Lead free motor fuel production

[57] ABSTRACT

A two-stage reforming process for the production of high-octane unleaded motor fuel from low-octane naphthas. The paraffinic raffinate from an intermediate extractive distillation step is reformed over a steam-active catalyst. Several product streams produced during the various process steps are combined to produce a high-octane motor fuel.

Claims, 1 Drawing Figure

883-418

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3,883,418

LEAD FREE MOTOR FUEL PRODUCTION

This invention relates to a hydrocarbon conversion process. More particularly, this invention relates to the treatment of naphtha stocks containing naphthenes and paraffins for the manufacture of high-octane number motor fuels or motor fuel components.

The development and introduction by automotive engine manufacturers of high-compression, highperformance engines has required the petroleum industry to devote a considerable portion of its research efforts to the problem of discovering routes to highoctane gasoline suitable for use as a motor fuel. As the performance characteristics of the engines increase, higher octane motor fuels are required and slight variances in octane numbers become a critical parameter in an engine’s performance. For example, an octane difference in a motor fuel of as little as 2-3 numbers can be the difference between a quiet or a knocking engine. Historically, almost all other routes currently used commercially depend to some extent upon the use of lead alkyls such as tetraethyl lead as additives to improve antiknock characteristics of gasolines. However, the demand for clear, unpolluted air has placed an emphasis on developing high-octane gasolines that do not employ antiknock additives such as tetraethyl lead, which can pollute the air when expelled with the engine exhaust.

It is an object of this invention to provide a process for the conversion of hydrocarbon feedstocks.

It is another object of this invention to provide a process for producing high-octane motor fuel or motor fuel components from low-octane naphtha feedstocks.

These and other objects, aspects and advantages of the invention will be apparent from the disclosure, claims and attached drawing.

It has been discovered that the octane number of hydrocarbon feedstocks can be substantially increased without the necessity of adding lead-containing compounds such as tetraethyl lead by a combination treating process comprising dual-stage reforming of said feedstock. More particularly, in accordance with the invention, naphtha feedstocks containing paraffins and naphthenes are contacted with an acidic reforming catalyst in a first reaction zone under reforming conditions selected to effect selective dehydrogenation of naphthenes and formation of aromatics with a minimum of paraffin conversion. The liquid effluent reformate from the first reforming zone is subjected to fractional distillation to produce a light fraction boiling below about 1 10° F., an intermediate fraction boiling in the range of about 1 20° to about 260° F., and a heavy fraction boiling above about 260° F. The intermediate fraction from the fractional distillation zone is subjected to extractive distillation to produce a paraffinic raffinate and an aromatic extract. The paraffinic raffinate is contacted with a steam-active catalyst under reforming conditions selected to effect dehydrogenation and cyclization of paraffins and dehydrogenation of naphthenes. The effluent from the second reforming zone is blended with the light fraction from the fractional distillation zone, the heavy fraction from the fractional distillation zone, and the aromatic extract stream from the extractive distillation zone to produce high-octane number unleaded motor fuel or motor fuel components having an unleaded ASTM research octane number of at least about 95.

The process of this invention is particularly applicable to the treating of naphtha fractions boiling within the range of about 125° to 475° F. Although naphtha fractions produced by thermal or catalytic cracking may be processed, straight-run naphthas containing straight-chain and nonstraight-chain hydrocarbons are preferred. A typical naphtha fraction which is suitable for use in the practice of the invention will contain from 0 to 75 volume percent naphthenes; 0 to 50 percent aromatics; and from 3 to 90 percent paraffins, including normal paraffins and isoparaffins. Thus, a typical straight-run stock with a boiling range of about 140° to 450° F. may comprise about 40 volume percent naphthenes, 50 volume percent paraffins and 10 volume percent aromatics. The normal paraffinic components may consist of about 6 to 100 percent of normal paraffins. The naphthene component of such a stock will ordinarily comprise about equal proportions of 5 carbon ring compounds and 6 carbon ring compounds.

In the first reforming zone of the invention process, the reforming catalyst is selected from the group of catalysts which are highly selective is catalyzing isomerization of substituted 5 carbon rings to form 6 carbon rings and dehydrogenating 6 carbon rings to the corresponding aromatic hydrocarbons. The extent of the reaction in the first stage is limited so that the paraffins are largely unreacted. The catalyst and conditions employed in the first stage are such that the reaction is highly selective in promoting dehydrogenation and the reaction is accompanied by a minimum of cracking, splitting off of hydrocarbon radicals, and the formation of hydrocarbon gases. The result is that the gaseous products of the first stage reaction consist of at least 75 volume percent hydrogen and may typically comprise 95 volume percent hydrogen. To achieve maximum selectivity, the first stage reforming reaction is advantageously conducted in a manner short of complete reaction of the naphthene and with substantial freedom from the formation of carbonaceous deposits on the catalyst.

The reformed naphtha, liquid product from the first reforming stage, comprises aromatics, unreacted paraffins and a relatively small proportion of unreacted naphthenes. The reformed naphtha is then subjected to fractional distillation to produce a relatively lowboiling fraction having a boiling range below about 110° F., an intermediate fraction boiling in the range of about 120° to about 260° F., and a remaining relatively heavy fraction boiling above about 260° F. The intermediate fraction boiling within the range of about 1 20° to about 260° F. is then subjected to extractive distillation to produce a paraffinic raffinate and an aromatic extract. The paraffinic raffinate from the extractive distillation is subjected to further reforming in a second stage under conditions selected to effect dehydrogenation and cyclization of paraffins and dehydrogenation of residual naphthene from the first stage. Extensive cracking is avoided although some hydrocracking occurs, and there is a moderate formation of olefins. In the second reforming stage the naphthene and paraffin content of the naphtha is reduced and the aromatic content further increased.

The relatively low-boiling fraction and the relatively heavy fraction from the fractional distillation zone can be blended with the aromatic extract from the extractive distillation zone and the reformate from the second stage reforming step. In this case, a greater number of

3,883,418 barrels of naphtha are produced having a given octane number than are produced if all of the first stage reformate is charged to the second stage reformer. This is accounted for by the fact that the reformate from the first reforming zone consists of hydrocarbons which are not susceptible to improvement by further reforming but are converted to hydrocarbons boiling below the motor fuel distillation range.

The catalyst employed in the first reforming stage of the process of this invention can be any dual function isomerization/dehydrogenation catalyst conventionally employed in the reforming of hydrocarbon feedstocks. A particularly preferred catalyst is platinum on alumina containing from about 0.1 to about 5 weight percent platinum. Catalysts comprising about 0.5 percent platinum on gamma-alumina and 0.6 percent platinum on eta-alumina are particularly effective in the process of this invention. The first reforming stage is conducted under a pressure in the range of about 200 to 700 psig at temperatures in the range of about 850° to 975° F. and with space velocities in the range of about 3 to about 20 volumes of feedstock per hour per volume of catalyst. The operation is preferably conducted in the presence of hydrogen recycle gas containing about 80 to 95 percent hydrogen which is recycled at a rate in the range of about 4,000 to 8,000 cubic feet per barrel of liquid charged. In a typical operation, the naphtha is contacted with a platinum-alumina catalyst at a temperature of 875° to 975° F., a pressure of 250 psig, a space velocity of 3 volumes of oil per hour per volume of catalyst, and with a recycle gas rate of 8,000 cubic feet per barrel of naphtha.

A unique feature of the invention is the use, in the second reforming zone, of a steam-stable catalyst composition consisting essentially of at least Group VIII metal or metal compound capable of reduction selected from the group consisting of nickel, platinum, ruthenium, rhodium, palladium, osmium, iridium and mixtures thereof; at least one tin group metal or metal compound capable of reduction selected from the group consisting of tin, germanium or lead; and a support material selected from the group consisting of at least one Group 11 metal aluminate or aluminate spinel. A presently preferred catalyst composition comprises platinum-tin-zinc aluminate.

The steam-active catalysts which are employed in the second reforming stage of the invention can be prepared by any means known in the art. Preferably, the Group II metal aluminate or aluminate spinel support materials will be calcined at a temperature in the range of about 700° to about 2,500° F , preferably in the range of about 1750° to about 2,300° F. for from about I to about 100 hours. The Group VIII metal content of the catalyst will generally be in the range of about 0.01 to about 5 weight percent, based on support, preferably in the range of about 0.1 to about I weight percent. The tin group content will normally be in the range of about 0.01 to about 5, preferably 0.1 to about 1, weight percent. Particularly preferred composites will additionally contain from about 0.01 to about 10, preferably about 0.1 to about 5, weight percent of at least one alkali metal or alkaline earth metal compound which can function to reduce cracking activity and stabilize the catalyst. A particularly effective catalyst is a zinc aluminate support containing a slight excess of zinc which has been impregnated with 0.4-().6 weight percent platinum and 0.4-1 weight percent tin.

The paraffinic raffinate from the extractive distillation zone is contacted in the second reforming zone with the steam-stable catalyst as described at temperatures in the range of about 750° to about 1,250° F., 5 preferably about 900° to about 1,050° F.; and at space velocities in the range of about 0.1 to about 10, preferably 0.5 to about 5, volumes of raffinate per hour per volume of catalyst. Pressures below 700 psig, e.g., atmospheric to about 500 psig, preferentially about 50 to 10 about 300 psig, are preferred. The second stage reforming operation is effected in the presence of steam with a steamrhydrocarbon mol ratio in the range of about 0.5 to about 30, preferably in the range of about 3 to about 20, being employed.

If desired, the second stage reforming operation can be conducted in an atmosphere of hydrogen and, accordingly, hydrogen-rich gas may be recycled at rates up to about 2,000 cubic feet per barrel of feed. Since the first reforming stage produces an excess of hydro20 gen, the excess can be directed to the second stage to supply at least a part of the hydrogen required therein and thereby supplement or supplant recycle of gas in the second reforming stage.

In a typical embodiment of the process of this inven2-5 tion, the paraffinic raffinate is contacted in the second reforming stage with a platinum-tin-zinc aluminate catalyst at a temperature of 1,040° to 1,080° F., a pressure of 65 psig, a space velocity in the range of about 0.5 to 1 volume of raffinate per volume of catalyst, a steam :³θ raffinate mol ratio in the range of 5-10:1, and a gas recycle rate of about 1-2 mols of hydrogen per mol of raffinate feed.

The accompanying drawing is a flow sheet of a process in which a full boiling range naphtha is processed ³⁵ for the production of high-octane motor fuel in accordance with the present invention.

Referring to the drawing, a naphtha fraction in the 125°-475° F. boiling range is introduced through line 1 to a first reforming zone SO. In first reforming zone ⁴⁰ 50, the naphtha feedstock is contacted with an acidic reforming catalyst to selectively convert naphthenes to aromatics with a minimum of paraffin conversion. The liquid naphtha reformate product is drawn off from the first reforming zone and passed through line 2 to first ⁴⁵ fractionation zone 55. In fractionation zone 55, the reformate is separated into a first fraction boiling below about 110° F., a second fraction boiling in the range of about 120° to about 260° F., and a third fraction boiling above about 260° F. The second or intermediate frac⁵⁰ tion boiling in the range of about 120° to about 260° F. is passed through line 5 to extractive distillation zone 60. In extractive distillation zone 60, operated conventionally as in, for example, U.S. Pat. No. 3,551,327, the intermediate fraction is separated into a paraffinic raffinate and an aromatic extract.

The paraffinic raffinate is drawn off from extractive distillation zone 60 and passed through line 7 to second reforming zone 65. In second reforming zone 65, the ₆₀ paraffinic raffinate is contacted with a steam-stable catalyst to effect dehydrogenation and cyclization of paraffins and dehydrogenation of naphthenes. The liquid reformate product from second reforming zone 65 is withdrawn through line 8 and passed to motor fuel ₆₅ blending zone 70, where it is combined with the light boiling reformate fraction produced in fractionation zone 55, the heavy fraction produced in fractionation zone 55 and the aromatic extract produced in extrac3,883,418 tive distillation zone 60, withdrawn through lines 3, 4, and 6, respectively, and blended to produce a highoctane gasoline product suitable as a motor fuel or motor fuel blending stock.

Illustrative of the practice of this invention, a straight-run naphtha having a boiling range of 200° to 400° F.; containing 20 volume percent aromatics, 29 volume percent naphthenes, and 51 volume percent paraffins; and having ASTM research octane number of 48 clear, is reformed with a commercial platinumalumina reforming catalyst containing about 0.375 weight percent platinum and about 0.9 weight percent chlorine on alumina under the conditions and with the results shown in Table I.

TABLE I

Reactor Inlet Temp.. °F.920

Reactor Inlet Pressure, psig450

Recycle Gas (86% hydrogen), cu.ft./barrel7000

Space Velocity, Vol. Naphtha/hr/Vol. Catalyst1.64

Yield of C\' Catalytic Reformate. Vol. %88.3

ASTM Research Octane Number of Catalytic86.1

Reformate, Clear

The catalytic reformate shown in Table I is fractionated to produce a first fraction boiling below about 100° F., an intermediate fraction boiling in the range of 1 20°-260° F. and a third fraction boiling above about 260° F. The low boiling fraction comprises 15 volume percent of the total reformate and has an ASTM research octane number of 86.6 clear. The intermediate boiling reformate comprises 45 volume percent of the total reformate and has an ASTM research octane number of 72.3 clear. The high boiling reformate comprises 40 volume percent of the total reformate and has an ASTM research octane number of 100.8 clear.

The intermediate boiling fraction is passed through an extractive distillation zone and separated to obtain a paraffinic raffinate and an aromatic extract. The paraffinic raffinate comprises 64.4 percent of the intermediate fraction and has an ASTM research octane number of 51.5 clear. The aromatic extract comprises 35.6 volume percent of the intermediate fraction, about 90 percent aromatics, and has an ASTM research octane number of 109.0 clear. The aromatic extract from the extractive distillation zone is combined with the high boiling fraction from the fractionation zone to provide a blending stock having an ASTM research octane number of 103.0 clear.

The paraffinic raffinate is reformed in a second stage in contact with a platinum-tin-zine aluminate catalyst at a temperature in the range of l,040°-l,080° F., a pressure of 65 psig, a space velocity of 0.5-1.0 volumes of oil per hour per volume of catalyst, in the presence of steam at a steamiraffinate ratio of 5-10:1, and from 1-2 mols of hydrogen per mol of raffinate feed, to produce a reformate having an ASTM research octane number equivalent of 100 clear at a yield of 66.1 volume percent of the raffinate feed.

The light boiling reformate from the fractional distillation zone, the combined stream of aromatic extract and heavy boiling reformate from the fractional distillation zone, and the reformate product from the second reforming zone are blended to produce a motor fuel stock having an ASTM research octane number in the range of 100-105 clear at a yield of 90.5 volume percent of the first stage reformate.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof.