PROCESS FOR THE CONVERSION OF HYDROCARBON OILS

Abstract: A hydrocarbon oil with a nitrogen content below 25 ppmw having a boiling range entirely or substantially above 350°C comprising 1-50 %w of oil with an initial boiling point above 520°C, is selectively converted to middle distillates at elevated temperature and pressure in the presence of hydrogen with a sulphided supported catalyst comprising nickel and tungsten in a combined amount of 12.5-40 %w and 1-10 %w fluorine, based on total catalyst.

Description: PROCESS FOR THE CONVERSION OF HYDROCARBON OILS The present invention relates to a process for crer hydrocarbon oils to middle distillates, and to middle distillates thus obtained. Middle distillates, such as kerosine and gas oil, can be prodoed by hydrocracking higher boiling hydrocarbon fractions, such as flashed distillates, together with hydrogen at relatively high temperatures and pressures in the presence of a catalyst having a hydrogenating function and a cracking function. At present there is a need to process heavier feedstooks (e.g. blends of flashed distillates and residual fractions) in order to obtain valuable middle distillates in a greater yield frhn a given amount of crude oil than achieved by existing processes. Known hydrocracking catalysts for the preparation of middle distiliates appear to have unsatisfactory properties when such heavy feedetees are used. The selectivity of these catalysts in converting heavy feedstocks to middle disttilates is generally low, which means that a relatively large proportion of the feedstock is merited into low-boiling hydrocarbons. Furthermore the activity of these catalysts deceases in a relatively short time to an unacceptably low level, thus necessitating catalyst regeneration treatments which usually have a negative effect on total catalyst life. Moreover the conversion processes have to be stopped frequently in order to allow such treatments. By middle distillates are understood hydrocarbon oil frac- tions with a boiling range entirely or substantially between 150 and 370 OC. These middle distillates contain kerosine as well as gas oil components and can be fractionated into kerosine and gas oil by further distillation. By kerosine is understood a hydro carbon oil fraction which boils substantially in a temperature range of fran 150 to about 280 OC, preferably from 180 to 260 OC. By gas oil is understood a hydrocarbon oil which boils substantially in a temperature range of from 220 to 350 C (ASIM distillation) It has now been found that fluorine-containing supported catalysts having a high nickel and tungsten content exhibit both high selectivity for the preparation of middle distillates and high stability when a heavy hydrocarbon oil feedstock with a 1QW nitrogen content is used, whilst the conversicn at a given temperature to products boiling below 370 C is also high. The invention therefore relates to a process for converting hydrocarbon oils to middle distillates by contacting a hydro- carbon oil at elevated temperature and pressure in the presence of hydrogen with a catalyst, wherein a hydrocarbon oil with a nitrogen content below 25 ppmw having a boiling range entirely or substantially above 350 C comprising 1-50 %w of oil with an initial boiling point above 520 OC, is contacted with a sulphided seeeoreed catalyst wfiich comprises nickel and tungsten in a combined amount of 12.5-40 %w and fluorine in an amount of 1-10 %w, based on total catalyst. Preferably the hydrocarbon oil used as feed comprises 1-30 %w of a deasphalted residual oil with an initial boiling point above 520 C and 70-99 w of a flashed distillate with a boiling range entirely or substantially above 360 OC. The e use of hydrocabon oils having an initial boiling point above 370 C is especially preferred. Good results can also be obtained using a flashed distillate as feed. The above-mentioned flashed distillate is normally obtained by subjecting a long residue (an atmospheric distillation residue of a crude mineral oil) to flash distillation, also called eguiiibriwt distillation. The residual oil which can be used as part of the feed in the present process does not have to be derived fran the same type of crude mineral oil as the flashed distillate. It is preferably obtained by distillation of a long residue at reduced pressure and subsequently removing asphalt fran the remaining residue (known as short residue). Deasphalting can be carried out by treating the short residue with a low-boiling paraffinic hydrc- carbon, such as ethane, propane, butane, pentane or a mixture thereof. The e preferred catalysts used in the process according to the present invention are those which comprise 20-25 %w of tungsten, based on total catalyst, and in which catalysts the tungsten/ nickel weight ratio lies between 3:1 and 6:1. Refractory oxides or mixtures thereof may be used as catalyst support, such as alumina, silica, silica-alumina, zirconia, magnesia and boria. The preferred catalyst support is alumina, containing less than 5 % by weight of silica. Most preference is given to &gamma;-alumina, containing less than 1 % by weight of silica. The metals may be incorporated by any method known in the art for the preparation of catalysts containing several ponents on a carrier, such as impregnation, ion-exchange or (co-)precipitation. A suitable method for preparing such catalysts is co-impregnation of the carrier material in one or more stages with an aqueous solution containing salts of tungsten and nickel. The incorporation of fluorine into the catalyst may be carried out in two ways. Fluorine can be incorporated into the catalyst by impregnating the latter during or aeter the catalyst pnparation with a suitable fluorine compound, such as ammonium fluoride. It is also possible to incorporate fluorine into the catalyst in situ in an early stage of the hydrooeeersi process for which the catalyst is used (for example during or after the start-up of the process). In situ fluoridation of the catalysts can be carried cut by adding a suitable fluorine compound, such as o-fluorotoluene, or difluoroethane, to the gas and/or liquid stream which is contacted with the catalyst. It is preferred to incorporate at least part of the fluorine into the catalyst by in situ fluoridation. Preferably the present catalysts comprise 4-7 % by weight of fluorine, based on total catalyst. In order to maintain the fluorine content of the preset catalyst at the desired level during the process ac- cording to the invention it is preferred to add intermittently or cartinuously to the hydrocarbon oil/hydrogen feed stream to the reactor an amount of fluorine oocccnds corresponding to 1-50, in particular 2-20, parts per million (by weight) of fluorine, calculated on the starting hydrocarbon oil. The catalysts which are used in the present process may also contain promotors such as boron and/or phosphorus. The catalysts are used in the sulphidic form. The catalysts may be sulphided by any method known in the art for the sulphidation of catalysts, for example, by contacting the catalyst with a inixture of hydrogen and hydrogen sulphide or with hydrogen and a sulphur-containing hydrocarbon oil, such as a sulphur-containing gas oil. In the latter case the temperature is gradually raised to the level of the reaction temperature. The process according to the invention may take place in the liquid phase or partly in the vapcur-, partly in the liquid phase. Application of a fixed catalyst bed is preferred in the present process, krt it is also possible to apply the catalyst in a fluidized or expanded bed. A very suitable embodiment is that in ch the hydrocarbon oil to be converted, which is entirely or substantially in the liquid phase, is trickled downward co-currently with the hydrogen-containing gas through a fieed catalyst bed. Suitable hydroconversion conditions for the process of the present invention are a temperature of 350-420 OC, a total pressure of 75-200 bar, a partial hydrogen pressure of 60-200 bar, a space velocity of 0.4-1.5 kg oil/l catalyst/hour and a hydrogen feed rate of 250-2500 Nl/kg oil feed. The conversion of hydrocarbon oils to middle distillates according to the present process is preferably carried out under the following conditions: a temperature of 360-4100C, a total pressure of 100-150 bar, a partial hydrogen pressure of 80-150 bar, a space velocity of 0.4-1.0 kg oil/l catalyst/hour and a hydrogen feed rate of 500-1500 Nl/kg oil feed. The hydrogen applied can be pure hydrogen or a hydrogencontaining gas, preferably comprising wDre than 70 vol.% of hydrogen, the hydrogen-containing gas may canprise up to 10 vol.% of hydrogen sulphide. According to the process of the invention a hydrocarbon oil feed stream should be used containing less than 25 parts per million by weight (ppmw) of nitrogen, and preferably less than 10 ppmw of nitrogen which may be present completely or for the greater part in the form of organic nitrogen compounds. It is also preferred that the starting hydrocarbon oil contains less than 3, and most preferably less than 1, ppmw of vanadium and nickel combined. In sate cases it may be necessary to subject the hydrocarbon oil to be converted to, a demetallization pre-treatment in order to reach these levels. When the feed does not comply with the above requirement for the nitrogen content it will be necessary to subject the feed to a denitrogenation pre-treatment. Such a pre-treatment can be carried out by contacting a hydrocarbon oil with a nitrogen content above 25 ppmw, preferably having a boiling range entirely or substantial- ly above 350 OC, with a suIphided, fluorine-containing catalyst comprising nickel and molybdenum on a carrier. Refractory oxides nay be used as catalyst support, the preferred support being gamma-alumina which contains less than 1 %w of silica. The preferred catalysts to be used in this pre-treatment comprise 1-5 %w of nickel and 5-15 %w of molybdenum both percentages based on total catalyst. The preferred molyb- denum:nickel weight ratio lies between 3:1 and 6:1. These metals may be incorporated into the catalyst by any method known in the art, for example by impregnation of alumina in one or more stages with an aqueous solution containing one or itcre salts of the metals The catalysts to be used in the pre-treatment preferably contain 0.5-7, most preferably 3-7 %w of fluorine, calculated on total catalyst. The incorporation of fluorine into these catalysts and their sulphiding may be carried out as described hereinbefore for the preparation of the catalysts used in the presently claimed process. The catalysts used in the pre-treatment may also contain promotors such as boron and/or phosphorus. Suitable caiditions for carrying out this pre-treatment are a temperature of 370-420 OC, a total pressure of 65-220 bar, a partial hydrogen pressure of 60-200 bar, a space velocity of 0.2-2 kg oil/l catalyst/hour and a hydrogen feed rate of 250-2500 Nl/kg oil. The gas streams separated fran the pre-treated feed, fran the converted hydrocarbon oil, and the residual fraction separted from the middle distillates obtained, can all be partially or completely recycled. The invention is illustrated by the following Example. Example Preparation of catalyst A A Ni/W/F/Al2O3 catalyst with a pore volume of 0.4 ml/g and a specific surface area of 150 mê/g containing 5.1 *z of nickel, 23.8 %w of tungsten and 5.5 %w of fluorine, all based on total catalyst was prepared by impregnating an alumina carrier (comprising substantially &gamma;- Al2O3), with a pore volume of 0.68 ml/g, a surface area of 250 m Ig and a compacted bulk density of 0.66 g/ml, with an aqueous solution containing nickel nitrate and ammonium meta-tungstate in an amount equalling the total carrier pore volume. The impregnated alumina was dried in air and subsequently calcined at 650 C for 1.5 hours. The product obtained was transferred to a reactor and sulphide in a flow of a sulphur-containing gas oil (1.5 %w S) with gas recycle for 48 hours at 375 OC, after which the reactor was cooled to 250 C for fluoriding the sulphided product in situ. The fluoriding procedure was carried out in the liquid phase using difluoroethane in gas oil (concentration equivalent to 300 ppmw fluorine). Preparation of catalyst B A Ni/Mo/P/F/Al2O3 catalyst with a pore volume of 0.4 n1/g and a specific surface area of 150 m2/g containing 2.7 %w of nickel, 13.2 %w of molybdenum, 3.0 %w of phosphorus and 6.0 %w of fluorine, all based on total catalyst, was prepared by impregnating an alumina carrier, comprising substantially y-alumina and having a pore volume of 0.76 ml/g; a surface area of 250 mi/g and a carpacted bulk density of 0.61 g/ml, with an aqueous solution comprising nickel nitrate, ammonium heptamolybdate and phosphoric acid in an amount equailing the total carrier pore volume. The impregnated alumina was dried in air and subsequently calcined at 450 C for 1.5 hours. The product obtained was transferred to a reactor and sulphided in a flow of a sulphur-containing gasoil (1.5 %w S) with gas recycle for 48 hours at 375 OC, after which the reactor was cooled to 250 C for fluoriding the sulphided product in situ. The fluoriding procedure was carried out in the liquid phase using difluoroethane in gasoil (concentration equivalent to 300 ppmw fluorine). Pre-treatment A hydrocarbon oil which was a blend of flashed distillates and deasphalted residual oils of Arabian and Iranian origins, had the following properties: elements: C 85.41 %w H 11.95 N 0.13 S 2.51 fraction boiling above 3700C 98 fraction boiling above 5200C 38 specific gravity 0.899 kg/l Ishis hydrocarbon oil could not be converted to middie distillates in one stage according to the presently claimed prooess because of the high nitrogen content of the oil, and was pre-treated in the presence of hydrogen and catalyst B. The pre-treatment experiment 1 of which the conditions and the results are given in Table A below, was carried out on a pilot-plant scale in an adiabatic mode of operation using two reactor vessels in series, each having a volume of 1250 ml; the first of these reactors contained 450 ml (470 g) and the second one 950 ml (1095 g) of catalyst B in the form of 1.5 mn dates. The hydrocarbon oil was led downward through the reactors co-currently with the hydrogen containing gas. Table A Experiment No. 1 catalyst B space velocity (kg.1-1.h-1) 0.35 cat. bed temperature ( C) 380 total pressure (bar) 125 partial hydrogen pressure (bar) 122 H2 feed rate (Nl H2/kg oil) 1250 conversion to 370 prod. (%w) 40 The fraction boiling substantially above 370 C (370+) of the product obtained fran Experiment 1 had the following prc, perties: composition: elements: C 86.03 %w H 13.97 %w N 4 ppmw S 50 ppmw total metal content < 1 ppmw fraction 370+ 98 %w fraction boiling above 5200C 17 %w specific gravity 0.819 kg/l This pre-treated hydrocarbon oil was led downward cocurrently with hydrogen-containing gas through a 1250 ml reactor vessel, containing 980 ml (1234 g) of catalyst A in the form of 1.5 rtm extrudates, in an adiabatic mode of operation, The conditions at which Experiments 2-5 were carried out and the results obtained are given in Table B. By "Conversion per pass (w%)" in Table B below is under stood: [fraction 370# in feed (%w)] - [fraction 370# in product (%w)] fraction 370# in feed (%w) *Selectivity to middle distillates" is defined as: fraction of middle distillates in product (%w) x 100 fraction 370 in product {%w) By "fraction 370" is understood the fraction boiling below 370 C. Table B Experiment No. 2 3 4 5 Catalyst B B A A apace velocity (kg.l-1.h-1) 0.5 0.7 0.5 0.7 initial bed temperature ( C) 375 380 365 370 total pressure (bar) 125 125 125 125 Partial hydrogen pressure (bar) 120 120 120 120 Hydrogen feed rate (Nl H2/kg oil) 1250 1250 1250 1250 Convrsion per pass (%w) 70 70 60 60 Selectivity to middle distllates (%w) 67 66 72 70 Decline rate ( C/1000 h) 10 52 5 16 Experiments 2 and 3 are comparative experiments, not according to the invention, because catalyst B does not contain tungsten. Experiments 4 and 5 are experiments according to the invention. From Table B it can be concluded that at a given apace velocity catalyst A is rmch more stable than catalyst B, because the decline rates (expressed as the necessary reactor tsreera- ture increase for maintaining constant conversion, in OC per 1000 hours) are much lower for catalyst A than for catalyst B. Catalyst A also exhibits higher selectivity for the preparation of middle distillates than catalyst B.

Claims: CLAIMS 1. A process for converting hydrooaoon oils to middle distillates by contacting a hydrocarbon oil at elevated temperature and pressure in the presence of hydrogen with a catalyst; characterized in that a hydrocarbon oil with a nitrogen content below 25 ppmw having a boiling range entirely or substantially above 350 C comprising 1-50 %w of oil with an initial boiling point above 520 OC, is contacted with a sulphide supported catalyst which comprises nickel and tungsten in a combined amount of 12.5-40 %w and fluorine in an amount of 1-10 %w, based on total catalyst. 2. A process according to claim 1, characterized in that a hydrocarbon oil is used comprising 1-30 %w of a deasphalted residual oil with an initial boiling point above 520 C and 70-99 %w of a flashed distillate with a boiling range entirely or substantially above 360 OC. 3. A process according to claim 1 or 2, characterized in that a hydrocarbon oil is used hang an initial boiling point above 370 OC. 4. A process according to any one of claims 1-3, characterized in that a hydrocarbon oil is used having a nitrogen content below 10ppmw. 5. A prooss according to any one of clams 1-4, characterized in that a hydrocarbon oil is used containing less than 3, and preferably less than 1, ppmw of vanadium and nickel combined. 6. A process according to any one of claims 1-5, characterized in that a catalyst is used comprising 20-25 %w of tungsten, based on total catalyst on alumina as support, and in which the tungsten/nickel weight ratio lies between 3:1 and 6:1. 7. A process according to any one of claims 1-6, characterized in that at least part of the fluorine has been incorporated into said catalyst by in situ fluoridation. 8. A process according to any one of claims 1-7, characterized in that a catalyst is used ccttprising 4-7 %w of fluorine, based on total catalyst. 9. A process according to any one of claims 1-8, chracerized in that it is carried out at a temperature of 350-420 C, a total pressure of 75-200 bar, a space velocity of 0.4-1.5 kg oil/l catalyst/hour and a hydrogen feed rate of 250-2500 Nl/kg oil and preferably at a temperature of 360-410 OC, a total pressure of 100-150 bar, a space velocity of 0.4-1.0 kg oil/l catalyst/hour and a hydrogen feed rate of 500-1500 Nl/kg oil. 10. A process according to any one of claims 1-9, characterized in that a hydrocarbon oil is used which has been obtained by oontactitg.a hydrocarbon oil with a nitrogen content above 25 ppmw having a boiling range entirely or sLtstantially above 350 C with a sulphided, fluorine containing catalyst comprising nickel and irolybdenum on a carrier. 11. A process according to any one of claims 1-10 substantially as hereinbefore described, with special reference to the Example. 12. Middle distillates prepared according to a process as clairred in any one of claims 1-11.

Inventors: JANSSEN, MARTINUS MARIA PETRUS, MAXWELL, IAN ERNEST, POTT, GERARD TJARKO, VAN DER LINDE, BEREND JACOB
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1983
Main classification: C10G47
IPC codes: B01J27, C10G47, B01J23