Hydroisomerisation of a predominantly n-paraffin feed to produce high purity solvent compositions

Abstract: A process for the hydroisomerization of a predominantly C 8 -C 20 n-paraffinic feed to produce a high purity C 8 -C 20 paraffinic solvent composition having superior low temperature properties, and low viscosities. The feed is contacted, with hydrogen, over a dual functional catalyst to hydroisomerize and convert the feed to a product comprising a mixture of n-paraffins and isoparaffins, the isoparaffins component of which contains greater than 50 percent of mono-methyl species, with the molar ratio of isoparaffins : n-paraffins ranging from 0.5:1 to 9:1.

Description: This invention relates to a hydroisomerization process for the production, from paraffin feeds, of high purity paraffinic solvent compositions characterized as mixtures of C 8 -C 20 n-paraffins and isoparaffins, with the isoparaffins preferably containing predominantly methyl branching, having an isoparaffin:n-paraffin ratio sufficient to provide products having superior low temperature properties and low viscosities. Paraffinic solvents provide a variety of industrial uses. For example, NORPAR solvents, several grades of which are marketed by Exxon Chemical Company, e.g., are constituted almost entirely of C 10 -C 15 linear, or normal paraffins (n-paraffins). They are made by molecular sieve extraction of kerosene, for example via the ENSORB process. These solvents, because of their high selective solvency, low reactivity, mild odor and relatively low viscosity, are used in aluminum rolling oils, as diluent solvents in carbonless copy paper, and in spark erosion machinery. They are used successfully in pesticides, both in emulsifiable concentrates and in formulations to be applied by controlled droplet application, and can even meet certain FDA requirements for use in food-related applications. The NORPAR solvents, while having relatively low viscosity, have relatively high pour points. If a wider than C 15 n-paraffin cut were to be employed as feed for molecular sieve extraction then, since the C 15 + n-paraffins have low melting points, this will only worsen the pour point. Three typical grades of NORPAR solvents are NORPAR 12, NORPAR 13, and NORPAR 15; the numerals 12, 13, and 15 respectively, designating the average carbon number of the paraffins contained in the paraffinic mixture. Solvents with an average carbon number of 14 rarely meet the specifications of the specialty solvent market, and consequently such solvents are generally downgraded and sold as fuel. The NORPAR 15 solvent, while it generally meets the specifications of the specialty solvent market, has a relatively high melting point and must be stored in heated tanks. Solvents constituted of mixtures of highly branched paraffins, or isoparaffins, with very low n-paraffin content, are also commercially available. For example, several grades of ISOPAR solvents, i.e., isoparaffins or highly branched paraffins, are supplied by Exxon Chemical Company. These solvents, derived from alkylate bottoms (typically prepared by alkylation), have many good properties; e.g., high purity, low odor, good oxidation stability, low pour point, and are suitable for many food-related uses. Moreover, they possess excellent low temperature properties. However, the ISOPAR solvents have relatively high viscosities, e.g., as contrasted with the NORPAR solvents. There is need of a solvent which possesses substantially the desirable properties of both the NORPAR and ISOPAR solvents, but particularly a solvent having the general combination of low viscosity (such as that of the NORPAR solvents) and low temperature properties (such as those of the ISOPAR solvents). US-A-4855530 discloses and claims an isomerization process in which a hydrocarbon feedstock comprising C 10 + n-paraffins wherein the aromatic content of the feedstock is less than about 20 weight per cent of the feedstock, is contacted under isomerization conditions with a catalyst comprising a large pore zeolite selected from the group consisting of ZSM-20 and zeolite Y having a silica/alumina ratio greater than 10:1 and a hydrocarbon absorption capacity of at least 6% by weight at 50°C and a hydrogenation component being preferably a Group metal to convert at least a portion of said n-paraffin to iso-paraffins. FR-A-2137490 and its US counterpart, US-A-3709817, disclose a hydrocarbon conversion process which comprises contacting a paraffin hydrocarbon containing at least 6 carbon atoms with hydrogen, a fluorided Group VII-B or VIII metal-alumina catalyst and water wherein water is present during said contacting in an amount of from about 3.5 x 10 -5 to 5 x 10 -4 gram mole of water per hour per gram of said catalyst. Martens et al "Selective Isomerization of Hydrocarbon chains on External Surfaces of Zeolite Crystals"; Angewandte Chemie International Edition in English, vol 34(22), 1995, pages 2528-2530, disclose contacting the external surfaces ofplatinum-impregnated zeolites with n-alkanes and alkylcycloalkanes at temperatures from 430 to 495°K. The zeolites employed included ZSM-22 and USY, and the feedstocks included heptadecane. Isomerization to products including branched isomers was observed. Some of the branched isomers included mono-branched isoheptadecane. Salakh et al: "The Composition of Isomenzation Products of Higher n-Alkanes": Chemistry and Technology of Fuels and Oils, vol 8 (5-6), 1972, pages 328-330; XP001028905; disclose studies of the isomerization of C 10 - C 18 alkanes in the presence of a catalyst of MoO 3° .Al203 at 430°C a space velocity of 0.8h -1 and a hydrogen pressure of 30 atmospheres(2.069 bar). The hydrogen: hydrocarbon molar ratio was 50:1. The resulting hydroisomerates included n-alkanes, monosubstituted and disubstituted hydrocarbons, and the monosubstituted hydrocarbons included methyl-substituted derivatives. Molar ratio of iso- to n-paraffins was approximately 1:1 - 3:1 with a monomethyl content of produced isoparaffins of over 50 %. WO 97/21787, which was published after the priority and application dates of the present patent application, discloses a high purity solvent composition which comprises a mixture of paraffins of carbon number ranging from about C 8 to about C 20 , has a molar ratio of isoparaffins:n-paraffins ranging from about 0.5:1 to about 9:1 and the isoparaffins of the mixture contain greater than 50% of the mono-methyl species, based on the total weight of the isoparaffins of the mixture. WO 97/21787 also discloses a process for the production of a high purity solvent composition as described in the previous paragraph which comprises contacting a C 5 + paraffinic feed, with hydrogen, over a dual functional catalyst to produce hydroisomerization and hydrocracking reactions and 700°F+ (371.1°C+) conversion levels ranging from about 20% to about 90% on a once through basis based on the weight of total feed, to produce a crude fraction boiling between about C 5 and 1050°F, (565.6°C) topping said crude fraction by atmospheric distillation to produce a low boiling fraction having an upper end boiling point between about 650°F (343.3°C) and about 750°F (398.9°C) and recovering from the low boiling fraction said high purity solvent composition. The present invention provides a process for the production of high purity solvent compositions having superior low temperature properties and low viscosities which comprises: contacting in a reaction zone a feed constituted predominantly of n-paraffins of carbon number ranging from C8 to C20 with hydrogen over a dual function catalyst comprised of a Group VIII metal component catalytically active for dehydrogenation of the paraffinic feed and an amorphous silica-alumina component active in producing olefin cracking and hydroisomerization reactions at hydroisomerization conditions including a temperature in the range of from 204.4 to 454.4°C (400 to 850°F), a pressure in the range of from 790.9 kPa to 10.44 MPa (100 to 1500 psig), a hydrogen treat gas rate of from 178 to 1780 m3 H2/m3 feed, and a space velocity in the range of from 0.5 to 10 w/h/w to hydroisomerize and convert the feed to an effluent comprising a mixture of isoparaffins containing more than 50% of mono-methyl species with minimum formation of branches having substituent groups of carbon number exceeding 1, based on the total weight of isoparaffins in the mixture; and recovering as a product of said reaction zone a high purity paraffinic solvent composition of carbon number ranging from C 8 to C 20 rich in isoparaffins which contain more than 50% of said monomethyl species and having a molar ratio of isoparaffins:n-paraffins in a range of from 0.5:1 to 9:1. Preferably, the isoparaffins of the product mixture contain greater than 70 percent of the mono-ethyl species, based on the total weight of isoparaffins in the mixture. The product solvent composition has an isoparaffin:n-paraffin ratio ranging from 0.5:1 to 9:1, preferably form 1:1 to 4:1. The product solvent composition preferably within a range of from 176.7 to 343.3°C (320 to 650°F), and more preferably within a range from 176.7 to 287.8°C (350 to 550°F). To prepare different solvent grades, the paraffinic solvent mixture may be generally fractionated into cuts having narrow boiling ranges, e.g. 55.6°C (100°F) or 27.8°C (50°F) boiling ranges. In the hydroisomerisation reaction, a major concentration of the paraffinic feed is converted into isoparaffins which contain one or more methyl branches, with little or no cracking of the molecules. The carbon number distribution of the molecular constituents of the products is essentially the same as that of the feed. A feed constituted of an essentially C 8 to C 20 paraffinic mixture of n-paraffins will produce a product rich in C 8 to C 20 isoparaffins which contain greater than 50 percent mono-methyl paraffins, and preferably greater than 70 percent mono-methyl paraffins, based on the weight of the product. A feed constituted of an essentially C 10 -C 16 paraffinic mixture of n-paraffins will produce a product constituted essentially of a C 10 -C 16 paraffinic mixture of isoparaffins which contains greater than 50 percent mono-methyl paraffins, and preferably greater than 70 percent mono-methyl paraffins, based on the weight of the product. The solvent product has an isoparaffin:n-paraffin ratio ranging from about 0.5:1 to about 9:1, preferably about 1:1 to about 4:1, and preferably boils within a range of from about 320°F (160°C) to about 650°F (343.3°C), more preferably from about 350°F (176.7°C) to about 550°F (287.8°C). The properties of these solvents e.g., viscosity, solvency and density, are similar to NORPAR solvents of similar volatility but have significantly improved low temperature properties (e.g., lower pour or lower freeze points). These solvents also have significantly lower viscosities than ISOPAR solvents of similar volatility. In fact, these solvents combine many of the most desirable properties found in the NORPAR and ISOPAR solvents. The solvents made by the process of this invention have the good low temperature properties of ISOPAR solvents and the low viscosities of the NORPAR solvent; and yet maintain most of the other important properties of these solvents. The C 8 -C 20 paraffinic feed, or C 10 -C 16 paraffinic feed, is preferably one obtained from a Fischer-Tropsch process; a process known to produce substantially n-paraffins having negligible amounts of aromatics, sulfur and nitrogen compounds. The Fischer-Tropsch liquid, and wax, is characterized as the product of a Fischer-Tropsch process wherein a synthetic gas, or mixture of hydrogen and carbon monoxide, is processed at elevated temperature over a supported catalyst comprised of a Group VIII metal, or metals, of the Periodic Table Of The Elements (Sargent-Welch Scientific Company, Copyright 1968), e.g., cobalt, ruthenium, iron, etc., especially cobalt which is preferred. A distillation showing the fractional make up (±10 wt.% for each fraction) of a typical Fischer-Tropsch reaction product is as follows: Boiling Temperature Range Wt.% of Fraction IBP - 320°F (160°C) 13 320 - 500°F (160 - 260°C) 23 500 - 700°F (260 - 371.1°C) 19 700 - 1050°F (371.1 - 565.6°C) 34 1050°F+ (565.6°C) 11 100 The NORPAR solvents, which are predominantly n-paraffins, can be used as feeds and upgraded to solvents having lower pour points. A solvent with an average carbon number of 14 is, e.g., a suitable and preferred feed, and can be readily upgraded to solvents having considerably lower pour points, without loss of other important properties. The paraffinic feed is contacted, with hydrogen, at hydroisomerization conditions over a bifunctional catalyst, or catalyst containing a metal, or metals, hydrogenation component and an acidic oxide support component active in producing hydroisomerization reactions. Preferably, a fixed bed of the catalyst is contacted with the feed at temperature ranging from about 400°F (204.4°C) to about 850°F (454.4°C), preferably from about 550°F (287.8°C) to about 700°F (371.1°C), and at pressures ranging generally from about 100 pounds per square inch gauge (psig) to about 1500 psig, preferably from about 250 psig (17.24 bar G) to about 1000 psig (68.97 bar G) sufficient to hydroisomerize, but avoid cracking, the feed. Hydrogen treat gas rates range from about 1000 SCFB (177.9 m 3 /m 3 ) to about 10,000 SCFB (1778.9 m 3 /m 3 ), preferably from about 2000 SCFB (355.8 m 3 /m 3 ) to about 5000 SCFB (889.5 m 3 /m 3 ), with negligible hydrogen consumption. Space velocities range generally from about 0.5 W/Hr/W to about 10 W/Hr/W, preferably from about 1.0 W/Hr/W to about 5.0 W/Hr/W. The active metal component of the catalyst is preferably a Group VIII metal, or metals, of the Periodic Table Of The Elements (Sargent-Welch Scientific Company Copyright 1968), suitably in sulfided form, in amount sufficient to be catalytically active for dehydrogenation of the paraffinic feed. The catalyst may also contain, in addition to the Group VIII metal, or metals, a Group IB and/or a Group VIB metal, or metals, of the Periodic Table. Generally, metal concentrations range from about 0.05 or 0.1 percent to about 20 percent, based on the total weight of the catalyst (wt%), preferably from about 0.1 wt. percent to about 10 wt. percent. Exemplary of such metals are such non-noble Group VIII metals as nickel and cobalt, or mixtures of these metals with each other or with other metals, such as copper, a Group IB metal, or molybdenum, a Group VIII metal. Palladium and platinum are exemplary of suitable Group VIII noble metals. The metal, or metals is incorporated with the support component of the catalyst by known methods, e.g., by impregnation of the support with a solution of a suitable salt or acid of the metal, or metals, drying and calcination. The catalyst support is constituted of metal oxide, or metal oxides, components at least one component of which is an acidic oxide active in producing olefin cracking and hydroisomerization reactions. Exemplary oxides include silica, silica-alumina, clays, e.g., pillared clays, magnesia, titania, zirconia, halides, e.g., chlorided alumina. The catalyst support is preferably constituted of silica and alumina, a particularly preferred support being constituted of up to about 35 wt.% silica, preferably from about 2 wt.% to about 35 wt.% silica, and having the following pore-structural characteristics: Pore Radius, Å (nm) Pore Volume 0-300 (0 - 30) >0.03 ml/g 100-75,000 (10 - 7,500) <0.35 ml/g 0-30 (0 - 3.0 <25% of the volume of the pores with 0-300 Å (0 - 30 nm) radius 100-300 (10 - 30) <40% of the volume of the pores with 0-300 Å (0 - 30 nm) radius The base silica and alumina materials can be, e.g., soluble silica containing compounds such as alkali metal silicates (preferably where Na 2 O:SiO 2 = 1:2 to 1:4), tetraalkoxy silane, orthosilic acid ester, etc.; sulfates, nitrates, or chlorides of aluminum, alkali metal aluminates; or inorganic or organic salts of alkoxides or the like. When precipitating the hydrates of silica or alumina from a solution of such starting materials, a suitable acid or base is added and the pH is set within a range of about 6.0 to 11.0. Precipitation and aging are carried out, with heating, by adding an acid or base under reflux to prevent evaporation of the treating liquid and change of pH. The remainder of the support producing process is the same as those commonly employed, including filtering, drying and calcination of the . support material. The support may also contain small amounts, e.g., 1-30 wt.%, of materials such as magnesia, titania, zirconia, hafnia. Support materials and their preparation are described more fully in U.S. Patent No. 3,843,509 incorporated herein by reference. The support materials generally have a surface area ranging from about 180-400 m 2 /g, preferably 230-375 m 2 /g, a pore volume generally of about 0.3 to 1.0 ml/g, preferably about 0.5 to 0.95 ml/g, bulk density of generally about 0.5-1.0 g/ml, and a side crushing strength of about 0.8 to 3.5 kg/mm. The hydroisomerization reaction is conducted in one or a plurality of reactors connected in series, generally from about 1 to about 5 reactors; but preferably the reaction is conducted in a single reactor. The paraffinic feed is fed, with hydrogen, into the reactor, or first reactor of a series, to contact a fixed bed of the catalyst at hydroisomerization reaction conditions sufficient to hydroisomerize and convert at least a portion of the feed to products suitable as high purity paraffinic solvent compositions, as previously described. If desired, the hydroisomerized product can be hydrotreated to remove trace amounts of impurities, if any, olefins, etc. This type of treatment may be sometimes desirable to render the product suitable to meet FDA specifications, or the like. The following exemplifies the more salient features of the invention. All parts, and percentages, are given in terms of weight unless otherwise specified. Example A vaporous feed containing 87.7 wt.% nC 14 was passed, with hydrogen at 1800 SCF/B (320.2m 3 /m 3 ) into a reactor and hydroisomerized over a fixed bed of a Pd catalyst (0.3 wt.% Pd on an amorphous silica-alumina support consisting of about 20 wt.% bulk SiO 2 + 80 wt.% Al 2 O 3 ), with minimal cracking of the feed, to produce a product having substantially the same carbon number distribution as the feed, but with considerably lower viscosities, and better low temperature properties than that of the feed. The carbon distribution numbers (C-No.) of the feed are given as follows: nC 12 0.045 wt.% nC 13 4.444 wt.% nC 14 87.697 wt.% nC 15 7.639 wt.% nC 16 0.175 wt.% The reaction was conducted with gradual increase of the space velocity of the entering feed, and temperature, to produce liquid products having the freeze points, and C 12 + yields given below: Space Velocity V/H/V Temp, (°F) °C %nC 14 In Product Freeze Point, °C C 12 + Yield wt.% on Feed 34.3 (636) 335.6 51.5 -4 99.1 34.8 (646) 341.1 39.1 -6.5 98.2 35.0 (656) 346.7 28.1 -11.5 96.6 37.1 (666) 352.2 21.1 -15.5 92.1 34.0 (667) 352.8 15.6 -20 89.3 40.2 (677) 358.3 12.3 -23.5 87.0 A complete yield workup of the liquid product obtained at a freeze point of -20°C is given in Table 1A. A workup of the product fractions obtained from the 15/5 distillation described above is given in Table 1B.

Claims: A process for the production of high purity solvent compositions having superior low temperature properties and low viscosities, which process comprises: contacting in a reaction zone a feed constituted predominantly of n-paraffins of carbon number in the range of from C8 to C20 with hydrogen over a dual function catalyst comprised of a Group VIII metal component which is active for the dehydrogenation of the paraffinic feed and an amorphous silica-alumina support active in producing olefin cracking and hydroisomerization reactions at hydroisomerization conditions including a temperature in the range of from 400 to 800 °F (204 to 427 °C) and a pressure in the range of from 100 to 1500 psig (790.9 kPa to 10.44 MPa), a hydrogen treat gas rate of from 1,000 to 10,000 scf/b (178 to 1780 m3 H2/m3 feed), and a space velocity in the range of from 0.5 to 10 w/h/w to hydroisomerize and convert the feed to an effluent comprising a mixture of isoparaffins containing more than 50 percent of mono-methyl species with minimum formation of branches having substituent groups of carbon number exceeding 1, based on the total weight of isoparaffins in the mixture; and recovering from said reaction zone effluent a high purity paraffinic solvent composition of carbon number in the range of from C8 to C20 rich in isoparaffins and which contains more than 50 % of said monomethyl species and having a molar ratio of isoparaffins to n-paraffins in the range of from 0.5:1 to 9:1. The process of Claim 1, wherein the feed is constituted predominantly of n-paraffins of carbon number ranging from C 10 to C 16 , and a product is recovered having carbon numbers ranging from C 10 to C 16 . The process of claim 1 or claim 2 wherein the feed is hydroisomerized in the temperature range 550°F to 700°F (288 to 371°C), at pressures ranging from 250 psig to 1000 psig (1.83 to 7.0 MPa), hydrogen treat gas rates ranging from 2000 SCFB to 5000 SCFB (356 to 890 std m 3 /m 3 ),, and at space velocities ranging from 1.0 W/Hr/W to 5.0 W/Hr/W. The process of any one of claims 1 to 3 wherein the catalyst is comprised of a Group IB or Group VIB metal, or metals, or both a Group IB and VIB metal, or metals in addition to the Group VIII metal, or metals. The process of Claim 4, wherein the concentration of the metal, or metals, ranges from 0.1 percent to 20 percent, based on the total weight of the catalyst, the Group IB metal is copper, the Group VIB metal is molybdenum, and the Group VIII metal is palladium, platinum, nickel or cobalt. The process of any one of claims 1 to 5 wherein a high purity paraffinic solvent composition product is recovered which boils at a temperature in the range 320°F to 650°F (160 to 343°C). The process of any one of claims 1 to 6 wherein a high purity solvent composition product is recovered and which is characterized as a mixture of paraffins of carbon number ranging from C 10 to C 16 , has a molar ratio of isoparaffins n-paraffins ranging from 1:1 to 4:1 and the isoparaffins of the mixture contain greater than 70 percent of the monomethyl species, based on the weight of the mixture.

Inventors: RYAN DANIEL FRANCIS, SILVERBERG STEVEN EARL, WITTENBRINK ROBERT JAY, RYAN, DANIEL FRANCIS, SILVERBERG, STEVEN EARL, WITTENBRINK, ROBERT JAY
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
Application year: 1997
Main classification: C10G45
IPC codes: C10G45, B01J23