Process for recovering lower carbon olefins from product gas for production of olefins

• US 20080209942A1
• Filed: 09/29/2006
• Published: 09/04/2008
• Est. Priority Date: 09/29/2005
• Status: Active Grant

• Current Assignee: China Petroleum & Chemical Corporation (Central People's Government of The People's Republic of China), Sinopec Engineering Incorporation (China Petrochemical Corporation)
• Original Assignee: China Petroleum & Chemical Corporation (Central People's Government of The People's Republic of China), Sinopec Engineering Incorporation (China Petrochemical Corporation)
• Inventors: Sheng, Zaihang, Wang, Zhenwei, Zhao, Xueliang
• Granted Patent: US 7,707,852 B2
• Time in Patent Office: Days
• US Class Current: 62/630
• CPC Class Codes: C07C 11/04 Ethylene
• CPC Class Codes: C07C 7/09 by fractional condensation
• CPC Class Codes: F25J 2200/90 Details relating to column internals, e.g. structured packing, gas or liquid distribution
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: Y02P 30/20 using bio-feedstock
• CPC Class Codes: Y02P 30/40 Ethylene production

Abstract

The present invention concerns a process for recovering lower carbon olefins from MTO or DTO product gas. Said process primarily comprises the product gas compressing, pre-deethanizing, demethanizing and ethylene recovering apparatus, depropanizing column, ethylene rectification column, propylene rectification column and the like. In addition, the process of the present invention needs no independent ethylene cooling system, and the ethylene recovery rate may achieve 99.5%.

Claims

1. A process for recovering lower carbon olefins, from a product gas, wherein said product gas is a mixed gas obtainable from the methanol and/or dimethyl ether to olefin conversion, said process comprising deethanizing said product gas to obtain C₂ and light components at the top of the column and C₃ and heavy components at the bottom of the column, and demethanizing C₂ and light components to obtain a tail gas and liquid phase C₂ component, condensing said tail gas and recovering the condensed liquid phase back to said demethanizing step.

2. The process according to claim 1, further comprising increasing the product gas pressure to 2.0-4.0 MpaG before separation of the product gas.

3. The process according to claim 1, wherein the liquid phase material extracted from the top of the deethanizing column is used as a coolant for condensing the tail gas at a temperture from −

60 to −

98°

C.

4. The process according to claim 1, further comprising ethylene rectifying the liquid phase C₂ component to obtain an ethylene product and ethane.

5. The process according to claim 4, wherein said ethylene product or ethane is replaceably or additionally used as a coolant for condensing the tail gas.

6. The process according to claim1, further comprising depropanizing C₃ and heavy components, separating out C₃ component, and propylene rectifying said C₃ component to obtain a propylene product.

7. The process according to claim 1, further comprising rectifying the tail gas before condensation to recover ethylene in said tail gas, and recovering said ethylene back to said deethanizing step.

8. The process according to claim 1, wherein the tail gas is condensed with a condenser.

9. The process according to claim 8, wherein the tail gas is condensed with a plate type condenser or a plate-fin type condenser.

10. The process according to claim 1, wherein the product gas is a mixed gas obtained in the methanol to olefin process.

11. The process according to claim 10, comprising

(1) increasing the product gas pressure to 2.0-4.0 MpaG;

(2) introducing the pressure increased product gas into the deethanizing column (10), to separate C₂ and light components from C₃ and heavy components;

(3) feeding C₂ and light components into the demethanizing coulm (13), to obtain the tail gas and liquid phase C₂ component;

(4) feeding the liquid phase C₂ component into the ethylene rectifying column (22), to obtain an ethylene product and ethane; and

(5) feeding C₃ and heavy components into the depropanizing column (23), to separate out C₃ component, and feeding C₃ component into the propylene rectifying column (25), to obtain a propylene product;

wherein the materials at the top of the demethanizing column (13) are fed into the reflux tank (17) to separate the tail gas from the mixed C₂ component stream;

the tail gas in the reflux tank (17) is fed into the condenser (19) for condensation, and the condensed material stream is refluxed back to the demethanizing column (13), wherein the coolant in the condenser (19) is one selected from the group consisting of

c. the material stream extracted from the top of the deethanizing column, or mixed C₂ component stream extracted from the reflux tank; and

d. ethylene product and/or ethane.

12. The process according to claim 11, comprising rectifying the tail gas via the rectification column section (18) before condensing the tail gas, wherein the rectification column section (18) is linked with the reflux tank (17) at the bottom of said section, and with the condenser (19) at the top of said section.

13. The process according to claim 12, wherein the condenser (19( is a plate type condenser or a plate-fin type condenser.

14. The process according to claim 13, wherein the reflux tank (17), the rectification column section (18), and the plate type condenser are integrated together.

15. The process according claim 11, wherein the demethanizing column (13) further comprises the column top condenser (15), and said column top condenser (15), the reflux tank (17), the rectification column section (18), and the plate type condenser are integrated together.

16. The process according to claim 10, comprising

(1) increasing the pressure of the product gas (1) to 2.0-4.0 MpaG via the pressure-increasing device (2), and removing unreacted methanol and dimethyl ether and CO₂ produced thereby in the product gas (1);

(2) subjecting the pressure-increased product gas to gas liquid separation after colling, feeding the gas phase into a desiccator to remove water, and then into the deethanizing column (10) to separate C₂ and light components from C₃ and heavy components, feeding C₂ and light components into the C₂ hydrogenation system (12) to remove ethylene, to obtain hydrogenated material stream;

(3) feeding the hydrogenated material stream into the demethanizing column (13) after cooling, the materials at the top of the demethanizing column (13) being fed into the reflux tank (17) to separate the tail gas from the mixed C₂ component stream, the tail gas in the reflux tank (17) being fed inti the rectification column section (18) having the condenser (19) at the top thereof, the condensed material stream being refluxed back to the demethanizing column (13), wherein the coolant in the condenser (19) is one selected from the group consisting of

a. the material stream extracted from the top of the deethanizing column, or the mixed C₂ component stream extracted from the reflux tank;

b. ethylene product and/or ethane.

(4) the materials at the bottom of the demethanzing column (13) being fed into the ethylene rectification column (22) to obtain ethylene product at the top the column (22) and ethane at the bottom the column (22); and

(5) the materials at the bottom of the deethanizing column (10) are fed into the depropanizing column (23) to obtain C₃ components at the top of the column (23) and ethane at the bottom the column (23); and

then C₃ components are fed into the propylene rectification column (25) to obtain propylene product at the top of the column (25) and propane at the bottom the column (25).