Method for deep desulfurization of gasoline

Abstract

The present invention provides a method for deep desulfurization of gasoline. The method includes steps of: cutting a gasoline feedstock into light, medium, and heavy gasoline fractions; the medium gasoline fraction being subjected to adsorption desulfurization to obtain a desulfurized medium gasoline fraction; the heavy gasoline fraction being subjected to selective hydrodesulfurization to obtain a desulfurized heavy gasoline fraction; mixing the light gasoline fraction with the desulfurized medium gasoline fraction and the desulfurized heavy gasoline fraction to obtain a desulfurized gasoline, where, a cutting temperature of the light and the medium gasoline fractions is 35-60 C., a cutting temperature of the medium and the heavy gasoline fractions is 70-130 C. The method according to the present invention not only can realize deep desulfurization of gasoline, but also has a less loss of octane number.

Claims

1. A method for deep desulfurization of gasoline, comprising steps of: cutting a gasoline feedstock into a light gasoline fraction, a medium gasoline fraction, and a heavy gasoline fraction; subjecting the medium gasoline fraction to adsorption desulfurization to obtain a desulfurized medium gasoline fraction; subjecting the heavy gasoline fraction to selective hydrodesulfurization to obtain a desulfurized heavy gasoline fraction; and mixing the light gasoline fraction with the desulfurized medium gasoline fraction and the desulfurized heavy gasoline fraction to obtain a desulfurized gasoline; wherein, a cutting temperature of the light and the medium gasoline fractions is 35-60 C., and a cutting temperature of the medium and the heavy gasoline fractions is 70-130 C.; wherein the adsorption desulfurization is conducted using a desulfurization adsorbent, the desulfurization adsorbent is obtained by loading an active metal component onto a composite carrier made of zeolite and active carbon which are subjected to alkali treatment respectively, wherein, the active metal is selected from one or more elements of IA, VIII, IB, IIB and VIB groups in the periodic table; the method further comprising: washing the desulfurization adsorbent which has been subjected to the adsorption desulfurization with a steam to collect a sulfur-rich component; and subjecting the sulfur-rich component and the heavy gasoline fraction to the selective hydrodesulfurization after mixing them together.

2. The method for deep desulfurization of gasoline according to claim 1, wherein, before cutting the gasoline feedstock into the light, the medium and the heavy gasoline fractions, the gasoline feedstock is firstly subjected to demercaptan treatment.

3. The method for deep desulfurization of gasoline according to claim 1, wherein, before the mixing, the light gasoline fraction is firstly subjected to demercaptan treatment to obtain a demercaptan light gasoline fraction, and then the demercaptan light gasoline fraction is mixed with the desulfurized medium gasoline fraction and the desulfurized heavy gasoline fraction to obtain the desulfurized gasoline.

4. The method for deep desulfurization of gasoline according to claim 3, wherein, the demercaptan light gasoline fraction is mixed with the desulfurized medium gasoline fraction and the desulfurized heavy gasoline fraction after being subjected to adsorption desulfurization to obtain the desulfurized gasoline.

5. The method for deep desulfurization of gasoline according to claim 1, wherein, in the composite carrier, the zeolite and the active carbon have a mass ratio of (20-80):(80-20).

6. The method for deep desulfurization of gasoline according to claim 1, wherein, the zeolite is an X type, a Y type or a ZSM-5 type zeolite.

7. The method for deep desulfurization of gasoline according to claim 1, wherein, the active metal is at least two selected from Ni, Fe, Ag, Co, Mo, Zn and K.

8. The method for deep desulfurization of gasoline according to claim 1, wherein, the active metal has a loading of 2-30 mass % on the composite carrier, based on the total amount of the composite carrier and the active metal.

9. The method for deep desulfurization of gasoline according to claim 1, wherein, the light gasoline fraction is mixed with the desulfurized medium gasoline fraction and the desulfurized heavy gasoline fraction after adsorption desulfurization to obtain the desulfurized gasoline.

10. The method for deep desulfurization of gasoline according to claim 1, wherein, the adsorption desulfurization is conducted using a fixed bed at an atmospheric pressure, and a temperature of the adsorption desulfurization is controlled between 20-100 C., a flow rate of the medium gasoline fraction is 0.3-1 mL/min.

11. The method for deep desulfurization of gasoline according to claim 1, further comprising: after washing the desulfurization adsorbent which has been subjected to the adsorption desulfurization with the steam, drying the washed desulfurization adsorbent with nitrogen at a temperature of 200-400 C., and cooling the dried desulfurization adsorbent with nitrogen to realize regeneration of the desulfurization adsorbent.

12. The method for deep desulfurization of gasoline according to claim 1, wherein, the heavy gasoline fraction and hydrogen are subjected to selective hydrodesulfurization in the presence of a selective hydrodesulfurization catalyst to obtain desulfurized heavy gasoline fraction, wherein, a temperature of the selective hydrodesulfurization is 200-300 C., a pressure thereof is 1.5-2.5 MPa, a liquid hourly space velocity is 1-5 h-1, and a volume ratio of hydrogen to oil is 400-600.

13. The method for deep desulfurization of gasoline according to claim 12, wherein, the selective hydrodesulfurization catalyst is obtained by a carrier loading an active metal component, wherein the carrier is a zeolite or a metal oxide, and the active metal comprises Co and Mo.

14. The method for deep desulfurization of gasoline according to claim 13, wherein, Co and Mo have an overall loading of 5-20% on the carrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a curve of absorption and desorption isotherms of a ZSM-5 zeolite before and after alkali treatment according to Embodiment 1;

(2) FIG. 2 is a curve of pore diameter distribution of a ZSM-5 zeolite before and after alkali treatment according to Embodiment 1;

(3) FIG. 3 is a process flow chart of a method for deep desulfurization of gasoline according to Embodiment 1;

(4) FIG. 4 is a process flow chart of a method for deep desulfurization of gasoline according to Embodiment 2;

(5) FIG. 5 is a process flow chart of a method for deep desulfurization of gasoline according to Embodiment 3; and

(6) FIG. 6 is a process flow chart of a method for deep desulfurization of gasoline according to Embodiment 4.

DETAILED DESCRIPTION

(7) In order to make objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in embodiments of the present invention are hereinafter described clearly and completely with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of embodiments of the present invention, rather than all embodiments of the present invention. All other embodiments obtained by those skilled in the art based on embodiments of the present invention without any creative efforts shall fall within the protection scope of the present invention.

Embodiment 1

(8) 1. Prepare a Desulfurization Adsorbent

(9) 1) Prepare a Zeolite and an Active Carbon Subjected to Alkali Treatment

(10) After elevating temperatures of two 500 mL of NaOH solutions at a concentration of 0.3 mol/L to about 70 C. by a water bath, adding 25 g of ZSM-5 type zeolite and 25 g of active carbons therein respectively, immediately lowering a temperature of the mixture to room temperature by an ice bath after stirring for about 200 minutes, filtering the mixture, filtering and washing filter cake with deionized water several times till pH value of the filtrate is about 7, placing the obtained filter cake into an oven at a temperature of 110 C. to be dried for 4 h, and thus preparing a ZSM-5 zeolite subjected to alkali treatment and an active carbon subjected to alkali treatment respectively, wherein, curves of absorption and desorption isotherms and pore diameter distribution of the ZSM-5 zeolite before and after alkali treatment can be seen from FIG. 1 and FIG. 2 respectively.

(11) In addition, an ASAP2000 type automatically physical adsorption instrument is used to measure specific surface areas and pore diameter distributions of the ZSM-5 zeolite and the active carbon, and results are as shown in Table 1.

(12) TABLE-US-00001 TABLE 1 Total pore Medium pore Average Total specific volume volume pore surface area V/ V.sub.meso/ diameter Carrier S.sub.BET/(m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) d/(nm) ZSM-5 zeolite 380 0.212 0.041 2.241 before alkali treatment ZSM-5 zeolite 427 0.430 0.300 4.031 after alkali treatment Active carbon 1190 0.701 0.326 2.321 before alkali treatment Active carbon 1254 0.742 0.358 2.427 after alkali treatment

(13) It can be seen from FIG. 1 that: the ZSM-5 zeolite before alkali treatment exhibits an I-type isotherm which is characterized by micropore properties, the desorption isotherm thereof is almost overlapped with the adsorption isotherm; whereas the ZSM-5 zeolite after alkali treatment exhibits an IV-type isotherm with obvious characteristics, which presents a continuous adsorption state till a saturation pressure within the entire measured pressure range, and which conducts desorption gradually with decrease in pressure during the desorption firstly, when the pressure reaches a certain value, the desorption amount surges suddenly to form a relatively steep curve, and then it overlapped with the adsorption isotherm as pressure further decreases, thus it indicates that a great number of mesopores (medium pores) are generated in the ZSM-5 zeolite after alkali treatment.

(14) It can be seen from FIG. 2 that, the ZSM-5 zeolite before alkali treatment is mainly micropores, there is a wide distribution before 2 nm and a small peak at a position of 3.5 nm, and substantially no pores after 4 nm, an obtained average pore diameter calculated using a t-plot method is about 2.3 nm; there is still a distribution of a part of micropores before 2 nm for the ZSM-5 zeolite after alkali treatment, and a strong peak at a position of about 3.8 nm, the peak height is almost about 11 times the height of the ZSM-5 zeolite before alkali treatment, and there is also a relative wide distribution of pores after 4 nm

(15) Meanwhile, results of Table 1 indicate that: a medium pore volume and an average pore diameter of the ZSM-5 zeolite subjected to alkali treatment are increased significantly, which indicates that a large number of micropores are converted into medium pores, thereby forming a composite pore structure of a mesopore and a micropore; the total specific surface area, the total pore volume, the medium pore volume and the average pore diameter of the active carbon subjected to alkali treatment are all increased.

(16) 2) Prepare a Composite Carrier

(17) Placing the ZSM-5 zeolite subjected to alkali treatment and the active carbon subjected to alkali treatment in a mortar to be ground into powders after mixing them at a mass ratio of 40:60, then placing the mixture in an oven at a temperature of 120 C. to be dried for 6 h, thereby preparing a composite carrier.

(18) 3) Prepare a Desulfurization Adsorbent

(19) The composite carrier obtained above is firstly subjected to incipient wetness impregnation with a K.sub.2SO.sub.4 solution, after washing, drying and calcinating, then the composite carrier impregnated with K.sub.2SO.sub.4 is subjected to incipient wetness impregnation with NiSO.sub.4, and after washing, drying and calcinating, a desulfurization adsorbent is prepared;

(20) The washing, the drying and the calcinating described above are specifically: after washing the impregnated material with deionized water, drying it for 20 hours at a temperature of 120 C., after cooling the dried material down to room temperature, elevating the temperature to 400 C. at a speed of 6 C./min firstly, and then elevating the temperature to 550 C. at a speed of 3 C./min, conducting calcinations for 4 hours at the temperature of 550 C.

(21) In the desulfurization adsorbent prepared above, K has a loading of about 5% on the composite carrier, Ni has a loading of about 10% on the composite carrier; moreover, K and Ni which are loaded on the composite carrier have a mass ratio of 0.5:1. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.514, and its lifespan lasts for 8-9 h.

(22) In the present invention, a sulfur capacity is a total sulfur content (by gram) desulfurized when 1 g desulfurization adsorbent reduces the total sulfur content in the gasoline feedstock below 10 ppmw, for instance, when the sulfur capacity is 0.514, it indicates that the total sulfur content desulfurized is 0.514 g on 1 g of desulfurization adsorbent to reduce the total sulfur content in the gasoline feedstock below 10 ppmw.

(23) 2. Prepare a Selective Hydrodesulfurization Catalyst

(24) A ZSM-5 zeolite (carrier) is firstly subjected to incipient wetness impregnation with a CoSO.sub.4 solution, after washing, drying and calcinating, then the ZSM-5 zeolite impregnated with the CoSO.sub.4 solution is subjected to incipient wetness impregnation with an aqueous solution of (NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O, and after washing, drying and calcinating, a selective hydrodesulfurization catalyst is prepared, wherein, a specific operation of the washing, the drying and the calcinating refer to step 1.

(25) A total specific surface area of the selective hydrodesulfurization catalyst prepared above is about 356 m.sup.2/g, a total pore volume is about 0.315 cm.sup.3.Math.g.sup.1, Co has a loading of about 4% on the carrier, Mo has a loading of about 10% on the carrier; moreover, Co and Mo which are loaded on the carrier have a mass ratio of 0.4:1.

(26) 3. Gasoline Desulfurization

(27) Fluid catalytic cracking gasoline which is produced from Daqing atmospheric heavy oil subjected to catalytic cracking is taken as a feedstock (see Table 2 for its composition), and a process flow of desulfurization of the gasoline feedstock can be seen from FIG. 3.

(28) Firstly, a mercaptan conversion method (an alkali-free deodorization process) is used to conduct a demercaptan treatment for the gasoline feedstock, where an operating pressure of the reactor may be controlled at about 0.5 MPa, a reacting temperature is about 40 C., a feeding space velocity is 1.0 h.sup.1 and a volume ratio of an air flow to a feeding flow is about 0.5, the demercaptan gasoline and a first sulfur-rich component are collected, and the first sulfur-rich component is incorporated into heavy gasoline fraction to proceed with a next step.

(29) The demercaptan gasoline is cut into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 60 C., and a cutting temperature of the medium and the heavy gasoline fractions is 100 C.

(30) Filling the desulfurization adsorbent prepared above into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.5 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 150 C. for 3 h for washing, collecting a second sulfur-rich component, incorporating the second sulfur-rich component into the heavy gasoline fraction to proceed with a next step. Moreover, sweeping the washed desulfurization adsorbent with nitrogen at a temperature of 300 C. for 30 min for drying, and sweeping the dried desulfurization adsorbent with nitrogen at a room temperature (30 C.) for 30 min for cooling, so that the desulfurization adsorbent is regenerated, a sulfur capacity of the desulfurization adsorbent which has been regenerated three times is 0.473, and its lifespan lasts for about 7 h.

(31) Filling the selective hydrodesulfurization catalyst prepared above into the fixed bed reactor, the heavy gasoline fraction which is incorporated with the first sulfur-rich component and the second sulfur-rich component are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 260 C., a reacting pressure is 1.8 MPa, a liquid hourly space velocity is 3.0 h.sup.1, and a volume ratio of hydrogen to oil is 500, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the light gasoline fraction and the desulfurized medium gasoline fraction to prepare desulfurized gasoline, and the composition thereof see Table 2.

Embodiment 2

(32) Fluid catalytic cracking gasoline which is produced from Daqing atmospheric heavy oil subjected to catalytic cracking according to Embodiment 1 is taken as a feedstock, and a process flow of desulfurization of the gasoline feedstock can be seen from FIG. 4.

(33) Firstly, cutting the gasoline feedstock into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 60 C., and a cutting temperature of the medium and the heavy gasoline fractions is 100 C.

(34) The light gasoline fraction is enabled to be in contact with alkali solution for demercaptan treatment in an extraction system, where the alkali used is a NaOH solution in a mass content of 20%, a volume ratio of the light gasoline fraction to the NaOH solution is 5:1, an operating temperature is 30 C., the demercaptan light gasoline fraction and extracted oil are collected, and the extracted oil is incorporated into the heavy gasoline fraction to proceed with a next step.

(35) Filling the desulfurization adsorbent prepared in Embodiment 1 into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.5 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 150 C. for 3 h for washing, collecting a sulfur-rich component, incorporating the sulfur-rich component into the heavy gasoline fraction to proceed with a next step.

(36) Filling the selective hydrodesulfurization catalyst prepared in Embodiment 1 into the fixed bed reactor, the heavy gasoline fraction which is incorporated with extracted oil and the sulfur-rich component are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 260 C., a reacting pressure is 1.8 MPa, a liquid hourly space velocity is 3.0 h.sup.1, and a volume ratio of hydrogen to oil is 500, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the demercaptan light gasoline fraction and the desulfurized medium gasoline fraction to prepare desulfurized gasoline, and the composition thereof see Table 2.

(37) TABLE-US-00002 TABLE 2 Composition of Gasoline before and after Desulfurization Desulfurized Desulfurized Gasoline gasoline in gasoline in Items feedstock Embodiment 1 Embodiment 2 Density (20 C.), g/cm.sup.3 0.7012 0.7280 0.7236 Sulfur content, ppmw 282 10 10 Group Paraffin 35.0 46.8 45.7 composition, Olefin 48.2 23.8 24.0 m % Naphthene 6.3 12.1 12.4 Aromatics 10.5 17.3 17.9 Octane RON 90.2 89.6 89.6 number MON 80.9 80.5 80.5

(38) It can be seen from Table 2 that:

(39) The method for deep desulfurization of gasoline as described in Embodiment 1 and Embodiment 2 of the present invention not only can reduce sulfur content in the gasoline feedstock to below 10 ppm, but also can control olefin content below 24%, and loss of octane number is only 0.6.

Embodiment 3

(40) 1. Prepare Desulfurization Adsorbent

(41) 1) Prepare a Zeolite and an Active Carbon Subjected to Alkali Treatment

(42) After elevating temperatures of two 500 mL of NaOH solutions at a concentration of 0.2 mol/L to about 80 C. by a water bath, adding 25 g of Y type zeolite and 25 g of active carbons therein respectively, immediately lowering a temperature of the mixture to room temperature by an ice bath after stirring for about 120 minutes, filtering the mixture, filtering and washing a filter cake with deionized water several times till pH value of the filtrate is about 7, placing the filter cake obtained into an oven at a temperature of 120 C. to be dried for 3 h, and thus preparing an Y type zeolite subjected to alkali treatment and an active carbon subjected to alkali treatment respectively; specific surface areas and pore diameter distributions of the Y type zeolite and the active carbon are as shown in Table 3.

(43) TABLE-US-00003 TABLE 3 Specific Surface Areas and Pore Diameters of Y Type Zeolite and Active Carbon Total pore Medium pore Average Total specific volume volume pore surface area V/ V.sub.meso/ diameter Carrier S.sub.BET/(m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) d/(nm) Y type zeolite 706 0.390 0.053 2.001 before alkali treatment Y type zeolite 713 0.462 0.118 2.139 after alkali treatment Active carbon 1190 0.701 0.326 2.321 before alkali treatment Active carbon 1233 0.729 0.355 2.346 after alkali treatment

(44) 2) Prepare a Composite Carrier

(45) Placing the Y type zeolite subjected to alkali treatment and the active carbon subjected to alkali treatment in a mortar to be ground into powders after mixing them at a mass ratio of 20:80, then placing the mixture in an oven at a temperature of 110 C. to be dried for 6 h, thereby preparing a composite carrier.

(46) 3) Prepare a Desulfurization Adsorbent

(47) The composite carrier obtained above is firstly subjected to incipient wetness impregnation with a ZnSO.sub.4 solution, after washing, drying and calcinating, then the composite carrier impregnated with the ZnSO.sub.4 solution is subjected to incipient wetness impregnation with Fe.sub.2(SO.sub.4).sub.3, thereby preparing a desulfurization adsorbent after washing, drying and calcinating;

(48) The washing, the drying and the calcinating described above are specifically: after washing the impregnated material with deionized water, drying it for 24 hours at a temperature of 110 C., after cooling the dried material down to a room temperature, elevating the temperature to 400 C. at a speed of 6 C./min firstly, and then elevating the temperature to 450 C. at a speed of 3 C./min, conducting calcination for 6 hours at a temperature of 450 C.

(49) In the desulfurization adsorbent prepared above, Zn has a loading of about 10% on the composite carrier, Fe has a loading of about 10% on the composite carrier; moreover, Zn and Fe which are loaded on the composite carrier have a mass ratio of 1:1. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.481, and its lifespan lasts for 7-8 h.

(50) 2. Prepare a Selective Hydrodesulfurization Catalyst

(51) Preparing a selective hydrodesulfurization catalyst according to the method described in Embodiment 1, whereas the difference lies in controlling Co to have a loading of about 6% on the carrier, and controlling Mo to have a loading of about 10% on the carrier; moreover, Co and Mo which are loaded on the carrier have a mass ratio of 0.6:1.

(52) 3. Gasoline Desulfurization

(53) Fluid catalytic cracking gasoline from Daqing is taken as a feedstock (the composition thereof see Table 4), and a process flow of desulfurization of the gasoline feedstock as shown in FIG. 5.

(54) Firstly, a mercaptan conversion method (an alkali-free deodorization process) is used to conduct demercaptan treatment for the gasoline feedstock, where an operating pressure of the reactor may be controlled at about 0.3 MPa, a reacting temperature is about 60 C., a feeding space velocity is 1.5 h.sup.1 and a volume ratio of an air flow to a feeding flow is about 1.0, the demercaptan gasoline and a first sulfur-rich component are collected, and the first sulfur-rich component is incorporated into the heavy gasoline fraction to proceed with a next step.

(55) The demercaptan gasoline is cut into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 50 C., and a cutting temperature of the medium and the heavy gasoline fractions is 90 C.

(56) Filling the desulfurization adsorbent prepared above into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the light gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.3 mL/min to obtain a desulfurized light gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 180 C. for 1 h for washing, collecting a second sulfur-rich component, incorporating the second sulfur-rich component into the heavy gasoline fraction to proceed with a next step. Moreover, sweeping the washed desulfurization adsorbent with nitrogen at a temperature of 400 C. for 10 min for drying, and sweeping the dried desulfurization adsorbent with nitrogen at room temperature (10 C.) for 10 min for cooling, so that the desulfurization adsorbent is regenerated.

(57) At a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.3 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 180 C. for 1 h for washing, collecting a third sulfur-rich component, incorporating the third sulfur-rich component into the heavy gasoline fraction to proceed with a next step. Moreover, sweeping the washed desulfurization adsorbent with nitrogen at a temperature of 400 C. for 10 min for drying, and sweeping the dried desulfurization adsorbent with nitrogen at room temperature (10 C.) for 10 min for cooling, so that the desulfurization adsorbent is regenerated, a sulfur capacity of the desulfurization adsorbent which has been regenerated three times is 0.481, and its lifespan lasts for about 7 h.

(58) Filling the selective hydrodesulfurization catalyst prepared above into the fixed bed reactor, the heavy gasoline fraction which is incorporated with the first, the second and the second sulfur-rich components are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 300 C., a reacting pressure is 1.5 MPa, a liquid hourly space velocity is 4.0 h.sup.1, and a volume ratio of hydrogen to oil is 600, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the desulfurized light gasoline fraction and the desulfurized medium gasoline fraction to prepare desulfurized gasoline, and the composition thereof see Table 4.

Embodiment 4

(59) Fluid catalytic cracking gasoline from Daqing in Embodiment 3 is taken as a feedstock, and a process flow of desulfurization of the gasoline feedstock as can be seen from FIG. 6.

(60) Firstly, cutting the gasoline feedstock into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 50 C., and a cutting temperature of the medium and the heavy gasoline fractions is 90 C.

(61) The light gasoline fractions are enabled to be in contact with alkali solution for demercaptan treatment in an extraction system, where the alkali used is NaOH solution in a mass content of 10%, and a volume ratio of the light gasoline fraction to NaOH solution is 5:1, an operating temperature is 45 C., the demercaptan light gasoline fraction and extracted oil are collected, and the extracted oil is incorporated into the heavy gasoline fraction to proceed with a next step.

(62) Filling the desulfurization adsorbent prepared in Embodiment 3 into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the demercaptan light gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.3 mL/min to obtain a desulfurized light gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 180 C. for 1 h for washing, collecting a first sulfur-rich component, incorporating the first sulfur-rich component into the heavy gasoline fraction to proceed with a next step.

(63) At a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.3 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 180 C. for 1 h for washing, collecting a second sulfur-rich component, incorporating the second sulfur-rich component into the heavy gasoline fraction to proceed with a next step.

(64) Filling the selective hydrodesulfurization catalyst prepared in Embodiment 3 into the fixed bed reactor, the heavy gasoline fraction which is incorporated with extracted oil, the first and the second sulfur-rich components are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 300 C., a reacting pressure is 1.5 MPa, a liquid hourly space velocity is 4.0 h.sup.1, and a volume ratio of hydrogen to oil is 600, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the desulfurized light gasoline fraction and the desulfurized medium gasoline fraction to prepare the desulfurized gasoline, and the composition thereof see Table 4.

(65) TABLE-US-00004 TABLE 4 Composition of Gasoline before and after Desulfurization Desulfurized Desulfurized Gasoline gasoline in gasoline in Items feedstock Embodiment 3 Embodiment 4 Density (20 C.), g/cm.sup.3 0.7012 0.7202 0.7216 Sulfur content, ppmw 282 10 10 Group Paraffin 35.0 46.2 47.1 composition, Olefin 48.2 23.3 23.6 m % Naphthene 6.3 12.6 11.9 Aromatics 10.5 17.9 17.4 Octane RON 90.2 89.5 89.4 number MON 80.9 80.2 80.0

(66) It can be seen from Table 4 that:

(67) The method for deep desulfurization of gasoline as described in Embodiment 3 and Embodiment 4 of the present invention not only can reduce sulfur content in the gasoline feedstock to below 10 ppm, but also can control olefin content below 24%, and loss of octane number is only 0.7.

Embodiment 5

(68) 1. Prepare a Desulfurization Adsorbent

(69) 1) Prepare a Zeolite and an Active Carbon Subjected to Alkali Treatment

(70) After elevating temperatures of two 500 mL of NaOH solution at a concentration of 0.2 mol/L to about 70 C. by a water bath, adding 25 g of ZSM-5 type zeolite and 25 g of active carbons therein respectively, immediately lowering a temperature of the mixture to room temperature by an ice bath after stirring for about 90 minutes, filtering the mixture, filtering and washing a filter cake with deionized water several times till pH value of the filtrate is about 7, placing the filter cake obtained into an oven at a temperature of 120 C. to be dried for 3 h;

(71) Repeating the above steps one time respectively for the ZSM-5 type zeolite and the active carbon obtained (that is, conducting alkali treatment twice), and thus preparing a ZSM-5 type zeolite subjected to alkali treatment and an active carbon subjected to alkali treatment; specific surface areas and pore diameter distributions of the ZSM-5 type zeolite and the active carbon as shown in Table 5.

(72) TABLE-US-00005 TABLE 5 Specific Surface Areas and Pore Diameters of ZSM-5 Type Zeolite and Active Carbon Total pore Medium pore Average Total specific volume volume pore surface area V/ V.sub.meso/ diameter Carrier S.sub.BET/(m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) d/(nm) ZSM-5 before 380 0.212 0.041 2.241 alkali treatment ZSM-5 after 432 0.433 0.302 4.030 alkali treatment Active carbon 1190 0.701 0.326 2.321 before alkali treatment Active carbon 1259 0.749 0.363 2.430 after alkali treatment

(73) 2) Prepare a Composite Carrier

(74) Placing the ZSM-5 type zeolite subjected to alkali treatment and the active carbon subjected to alkali treatment in a mortar to be ground into powders after mixing them at a mass ratio of 20:80, then placing the mixture in an oven at a temperature of 100 C. to be dried for 8 h, thereby preparing a composite carrier.

(75) 3) Prepare a Desulfurization Adsorbent

(76) The composite carrier obtained above is subjected to incipient wetness impregnation with a ZnSO.sub.4 solution, after washing, drying and calcinating, then the composite carrier impregnated with the ZnSO.sub.4 solution is subjected to incipient wetness impregnation with Fe.sub.2(SO.sub.4).sub.3, and after washing, drying and calcinating, desulfurization adsorbent is prepared;

(77) The washing, the drying and the calcinating described above are specifically: after washing the impregnated material with deionized water, drying it for 20 hours at a temperature of 120 C., after cooling the dried material down to a room temperature, elevating the temperature to 400 C. at a speed of 6 C./min firstly, and then elevating the temperature to 600 C. at a speed of 3 C./min, and conducting calcinations for 6 hours at the temperature of 600 C.

(78) In the desulfurization adsorbent prepared above, Zn has a loading of about 5% on the composite carrier, Fe has a loading of about 10% on the composite carrier; moreover, Zn and Fe which are loaded on the composite carrier have a mass ratio of 0.5:1. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.49, and its lifespan lasts for about 8 h.

(79) 2. Gasoline Desulfurization

(80) Fluid catalytic cracking gasoline from Jinan is taken as a feedstock (the composition thereof see Table 6).

(81) Firstly, a mercaptan conversion method (an alkali-free deodorization process) is used to conduct demercaptan treatment for the gasoline feedstock, where an operating pressure of the reactor may be controlled at about 1 MPa, a reacting temperature is about 30 C., a feeding space velocity is 0.5 h.sup.1 and a volume ratio of an air flow to a feeding flow is about 0.2, the demercaptan gasoline and a first sulfur-rich component are collected, and the first sulfur-rich component is incorporated into the heavy gasoline fraction to proceed with a next step.

(82) The demercaptan gasoline is cut into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 50 C., and a cutting temperature of the medium and the heavy gasoline fractions is 90 C.

(83) Filling the desulfurization adsorbent prepared above into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.8 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 160 C. for 2 h for washing, collecting a second sulfur-rich component, incorporating the second sulfur-rich component into the heavy gasoline fraction to proceed with a next step. Moreover, sweeping the washed desulfurization adsorbent with nitrogen at a temperature of 300 C. for 45 min for drying, and sweeping the dried desulfurization adsorbent with nitrogen at a room temperature (25 C.) for 45 min for cooling, so that the desulfurization adsorbent is regenerated, a sulfur capacity of the desulfurization adsorbent which has been regenerated three times is 0.457, and its lifespan lasts for about 7 h.

(84) Filling the selective hydrodesulfurization catalyst prepared in Embodiment 1 into the fixed bed reactor, the heavy gasoline fraction which is incorporated with the first sulfur-rich component and the second sulfur-rich component are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 300 C., a reacting pressure is 2.5 MPa, a liquid hourly space velocity is 2.0 h.sup.1, and a volume ratio of hydrogen to oil is 400, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the light gasoline fraction and the desulfurized medium gasoline fraction to prepare a desulfurized gasoline, and the composition thereof see Table 6.

Embodiment 6

(85) Fluid catalytic cracking gasoline from Jinan in Embodiment 5 is taken as a feedstock.

(86) Firstly, cutting the gasoline feedstock into light, medium and heavy gasoline fractions, where a cutting temperature of the light and the medium gasoline fractions is 50 C., and a cutting temperature of the medium and the heavy gasoline fractions is 90 C.

(87) The light gasoline fraction is enabled to be in contact with alkali solution for demercaptan treatment in an extraction system, where the alkali used is NaOH solution in a mass content of 30%, a volume ratio of the light gasoline fraction to the NaOH solution is 5:1, an operating temperature is 60 C., the demercaptan light gasoline fraction and extracted gasoline are collected, and the extracted gasoline is incorporated into the heavy gasoline fraction to proceed with a next step.

(88) Filling the desulfurization adsorbent prepared in Embodiment 5 into a fixed bed reactor, at a temperature of 30 C. and in a condition of atmospheric pressure, the medium gasoline fraction being subjected to adsorption desulfurization at a flow rate of 0.8 mL/min to obtain a desulfurized medium gasoline fraction; in addition, after the adsorption desulfurization, sweeping the desulfurization adsorbent which is subjected to the adsorption desulfurization with steam at a temperature of 160 C. for 2 h for washing, collecting a first sulfur-rich component, incorporating the first sulfur-rich component into the heavy gasoline fraction to proceed with a next step.

(89) Filling the selective hydrodesulfurization catalyst prepared in Embodiment 2 into the fixed bed reactor, the heavy gasoline fraction which is incorporated with extracted oil and the first sulfur-rich component are subjected to selective hydrodesulfurization in a condition where a reacting temperature is 300 C., a reacting pressure is 2.5 MPa, a liquid hourly space velocity is 2.0 h.sup.1, and a volume ratio of hydrogen to oil is 400, thereby obtaining a desulfurized heavy gasoline fraction. Mixing the desulfurized heavy gasoline fraction with the demercaptan light gasoline fraction and the desulfurized medium gasoline fraction to prepare a desulfurized gasoline, and the composition thereof see Table 6.

(90) TABLE-US-00006 TABLE 6 Composition of Gasoline before and after Desulfurization Desulfurized Desulfurized Gasoline gasoline in gasoline in Items feedstock Embodiment 5 Embodiment 6 Density (20 C.), g/cm.sup.3 0.7562 0.7750 0.7783 Surfur content, ppmw 421 10 10 Group Paraffin 25.6 35.7 35.8 compostion, Olefin 30.9 13.7 13.6 m % Naphthene 8.9 13.5 14.4 Aromatics 34.6 37.1 36.2 Octane number RON 89.2 88.7 88.4 MON 80.1 79.6 79.5

(91) It can be seen from Table 6 that:

(92) The method for deep desulfurization of gasoline as described in Embodiment 5 and Embodiment 6 of the present invention not only can reduce sulfur content in the gasoline feedstock to below 10 ppm, but also can control olefin content to below 24%, and loss of octane number is only 0.5.

Comparative Embodiment 1

(93) After preparing a ZSM-5 type zeolite subjected to alkali treatment according to the method described in Embodiment 1, the ZSM-5 type zeolite subjected to alkali treatment is subjected to incipient wetness impregnation with a K.sub.2SO.sub.4 solution and a NiSO.sub.4 solution according to the method described in Embodiment 1 sequentially, and washing, drying and calcinating, thereby preparing a desulfurization adsorbent. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.286, and its lifespan is only 3-4 h.

Comparative Embodiment 2

(94) After preparing an active carbon subjected to alkali treatment according to the method described in Embodiment 1, the active carbon subjected to alkali treatment is subjected to incipient wetness impregnation with a K.sub.2SO.sub.4 solution and a NiSO.sub.4 solution according to the method described in Embodiment 1 sequentially, and washing, drying and calcinating, thereby preparing a desulfurization adsorbent. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.236, and its lifespan is only 3-4 h.

Comparative Embodiment 3

(95) Placing a ZSM-5 type zeolite (without alkali treatment) and an active carbon (without alkali treatment) in Embodiment 1 into a mortar to ground after directly mixing them at a mass ratio of 40:60, then placing it in an oven at a temperature of 120 C. to be dried for 6 h, thereby preparing a composite carrier.

(96) The composite carrier is subjected to incipient wetness impregnation with a K.sub.2SO.sub.4 solution and a NiSO.sub.4 solution according to the method described in Embodiment 1 sequentially, and washing, drying and calcinating, thereby preparing a desulfurization adsorbent. Upon detection, a sulfur capacity of the desulfurization adsorbent is 0.155, and its lifespan is only 2-3 h.

(97) Finally, it should be noted that the foregoing examples are merely intended for describing technical solutions of the present invention rather than limiting the present invention. Although the present invention is described in detail with reference to the foregoing examples, those skilled in the art should understand that: they may still make modifications to the technical solutions described in the foregoing examples, or make equivalent replacements to some or all technical features thereof; however, these modifications or replacements do not make the essence of corresponding technical solutions depart from the scope of the technical solutions in the examples of the present invention.