Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G35/00—Reforming naphtha
  • C10G35/04—Catalytic reforming
  • C10G35/06—Catalytic reforming characterised by the catalyst used
  • C10G35/065—Catalytic reforming characterised by the catalyst used containing crystalline zeolitic molecular sieves, other than aluminosilicates
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G2400/00—Products obtained by processes covered by groups C10G9/00 - C10G69/14
  • C10G2400/30—Aromatics

Definitions

• This invention relates to the preparation of streams containing recoverable benzene, toluene, and xylenes ("BTX") from initial by-product effluent streams that contain other components, notably monoolefins and diolefins.
• the invention concerns the removal by conversion of these other components which ordinarily prevent recovery by distillation or solvent extraction of benzene-toluene-xylenes aromatics from the streams.
• it concerns a low severity process for treating the by-product streams with a specified catalyst, and under defined reaction conditions, both to produce benzene-toluene-xylenes from the initial stream and to reduce or eliminate those components that otherwise would interfere with the economic recovery of these aromatics from the streams.
• the total reactor effluent will contain not only the desired olefin or diolefin, but a variety of other components, ranging from methane gas to high boiling polycyclic hydrocarbons.
• These by-products are conventionally separated, usually by distillation and/or absorption, so as to concentrate the main desired products for ultimate recovery, and to produce one or more by-product effluent streams.
• the by-product effluents contain a mixture of hydrocarbon types, including paraffins, monoolefins, diolefins,. aromatics, cyclics, and various substituted and polynuclear aromatics. Unless the by-product effluent stream or streams contains a particularly valuable or desirable component, making removal economical, the by-product effluent streams are of only limited utility.
• the lighter gases are useful only as . fuel, while the heavier, normally liquid, components usually termed "dripolene,” if not hydrogenated and then subjected to BTX extraction, are customarily either burned locally as fuel or else hydrogenated to saturate the unstable diolefins, and then blended with other gasoline fractions as motor fuel.
• a further object is to provide a process for treating such by-product effluent stream in a simplified, low severity, operation so as both to produce benzene-toluene-xylenes (BTX), and, simultaneously, to decrease the content of interfering components.
• Still another object is to remove those monoolefins and diolefins which have heretofore interfered with the solvent extraction of BTX from dripolene and the like.
• a stream from which benzene, toluene, and xylenes may be recovered readily is prepared by contacting a pyrolitic hydrocarbon cracking by-product effluent stream, containing substantial amounts of interfering monoolefins and diolefins, with a silicalite molecular sieve catalyst under low severity hydrocarbon processing conditions.
• a silicalite molecular sieve catalyst under low severity hydrocarbon processing conditions.
• a further important advantage of the invention resides in its ability to process any of a variety of the by-product effluent streams from pyrolitic cracking processes.
• these by-product effluent streams customarily include a C 4 fraction composed predominantly of butanes, butenes, and butadiene; a C 5 fraction composed mainly of pentanes, pentenes, pentadienes and cyclic C 5 compounds; a C 6 -C 8 "dripolene" fraction containing BTX aromatics together with interfering olefins (i.e., having a similar boiling range): and a C 9 -plus fraction, including some BTX along with higher alkylated benzenes and polynuclear aromatics and aliphatics.
• Each of these streams, plus others that may be present in a particular plant may be processes according to the invention.
• silicalite catalyst of the present invention is described in Grose et al. U.S. 4,061,724, and its structure is described in an article by Flanigen et al., "Silicalite, a new hydrophobic crystalline silica molecular sieve," Nature 271 512 (9 February 1978). It is a crystalline silica polymorph having identifiable X-ray diffraction characteristics and other properties that have been described in the two references above. An interpretation of the descriptive data is included in an article by Olson et al., "Chemical and physical properties of the ZSM-5 substitutional series," J. Catal., 61 (1980).
• silicalite may exist in two crystallographically distinct forms, termed, “silicalite-l” and “silicalite-2,” according to Bibby, "NH4-tetra-alky1 ammonium system in the synthesis of zeolites," Nature, 285, 3-31 (1 May 1980).
• the thermal pyrolysis, or cracking, of petroleum fractions may utilize as feed stocks hydrocarbons such as ethane, LPG (li q uefiled petroleum gas, chiefly propane with a few percent butanes), naphtha, heavy gas oil, or crude petroleum oil. These are subjected to controlled high temperature, low pressure, short time, pyrolitic cracking to produce the desired product or products. Thereafter the reactor effluent is subjected to a combination of condensation, fractional distillation, absorption, and perhaps other unit operations, to segregate various effluent streams enriched in one or more desirable components.
• the precise arrangement of product recovery streams forms no part of the present invention, and indeed it is probable that no two pyrolitic cracking plants utilize the same recovery scheme.
• the reactor effluent liquid may be subjected to fractional distillation to separate one or more fractions rich in benzene (B.P. 80.103°C.), toluene (B.P. 110.623°.), and/or the xylenes, namely ethylbenzene (B.P. l36.l87°C), p-xylene (B.P. 138.348°C.), m-xylene (B.P. 139. 102°C.), and o-xylene (B.P. 144,414°C.).
• This fraction, or fractions is desirably solvent extracted, as for example by the Udex or Sulfolane process, to recover the BTX aromatic/ aromatics.
• solvent extraction is ineffective to extract the aromatics from the remaining aliphatics, inasmuch as solvents selective for aromatics will also extract many olefins and diolefins.
• the diolefins and the aromatics cannot be separated by fractional distillation; for example, benzene, with a boiling point of 80.103°C., is not easily distilled from the 2,4 hexadienes, which boil at about 80.0°C.
• the various dimethylpentenes boil within a range of 72.2°C. to 85.0°C.
• the total reactor effluent may be segregated into a predominantly gaseous fraction including recoverable ethylene and propylene; a crude C 4 fraction, a distillation cut which includes hydrocarbons with primarily four carbon atoms each; a crude C 5 fraction, another distillation cut which primarily contains hydrocarbon molecules with five carbon atoms each, and generally containing a large quantity of unsaturated and cyclic compounds, including olefins and lesser amounts of C 4 's and ligher, C 6 's and heavier; a C 6 -C 8 fraction, sometimes referred to as pyrolysis gasoline or dripolene; and a Cg plus fraction, a heavier distillation cut which primarily includes hydrocarbons with at least nine carbon atoms, along with lesser amounts of C 5 -C 8 hydrocarbons.
• the C 9 fraction generally is produced as the distillation bottoms from the processing of dripolene to remove pyrolysis gasoline, and contains components as widely varying as styrene, ethyl- toluenes, and trimethylbenzenesto heavier compounds including ethylnaphthalene, diphenyl, and dimethylnaphthalene.
• compositions may vary quite widely, depending upon the initial feed to the pyrolitic cracking unit, the type of pyrolitic cracking unit, conditions in the pyrolitic unit, and the type and conditions of the product recovery section.
• the by-product effluent streams may likewise be blended with each other where this is desired, or may include recycle components from elsewhere in the product recovery section.
• silicalite a newly discovered crystalline silica polymorph described in Grose et al. U.S. 4,061,724 and in the other references cited previously. It consists of silica, but unlike many of the more common forms of silica, has an open porous structure, with a pore diameter of about 6 Angstrom units, and a pore volume of about 0.18 cc/gram as determined by adsorption. It has a density (as-synthesized) of 1.99 + 0.05 g/cc. Its refractive index is 1.48 + 0.01 as synthesized, or 1.39 + 0.01 after calcining at 600°C. for one hour.
• the X-ray powder diffraction pattern of silicalite (600°C. calcination in air for one hour) has as its six strongest lines (i.e., interplanar spacings) those set forth in the table below, where "S” is strong, and "VS” is very strong:
• silicalite After 600°C. calcination and washing with 1 N HC1 shows that it consists of Si0 2 , with only insignificant impurities.
• Alumina a common impurity, is present to the extent of less than 1 aluminum atom per unit cell of 92 Si atoms.
• Silicalite exhibits essentially no detectible ion exchange properties, in contrast to the conventional zeolitic molecular sieves.
• Silicalite is readily prepared by the procedure of the Grose et al. patent. This involves the hydrothermal crystallization of.a reaction mixture comprising water, a source of silica, and an alkylonium compound at a pH of 10 to 14 to form a hydrous crystalline precursor, and subsequently calcining that precursor to decompose aklylonium moieties. Thereafter, the calcined precursor is desirably washed to remove any metals or trace contaminants.
• silicalits When used in the present process, silicalits may be employed either alone or in intimate admixture with independently active catalytic components, as for example the noble metals such as platinum, or other catalytically active metals such as molybdemun, vanadium, zinc, etc.
• independently active catalytic components as for example the noble metals such as platinum, or other catalytically active metals such as molybdemun, vanadium, zinc, etc.
• the techniques of introducing catalytically active metals to a molecular sieve zeolite are disclosed in the literature, and with the exception of cation exchange, preexisting metal incorporation techniques are suitable. See, for example, Rabo et al. U.S. 3,236,761 and U.S. 3,236,762.
• silicalite catalyst depends on the type of catalytic reactor being employed.
• Silicalite by itself is a fine-grain granule or powder, and is desirably compacted into a more readily usable form (e.g., larger agglomerates), usually with a silica or alumina binder for fluidized bed reaction, or pills, prills, spheres, extrudates, or other shapes of controlled size to accord adequate catalyst-reactant contact.
• the catalyst may be employed either as a fluidized catalyst, or in a fixed or moving bed, and in one or more reaction stages.
• reaction conditions are low severity as compared with many preexisting processes.
• conversion parameters while broad, may be selected to provide a high degree of versatility, depending upon the feed composition and on the desired product quality.
• the pressure almost uniquely, is desirably quite low. Atmospheric pressure operation has been used successfully in the laboratory, but under specific conditions may be as high as 100 atmospheres or more. A desirable range is from atmospheric pressure to about 7 atmospheres. High pressures facilitate hydrogenation; lower pressures facilitate dehydrocyclization. The optimum pressure will therefore depend on process economics, considering whether it is more desirable to hydrogenate olefins than to produce a high yield of BTX aromatics.
• Process stream flow rate as expressed in units of weight hourly space velocity (WHSV), or weight of hydrocarbon feed per unit weight of catalyst, is suitably within the range of about 0.1 to about 20, more desirably about 0.5-5.0.
• WHSV weight hourly space velocity
• High WHSV's permit more economic plant construction, while lower WHSV's permit more complete reaction at given temperature- pressure conditions.
• a gaseous or gasifiable diluent may be introduced along with the hydrocarbon feed to the silicalite catalyst.
• This diluent may be inert, typified by steam, nitrogen or a low boiling paraffin, or may be reactive with the feed under catalysis conditions (e.g., hydrogen).
• Hydrogen is particularly desirable as it minimizes coke formation and deposition on the catalyst, with resulting premature deactivation, and also facilitates hydrogenation. As demonstrated below, however, the technique of the present invention need not utilize hydrogen.
• diluent/hydrocarbon molar (gas volume) ratios optimally, of from 0.1 to about 10 may be employed.
• the catalyst be regenerated, either periodically or continuously, to remove the carbonaceous coke-like deposits from the catalyst.
• a portion of the catalyst is continuously withdrawn from the reactor and then subjected to regeneration by combustion with air or other oxygen containing gas, after which it is continuously recycled to the reactor.
• the removal of catalyst followed by regeneration may be effected either continuously or periodically.
• a fixed bed operation it is generally desirable that two or more reactors be used in parallel, so that when one is processing the hydrocarbon feed, the other is out of service and being regenerated. Regeneration conditions of approximately 450-650°C., preferably 500-600°C. may be employed.
• a C 9 plus by-product hydrocarbon effluent from the thermal pyrolysis unit was reacted over 37g of 1/16 inch extrudates of silicalite with a 20% alumina binder.
• the reaction vessel was a 3/4 inch OD stainless steel tubular reactor.
• reaction pressure was ambient; the reaction temperature was approximately 503°C.; and the space velocity of the feed varied from 0.57-0.69 g/feed/g catalyst/hr.
• the feed had the following analysis:
• the gas samples were analyzed on a Hewlett Packard 5830A gas chromatograph equipped with a thermal conductivity detector.
• the thermal conductivity detector temperature was set at 250°C., and the column temperature was ambient (approximately 20-22°C.).
• Gas samples were injected into the column off-line, through an eight port gas switching valve, via a gas syringe.
• the sample gas volume was approximately 0.3cc; the carrier gas rate was 30cc/min of helium.
• Liquid samples for both product and feed were analyzed on a Hewett Packard 5730A gas chromatograph, using a 5705A thermal conductivity detector.
• the detector temperature was set at 250°C.
• the column was maintained in an oven, with a temperature programmed form 55°C. to 190°C. at 4°C./min; the injector temperature was 250°C.
• a sample size of approximately 2 ml. was used, and the helium carrier gas rate was 30 cc/min.

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• 1983
  • 1983-04-29 EP EP83200610A patent/EP0093475A1/en not_active Ceased
  • 1983-04-30 JP JP7496383A patent/JPS58203923A/ja active Pending

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