Process for deeply desulfurizing catalytic cracking gasoline

Abstract

The present invention provides a process for desulfurizing gasoline fraction by solvent extraction: introducing the gasoline fraction into an extraction tower at a lower-middle part thereof, introducing a solvent into the extraction tower at the top thereof, injecting saturated C5 hydrocarbon into a reflux device at the bottom of the extraction tower, wherein the gasoline fraction which is desulfurized flows out from the top of the extraction tower; the solvent that has extracted sulfide, aromatics and C5 hydrocarbon flows out from the bottom of the extraction tower, and is separated into a C5 hydrocarbon-containing light component, a sulfur-rich component, water and the solvent. The present invention also provides a process for deeply desulfurizing catalytic cracking gasoline, which flexibly combines the process described above and an existing desulfurization technology.

Claims

1. A process for desulfurizing a catalytic cracking gasoline fraction by solvent extraction, comprising steps of: introducing the gasoline fraction into an extraction tower at an about middle part thereof, introducing a solvent into the extraction tower at the top thereof, and injecting saturated C5 hydrocarbon into a reflux device at the bottom of the extraction tower, wherein the temperature at the top of the extraction tower is controlled between 6580 C., the temperature at the bottom of the extraction tower is controlled between 5060 C., and the pressure (absolute) at the top of the extraction tower is controlled between 0.50.6 MPa, a feeding ratio by volume of the solvent to the gasoline fraction is controlled between 2.03.0, and a feeding ratio by volume of the saturated C5 hydrocarbon to the gasoline fraction is controlled between 0.20.3, and wherein the gasoline fraction and the solvent are contacted at an upper section of the extraction tower via a multi-stage countercurrent, meanwhile the saturated C5 hydrocarbon and the solvent are contacted at a lower section of the extraction tower, the gasoline fraction which is desulfurized by extraction flows out from the top of the extraction tower, as a material A, and the solvent that has extracted sulfide, aromatics and the C5 hydrocarbon flows out from the bottom of the extraction tower, as a material B; washing the material A for removing solvent therein, to obtain a desulfurized gasoline fraction; further treating the material B to separate a C5 hydrocarbon-containing light component, a sulfur-rich component, water and the solvent, wherein the C5 hydrocarbon-containing light component contains the saturated C5 hydrocarbon and a C5 olefin, wherein the further treating the material B specifically comprises steps of: {circle around (1)} introducing the material B into an extraction distillation tower at the top thereof, wherein the pressure (absolute) of the extraction distillation tower is controlled between 0.150.3 MPa, and the temperature at the bottom of the extraction distillation tower is controlled between 150180 C., the C5 hydrocarbon-containing light component is distilled out as material C from the top of the extraction distillation tower, and a sulfur-rich solvent is obtained as material D at the bottom of the extraction distillation tower; {circle around (2)} after being condensed, returning the material C obtained in step {circle around (1)} to the reflux device at the bottom of the extraction tower; introducing the material D into a recycling tower from a middle part thereof, wherein the pressure (absolute) of the recycling tower is controlled between 0.0150.05 MPa, and the temperature at the bottom of the recycling tower is controlled between 130180 C.; a material E, i.e, a sulfur-rich oil containing sulfide, aromatics and cycloolefin, is obtained at the top of the recycling tower; a material F that mainly contains solvent is obtained at the bottom of the recycling tower; and {circle around (3)} after being condensed, conducting a water oil separation on the material E obtained in step {circle around (2)}, to obtain water and a sulfur-rich component G; returning a portion of the water to the top of the recycling tower in step {circle around (2)}, and returning the rest as washing water to the step of washing the material A for removing solvent; returning the material F obtained in step {circle around (2)}, after heat-exchange, to the top of the extraction tower for recycling; wherein the solvent is a mixed solvent containing one or two of diethylene glycol, triethylene glycol, tetraethylene glycol, dimethyl sulfoxide, sulfolane, N-formyl morpholine, N-methyl pyrrolidone, polyethylene glycol, and propylene carbonate; and the water content of the solvent is 0.60.8% by weight.

2. The process for desulfurizing a gasoline fraction by solvent extraction according to claim 1, wherein the gasoline fraction is a light gasoline fraction with a boiling point of less than 130 C.

3. The process for desulfurizing a gasoline fraction by solvent extraction according to claim 1, wherein the water for washing the material A accounts for 1.010.0% by weight of the material A.

4. The process for desulfurizing a gasoline fraction by solvent extraction according to claim 1, wherein: in step {circle around (1)}, the pressure of the extraction distillation tower is controlled at 0.2 MPa, and the temperature at the bottom of the extraction distillation tower is controlled at 160 C.; in step {circle around (2)}, the pressure of the recycling tower is controlled between 0.0350.045 MPa, and the temperature at the bottom of the recycling tower is controlled between 165175 C.

5. A process for deeply desulfurizing catalytic cracking gasoline, comprising steps of: 1) separating the catalytic cracking gasoline into a light gasoline fraction, a medium gasoline fraction and a heavy gasoline fraction, wherein the cutting point between the light gasoline fraction and the medium gasoline fraction is 3550 C., the cutting point between the medium gasoline fraction and the heavy gasoline fractions 70130 C.; 2) conducting a mercaptan removal treatment on the light gasoline fraction obtained in step 1), to obtain a desulfurized light fraction having a sulfur content of less than 10 ppm and a sulfur-rich component H; 3) treating the medium gasoline fraction obtained in step 1) according to the process for desulfurizing a gasoline fraction by solvent extraction as claimed in claim 1, to obtain a desulfurized medium fraction having a sulfur content of less than 10 ppm and a sulfur-rich component G; and 4) conducting a desulfurization treatment on the heavy gasoline fraction obtained in step 1), together with the sulfur-rich component H obtained in step 2) and the sulfur-rich component G obtained in step 3) by using a selective hydrodesulfurization process, to obtain a desulfurized heavy fraction having a sulfur content of less than 10 ppm.

6. The process for deeply desulfurizing catalytic cracking gasoline according to claim 5, wherein: before separating catalytic cracking gasoline in step 1), micromolecular mercaptan in the catalytic cracking gasoline is converted into macromolecular sulfide with a high boiling point via an alkali-free sweetening or prehydrogenation process.

7. The process for deeply desulfurizing catalytic cracking gasoline according to claim 5, wherein: the light gasoline fraction obtained in step 2) is introduced into the reflux device of the extraction tower used in the extraction desulfurization process in step 3).

8. A process for deeply desulfurizing catalytic cracking gasoline, comprising steps of: i) separating the catalytic cracking gasoline into a light gasoline fraction I and a heavy gasoline fraction I at a cutting point of 50130 C.; ii) treating the light gasoline fraction I obtained in step i) according to the process for desulfurizing a gasoline fraction by solvent extraction in claim 1, to obtain a desulfurized light fraction I having a sulfur content of less than 10 ppm and a sulfur-rich component J; and iii) conducting a desulfurization treatment on the heavy gasoline fraction I obtained in step i) together with the sulfur-rich component J obtained in step ii) by using a selective hydrodesulfurization process, to obtain a desulfurized heavy fraction I having a sulfur content of less than 10 ppm.

9. The process for deeply desulfurizing catalytic cracking gasoline according to claim 8, wherein: in step ii), the light gasoline fraction I obtained in step i) is subjected to a mercaptan removal treatment firstly, and then the resulting mercaptan-removed light gasoline fraction I is finely cut into a light gasoline fraction II and a medium gasoline fraction I at a cutting point of 3550 C., and then the medium gasoline fraction I is subjected to the desulfurizing treatment according to the process for desulfurizing a gasoline fraction by solvent extraction in claim 1 to obtain a desulfurized medium fraction I having a sulfur content of less than 10 ppm and a sulfur-rich component K; and the sulfur-rich component K instead of the sulfur-rich component J is introduced into the step iii) to be desulfurized together with the heavy gasoline fraction.

10. The process for deeply desulfurizing catalytic cracking gasoline according to claim 8, wherein: in step ii), the light gasoline fraction I obtained in step i) is subjected to a mercaptan removal treatment by extraction firstly to obtain a mercaptan-removed light gasoline fraction I and a sulfur-rich component L, and then the mercaptan-removed light gasoline fraction I is subjected to the desulfurizing treatment according to the process for desulfurizing a gasoline fraction by solvent extraction in claim 1 to obtain a desulfurized light fraction II having a sulfur content of less than 10 ppm and a sulfur-rich component M; and the sulfur-rich component L and the sulfur-rich component M instead of the sulfur-rich component J are introduced into the step iii) to be desulfurized together with the heavy gasoline fraction.

11. The process for desulfurizing a gasoline fraction by solvent extraction according to claim 1, wherein the gasoline fraction is a light gasoline fraction with a boiling range of 40100 C.

12. The process for desulfurizing a gasoline fraction by solvent extraction according to claim 1, wherein the water for washing the material A accounts for 24% by weight of the material A.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a process flow chart of a process for desulfurizing a gasoline fraction by solvent extraction according to the present invention.

(2) Reference numerals in FIG. 1 are illustrated as follows: 1. extraction tower; 2. washing tower; 3. extraction distillation tower; 4. recycling tower; 5. sulfur-rich oil tank; 6. water fractionation tower; 7. reflux accumulator; 8. solvent regeneration tower.

(3) FIG. 2 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 3 of the present invention.

(4) FIG. 3 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 4 of the present invention.

(5) FIG. 4 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 5 of the present invention.

(6) FIG. 5 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 6 of the present invention.

(7) FIG. 6 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 7 of the present invention.

(8) FIG. 7 is a process flow chart of a process for deeply desulfurizing catalytic cracking gasoline according to Embodiment 8 of the present invention.

DETAILED DESCRIPTION

(9) The process for desulfurizing gasoline fractions by solvent extraction according to the present invention, as shown in FIG. 1, includes steps of: introducing a gasoline fraction into an extraction tower 1 from the lower middle part thereof, introducing a solvent into the extraction tower 1 from the top thereof, at the same time injecting pentane into a reflux device at the bottom of the extraction tower 1, where the temperature at the top of the extraction tower is controlled between 55100 C., the temperature at the bottom of the extraction tower is controlled between 4080 C., and the pressure (absolute) at the top of the extraction tower is controlled between 0.20.7 MPa, a feeding ratio of the solvent to the gasoline fraction is controlled between 1.05.0, and a feeding ratio of the pentane to the gasoline fraction is controlled between 0.10.5, and where the gasoline fraction and the solvent are contacted at the upper section of the extraction tower 1 via a multi-stage countercurrent, meanwhile the pentane and the solvent are contacted fully at the lower section of the extraction tower 1, the gasoline fraction after being desulfurized by extraction flows out from the top of the extraction tower 1 as a material A, and a mixture of sulfur-containing solvent and pentane flows out from the bottom of the extraction tower 1 as a material B; the material A is introduced into a washing tower 2 and is washed to remove the solvent, obtaining a desulfurized gasoline fraction. The material B is a rich solvent with dissolved sulfide and C5 hydrocarbon-containing light component, which enters into an extraction distillation tower 3 at the top thereof after undergoing heat-exchange with a lean solvent, to conduct extraction and distillation, after that, a light fraction with a relatively low boiling point distilled out from the top of the extraction distillation tower is condensed, and then returned to the reflux device at the bottom of the extraction tower 1 after separating water there from via a reflux accumulator 7; a rich solvent with concentrated sulfur content comes out of the bottom of the extraction distillation tower 3 to be transported to the middle part of a recycling tower 4, in which sulfur-rich oil (including sulfide, aromatics, cycloolefin, etc.) is separated from the solvent via reduced pressure stripping distillation, the distillate from the top of the recycling tower 4 is condensed and then enters a sulfur-rich oil tank 5 to realize water oil separation, a part of the water separated by the sulfur-rich oil tank 5 is returned into the top of the recycling tower 4 as a backflow, and the rest is transported into the washing tower 2 as washing water; the sulfur-rich component separated by the sulfur-rich oil tank 5 may be subjected to selective hydrodesulfurization together with heavy gasoline, or be subjected to further extraction and distillation to recover thiophene and methylthiophene; most of the lean solvent flowing out from the bottom of the recycling tower 4 serves as a heat source of a reboiler at the bottom of a water fractionation tower 6 firstly, and then is returned to the top of the extraction tower 1 to complete solvent circulation after heat-exchange with the rich solvent from the bottom of the extraction tower 1; the water coming out from the bottom of the washing tower 2 and the water separated by the reflux accumulator 7 are merged into the water fractionation tower 6 at the top thereof, trace organics contained in the water are stripped out to return to the reflux accumulator 7, solvent-containing water at the bottom of the water fractionation tower 6 is transported to the bottom of the recycling tower 4 to recover the solvent; a small portion of the lean solvent out from the bottom of the recycling tower 4 is directly transported to the middle part of a solvent regeneration tower 8, vapors generated at the bottom of the water fractionation tower 6 enter the bottom of the solvent regeneration tower 8, in which the lean solvent is subjected to vacuum steam distillation, solvent vapor and water vapor coming from the top of the solvent regeneration tower 8 enter the bottom of the recycling tower 4. The solvent regeneration tower 8 is subjected to irregular slag discharge from its bottom, to remove solvent degradation products, and thus ensuring service performance of system circulating solvent.

(10) In addition to receiving simple saturated C5 hydrocarbon and various backflows involved in the above process, the reflux device at the bottom of the extraction tower 1 may also receive a saturated C5 fraction from the top of a reformed prefractionation tower in the prior art or light fractions of catalytic gasoline as backflows of the extraction tower 1.

(11) Embodiment 1

(12) According to the method and procedures above, a desulfurized product is obtained using a gasoline fraction with a boiling range of 40100 C. and sulfur content of 200-400 ppm as a raw material according to process conditions as shown in table 1 below. Yield of the desulfurized product is higher than 95% m (mass), and the sulfur content of desulfurized products is lower than 5 ppm.

(13) TABLE-US-00001 TABLE 1 Item Range Temperature at the top of the extraction tower, C. 65~70 Temperature at the bottom of the extraction tower, C. 50~55 Pressure (absolute) at the top of the extraction tower, MPa 0.5~0.6 Solvent ratio (relative to feeding) 2.0~2.5 Reflux ratio (relative to feeding) 0.2~0.25 Water content of lean solvent, % 0.6~0.65 Pressure (absolute) of the extraction distillation tower, MPa 0.2 Temperature at the bottom of the extraction distillation 160 tower, C. Pressure (absolute) of the recycling tower, MPa 0.035~0.040 Temperature at the bottom of the recycling tower, C. 165~170 Washing water content (relative to product), % 2~3

(14) Embodiment 2

(15) According to the method and procedures above, a desulfurized product is obtained using a gasoline fraction with a boiling range of 40100 C. and sulfur content of 600-800 ppm as a raw material according to process conditions as shown in table 2 below. Yield of the desulfurized product is higher than 95% m, and the sulfur content of the desulfurized products is lower than 10 ppm.

(16) TABLE-US-00002 TABLE 2 Item Range Temperature at the top of the extraction tower, C. 80~100 Temperature at the bottom of the extraction tower, C. 60~80 Pressure (absolute) at the top of the extraction tower, MPa 0.2~0.5 Solvent ratio (relative to feeding) 1.0~2.0 Reflux ratio (relative to feeding) 0.3~0.5 Water content of lean solvent, % 0.8~0.9 Pressure (absolute) of the extraction distillation tower, MPa 0.2 Temperature at the bottom of the extraction distillation 180 tower, C. Pressure (absolute) of the recycling tower MPa 0.015~0.35 Temperature at the bottom of the recycling tower, C. 130~160 Washing water content (relative to a product), % 4.0~10.0

(17) Embodiment 3

(18) A universal process for deeply desulfurizing catalytic cracking gasoline, its process flow is shown in FIG. 2, in particular includes steps of:

(19) 1) separating the catalytic cracking gasoline into a light gasoline fraction, a medium gasoline fraction and a heavy gasoline fraction, where the cutting point between the light gasoline fraction and the medium gasoline fraction is 40 C., and the cutting point between the medium gasoline fraction and the heavy gasoline fraction is 100 C.;

(20) 2) removing mercaptan from the light gasoline fraction obtained from step 1), using a process such as that described in ZL200910250279.8 for removing mercaptan sulfur from a C5 fraction by extracting the mercaptan sulfur into a pure alkali liquor, to obtain a desulfurized light fraction having a sulfur content of less than 10 ppm and a sulfur-rich component H; generally the yield of the desulfurized light gasoline may reach 2030%(mass) of total amount of full-range gasoline;

(21) 3) treating the medium gasoline fraction obtained from step 1) according to the desulfurizing process by solvent extraction as described in Embodiment 1, where the desulfurized light fraction obtained from step 2) enters the reflux device of the extraction tower 1 as described in Embodiment 1 as a backflow, and enters into the extraction tower together with the medium gasoline fraction for treatment, and finally obtaining a desulfurized fraction having a sulfur content of less than 5 ppm and a sulfur-rich component G; and

(22) 4) conducting a desulfurization treatment on the heavy gasoline fraction obtained from step 1), together with the sulfur-rich component H obtained from step 2) and the sulfur-rich component G obtained from step 3), all of which have low olefin content and high sulfur content, by using a universal selective hydrodesulfurization technology, such as S-zorb, RSDS, OCT-M, Prime-G+, CODS, etc., to obtain a desulfurized heavy fraction having a sulfur content of less than 10 ppm.

(23) Embodiment 4

(24) A process for deeply desulfurizing catalytic cracking gasoline, its process flow is shown in FIG. 3, in particular includes steps of:

(25) 1) treating the catalytic cracking gasoline by an alkali-free sweetening or Prime-G+ prehydrogenation process, to convert micromolecular mercaptan therein into macromolecular sulfide with a high boiling point;

(26) 2) separating the catalytic cracking gasoline treated in step 1) into a light gasoline fraction, a medium gasoline fraction and a heavy gasoline fraction, where the cutting point between the light gasoline fraction and the medium gasoline fraction is 36 C., and the cutting point between the medium gasoline fraction and the heavy gasoline fraction is 100 C.;

(27) 3) treating the medium gasoline fraction obtained from step 2) according to the desulfurizing process by solvent extraction as described in Embodiment 1, to obtain a desulfurized medium fraction having a sulfur content of less than 5 ppm and a sulfur-rich component G; and

(28) 4) conducting a desulfurization treatment on the heavy gasoline fraction obtained from step 2) together with the sulfur-rich component G obtained from step 3), all of which have a low olefin content and a high sulfur content, by using a universal selective hydrodesulfurization technology, such as S-zorb, RSDS, OCT-M, Prime-G+, CODS, etc., to obtain a desulfurized heavy fraction having a sulfur content of less than 10 ppm.

(29) This process is particularly suitable to such a company that has already had a light fraction mercaptan conversion technology (such as Prime-G+ or alkali-free sweetening).

(30) Embodiment 5

(31) A process for deeply desulfurizing catalytic cracking gasoline, its process flow is shown in FIG. 4, in particular includes steps of:

(32) i) separating the catalytic cracking gasoline into a light gasoline fraction I and a heavy gasoline fraction I at a cutting point of 3570 C.;

(33) ii) treating the light gasoline fraction I obtained from step i) according to the process for desulfurizing gasoline fractions by solvent extraction as described in Embodiment 1, to obtain a desulfurized light fraction I having a sulfur content of less than 10 ppm and a sulfur-rich component J; and

(34) iii) conducting a desulfurization treatment on the heavy gasoline fraction I obtained from step i) together with the sulfur-rich component J obtained from step ii) by using an S-zorb selective hydrodesulfurization process, to obtain a desulfurized heavy fraction I having a sulfur content of less than 10 ppm.

(35) This process is particularly suitable to such a company that has already had the S-zorb desulfurization technology.

(36) Embodiment 6

(37) A process for deeply desulfurizing catalytic cracking gasoline, its process flow is shown in FIG. 5, in particular includes steps of:

(38) i) separating the catalytic cracking gasoline into a light gasoline fraction I and a heavy gasoline fractions I at a cutting point of 70120 C.;

(39) ii) conducting a removing mercaptan treatment on the light gasoline fraction I obtained from step i) by using a conventional extraction oxidation method firstly, and then finely separating the treated light gasoline fraction I into a light gasoline fraction II and a medium gasoline fraction I at a cutting point of 3550 C.;

(40) iii) treating the medium gasoline fraction I separated in step ii) according to the process for desulfurizing gasoline fractions by solvent extraction as described in Embodiment 1, to obtain a desulfurized medium fraction I having a sulfur content of less than 10 ppm and a sulfur-rich component K; and

(41) iv) conducting a desulfurization treatment on the heavy gasoline fraction I obtained from step i) together with the sulfur-rich component K obtained from step iii) by using an S-zorb selective hydrodesulfurization process, to obtain a desulfurized heavy fraction I having a sulfur content of less than 10 ppm.

(42) This process is particularly suitable to such a company that has already had the RSDS desulfurization technology.

(43) Embodiment 7

(44) A process for deeply desulfurizing catalytic cracking gasoline, its process flow is shown in FIG. 6, in particular includes steps of:

(45) i) separating the catalytic cracking gasoline into a light gasoline fraction I and a heavy gasoline fraction I at a cutting point of 7090 C.;

(46) ii) conducting a removing mercaptan treatment on the light gasoline fraction I obtained from step i) by using the method recorded in ZL200910250279.8 firstly, to obtain a light gasoline fraction I and a sulfur-rich component L, and then treating the light gasoline fraction I according to the process for desulfurizing gasoline fractions by solvent extraction as described in Embodiment 1, to obtain a desulfurized light fractions II having a sulfur content of less than 10 ppm and a sulfur-rich component M; and

(47) iii) conducting a desulfurization treatment on the heavy gasoline fraction I obtained from step i) together with the sulfur-rich component L and the sulfur-rich component M obtained from step ii) by using an S-zorb selective hydrodesulfurization process, to obtain a desulfurized heavy fraction I having a sulfur content of less than 10 ppm.

(48) This process is particularly suitable to a company that has already had the stable light and heavy fractions separating technology.

(49) Embodiment 8

(50) A process available for deeply desulfurizing a full-range catalytic cracking gasoline, its process flow is shown in FIG. 7, in particular includes steps of:

(51) I) treating the full-range catalytic cracking gasoline according to the desulfurization process by solvent extraction as described in Embodiment 1, to obtain a desulfurized component and a sulfur-rich component N; and

(52) II) conducting a selective hydrodesulfurization treatment on the sulfur-rich component N obtained from step I), to obtain a desulfurized component having a sulfur content of less than 10 ppm.