FULL CONVERSION METHOD AND DEVICE FOR PRODUCING LIGHT AROMATIC HYDROCARBONS FROM LIGHT CYCLE OIL

Abstract

Provided are a full conversion process and a device thereof for producing light aromatic hydrocarbon from LCO. The process includes the steps of: subjecting LCO stream to hydrofining and impurity separation, then performing selective conversion reaction, and separating the mixed aromatic hydrocarbons generated to sequentially separate out light aromatic hydrocarbons such as benzene-toluene and xylene, C.sub.9A aromatic hydrocarbons, C.sub.10A aromatic hydrocarbons and a bottom heavy tail oil; feeding the bottom heavy tail oil into a post-saturation selective reactor, subjecting to high-selectivity hydrogenation saturation under the conditions of low temperature and low pressure to provide a product having one benzene ring, and then returning the product back to the selective conversion reactor. The full-cut conversion of producing light aromatic hydrocarbon from LCO is achieved, resulting in the technical effects of high yields of monocyclic aromatic hydrocarbons such as benzene-toluene, xylene, C.sub.9A aromatic hydrocarbons, C.sub.10A aromatic hydrocarbons and the like.

Claims

1. A process of producing light aromatics from light cycle oil, i.e., LCO, comprising the steps of: 1) feeding LCO into a first reaction zone for hydrofining, to provide a first stream; 2) feeding the first stream to a second reaction zone for selective conversion, to provide a second stream, wherein the first stream is optionally subjected to impurity separation in a second separation zone before being fed to the second reaction zone; 3) subjecting the second stream to a first separation in a first separation zone, to provide a third stream comprising C.sub.10+ heavy aromatics at the bottom of the first separation zone; 4) feeding the third stream to a post-saturation selective reaction zone for hydrogenation saturation, to provide a fourth stream; 5) recycling the fourth stream to the second reaction zone.

2. The process according to claim 1, wherein: in addition to the third stream, the step 3) also provides fractions including C.sub.6-C.sub.8 aromatic hydrocarbon stream, and a stream containing C.sub.9 aromatic hydrocarbons and C.sub.10 aromatic hydrocarbons, wherein the C.sub.6-C.sub.8 aromatic hydrocarbon stream comprises at least one of benzene, toluene and xylene.

3. The process according to claim 1, wherein: in the step 2), the impurity separation is carried out comprising subjecting the first stream to gas-liquid separation and stripping of hydrogen sulfide.

4. The process according to claim 1, wherein: in the step 3), the first separation of the second stream comprises gas-liquid separation and rectification; and the rectification comprises depentanizing, deheptanizing, xylene removal and heavy aromatics removal; wherein a stream rich in a benzene-toluene fraction obtained from deheptanizing is subjected to an extraction separation.

5. The process according to claim 1, wherein: the reaction conditions for the first reaction zone comprise: a volume ratio of hydrogen to oil of 500-3000 Nm.sup.3/m.sup.3; and/or an inlet temperature of the reactor of 280-420° C.; and/or a partial pressure of hydrogen of 5-10 MPa; and/or a space velocity of 0.5-2.0 h.sup.−1.

6. The process according to claim 1, wherein: in the step 2), the selective conversion is carried out in the presence of a selective conversion catalyst comprising, in parts by weight: a2) 5-80 parts of solid acid zeolite; b2) 0.05 to 8 parts of a metal from Group VIII; c2) 3-25 parts of an oxide of metal from Group VIB; d2) 0.1-2 parts of a sulfide of metal from Group VIB; and e2) 20-95 parts of a first binder.

7. The process according to claim 6, wherein: the solid acid zeolite is at least one of mordenite, β-zeolite, ZSM zeolite, EU-1 zeolite, SAPO zeolite and Y zeolite; the metal from Group VIII is at least one of platinum, palladium, cobalt, nickel and iridium; the oxide of metal from Group VIB is at least one of molybdenum oxide and tungsten oxide; the sulfide of metal from group VIB is at least one of molybdenum sulfide and tungsten sulfide; and the first binder is at least one of alumina, a silica-alumina composite, a titania-alumina composite, and a magnesia-alumina composite.

8. The process according to claim 1, wherein: the reaction conditions for the second reaction zone comprise: a volume ratio of hydrogen to oil of 800-5000 Nm.sup.3/m.sup.3; and/or an inlet temperature of the reactor of 280-450° C.; and/or a partial pressure of hydrogen of 5-10 MPa; and/or a space velocity of 0.5-2.0 h.sup.−1.

9. The process according to claim 1, wherein: in the step 4), the hydrogenation saturation is carried out in the presence of a post-saturation selective catalyst, which comprises, in parts by weight: a3) 10-90 parts of amorphous silica-alumina, wherein the silica content of the amorphous silica-alumina is 3-20 wt %; b3) 0.1 to 5.0 parts of a metal from Group VIII; and c3) 5-80 parts of a second binder; the metal from group VIII is at least one selected from platinum, palladium, cobalt, nickel and iridium; and the second binder is alumina.

10. The process according to claim 1, wherein: the reaction conditions for the post-saturation selective reaction zone comprise: a volume ratio of hydrogen to oil of 200-3000 Nm.sup.3/m.sup.3; and/or an inlet temperature of the reactor of 100-300° C.; and/or a partial pressure of hydrogen of 1.0-4.0 MPa; and/or a space velocity of 0.1-5.0 h.sup.−1.

11. A device for carrying out the process according to claim 1, for producing light aromatics from LCO, comprising: a first reaction zone for hydrofining; configured to receive the LCO and to discharge a first stream; a second reaction zone for selective conversion; configured to receive the first stream and to discharge a second stream; a first separation zone; configured to receive the second stream; and to discharge the third stream at the bottom; a post-saturation selective reaction zone for hydrogenation saturation; configured to receive the third stream and to discharge a fourth stream; and a first pipeline; configured to recycle the fourth stream to the second reaction zone.

12. The device according to claim 11, wherein: the reactor of the first reaction zone is a fixed bed reaction system; and/or the reactor of the second reaction zone is a fixed bed reaction system; and/or the reactor of the post-saturation selective reaction zone is a fixed bed reaction system.

13. The device according to claim 12, wherein: the fixed bed reaction system of the first reaction zone is equipped with a hydrogen recycling system; and/or the fixed bed reaction system of the second reaction zone is equipped with a hydrogen recycling system; and/or the fixed bed reaction system of the post-saturation selective reaction zone is a liquid phase hydrogenation reaction system without a hydrogen recycling system.

14. The device according to claim 11, wherein: the first separation zone comprises a gas-liquid separator and a rectifying column, which are optionally connected in series, for sequentially separating fractions comprising a benzene-toluene stream, a xylene stream, a stream containing C.sub.9 aromatic hydrocarbons and C.sub.10 aromatic hydrocarbons, and the third stream containing C.sub.10+ heavy aromatics; the rectifying column comprises, optionally connected in series, a depentanizer, a deheptanizer, a xylene column, and a heavy aromatics column.

15. The device according to claim 14, wherein: the first separation zone comprises a deheptanizer and, downstream thereof, an extraction device of benzene-toluene fraction, for separating the—stream rich in benzene-toluene fraction separated from the deheptanizer.

16. The device according to claim 11, wherein: a second separation zone is arranged between the first reaction zone and the second reaction zone, for separating impurities comprising hydrogen sulfide and ammonia in the first stream; and the second separation zone is configured to receive the first stream and to discharge a gas phase, a hydrogen sulfide and an ammonia stream, and an impurity-separated first stream.

17. The device according to claim 16, wherein: the second separation zone comprises a gas-liquid separator and a stripping device.

Description

DESCRIPTION OF DRAWINGS

[0099] FIG. 1 is a schematic process flow chart of the present invention for a full conversion process of producing light aromatics from LCO.

DESCRIPTION OF THE REFERENCE SIGNS

[0100] 1 denotes raw material oil-LCO [0101] 2 denotes a first reaction zone [0102] 3 denotes an outlet stream from the first reaction zone—the first stream [0103] 4 denotes a gas-liquid separator [0104] 5 denotes a gas phase stream containing hydrogen sulfide and ammonia [0105] 6 denotes a liquid phase stream after gas-liquid separation [0106] 7 denotes a stripping column for hydrogen sulfide [0107] 8 denotes a stripped stream containing hydrogen sulfide [0108] 9 denotes hydrofined LCO after removing hydrogen sulfide—the first stream with impurities separated out [0109] 10 denotes a selective conversion reactor [0110] 11 denotes a product of the selective conversion reaction—the second stream [0111] 12 denotes a first separation zone, comprising, for example, a gas-liquid separator, a depentanizer, a deheptanizer, a xylene column, a heavy aromatics column and the like rectifying columns, and a benzene-toluene fraction extraction device [0112] 13 denotes a stream of dry gas and C3-C5 light hydrocarbons separated from the first separation zone [0113] 14 denotes a benzene-toluene stream separated from the first separation zone [0114] 15 denotes a xylene stream separated from the first separation zone [0115] 16 denotes a stream containing C.sub.9 aromatic hydrocarbons and C.sub.10 aromatic hydrocarbons separated from the first separation zone [0116] 17 denotes a heavy tail oil stream separated from the first separation zone—the third stream [0117] 18 denotes a post-saturation selective reactor [0118] 19 denotes an outlet stream from the post-saturation selective reactor—the fourth stream [0119] 20 denotes a second separation zone (in the dotted line frame).

EMBODIMENTS

[0120] The present invention will be described in detail with reference to the Drawings and Examples, whilst it should be understood that the following

[0121] Examples are merely illustrative of the present invention and should not be taken as limiting the scope of the present invention. Instead, those skilled can realize that modifications and variations thereof that would occur to those skilled in the art upon reading the present disclosure are still covered by the protection scopes of the invention.

[0122] All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference in their entirety. _Unless defined specifically, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

[0123] When the present specification mentions a material, substance, method, step, device, or component, etc. with the derivative words “known to those skilled in the art”, “prior art” or the like, the term derived is intended to cover those conventionally used in the field of the present application, but also cover those that are not currently known, whilst will become known in the art to be useful for the similar purposes.

[0124] The endpoints of the ranges and any values disclosed in the text of the present application are not limited to the precise range or value, but should be understood to encompass values close to these ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to provide one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein. In the following, the various technical solutions can in principle be combined with each other to provide new technical solutions, which should also be regarded as specifically disclosed herein.

[0125] The preferred embodiments of the present invention have been described in detail; however, the present invention was not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications were all within the protection scope of the present invention.

[0126] It should be noted that, the various features to be described in the embodiments below may be combined in any suitable manner, and in order to avoid unnecessary repetition, the present invention does not separately describe various possible combinations.

[0127] In addition, any combination of the various embodiments of the present invention can be made, and the same should be considered as the content of the present invention as long as the idea of the present invention was not violated.

[0128] Unless otherwise specified specifically, reference to pressure in this specification denotes a gauge pressure.

[0129] Unless otherwise specified specifically, reference to space velocity in this specification denotes a liquid hourly space velocity LHSV.

[0130] Unless otherwise specified specifically, all percentages, parts, ratios, etc. involved in this specification are indicated by weight, unless the basis on weight does not conform to the conventional understanding by those skilled in the art.

[0131] FIG. 1 is a schematic process flow chart of an exemplary embodiment of the process of producing light aromatic hydrocarbons from LCO fuel according to the present invention, in which various conventional devices such as pumps, compressors, heat exchangers, extraction devices, hydrogen pipelines, etc. are omitted, whilst such devices are well known to those skilled in the art. As shown in FIG. 1, the flow of an exemplary embodiment of the process of the present invention is described in detail as follows:

[0132] The LCO 1 serving as raw material oil is fed into a hydrofining device of the first reaction zone 2, to provide hydrofined LCO containing hydrogen sulfide and ammonia, namely the first reaction zone outlet stream 3 (the first stream); the first stream is fed to a gas-liquid separator 4 and a hydrogen sulfide stripping column 7 of the second separation zone 20, to separate out hydrogen sulfide and ammonia (through a gas phase stream 5 containing hydrogen sulfide and ammonia, and a stripped stream 8 containing hydrogen sulfide) obtained by denitrification and desulfurization in the hydrofining process, so as to provide an impurity-separated first stream 9. This stream is fed into the selective conversion device of the second reaction zone 10. A second reaction zone outlet stream 11 (the second stream), rich in light aromatic hydrocarbons such as benzene, toluene and xylene, C9A and C10A fractions, and heavy tail oil, is fed into a first separation zone 12, and is separated to provide stream 13 of dry gas and C3-C5 light hydrocarbons, a benzene-toluene stream 14, a xylene stream 15, a stream 16 containing C.sub.9 aromatic hydrocarbons and C.sub.10 aromatic hydrocarbons and a third stream 17 of a heavy tail oil containing C.sub.10+ heavy aromatics. The third stream 17 is fed into the post-saturation selective reactor 18 of the post-saturation selective reaction zone, and the post-saturation selective reactor outlet stream 19 (the fourth stream), without separation, is recycled to the selective conversion device of the second reaction zone 10.

[0133] Specifically, the first separation zone 12 comprises a gas-liquid separator, a depentanizer, a deheptanizer, a xylene column, a heavy aromatics column, and other rectifying columns, and a benzene-toluene fraction extraction device (not shown in the FIGURE), connected in series.

[0134] The composition analysis of the catalysts involved in the present invention is carried out by analytical methods known in the art. For example, the composition of the catalyst can be analyzed by ICP (inductively coupled plasma) and XRF (X-ray fluorescence) methods for the selective conversion catalyst. The composition ratio of the metal oxide and the metal sulfide, of Group VIB, is determined by XPS (X-ray photoelectron spectroscopy). ICP is measured using a Varian 700-ES series XPS instrument. XRF is measured using a Rigaku ZSX 100e model XRF instrument. XPS test conditions comprise: a Perkin Elmer PHI 5000C ESCA model X-ray photoelectron spectrometer, using an Mg K excitation light source, an operation voltage of 10 kV, a current of 40 mA, and a vacuum degree of 4.0×10-8 Pa.

[0135] In the invention, the family composition of the LCO and the hydrofined LCO, as well as the family composition of the heavy tail oil and the selectively saturated heavy tail oil, is analyzed (multidimensional chromatographic analysis) using a full two-dimensional gas chromatography/high-flux time-of-flight mass spectrometer (GCxGC-TOFMS) from LECO company, America.

[0136] In the present invention, the composition of the reactant stream (e.g., selectively conversed product, etc.) is determined by gas chromatography.

[0137] The chromatography model is Agilent 7890A, equipped with an FID detector, an FFAP capillary chromatographic column being used for separation. The chromatographic column is operated at temperature-programmed model, with an initial temperature of 90° C., kept for 15 minutes, then heated to 220° C. at the rate of 15° C./minute and kept for 45 minutes.

[0138] In the process of the invention, the retention rate of aromatic hydrocarbon in the hydrofining and selective saturation (post-saturation) processes is calculated as follows:

[00001]$\begin{array}{cc}\mathrm{Retention}\mathrm{rate}\mathrm{of}\mathrm{aromatics}=\frac{\begin{array}{c}\mathrm{aromatic}\mathrm{content}\mathrm{in}\mathrm{the}\mathrm{product}\\ \mathrm{from}\mathrm{hydrofining}\mathrm{or}\mathrm{selective}\mathrm{saturation}\end{array}}{\begin{array}{c}\mathrm{aromatic}\mathrm{content}\mathrm{in}\mathrm{the}\mathrm{raw}\mathrm{material}\mathrm{for}\\ \mathrm{hydrofining}\mathrm{or}\mathrm{selective}\mathrm{saturation}\end{array}}*100\%& \left(\mathrm{ii}\right)\end{array}$

[0139] The yield of monocyclic light aromatics such as benzene-toluene, xylene, C9A aromatics, C10A aromatics and the like is calculated as follows:

[00002]$\mathrm{Yield}\mathrm{of}\mathrm{BTX}+C9A+C10A=\frac{o\mathrm{utput}\mathrm{of}\mathrm{BTX}+C9A+C10A}{\mathrm{amount}\mathrm{of}\mathrm{the}\mathrm{raw}\mathrm{materials}}*100\%$

[0140] The raw materials of catalysts for the inventive and comparative examples were each commercially available.

Comparative Example 1

[0141] A LCO was processed by a two-stage process of hydrofining-selective conversion, namely, the LCO serving as raw material oil was subjected to hydrofining and impurity separation followed by hydrocracking, and then the product of hydrocracking was subjected to gas-liquid separation and rectification systems, to provide products of benzene-toluene, xylene, C.sub.9A aromatic hydrocarbons and C.sub.10A aromatic hydrocarbons, heavy tail oil and the like through separation. The process flow of comparative example 1 did not comprise the selective hydrosaturation of a heavy tail oil at >210° C. in a post-saturation selective reaction zone.

[0142] The analytical data of the LCO raw material and the hydrofined product were shown in Table 1, wherein the LCO had an aromatic content of 87.15 wt %. The hydrofining catalyst, selective conversion (hydrocracking) catalyst and the reaction conditions used were listed in

TABLE-US-00001 TABLE 1 Raw materials of Product from Item LCO hydrofining Density (4° C.) 0.953 0.932 Sulfur (wt ppm) 1070 87 Nitrogen (wt ppm) 632 8.6 Non-aromatic hydrocarbons (wt) 10.85 20.62 Monocyclic aromatic 37.40 53.71 hydrocarbons (wt %) Polycyclic aromatic hydrocarbons 51.75 25.67 (wt %) Distillation test (D-86) ° C. ° C. Initial boiling point 193 188  5% 212 210 10% 235 232 30% 246 237 50% 288 275 70% 315 313 90% 345 337 End point of distillation 372 363

TABLE-US-00002 TABLE 2 Catalyst of A1  3.0 wt % NiO-10.5 wt % MoO.sub.3- hydrofining 12.7 wt % WO.sub.3/73.8 wt % A1.sub.2O.sub.3 A1′ 3.1 wt % NiS-10.2 wt % MoS.sub.2- 13.2 wt % WS.sub.2/73.5 wt % Al.sub.2O.sub.3 Partial pressure of 6.5 MPa hydrogen for hydrofining Reaction temperature 315° C. at inlet of hydrofining LHSV space velocity 1.2 h.sup.−1 of hydrofining Ratio of hydrogen to oil 1500 (v/v) of hydrofining Catalyst B1 0.1 part of Pt/60 parts of USY zeolite- of selective conversion 39.9 parts of A1.sub.2O.sub.3 Partial pressure 7.0 MPa of hydrogen for selective conversion Reaction temperature 340° C. at inlet of selective conversion LHSV space velocity 1.0 h.sup.−1 of selective conversion Ratio of hydrogen to oil 1800 (v/v) of selective conversion

[0143] Preparation of the hydrofining catalyst A1 used: 2 g of sesbania powder, 9 ml of nitric acid and 60 ml of water were added into 100 g of pseudo-boehmite, kneaded into a cluster and extruded into strips, maintained at room temperature for 24 hours, dried at 100° C. for 12 hours, and calcinated at 550° C. in air atmosphere for 3 hours, to provide a hydrofining catalyst support. 7.90 g of nickel nitrate hexahydrate, 8.71 g of ammonium molybdate, 9.18 g of ammonium metatungstate and 10 ml of aqueous ammonia were dissolved in water to provide 50 ml of a clear solution. 50 g of the hydrofining catalyst support was added into said 50 ml of solution to soak for 3 hours in an isovolumetric soaking mode, dried at a temperature of 110° C. for 12 hours, and calcinated at a temperature of 500° C. in an air atmosphere for 4 hours, to provide a hydrofining catalyst A1. The catalyst A1 comprised 3.0 wt % NiO-10.5 wt % MoO.sub.3-12.7 wt % WO.sub.3/73.8 wt % Al.sub.2O.sub.3, namely, comprising three metals of nickel, molybdenum and tungsten.

[0144] A cyclohexane solution containing 0.5% of carbon disulfide was injected into a fixed bed reactor loaded with the hydrofining catalyst A1, heated from room temperature to a vulcanization end point temperature of 360° C. according to a program of 10° C./h, and kept for 12 h to finish pre-vulcanization of the hydrofining catalyst, to provide a vulcanized hydrofining catalyst A1′, which comprised: 3.1 wt % NiS-10.2 wt % MoS.sub.2-13.2 wt % WS.sub.2/73.5 wt % Al.sub.2O.sub.3 in which the metals from Group VIB and Group VIII were present in sulfided state.

[0145] The LCO and hydrogen were mixed and then fed into a hydrofining reactor to remove most of sulfur and nitrogen impurities therein, in which polycyclic aromatic hydrocarbons were saturated to be converted into hydrocarbons containing only one aromatic ring. Table 1 also listed the sulfur and nitrogen content, density, aromatic hydrocarbon content, and distillate distribution of the product from hydrofining.

[0146] The first stream obtained after hydrofining the LCO was subjected to impurity separation, comprising the steps of carrying out gas-liquid separation on the first stream, and stripping using nitrogen under normal pressure for 3 hours, to fully remove hydrogen sulfide dissolved in the first stream. The sulfur content and nitrogen contents of the hydrofined product (the impurity-separated first stream in liquid phase) were 87 ppm and 8.6 ppm, respectively. The retention rate of polycyclic aromatic hydrocarbons during the hydrofining was 89.04 wt %, calculated from the composition data of aromatics.

[0147] Table 2 also listed the composition of the selective conversion catalyst B1 used for the hydrocracking and the reaction conditions employed. The USY zeolite and alumina were kneaded, extruded and shaped, to provide the selective conversion catalyst support. Then, an appropriate amount of chloroplatinic acid was formulated into a clear solution, to soak the support in an isovolumetric soaking mode, dried, and calcinated in air at 500° C. for 2 hours, to provide a precursor of the selective conversion catalyst. The precursor of the selective conversion catalyst was reduced until 450° C. in the presence of hydrogen to provide the desired selective conversion catalyst B1, comprising: 0.1 part of Pt-60 parts of USY zeolite-39.9 parts of Al.sub.2O.sub.3. The catalyst bed was cooled to 340° C., and the hydrofined product after stripping (the impurity-separated first stream) was mixed with hydrogen, and fed into a selective conversion reactor, and the reaction product was fed to a gas-liquid separation and rectification system.

[0148] After gas-liquid separation and a rectification system, benzene-toluene, xylene, C.sub.9A aromatic hydrocarbons and C.sub.10A aromatic hydrocarbons were obtained through separation, and the yield of monocyclic light aromatic hydrocarbons such as benzene-toluene, xylene, C.sub.9A aromatic hydrocarbons and C.sub.10A aromatic hydrocarbons, was 21.48 wt % through calculation. The heavy tail oil at >210° C. had a yield of 38.27 wt %, a specific gravity of 0.935, and a sulfur and nitrogen content of respectively 19.5 ppm and 1.5 ppm. Multidimensional chromatographic analysis was carried out to provide a family composition of the third stream as follows: 41.98 wt % non-aromatic hydrocarbons, 26.38 wt % monocyclic aromatic hydrocarbons and 31.64 wt % polycyclic aromatic hydrocarbons.

Example 1

[0149] In the Example, a full conversion process of producing light aromatics from LCO was carried out according to the flow chart showed in FIG. 1. The LCO was subjected to hydrofining and impurity separation, followed by selective conversion (hydrocracking), and then the heavy tail oil at >210° C. was fed into a post-saturation selective reaction zone for a selective hydrosaturation, specifically:

[0150] The raw materials, the hydrofining catalyst, and the hydrofining reaction conditions were same as those in comparative example 1, and the selective conversion catalyst B2 (hydrocracking catalyst) and the selective conversion reaction conditions were shown in Table 3.

TABLE-US-00003 TABLE 3 Selective conversion 3.50 parts of Ni-5.00 parts of WO.sub.3- catalyst B2 0.27 parts of WS.sub.2/50 parts of β-zeolite-41.23 parts of Al.sub.2O.sub.3 Partial pressure of hydrogen 7.0 MPa for the selective conversion Temperature for the 340° C. at inlet selective conversion LHSV space velocity for the 1.0 h.sup.−1 selective conversion Ratio of hydrogen to oil for the 1600 (v/v) selective conversion

[0151] The composition of the selective conversion catalyst B2 and the reaction conditions used were listed in Table 3.

[0152] The selective conversion catalyst B2 was prepared as follows: 70 wt % of β-zeolite (with a silicon-aluminum molecular ratio SAR=25) and 30 wt % of alumina were kneaded, extruded and molded to provide the selective conversion catalyst support. Then, an appropriate amount of nickel nitrate and ammonium tungstate were formulated into a clear solution, to soak the support in an isovolumetric soaking mode, dried at 100° C., and calcinated in air at 500° C. for 2 hours, to provide a precursor of the selective conversion catalyst. The precursor of the selective conversion catalyst was reduced to 450° C. for 4 hours in the presence of hydrogen, cooled to 330° C., and then dimethyl disulfide was injected for vulcanization for 4 hours, to provide the desired selective conversion catalyst B2. Based on 100 parts by weight of the total weight of the catalyst, the catalyst B2 comprised: 3.5 parts of Ni-5.0 parts of WO.sub.3 −0.27 part of WS.sub.2 −50 parts of β-zeolite-41.23 parts of Al.sub.2O.sub.3.

[0153] The first stream obtained from the LCO after hydrofining was subjected to impurity separation, wherein the first stream was subjected to gas-liquid separation, and stripped with nitrogen for 3 hours under normal pressure, to fully remove hydrogen sulfide dissolved in the first stream. The hydrofined product after stripping (the impurity-separated first stream) was mixed with hydrogen, fed into a selective conversion reactor, and the reaction product was fed to a gas-liquid separation and rectification system.

[0154] After gas-liquid separation and a rectification system, benzene-toluene, xylene, C9A aromatic hydrocarbons and C1 OA aromatic hydrocarbons were obtained through separation, and the yield of monocyclic light aromatic hydrocarbons such as benzene-toluene, xylene, C9A aromatic hydrocarbons and C10A aromatic hydrocarbons, was 32.27 wt % through calculation. The heavy tail oil at >210° C. (the third stream) had a yield of 24.75 wt %, a specific gravity of 0.957, and a sulfur and nitrogen content of respectively 25.4 ppm and 1.6 ppm. Multidimensional chromatographic analysis was carried out to provide a family composition of the third stream as showed in Table 4: 8.54 wt % non-aromatic hydrocarbons, 37.56 wt % monocyclic aromatic hydrocarbons and 53.90 wt % polycyclic aromatic hydrocarbons.

TABLE-US-00004 TABLE 4 Heavy fraction at >210° C. Density (4° C.) 0.957 Sulfur (wt ppm) 25.4 Nitrogen (wt ppm) 1.6 Non-aromatic hydrocarbons (wt %) 8.54 Monocyclic aromatic hydrocarbons (wt %) 37.56 Polycyclic aromatic hydrocarbons (wt %) 53.90

[0155] The post-saturation selective catalyst C2 for treating the heavy tail oil at >210° C. comprised: 0.05 wt % Pt-0.15 wt % Pd −4.5 wt % SiO.sub.2−95.3 wt % Al.sub.2O.sub.3 The post-saturation selective catalyst C2 was prepared as follows: a commercial amorphous silica-alumina material with 20 wt % of SiO.sub.2 was mixed with pseudo-boehmite, then a peptizing agent of nitric acid, an extrusion aid of sesbania powder and an appropriate amount of water were added, kneaded, extruded and shaped, dried in air at 100° C. for 24 hours, and then calcinated in air at 550° C. for 4 hours, to provide the catalyst support. An appropriate amount of chloroplatinic acid and palladium chloride was dissolved in water to provide a metal impregnation solution, to soak the catalyst support in an isovolumetric soaking mode, dried in air at 80° C. for 48 hours, and then calcinated in air at 480° C. for 2 hours, to provide the post-saturation selective catalyst C2. The post-saturated selective catalyst C2 was reduced in the presence of hydrogen with a reduction end temperature of 450° C., and kept for two hours.

[0156] An oversaturated amount of hydrogen was dissolved in the heavy tail oil at >210° C. through a hydrogen mixer and was fed into a selective saturation reactor, with reaction conditions of: a volume ratio of hydrogen to oil of 450 Nm.sup.3/m.sup.3, a reactor inlet temperature of 180° C., a partial pressure of hydrogen of 1.5 MPa, and a volume space velocity of the feed of 1.0 h.sup.−1. After the entire reaction system had been equilibrated, the analytical results for the products of the selective saturation were as shown in Table 5, wherein the sulfur and nitrogen contents were 16.8 ppm and 1.2 ppm, respectively. The retention rate of polycyclic aromatic hydrocarbons for the selective saturation process was 99.43 wt %, calculated from the aromatic composition data.

TABLE-US-00005 TABLE 5 Heavy fraction at >210° C. Density (4 °C) 0.939 Sulfur (wt ppm) 16.8 Nitrogen (wt ppm) 1.2 Non-aromatic hydrocarbons (wt %) 8.96 Monocyclic aromatic hydrocarbons (wt %) 59.82 Polycyclic aromatic hydrocarbons (wt %) 31.22

[0157] The heavy tail oil at >210° C. after selective saturation was returned to the selective conversion reactor, and stable stream balance was established. After gas-liquid separation and a rectification system, benzene-toluene, xylene, C9A aromatic hydrocarbons and C1 OA aromatic hydrocarbons were obtained through separation, and the yield of monocyclic light aromatic hydrocarbons such as benzene-toluene, xylene, C9A aromatic hydrocarbons and C10A aromatic hydrocarbons, was 46.35 wt % through calculation.

Example 2

[0158] In the Example, a full conversion process of producing light aromatics from LCO was carried out according to the flow chart showed in FIG. 1. The LCO was subjected to hydrofining and impurity separation, followed by selective conversion (hydrocracking), and then the heavy tail oil at >210° C. was fed into a post-saturation selective reaction zone for a selective hydrosaturation, specifically:

[0159] The raw materials, the hydrofining catalyst, and the hydrofining reaction conditions were same as those in comparative example 1, and the selective conversion catalyst B3 (hydrocracking catalyst) and the selective conversion reaction conditions were shown in Table 6.

TABLE-US-00006 TABLE 6 Selective conversion 0.2 part of Pd-6.5 parts of catalyst B3 Ni-4.2 parts of MoO.sub.2-7.9 parts of MoO3-1.1 parts of MoS.sub.2/35 parts of mordenite-10 parts of β-zeolite-11 parts of ZSM-5-24.1 parts of A1.sub.2O.sub.3 Partial pressure of hydrogen for 8.0 MPa the selective conversion Temperature for the 360° C. at inlet selective conversion LHSV space velocity for the 1.2 h.sup.−1 selective conversion Ratio of hydrogen to oil for the 2000 (v/v) selective conversion

[0160] The composition of the selective conversion catalyst B3 and the reaction conditions used were listed in Table 6.

[0161] The selective conversion catalyst B3 was prepared as follows: a hydrogen mordenite (SAR=45), hydrogen β-zeolite (SAR=25), hydrogen ZSM-5 (SAR=27) and pseudo-boehmite were fully mixed, kneaded, extruded, dried at 120° C., and calcinated in air atmosphere at 550° C. for 4 hours, to provide the required selective conversion catalyst support. Palladium chloride, nickel nitrate and ammonium molybdate were prepared into a tri-metal solution, to soak the catalyst support in an isovolumetric soaking mode, dried at 120° C. and then calcinated in an air atmosphere at 500° C. for 2 hours, to provide a precursor of the selective conversion catalyst. The precursor of selective conversion catalyst was reduced to 450° C. and kept for 8 hours in the presence of hydrogen, cooled to 330° C., and then dimethyl disulfide was injected for vulcanization for and keep 8 hours, to provide the desired selective conversion catalyst B3. Based on 100 parts by weight of the total weight of the catalyst, the catalyst B3 comprised: 0.2 part of Pd-6.5 parts of Ni-4.2 parts of MoO.sub.2 −7.9 parts of MoO.sub.3 −1.1 parts of MoS.sub.2 −35 parts of mordenite-10 parts of β-zeolite-11 parts of ZSM-5-24.1 parts of Al.sub.2O.sub.3.

[0162] The first stream obtained from the LCO after hydrofining was subjected to impurity separation: wherein the first stream was subjected to gas-liquid separation, and stripped with nitrogen for 3 hours under normal pressure, to fully remove hydrogen sulfide dissolved in the first stream. The hydrofined product after stripping (the impurity-separated first stream) was mixed with hydrogen, fed into a selective conversion reactor, and the reaction product was fed to a gas-liquid separation and rectification system.

[0163] After gas-liquid separation and a rectification system, benzene-toluene, xylene, C9A aromatic hydrocarbons and C1 OA aromatic hydrocarbons were obtained through separation, and the yield of monocyclic light aromatic hydrocarbons such as benzene-toluene, xylene, C9A aromatic hydrocarbons and C10A aromatic hydrocarbons, was 30.08 wt % through calculation. The heavy tail oil at >210° C. (the third stream) had a yield of 33.15 wt %, a specific gravity of 0.961, and a sulfur and nitrogen content of respectively 16.4 ppm and 0.8 ppm. Multidimensional chromatographic analysis was carried out to provide a family composition of the third stream as showed in Table 7: 7.58 wt % non-aromatic hydrocarbons, 38.12 wt % monocyclic aromatic hydrocarbons and 54.30 wt % polycyclic aromatic hydrocarbons.

TABLE-US-00007 TABLE 7 Heavy fraction at >210° C. Density (4° C.) 0.951 Sulfur (wt ppm) 16.4 Nitrogen (wt ppm) 0.8 Non-aromatic hydrocarbons (wt %) 7.58 Monocyclic aromatic hydrocarbons (wt %) 38.12 Polycyclic aromatic hydrocarbons (wt %) 54.30

[0164] The post-saturation selective catalyst C3 for treating the heavy tail oil at >210° C. comprised: 0.10 wt % Pt-0.30% Pd-4.0 wt % ni-6.0 wt % SiO.sub.2 −89.6 wt % Al.sub.2O.sub.3. The post-saturation selective catalyst C3 was prepared as follows: a commercial amorphous silica-alumina material with 9% of SiO.sub.2 was mixed with pseudo-boehmite, then a peptizing agent of nitric acid, an extrusion aid of sesbania powder and an appropriate amount of water were added, kneaded, extruded and shaped, dried in air at 100° C. for 24 hours, and then calcinated in air at 550° C. for 4 hours, to provide the catalyst support. Appropriate amounts of chloroplatinic acid, palladium chloride and nickel acetate were dissolved in water to provide a metal impregnation solution, to soak the catalyst support in an isovolumetric soaking mode, dried in air at 100° C. for 18 hours, then calcinated in air at 500° C. for 2 hours, to provide the post-saturation selective catalyst C3. The post-saturated selective catalyst C3 was reduced in the presence of hydrogen with a reduction end temperature of 450° C., and kept for two hours.

[0165] An oversaturated amount of hydrogen was dissolved in the heavy tail oil at >210° C. through a hydrogen mixer and was fed into a selective saturation reactor, with reaction conditions of: a volume ratio of hydrogen to oil of 600 Nm.sup.3/m.sup.3, a reactor inlet temperature of 150° C., a partial pressure of hydrogen of 2.0 MPa, and a volume space velocity of the feed of 1.5 hour.sup.−1. After the entire reaction system had been equilibrated, the analytical results for the products of the selective saturation were as shown in Table 8, wherein the sulfur and nitrogen contents were 11.3 ppm and 0.6 ppm, respectively. The retention rate of polycyclic aromatic hydrocarbons for the selective saturation process was 99.63 wt %, calculated from the aromatic composition data.

TABLE-US-00008 TABLE 8 Heavy fraction at >210° C. for selective saturation Density (4° C.) 0.942 Sulfur (wt ppm) 11.3 Nitrogen (wt ppm) 0.6 Non-aromatic hydrocarbons (wt %) 7.92 Monocyclic aromatic hydrocarbons (wt %) 66.35 Polycyclic aromatic hydrocarbons (wt %) 25.73

[0166] The heavy tail oil at >210° C. after selective saturation was returned to the selective conversion reactor, and stable stream balance was established. After gas-liquid separation and a rectification system, benzene-toluene, xylene, C9A aromatic hydrocarbons and C1 OA aromatic hydrocarbons were obtained through separation, and the yield of monocyclic light aromatic hydrocarbons such as benzene-toluene, xylene, C9A aromatic hydrocarbons and C10A aromatic hydrocarbons, was 47.98 wt % through calculation.