US3104957A - Production of gas suitable for use as town gas - Google Patents

Description

United States Patent 3,104,957 PRODUCTION 65 GAS SUITABLE FOR USE AS TOWN GAS Hubert Thomas Porter, Arthur Knowles Renshaw, and

Peter Thomas White, all of Snnbury-on-Thames, England, assignors to The British Petroleum (Company Limited, London, England, a British joint-stock corporation No Drawing. Filed Mar. 11, 1958, Ser. No. 720,537 Claims priority, application Great Britain Mar. 29, 1957 6 flaims. (Cl. 48-197) This invention relates to the production of gas suitable for use as town gas from hydrocarbon fractions of petroleum origin.

Traditionally, town gas has been obtained from the carbonisation of coal, but it has also been proposed to prepare it from petroleum fractions. \Vhen using petroleum fractions as starting materials, it is particularly advantageous economically if the process used produces one or more other valuable hydrocarbon products at the same time, and accordingly, the present invention has among its objects to provide a process in which both town gas and a normally-liquid product suitable for use in gasoline production or as a source of aromatics are produced.

According to the present invention, a fraction of petroleum origin consisting of or containing non-aromatic hydrocarbons and boiling within the gasoline or naphtha range is contacted at elevated temperature with a dehydrogenation and dehydrocyclisation catalyst under conditions such that a normally-liquid product with a higher aromatic content than the feedstock and a hydrogen-rich gas are produced, and the calorific value of the hydrogenrich gas is reduced to a value appropriate to the use of the gas as a town gas by dilution with a gas of lower calorific value. The gas of lower calorific value may contain noncombustible gases for example carbon dioxide and nitrogen.

In a preferred form of the invention, the light hydrocarbon fraction is contacted with a fluidised or moving bed of catalyst which is continuously or intermittently withdrawn from the reaction zone, regenerated in a stream of gas consisting principally of oxygen and nitrogen, and returned to the reaction zone, the flue gas from the catalyst regeneration process being used to reduce the calorific value of the hydrogen-rich gas.

A particularly suitable process for producing a higheraromatic content product and a make of hydrogen-rich gas from the said hydrocarbon fraction is one using a catalyst consisting essentially of chromium oxide supported on alumina carried out at a pressure of up to 50 p.s.i.g. (including atmospheric pressure or below) and without recycle of the hydrogen-rich gas produced or addition of extraneous hydrogen. The temperature range is from 4-50 to 580 C. and the space velocity from 0.1 to 1.0 v./v./hr. of liquid feedstock. The chromia on alumina catalyst may contain a minor proportion of one or more promoters for example a rare earth or mixture of rare earths, bismuth, boron, germanium or nickel, preferably in combination wiht an alkali metal, such as potassium. Another particularly effective pro- 'ice motor is a minor proportion of a spinel for example cobalt chromite, copper chromite, zinc titanate, or iron chromite, either as such or in the form of the naturallyoccurring ore chrome ironstone.

Preferably a substantial proportion of the feedstock boils below 100 C., particularly preferred feedstocks being a light straight-run distillate such as a light gasoline or a light relatively aromatic-free fraction of a catalytic reformate, for example a reformate obtained from a process using a platinum containing catalyst.

The normally-liquid product may be used in gasoline or as a source of aromatics, and the process conditions may be varied according to the use for which the product is intended. Increased severity increases the make of gas and the octane number of the liquid product but reduces the liquid yield. When carrying out the process for the production of towns gas and material for use in gasoline, the yields of gas and liquid and the octane number of the liquid product must be balanced against each other. On the other hand, when producing towns gas and a liquid product to be used as a source of aromatics, the decrease in overall liquid yield with increased severity may be advantageous rather than disadvantageous. This is because the yield of aromatics by weight of feed rises to a maximum with increased severity and thereafter stays substantially constant, although the overall liquid yield continuer, to decrease by conversion of olefins and parafiins to gas. Under the conditions of pressure and space velocity stated above, the maximum yield of aromatics occurs at about 525- 570 C. It is preferred to operate at the upper end of this range since, without affecting the yield of aromatics, an increased quantity of hydrogen-rich gas can be produced for conversion to town gas.

The specification for an acceptable town gas is laid down by the gas boards, and may include a preferred range for calorific value, specific gravity, and hydrogen content. Since an important combustible constituent of the hydrogen-rich gas is the hydrogen itself, these three values are interdependent and dilution to reduce the calorific value decreases the hydrogen content and increases the specific gravity. Any of these values, which can be determined by standard tests, may therefore be used as a guide to determining the degree of dilution required.

The invention is illustrated by the following examples.

EXAMPLE 1 A light gasoline was contacted in the vapour phase with a fluidised bed of catalyst consisting of 10% chromia on alumina, promoted with 1% of cerium oxide and 1% of potassium oxide (the percentages being by weight of catalyst stable at 1020 F.) under conditions set out in Table 1 below. The vapours after having been freed from catalyst dust, were compressed in two stages to p.s.i.g. and passed to a product recovery system in which a hydrogen-rich gas and a normally liquid fraction were separated by means of an absorber, a debutaniser and a re-run column. The hydrogen-rich gas was taken off overhead from the absorber, and the normally liquid fraction was taken oil overhead from the re-run column.

3 The fluidised catalyst reactor was associated in conventional manner with a catalyst'regenerator using air as the regenerating gas. The process conditions for the reactor and regenerator are set out in Table 1 below.

Inspection data on the light gasoline feed and the normally liquid fraction or product taken off overhead from the re-run column, are given in Table 2 below.

Table 2 Test. 1 Feed Product ASTM Distillation, 0.:

FBP 103 120 Specific gravity (1) 60 F./60 F 0. 676 O. 765 Octane number, research clear." 57 98 Aromatics, percent vol 2 48 Bromine No 0. 4 40 Sulphur, percent wt 0.015 0.007

From Table 2 it will be seen that a high-volatility gasoline fraction of 98 research octane number (clear) is a product of the process. At the same time, products having the general characteristics of a town gas were obtained by diluting the hydrogen-rich gas taken ofi overhead from the absorber with cooled regenerator flue gas. For a town gas with a calorific value of 500 B.t.u./ cu. ft, 100 volumes of dry absorber gas were mixed with 47.8 volumes of dry flue gas. Dry absorber gas and dry flue gas were also mixed in the required proportions to give a product having a specific gravity of 0.51.

Inspection data on the gases are set out in Table 3 below.

Table 3 Mixture Mixture Absorber Regenerto give to give gas, ator flue 500 gas with percent gas, Btu. sp. gr.

vol. percent gas, 0.51,

v01. percent percent vol vol.

trace 1 .1 0 .3 0 .3

Total 100 .0 100 .0 100 .0

Gross CV, B.t.u./eu. ft. 730 500 555 Sp. gr. (Air=1) 0 .34 1.03 0.56 0

EXAMPLE 2 A light gasoline was contacted with a fixed bed of catalyst consisting of 10% of chromia on alumina promoted with 1% of cerium oxide and 1% of potassium oxide (the percentages being by weight of catalyst stable at 1020 F.) under the following conditions:

Temperature 560 C., 1040 F. Pressure Atmospheric. Space velocity 0.2 v./v./hr. Recycle gas None.

Processing period 5 hours.

Details of the feed and the liquid product are set out in Table 4 below.

T able 4 Light gasoline 61.2 ON (Res) Clear (05-112 0.)

Feed

Hydrocarbon Type Analysis atcs The table shows a gain in aromatics of 28% by weight of feedstock. At the same time there was produced 2350 s.c.f. of gas per barrel of feed, or 320 lbs. per 1000 lbs. of feed. This gas contained 67% by volume of hydrogen. A further 60 lbs. of gas per 1000 lbs. of feed was taken oii overhead from the stabiliser used to debutanise the liquid product. The two gases were combined to give a gas with a density of 0.520 g./l. at 0 C. and 760 mm. Hg (0.40 specific gravity) and a calorific value of 833 B.t.u./cu. ft. The combined gases were diluted with an inert gas consisting principally of nitrogen and having a specific gravity of approximately 1 in proportion to give a final gas with a density of 0.7 g./l. at 0 C. and 760 Hg (0.54 specific gravity) and a calorific value of 620 B.t.u./cu. ft. The yield of this gas per 1000 lbs. of light gasoline feedstock was 12,400 cu. it.

We claim:

1. A process for the production of town gas and an aromatic-enriched product comprising contacting a relatively aromatic-free petroleum fraction boiling Within the range encompassed by the gasoline and naphtha range in a reaction zone with a dehydrogenation and dehydrocyclization catalyst consisting essentially of chromium oxide supported on alumina at a temperature of from 450 C. to 580 C., at a pressure not in excess of 50 p.s.i. ga., and in the absence of added hydrogen to the reaction zone to produce an aromatic-enriched product and a make of hydrogen-rich gas, recovering a normally liquid aromatic-enriched product and a hydrogen-rich gas, regenerating the spent dehydrogenation and dehydrocyclization catalyst in a regeneration zone by contacting same with a stream of oxygen-containing gas, recovering from the regeneration zone the regenerated catalyst for re-use in the contacting zone and a flue gas having a lower calorific value than said hydrogen-rich gas, and combining the recovered line gas with the hydrogen-rich gas to reduce the calorific value of said hydrogen-rich gas to a value appropriate to the use of the formed blended gas as a town gas.

2. A process in accordance with claim 1 wherein the temperature in the contacting zone is firom 525 C. to 570 C.

3. A process as claimed in claim 1 wherein a substantial proportion of the feedstock boils below C.

4 A process as claimed in claim 3 wherein the feed- References Cited in the file of this patent stock is a straight-run, light gasoline. UNITED STATES PATENTS 5. A process as claimed in claim 3 wherein the feedstock is a light relatively aromatic-free fraction of a it: 21 2 Catalyflc rfiformafe- 5 2,488,027 Page Nov. 15, 1949 6. The process of clann 1 wherem the catalyst 111 said 54 77 Leger F 13 1951 contacting zone is in a fluidized bed, and catalyst is con- 2,690,963 Herbst Oct. 5, 1954 tinuously withdrawn from the reaction zone; regenerated 2,707,147 Shapeleigh Apr. 26, 1955 in said regeneration zone and returned to the contacting 10 2,849,383 Hirschler Aug. 26, 1958 Zen 2,894,826 Stengle July 14, 1959

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF TOWN GAS AND AN AROMATIC-ENRICHED PRODUCT COMPRISING CONTACTING A RELATIVELY AROMATIC-FREE PETROLEUM FRACTION BOILING WITHIN THE RANGE ENCOMPASSED BY THE GASOLINE AND NAPHTHA RANGE IN A REACTION ZONE WITH A DEHYDROGENATION AND DEHYDROCYCLIZATION CATALYST CONSISTING ESSENTIALLY OF CHROMIUM OXIDE SUPPORTED ON ALUMINA AT A TEMPERATURE OF FROM 450*C. TO 580*C., AT A PRESSURE NOT IN EXCESS OF 50 P.S.I. GA., AND IN THE ABSENCE OF ADDED HYDROGEN TO THE REACTION ZONE TO PRODUCE AN AROMATIC-ENRICHED PRODUCT AND A MAKE OF HYDROGEN-RICH GAS; RECOVERING A NORMALLY LIQUID AROMATIC-ENRICHED PRODUCT AND A HYDROGEN-RICH GAS, REGENERATING THE SPENT DEHYDROGENATION AND DEHYDROCYCLIZATION CATALYST IN A REGENERTION ZONE BY CONTACTING SAME WITH A STREAM OF OXYGEN-CONTAINING GAS, RECOVERING FROM THE REGENERATION ZONE THE REGENERATED CATALYST FOR RE-USE IN THE CONTACTING ZONE AND A FLUE GAS HAVING A LOWER CALORIFIC VALUE THAN SAID HYDROGEN-RICH GAS, AND COMBINING THE RECOVERED FLUE GAS WITH THE HYDROGEN-RICH GAS TO REDUCE THE CALORIFIC VALUE OF SAID HYDROGEN-RICH GAS TO A VALUE APPROPRIATE TO THE USE OF THE FORMED BLENDED GAS AS A TOWN GAS.