethane gas from the removal of COS and CS2 in step 1) are sent to a deethanizer to remove ethane gas. The ethane gas contains not only C1, C2, C3 and other hydrocarbons produced by a normal gas fractionation device, but also most of the H2S generated in the hydrolysis process in step 1). The C3 in the bottom of the tower is automatically compressed to the propylene tower; 3) The deethanizer bottom liquid from step 2) enters a propylene tower for separation, the bottom of the tower is the propane product, and the top of the tower is propylene; 4) The propylene from the top of the tower in step 3) is sent to a primary H2S removal unit to remove H2S; 5) The propylene liquid from step 4) is continuously sent to a secondary hydrolysis unit and a secondary H2S removal unit to further remove COS, CS2 and H2S. The secondary hydrolysis unit is usually a container or a tower filled with a hydrolyzing agent, and the secondary H2S removal unit is usually a container or a tower filled with a H2S desulfurizing agent.

2. The process for preparing polymerization-grade propylene by separation of liquefied gas according to claim 1, characterized in that: The raw liquefied gas contains 1 to 50 ppmvol of total sulfur and 1 to 50 ppmvol of carbonyl sulfide.

3. The process for preparing polymerization-grade propylene by separation of liquefied gas according to claim 1, characterized in that: The primary hydrolysis unit is arranged before the deethanizer of the gas fractionation, including being arranged between the depropanizer and the deethanizer, or being arranged before the depropanizer.

4. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The hydrolysis unit has a reaction mechanism including COS+H2O=H2S+CO2; CS2+2H2O=2H2S+CO2, or other reaction processes that may generate a desulfurization reaction of H2S substances.

5. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The process of the primary H2S removal unit and the secondary H2S removal unit includes zinc oxide desulfurization, or other processes for removing H2S.

6. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The secondary hydrolysis unit and the secondary H2S removal unit are set according to the sulfur content requirements in the propylene product, or the secondary hydrolysis unit and the secondary H2S removal unit are not set according to the requirements of the propylene sulfur content, or a tertiary hydrolysis unit and a tertiary H2S removal unit are set as needed, and so on.

7. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The operating pressure of the hydrolysis process is 0.5-4.0 MPaG, and the operating temperature is 0-150°C.

8. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The operating pressure of the H2S removal process is 0.5-4.0 MPaG, and the operating temperature is 0-150°C.

9. The process for preparing polymerization-grade propylene by separating liquefied gas according to claim 1, characterized in that: The H2S desulfurizer is a zinc oxide desulfurizer or other non-renewable H2S desulfurizer.

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