PROCESS FOR PRODUCING AROMATICS, P-XYLENE AND TEREPHTHALIC ACID, AND DEVICE FOR PRODUCING AROMATICS

Abstract

The present invention relates to a process for producing aromatics, a process for producing p-xylene and terephthalic acid, and a device for producing aromatics. The process for producing aromatics at least comprises a step of producing C8 olefin from a compound having a lactone group and a step of producing aromatics from the C8 olefin. The process for producing aromatics has the characters of high yield of aromatics and high selectivity to xylene.

Claims

1. A process for producing aromatics, comprising the steps of a1) and b1) or comprising the steps of a2), b2) and c2): a1) a step of contacting a compound having a lactone group with an decarboxylation and dimerisation catalyst, under conditions for decarboxylation and dimerisation reaction, to produce a C8 olefin; and b1) a step of contacting the C8 olefin with an aromatization catalyst under aromatization reaction conditions, to produce aromatics, or a2) a step of contacting a compound having a lactone group with an decarboxylation catalyst, under decarboxylation reaction conditions, to produce a C4 olefin; and b2) a step of contacting the C4 olefin with a dimerisation catalyst, under dimerization reaction conditions, to produce a C8 olefin; and c2) a step of contacting the C8 olefin with an aromatization catalyst under aromatization reaction conditions, to produce aromatics, wherein, the compound having a lactone group has the structural formula (I): ##STR00003## in formula (I), R.sub.1 is selected from the group consisting of optionally substituted C.sub.1-20 linear or branched alkylene, optionally substituted C.sub.2-20 linear or branched alkenylene, optionally substituted C.sub.2-20 linear or branched alkynylene, optionally substituted C.sub.3-20 cycloalkylene and optionally substituted C.sub.6-20 arylidene, preferably selected from the group consisting of optionally substituted C.sub.2-10 linear or branched alkylene and optionally substituted C.sub.2-10 linear or branched alkenylene, more preferably C.sub.2-5 linear or branched alkylene, further preferably 1,2-ethylidene; and R.sub.2 is selected from the group consisting of hydrogen, optionally substituted C.sub.1-20 linear or branched alkyl and carboxyl, preferably selected from the group consisting of hydrogen and optionally substituted C.sub.1-10 linear or branched alkyl, more preferably selected from the group consisting of hydrogen and C.sub.1-4 linear or branched alkyl.

2. The process according to claim 1,wherein the conditions for the decarboxylation and dimerization reaction comprise: a reaction temperature of 160 to 400 degree Celsius, preferably 160 to 300 degree Celsius, a reaction pressure of 0.1 to 8 MPa, preferably 0.1 to 4 MPa, a WHSV for the compound having a lactone group of 0.1 to 15 hour.sup.?1, preferably 0.6 to 5 hour.sup.?1; or alternatively, the conditions for the decarboxylation reaction comprise: a reaction temperature of 100 to 350 degree Celsius, preferably 120 to 250 degree Celsius, a reaction pressure of 0.1 to 8 MPa, preferably 0.1 to 4 MPa, a WHSV for the compound having a lactone group of 0.1 to 15 hour.sup.?1, preferably 0.6 to 5 hour.sup.?1; or alternatively, the conditions for the dimerization reaction comprise: a reaction temperature of 160 to 400 degree Celsius, preferably 160 to 300 degree Celsius, a reaction pressure of 0.1 to 8 MPa, preferably 0.1 to 4 MPa, a WHSV for the C4 olefin of 0.1 to 15 hour.sup.?1, preferably 0.6 to 5 hour.sup.?1; or alternatively, the conditions for the aromatization reaction comprise: a reaction temperature of 420 to 800 degree Celsius, preferably 450 to 550 degree Celsius, a reaction pressure of 0.1 to 8 MPa, preferably 0.1 to 4 MPa, a WHSV for the C8 olefin of 0.3 to 10 hour.sup.?1, preferably 0.3 to 5 hour.sup.?1.

3. The process according to claim 1,wherein the compound having a lactone group is derived from a biomass material, preferably derived from one or more of xylitol, glucose, cellobiose, cellulose, hemicellulose and lignin, or derived from one or more of paper manufacture sludge, waste paper, bagasse, glucose, wood, corn cob, corn stover and straw stover.

4. The process according to claim 1,wherein the decarboxylation and dimerisation catalyst is one or more selected from the group consisting of acidic oxide, oxide of bismuth, strongly acidic cation exchange resin, molecular sieve, solid super acid and composite metal oxide; the decarboxylation catalyst is one or more selected from the group consisting of acidic oxide, strongly acidic cation exchange resin, molecular sieve, solid super acid and composite metal oxide, preferably one or more selected from the group consisting of acidic oxide, strongly acidic cation exchange resin and solid super acid, more preferably one or more selected from the group consisting of strongly acidic cation exchange resin and solid super acid; the dimerisation catalyst is one or more selected from the group consisting of acidic oxide, oxide of bismuth, strongly acidic cation exchange resin, molecular sieve, solid super acid and composite metal oxide, preferably molecular sieve; the aromatization catalyst is one or more selected from the group consisting of molecular sieve, solid super acid and composite metal oxide, preferably molecular sieve, in particular ZSM-5 or M/ZSM-5, wherein M is selected from the group consisting of Zn, Ga, Sn or a combination thereof.

5. The process according to claim 4, wherein the acidic oxide is one or more selected from the group consisting of solid oxide of an element from Group IIIA of the periodic table of elements and solid oxide of an element from Group IVA of the periodic table, preferably one or more selected from the group consisting of SiO.sub.2 and Al.sub.2O.sub.3, more preferably Al.sub.2O.sub.3, Al.sub.2O.sub.3SiO.sub.2 or SiO.sub.2, the oxide of bismuth is Bi.sub.2O.sub.3, and the strongly acidic cation exchange resin is one or more selected from the group consisting of macroporous sulfonic acidic cation exchange resin and halogen modified (preferably perfluorinated) sulfonic acidic cation exchange resin, more preferably one or more selected from the group consisting of Amberlyst? series resins and Nafion? series resins.

6. The process according to claim 4, wherein the acid strength D1 of the decarboxylation and dimerisation catalyst and the acid strength D2 of the aromatization catalyst satisfy the following formula (I),
D 1>D2 (I) or alternatively, the acid strength D11 of the decarboxylation catalyst, the acid strength D12 of the dimerisation catalyst and the acid strength D2 of the aromatization catalyst satisfy the following formula (II),
D11>D2>D 12 (II).

7. The process according to claim 4,wherein the molecular sieve is one or more selected from the group consisting of ZSM-type molecular sieve (preferably one or more selected from the group consisting of ZSM-5, ZSM-11, ZSM-22, ZSM-23 and ZSM-38), Y-type molecular sieve, beta-type molecular sieve, L-type molecular sieve, MCM-type molecular sieve (preferably one or more selected from the group consisting of MCM-22 and MCM-41), preferably one or more selected from the group consisting of ZSM-5, Y-type molecular sieve, beta-type molecular sieve and MCM-41, more preferably ZSM-5.

8. The process according to claim 7, wherein the molecular sieve is a molecular sieve composition, comprising the following components of a1), b1) and c1) or comprising the following components of a2) and c2: a1) 20 to 80 parts by weight (preferably 50 to 80 parts by weight) of the molecular sieve, and b1) 20 to 80 parts by weight (preferably 20 to 50 parts by weight) of a binder (preferably one or more selected from the group consisting of silica sol, pseudo-boehmite, alumina, acid treated clay, kaolin, montmorillonite, and bentonite, more preferably one or more selected from the group consisting of alumina, pseudo-boehmite and montmorillonite), and c1) 0 to 10 parts by weight (preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight) of an auxiliary, wherein the auxiliary is one or more selected from the group consisting of Na, Ca, K, Be, Mg, Ba, V, Nb, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Cu, Zn, Ga, Ru, Pd, Pt, Ag, B, Al, Sn, P, Sb, La and Ce, preferably one or more selected from the group consisting of Ca, K, Mg, Cr, Mo, Fe, Ni, Cu, Zn, Ga, Ru, Pd, Pt, Ag, B, Sn, P, La and Ce, more preferably one or more selected from the group consisting of Zn, Ga and Sn, or a2) 90 to 99.99 parts by weight (preferably 95 to 99.99 parts by weight) of the molecular sieve, and c2) 0.01 to 10 parts by weight (preferably 0.01 to 5 parts by weight) of an auxiliary, wherein the auxiliary is one or more selected from the group consisting of Na, Ca, K, Be, Mg, Ba, V, Nb, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Cu, Zn, Ga, Ru, Pd, Pt, Ag, B, Al, Sn, P, Sb, La and Ce, preferably one or more selected from the group consisting of Ca, K, Mg, Cr, Mo, Fe, Ni, Cu, Zn, Ga, Ru, Pd, Pt, Ag, B, Sn, P, La and Ce, more preferably one or more selected from the group consisting of Zn, Ga and Sn.

9. The process according to claim 1, wherein in step a1), the compound having a lactone group is contacted with catalyst bed layers containing the decarboxylation and dimerisation catalyst to produce a C8 olefin, the catalyst bed layers comprising at least two layers of the decarboxylation and dimerisation catalyst, wherein the acid strengths of any two adjacent layers of the decarboxylation and dimerisation catalysts are different.

10. The process according to claim 4, wherein the solid super acid is one or more selected from the group consisting of Lewis acid supported solid super acid, solid super acid as inorganic metal salt/Lewis acid composite and solid super acid as sulfated metal oxide.

11. The process according to claim 10, wherein the support of the Lewis acid supported solid super acid is one or more of selected from the group consisting of solid oxide of an element from Group IIIA and solid oxide of an element from Group IVA, of the periodic table, preferably one or more of selected from the group consisting of SiO.sub.2, B.sub.2O.sub.3 and Al.sub.2O.sub.3, the Lewis acid of the Lewis acid supported solid super acid is one or more selected from the group consisting of halide (preferably fluoride) of an element from Group VB, halide (preferably fluoride) of an element from Group IIIA and halide (preferably fluoride) of an element from Group VA of the periodic table of elements, preferably one or more selected from the group consisting of halide (preferably fluoride) of an element from Group VB and halide (preferably fluoride) of an element from Group VA of the periodic table of elements, further preferably one or more selected from the group consisting of PF.sub.3, AsF.sub.3, SbF.sub.3, BiF.sub.3, SbF.sub.5, TaF.sub.3, VF.sub.3 and NbF.sub.3, the Lewis acid supported solid super acid is preferably one or more selected from the group consisting of SbF.sub.5/SiO.sub.2Al.sub.2O.sub.3, PF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, AsF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, SbF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, BiF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, TaF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, VF.sub.3/Al.sub.2O.sub.3B203 and NbF.sub.3/Al.sub.2O.sub.3B.sub.2O.sub.3, the inorganic metal salt of the solid super acid as inorganic metal salt/Lewis acid composite is one or more selected from the group consisting of inorganic acid salt (preferably haloid acid salt, more preferably hydrochloride) of a metal element from Group IB, inorganic acid salt (preferably haloid acid salt, more preferably hydrochloride) of a metal element from Group IIB, inorganic acid salt (preferably haloid acid salt, more preferably hydrochloride) of a metal element from Group VII and inorganic acid salt (preferably haloid acid salt, more preferably hydrochloride) of a metal element from Group VIII of the periodic table of elements, preferably CuCl.sub.2, the Lewis acid of the solid super acid as inorganic metal salt/Lewis acid composite is one or more selected from the group consisting of halide (preferably chloride) of an element from Group VB, halide (preferably chloride) of an element from Group IIIA and halide (preferably chloride) of an element from Group VA of the periodic table of elements, preferably one or more selected from the group consisting of halide (preferably chloride) of an element from Group IIIA of the periodic table of elements, preferably A1C13, the solid super acid as inorganic metal salt/Lewis acid composite is preferably AlCl.sub.3CuCl.sub.2, the metal oxide of the solid super acid as sulfated metal oxide is oxide A of a metal element from Group IVB (preferably one or more selected from the group consisting of ZrO.sub.2 and TiO.sub.2) or is oxide B obtained by modifying the oxide A with one or more modifying elements selected from the group consisting of metal element from Group IIIA (in the form of oxide), metal element from Group VIIB (in the form of oxide), noble metal element from Group VIII (in the form of metal elementary substance), base metal element from Group VIII (in the form of oxide), metal element from Group VIB (in the form of oxide) and lanthanide metal element (in the form of oxide) of the periodic table of elements (the modifying element being preferably one or more selected from the group consisting of Fe, Pt, Re, Al, W, Cr, Mo and Mn), and the solid super acid as sulfated metal oxide is preferably one or more selected from the group consisting of SO.sub.4.sup.2?/ZrO.sub.2, S.sub.2O.sub.8.sup.2?/ZrO.sub.2, SO.sub.4.sup.2?/TiO.sub.2, SO.sub.4.sup.2?/ZrO.sub.2Fe.sub.3O.sub.4, Pt/SO.sub.4.sup.2?/TiO.sub.2, SO.sub.4.sup.2?/TiO.sub.2ZrO.sub.2, SO.sub.4.sup.2?/TiO.sub.2Al.sub.2O.sub.3, SO.sub.4.sup.2?/TiO.sub.2WO.sub.3, SO.sub.4.sup.2?/ZrO.sub.2Fe.sub.2O.sub.3Cr.sub.2O.sub.3, SO.sub.4.sup.2?/ZrO.sub.2WO.sub.3, SO.sub.4.sup.2?/TiO.sub.2MoO.sub.3, SO.sub.4.sup.2?/ZrO.sub.2Fe.sub.2O.sub.3MnO.sub.2, W modified SO.sub.4.sup.2?/Al.sub.2O.sub.3ZrO.sub.2 and Mo modified SI.sub.4.sup.2?/Al.sub.2O.sub.3ZrO.sub.2.

12. The process according to claim 11,wherein in the Lewis acid supported solid super acid, the Lewis acid is supported in an amount of 1 to 30 wt %, preferably 1 to 15 wt %, relative to the weight of the support. in the solid super acid as inorganic metal salt/Lewis acid composite, the weight ratio between the inorganic metal salt and the Lewis acid is 1-30:100, preferably 1-15:100, in the solid super acid as sulfated metal oxide, the metal oxide has a sulfated rate of 0.5-25 wt %, preferably 1-8 wt %, and in the oxide B, the weight ratio of the modifying element in the form of oxide (calculated as oxide) to the oxide A is 0.1-25:100, preferably 0.5-10:100, and the weight ratio of the modifying element in the form of metal elementary substance (calculated as metal) to the oxide A is 0.1-15:100, preferably 0.3-6:100.

13. The process according to claim 4,wherein the composite metal oxide is a composite oxide of oxide C of a metal element from Group IVB (preferably one or more selected from the group consisting of ZrO.sub.2 and TiO.sub.2, more preferably ZrO.sub.2) and one or more oxides D selected from the group consisting of oxide of a metal element from Group IIIA of the periodic table of elements, oxide of a metal element from Group VII, oxide of a metal element from Group VIB and lanthanide metal element of the periodic table of elements (preferably one or more selected from the group consisting of B.sub.2O.sub.3, Al.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, CrO.sub.3, MoO.sub.3, WO.sub.3, La.sub.2O.sub.3 and CeO.sub.2, more preferably one or more selected from the group consisting of MnO.sub.2, MoO.sub.3, WO.sub.3, La.sub.2O.sub.3 and CeO.sub.2), preferably a composite oxide of ZrO.sub.2 and one or more oxides D selected from the group consisting of MnO.sub.2, Mo.sub.2O.sub.3, WO.sub.3, La.sub.2O.sub.3 and CeO.sub.2.

14. The process according to claim 13, wherein the ratio of oxide C to oxide D is 60-99.9: 0.1-40, preferably 60-99:1-40, calculated in parts by weight.

15. The process according to claim 1,further comprising a step of catalytic conversion of the biomass material, optionally followed by catalytic hydrogenation, so as to produce the compound having a lactone group.

16. A process for producing p-xylene, comprising the steps of: a step of producing aromatics according to claim 1; and a step of separating p-xylene from the aromatics.

17. A process for producing terephthalic acid, comprising the steps of: a step of producing p-xylene according to claim 16; and a step of converting the p-xylene into terephthalic acid.

18. A device for producing aromatics, comprising the units of: an decarboxylation and dimerisation unit, constructed as being capable of contacting a compound having a lactone group with an decarboxylation and dimerisation catalyst, under conditions for decarboxylation and dimerization reaction, to produce a C8 olefin; and an aromatization unit, constructed as being capable of contacting the C8 olefin with an aromatization catalyst under aromatization reaction conditions, to produce aromatics, optionally, the device further comprising a catalytic conversion unit, or a combination of a catalytic conversion unit with a catalytic hydrogenation unit: the catalytic conversion unit being constructed as allowing catalytic conversion of the biomass material to generate a product comprising the compound having a lactone group; and the catalytic hydrogenation unit being constructed as being capable of increasing the proportion of the compound having a lactone group in the product through catalytically hydrogenating the product.

Description

EXAMPLES

[0150] The present invention will be further illustrated in more detail referring to the Examples below, whilst the present invention is not restricted to these Examples.

[0151] In the context of the specification, the yield of carbon as xylene is calculated according to the formula below.

[0152] The yield of carbon as xylene (%)=weight of xylene as a reaction product (g)/carbon weight of the compound having a lactone group as a reaction raw material * 100%.

[0153] An example for calculation is as follows:

[0154] 100 g of valerolactone is used as the compound having a lactone group, which comprises 68 g of carbon; then, if 50 g of xylene is obtained after reaction, the yield of carbon as xylene is 73.5%.

Example 1

[0155] Decarboxylation and dimerisation catalyst ZSM-5: 35 g of ZSM-5 having a ratio of Si:Al of 38 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0156] Production of aromatization catalyst ZSM-5: 35 g of hydrogenous ZSM-5 having a ratio of Si:Al of 100 was mixed with 35 g of an auxiliary of ?-alumina, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0157] Angelica lactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with Al.sub.2O.sub.3SiO.sub.2 catalyst (produced according to Example 1 of CN1393425A), and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst ZSM-5 produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 300 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 87%, and a selectivity to C8 olefin of 79%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, the aromatization catalyst ZSM-5, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 79%, and a yield of carbon as xylene of 54.3%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 2

[0158] 1000 g of straw stover was weighed and placed into a pressured reactor, 5000 g of water was added, and a 5 mol/L of sulphuric acid solution having 7 wt % of water was further added. The temperature was increased to 210 degree Celsius for reaction for 30 minutes, cooled, and the cooled reaction liquor was filtrated to provide a filter cake and a filtrate, which filtrate was a hydrolysate of cellulose. After reaction, the reaction resultant was analyzed using a mass spectra, which showed that the main product was levulinic acid at an output of 382 g. The levulinic acid obtained was hydrogenated on RuSn/C loaded with 2% metal in a fixed bed to provide ?-valerolactone, with a conversion of 99% and a yield of the product of 98%.

[0159] Production of decarboxylation and dimerisation catalyst A: a Mo modified SO.sub.4.sup.2?/Al.sub.2O.sub.3ZrO.sub.2 catalyst (produced according to Example 2 of CN200910011627.6, wherein for the incorporation of reactive metal using the method, only Mo was incorporated without incorporation of Ni).

[0160] Production of decarboxylation and dimerisation catalyst ZSM-5B: 65 g of hydrogenous ZSM-5 having a ratio of Si:Al of 100 was mixed with 35 g of pseudo-boehmite, 3.5 g of sesbania powder was added, and mixed homogeneously. Then, 108 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0161] Production of aromatization catalyst ZSM-5: 80 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 20 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0162] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst A, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst ZSM-5B, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 280 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 93%, and a selectivity to C8 olefin of 86%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, the aromatization catalyst ZSM-5, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 83%, and a yield of carbon as xylene of 66.4%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 3

[0163] Production of decarboxylation and dimerisation catalyst A: 50 g of beta having a ratio of Si:Al of 30 was mixed with 50 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0164] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 100 was mixed with 35 g of an auxiliary of ?-alumina, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0165] Aromatization catalyst HZSM-5: 35 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0166] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst A, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 280 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 99%, and a selectivity to C8 olefin of 93%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, an aromatization catalyst HZSM-5, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 86%, and a yield of carbon as xylene of 79.2%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 4

[0167] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0168] Aromatization catalyst LaHY: 35 g of HY-type molecular sieve having a ratio of Si:Al of 6 was mixed with 35 g of auxiliary of ?-alumina, 2.7 g of sodium carboxymethylcellulose was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide a further catalyst precursor, followed by loading 3% of La through an immersion method, to provide the LaY catalyst.

[0169] ?-lactone was added into an decarboxylation reactor R1, in which the upper layer of the catalyst bed layers was loaded with SO.sub.4.sup.2?/Al.sub.2O.sub.3ZrO.sub.2 catalyst (produced according to Example 1 of CN200910011627.6), and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 250 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 99%, and a selectivity to C8 olefin of 89%. After separation, the C8 olefin was fed into an aromatization reactor R.sub.2 for aromatization under the actions of a temperature of 450 degree Celsius, an aromatization catalyst LaHY, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 88%, and a yield of carbon as xylene of 77.5%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 5

[0170] Decarboxylation and dimerisation catalyst B: 60 g of Y-type molecular sieve having a ratio of Si:Al of 8 was mixed with 40 g of an auxiliary of ?-alumina, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of phosphoric acid comprising 5.5 wt % of phosphoric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0171] Aromatization catalyst MCM-22: 70 g of Y having a ratio of Si:Al of 10 was mixed with 30 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0172] ?-heptalactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with Amberlyst catalyst (Amberlyst? 15WET), and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 180 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 96%, and a selectivity to C8 olefin of 81%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 500 degree Celsius, an aromatization catalyst MCM-22, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 94%, and a yield of carbon as xylene of 73.1%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 6

[0173] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 100 was mixed with 45 g of pseudo-boehmite, 3.2 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0174] Aromatization catalyst ZSM-5: 35 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0175] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with Amberlyst catalyst (Amberlyst? 15WET), and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 180 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 96%, and a selectivity to C8 olefin of 91%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, the aromatization catalyst ZSM-5, and a space velocity of 2 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 86%, and a yield of carbon as xylene of 75.1%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 7

[0176] Decarboxylation and dimerisation catalyst: 60 g of Y having a ratio of Si:Al of 10 was mixed with 40 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide a further catalyst precursor, followed by loading 3% of La through an immersion method, to provide the LaHY catalyst.

[0177] Aromatization catalyst ZSM-5: 35 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0178] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which decarboxylation and dimerisation was conducted under conditions of the decarboxylation and dimerisation catalyst, a temperature of 180 degree Celsius and a WHSV of 1.5 6h.sup.?1, resulting in a conversion of 91%, and a selectivity to C8 olefin of 89%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 550 degree Celsius, an aromatization catalyst ZSM-5, and a space velocity of 1.5 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 86%, and a yield of carbon as xylene of 69.7%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 8

[0179] Production of decarboxylation catalyst A: 50 g of beta having a ratio of Si:Al of 20 was mixed with 50 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0180] Production of dimerisation catalyst B: 65 g of hydrogenous ZSM-5 having a ratio of Si:Al of 100 was mixed with 35 g of pseudo-boehmite, 3.5 g of sesbania powder was added, and mixed homogeneously. Then, 108 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0181] Production of aromatization catalyst ZSM-5: 80 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 20 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0182] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with decarboxylation catalyst A, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 280 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 96%, and a selectivity to C8 olefin of 93%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 500 degree Celsius, an aromatization catalyst ZSM-5, and a space velocity of 1.5 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 88%, and a yield of carbon as xylene of 78.6%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 9

[0183] Production of decarboxylation catalyst A: 50 g of beta having a ratio of Si:Al of 20 was mixed with 50 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0184] Production of dimerisation catalyst B: 65 g of hydrogenous ZSM-5 having a ratio of Si:Al of 100 was mixed with 35 g of pseudo-boehmite, 3.5 g of sesbania powder was added, and mixed homogeneously. Then, 108 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0185] Production of aromatization catalyst ZSM-5: 80 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 20 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0186] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation catalyst A, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 280 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 97%, and a selectivity to C8 olefin of 92%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, an aromatization catalyst ZSM-5, and a space velocity of 1.5 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 90%, and a yield of carbon as xylene of 80.3%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 10

[0187] Decarboxylation and dimerisation catalyst A: 60 g of Y having a ratio of Si:Al of 6 was mixed with 40 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0188] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 50 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0189] Aromatization catalyst Zn-ZSM-5: 35 g of ZSM-5 molecular sieve having a ratio of Si:Al of 150 was mixed with 35 g of an auxiliary of ?-alumina, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide a pre-catalyst. The pre-catalyst was immersed with Zn, in an amount of 1.5 wt % of the pre-catalyst, and dried and calcined to provide the Zn-ZSM-5.

[0190] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst A produced above, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 250 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 99%, and a selectivity to C8 olefin of 96%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 480 degree Celsius, an aromatization catalyst Zn-ZSM-5, and a space velocity of 1.5 to provide a stream containing a xylene product, with a selectivity to xylene of 91%, and a yield of carbon as xylene of 86.5%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Example 11

[0191] Decarboxylation and dimerisation catalyst A: 60 g of Y having a ratio of Si:Al of 6 was mixed with 40 g of pseudo-boehmite, 3.9 g of sesbania powder was added, and mixed homogeneously. Then, 68.6 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0192] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 50 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0193] Aromatization catalyst Ga-ZSM-5: 35 g of ZSM-5 molecular sieve having a ratio of Si:Al of 150 was mixed with 35 g of an auxiliary of ?-alumina, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide a pre-catalyst. The pre-catalyst was immersed with Ga, in an amount of 1.5 wt % of the pre-catalyst, and dried and calcined to provide the Ga-ZSM-5.

[0194] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst A produced above, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was conducted under conditions of a temperature of 250 degree Celsius and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 99%, and a selectivity to C8 olefin of 95%. After separation, the C8 olefin was fed into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, an aromatization catalyst Ga-ZSM-5, and a space velocity of 1.5 h.sup.?1, to provide a stream containing a xylene product, with a selectivity to xylene of 91%, and a yield of carbon as xylene of 85.6%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. The olefin obtained was further separated to provide light aromatics comprising benzene, toluene and the like, simultaneously providing PX in high-purity. In addition, an additional part was obtained as a heavy component from the column bottom. Hydrogen out of the column top could be used as a raw material for hydrogenating oligomers into gasoline or diesel oil, while the heavy component from the column bottom could be used as a raw material for diesel oil or be combusted to supply heat.

Comparative example 1

[0195] Decarboxylation and dimerisation catalyst A: 35 g of ZSM-5 having a ratio of Si:Al of 150 was mixed with 35 g of pseudo-Boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0196] Decarboxylation and dimerisation catalyst B: 35 g of ZSM-5 having a ratio of Si:Al of 25 was mixed with 35 g of pseudo-boehmite, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0197] Aromatization catalyst ZSM-5: 35 g of ZSM-5 molecular sieve having a ratio of Si:Al of 500 was mixed with 35 g of an auxiliary of ?-alumina, 2.7 g of sesbania powder was added, and mixed homogeneously. Then, 48 g of an aqueous solution of nitric acid comprising 5.5 wt % of nitric acid was added, mixed and kneaded for shaping, and extruded as a strip. The catalyst precursor obtained was dried at a temperature of 120 degree Celsius for 8 h, and calcined at a temperature of 500 degree Celsius for 2 h, to provide the catalyst.

[0198] ?-valerolactone was added into an decarboxylation and dimerisation reactor R1, in which the upper layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst A, and the lower layer of the catalyst bed layers was loaded with the decarboxylation and dimerisation catalyst B produced above, two catalyst layers having a same packing height. Decarboxylation and dimerisation was carried out under conditions of a temperature of 250 degrees C. and a WHSV of 1.5 h.sup.?1, resulting in a conversion of 83%, and a dramatically decreased selectivity to C8 olefin of 26% due to too strong acidity of the decarboxylation and dimerisation catalyst B which led the intermediate products including C4 olefin and the like to rapid coking. The C8 olefin was fed, after separation, into an aromatization reactor R2 for aromatization under the actions of a temperature of 450 degree Celsius, an aromatization catalyst ZSM-5, and a space velocity of 1.5 11.sup.1, to provide a stream containing a xylene product, with a selectivity to xylene of 56%. The olefin not reacted completely could be recycled to the dimer reactor for continued reaction. However, owing to the catalyst deactivation, catalyst performance degraded so rapidly that PX in high-purity could not be obtained.

[0199] Although the embodiments of the present invention have been illustrated in detail above referring to the Examples, it should be understood that the protection scopes of the present invention are no restricted thereto; instead, the protection scopes are defined by the claims attached. Those skilled in the art can make appropriate modification to these embodiments without departing the technical idea and spirit of the invention, while the modified embodiments are also included within the protection scopes of the invention obviously.