PROCESS FOR PRODUCTION OF DIMETHYLNAPHTHALENES

Abstract: A process for production of dimethylnaphthalenes is disclosed, comprising a raffinate resulting from the recovery of normal paraffins form a hydrodesulfurized kerosene fraction to reforming reaction and then recovering dimethylnaphthalenes from the product oil.

Description: FIELD OF THE INVENTION The present invention relates to a process for production of dimethylnaphthalenes from a raffinate resulting from recovery of normal paraffins from a hydrodesulfurized kerosene fraction (i.e. the normal paraffin depleted fraction). BACKGROUND OF THE INVENTION 2,6- or 2,7-naphthalenedicarboxylic acid obtained by oxidation of dimethylnaphthalenes, particularly 2,6- or 2,7-dimethylnaphthalene, is used as a starting material for production of polyesters such as polyethylene naphthalates. These polyesters provide synthetic fibers and films having excellent characteristics. It has therefore been desired to develop a process for producing 2,6- or 2,7-dimethylnaphthalene at low costs and with high quality. Dimethylnaphthalenes are contained in coal tar or a cycle oil in the fluid catalytic cracking process and, thus, a method of recovering dimethylnaphthalenes by distillation of coal tar or the cycle oil has been proposed (see, for example, JP-A-60-69042 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")). In the method of recovering dimethylnaphthalenes from coal tar or the cycle oil in the fluid catalytic cracking process since the cycle oil contains a high concentration of nitrogen and sulfur compounds, the dimethylnaphthalenes obtained are contaminated with these nitrogen and sulfur compounds. These nitrogen and sulfur compounds accelerate catalyst poisoning in isomerization of substituted dimethylnaphthalenes other than 2,6- or 2,7-dimethylnaphtha-lene, and further in adsorption separation of 2,6- or 2,7-dimethylnaphthalene by the use of a zeolite and so on. It is therefore necessary to decrease the amounts of nitrogen and sulfur compounds in dimethylnaphthalenes to about 10 ppm or less. Concerning hydrotreating to decrease the amounts of the nitrogen and sulfur compounds to about 10 ppm or less, it should be carried out under severe conditions. Hydrotreating under such severe conditions inevitably causes hydrogenation and cracking of dimethylnaphthalenes, resulting in a great reduction in yield of dimethylnaphthalenes. Thus, additional dehydrogenation is needed, and a problem arises in that the production cost is markedly increased. Normal paraffins are recovered from a kerosene fraction as a starting material for production of linear alkylbenzene sulfonates (LAS) as synthetic detergents. As a result of investigations, it has been found that a product oil obtained by reforming reaction of the above-described raffinate contains a large amount of dimethylnaphthalenes and that the product is almost free from nitrogen and sulfur compounds. It is reported that catalytic reforming of a kerosene fraction provides heavy aromatic compounds and that the heavy aromatic compounds contain dimethylnaphthalenes ( Sekiyu Gakkaishi , Vol. 13, No. 6 (1970), pp. 468-474). But, astonishingly, by the reforming reaction of the raffinate, dimethylnaphthalenes can be formed inan amount of about 1.5 times that in the reforming reaction of the kerosene fraction. SUMMARY OF THE INVENTION An object of the present invention provides a process in which dimethylnaphthalenes with a low content of sulfur and nitrogen compounds can be produced in high yield. That is, the present invention relates to a process for producing dimethylnaphthalenes which comprises subjecting a raffinate resulting from recovery of normal paraffins from a hydrodesulfurized kerosene fraction (i.e. the normal paraffin depleted fraction) to reforming reaction and then recovering dimethylnaphthalenes from the product oil. DETAILED DESCRIPTION OF THE INVENTION The hydrodesulfurized kerosene fraction as referred to herein is a kerosene fraction obtained by atmospheric distillation of a crude oil or cracking oil, etc., generally a distillate within the boiling range of from 150 to 300°C, which has been subjected to desulfurization under the commonly used hydrodesulfurization conditions, for example, with catalysts prepared by supporting at least one of cobalt, nickel, molybdenum, and tungsten on a carrier such as alumina or silica-alumina and under conditions of temperature range of from 280 to 430°C, pressure range of from 10 to 200 k g /cm² (981 to 19612 kPa) liquid hourly space velocity (LHSV) range of from 0.5 to 15 h⁻¹, and hydrogen recycle amount range of from 70 to 2,400 Nm³/kl. A kerosene fraction with reduced sulfur and nitrogen contents to about 50 ppm or less is preferably used. In the present invention, a raffinate resulting from the recovery of normal paraffins from the above-described hydrodesulfurized kerosene fraction is used. This recovery of normal paraffins is preferably carried out by adsorption separation using a molecular sieve, such as by the Iso-Siv method (cf. Hydrocarbon Processing , 59 , No. 5, May, 1980, pp. 110-114), the Molex method (cf. D.B.Broughton et al., Petrol. Refiner. , 40 (5), 173 (1961), and the BP method (cf. A.A. Yeo et al., Six World Petroleum congress , Sect. IV-Paper 15 (1963)). As the raffinates, those in which at least 50% by weight, particularly from 70 to 95% by weight, of normal paraffins in the kerosene fraction are recovered are preferred from the viewpoint of yield of dimethylnaphthalenes. In this case, the order of the hydrodesulfurization and the recovery of normal paraffins is not critical. It is, however, preferred from the viewpoint of catalyst poison of zeolite that the hydrodesulfurization is first carried out. For the reforming reaction, a catalytic reforming process which is widely used for production of high-octane value gasoline from a naphtha fraction and so forth can be employed. This can be carried out by the use of, e.g., a catalyst prepared by supporting platinum alone or in combination with rhenium, germanium, tin, iridium, or ruthenium on a carrier of alumina and under conditions of temperature range of from 400 to 550°C, pressure range of from 1 to 100 kg/cm² (98 to 9807 kPa), liquid hourly space velocity (LHSV) range of from 0.1 to 3 h⁻¹, and hydrogen/oil molar ratio range of from 0.5 to 20. In another embodiment, the reforming reaction can be carried out by the use of a zeolite, or crystalline aluminosilicate, silica, alumina, zirconia, titania, chromia, solid phosphoric acid, or oxides of indium, lanthanum, manganese, cerium or tin, or acidic refractories containing a mixture of two or more thereof, or catalysts prepared by containing therein or supporting thereon metals such as platinum, palladium, and rhenium and under conditions of temperature range of from 250 to 700°C, pressure range of from 1 to 100 kg/cm² (98 to 9807 kPa), LHSV range of from 0.1 to 20 h⁻¹, and hydrogen/oil molar ratio range of from 0.5 to 20. The product oil after the reforming reaction contains a relatively high concentration of dimethylnaphthalenes, and the dimethylnaphthalenes are recovered by techniques such as distillation, solvent extraction, conventional crystallization, high-pressure crystallization (cf. Kagaku Kogaku, 51 , No. 6, 428-433 (1987)), and combinations thereof. The recovery by distillation is preferred from the economic standpoint, and by collecting a 255-270°C fraction, a high concentration of dimethylnaphthalenes can be obtained. 2,6- and 2,7-dimethylnaphthalnes are separated and recovered from the dimethylnaphthalenes by known techniques such as the adsorption separation method using a zeolite, the crystallization method, and the separation method through the formation of a complex compound. The residue after the recovery is isomerized by the use of an isomerization catalyst and recycled for the above-described separation and recovery. In accordance with the present invention, dimethylnaphthalenes are recovered from a product oil resulting from the reforming reaction of a hydrodesulfurized kerosene fraction. Thus, dimethylnaphthalenes with a low content of sulfur and nitrogen compounds can be produced in quite high yield. The present invention is described in greater detail with reference to the following examples. EXAMPLES 1 AND 2, AND COMPARATIVE EXAMPLE 1 A desulfurized kerosene fraction having properties shown in Table 1, as obtained by hydrodesulfurization of a kerosene fraction, and a raffinate having properties as shown in Table 1, as obtained by recovering 90% by weight of normal paraffins from the above-described kerosene fraction by the use of a molecular sieve, were used as starting materials and subjected to reforming reaction by the use of a catalytic reforming catalyst comprising an alumina carrier having supported thereon 0.2% by weight of platinum and under the conditions as shown in Table 2. Properties of the product oil and the dimethylnaphthalene content are shown in Table 2. The product oil was subjected to atmospheric distillation, and a 255-265°C fraction was collected. The purity of dimethylnaphthalenes was 65%. EXAMPLES 3 TO 5, AND COMPARATIVE EXAMPLE 2 Raffinates in which the percent recovery of normal paraffins was adjusted to 50% by weight and 70% by weight by adding the normal paraffins recovered in each of Examples 1 and 2 to the raffinate used in each of Example 1 and 2, and for comparison, the desulfurized kerosene used in Comparative Example 1 were subjected to reforming reaction by the use of a catalytic reforming catalyst comprising an alumina carrier having supported thereon 0.2% by weight of platinum and under the conditions of pressure of 25 kg/cm² (2452 kPa), temperature of 490°C, LHSV of 0.8 h⁻¹, and hydrogen/oil molar ratio of 6. Properties and composition of the product oil are shown in Table 3. As apparent from the foregoing results, by reforming reaction of a raffinate resulting from the recovery of normal paraffins from a desulfurized kerosene fraction, dimethylnaphthalenes can be obtained in the concentration of about 1.5 times that from the desulfurized kerosene fraction.

Claims: A process for producing dimethylnaphthalenes which comprises subjecting a raffinate resulting from the recovery of normal paraffins from a hydrodesulfurized kerosene fraction (i.e. the normal paraffin depleted fraction) to reforming reaction and then recovering dimethylnaphthalenes from the product oil. The process as claimed in Claim 1, wherein the raffinate is a raffinate resulting from the recovery of at least 50% by weight of normal paraffins from a hydrodesulfurized kerosene fraction. The process as claimed in Claim 1, wherein the reforming reaction is carried out by the use of a catalyst prepared by supporting platinum alone or in combination with rhenium, germanium, tin, iridium, or rhutenium on an alumina carrier and under the conditions of temperature range of from 400 to 550°C, pressure range of from 1 to 100 kg/cm² (98 to 9807 kPa), liquid hourly space velocity range of from 0.1 to 3 h⁻¹ and hydrogen/oil molar ratio range of from 0.5 to 20. The process as claimed in Claim 1, wherein the reforming reaction is carried out by the use of a zeolite, or crystalline aluminosilicate, silica, alumina, zirconia, titania, chromia, solid phosphoric acid, or oxides of indium, lanthanum, manganese, cerium or tin, or acidic refractories containing a mixture of two or more thereof, or a catalyst prepared by containing therein or supporting thereon a metal selected from platinum, palladium, and rhenium under the conditions of temperature range of from 250 to 700°C, pressure range of from 1 to 100 kg/cm² (98 to 9807 kPa), liquid hourly space velocity range of from 0.1 to 20 h⁻¹, and hydrogen/oil molar ratio range of from 0.5 to 20. The process as claimed in Claim 3, wherein the catalyst for the reforming reaction is a catalyst for catalytic reforming of naphtha. The process as claimed in Claim 1, wherein the recovery of dimethylnaphthalenes is carried out by distillation, solvent extraction, conventional crystallization, or high-pressure crystallization, or a combination thereof. The process as claimed in Claim 6, wherein the recovery of dimethylnaphthalenes is carried out by distillation to collect a 255-270°C fraction. The process as claimed in Claim 1, wherein the recovery of dimethylnaphthalenes is finally the separation and recovery of 2,6- and 2,7-dimethylnaphthalenes. The process as claimed in Claim 1 wherein the hydrodesulfurized kerosene fraction is a kerosene fraction with reduced sulfur and nitrogen contents to 50 ppm or less. A process as in claim 1, wherein 2,6- and 2,7-dimethylnaphthalenes are recovered from the dimethylnaphthalenes by any one or more methods of adsorption separation, crystallization, or separation forming a complex compound; and then the recovery residue is isomerized into 2,6- and 2,7-dimethylnaphthalenes.

Inventors: AIZAWA, SHIROU, YANO, KYOJI, AIZAWA, SHIROU, C/O NIPPON MINING CO. LTD., YANO, KYOJI, C/O NIPPON MINING CO. LTD.
Applicants: NIPPON MINING COMPANY LIMITED
Application year: 1988
Main classification: C10G45
IPC codes: C10G69, C10G45