US2427988A - Process for removing sulphur compounds from hydrocarbons - Google Patents

Description

Patented Sept. 23, 1947 2,427,988 PROCESS FOR REMOVING SULPHUR COM- POUNDS FRsQM HYDROCARBONS Philip J. Wilson, Jr., Joseph H,

M. Sommerfeld, Pittsburgh, Pa., assignors Steel Corporation,

Carnegie-Illinois tion of New Jersey No Drawing. Application Wells, and Pauline,

to a corpora- April 24, 1945,

Serial No. 590,120

8 Claims. (01. 20242) For the production of many chemical products mployed in industriessuch as the explosives and dye industries, there are required large quantities of pure benzene, which forms the starting material for a wide variety of such products. Thus pure benzene is employed in' the manufacture of phenol, and in the production of nitrobenzene chrysene, and innumerable other compounds, are obtained by the dry distillation of coal. present in coal tar and light oils which are produced in great quantities in the manufacture of illuminating gas and in the coke industry.

The rapid, well known development of the chemistry of the benzene derivatives is due largely oven light oils, to various technical industries. While in the case of the paraffins, their very nature renders them ceutical products.

Coal tar and coke oven light oils contain not only aromatic hydrocarbons, but alsop'arafilns, thiophene, methylated thiophenes, phenols, pyridine bases, related compounds, and their derivatives. Coke oven light oil, which is one of the greatest sources for the recovery of benzene, is usually recovered by scrubbing the coke oven gas with a straw or absorbent oil. containing in solution benzene and its homologues, together with lesser amounts of parafiins, thiophene, pyridine, and other compounds, is steam distilled to produce an overhead distillate which is the light oil itself. This is an oil specifically lighter than water and usually boiling up to to 200 C. This light oil or suitable fractions recovered from it by distillation are freed from resins, olefins, pyridine bases, and other unsaturated compounds, by washing with 66 B. sulphuric acid in suitable amounts, for instance 5400 pounds of the acids to 5500 gallons of the oil, The acid is drained from the agitator and the acidified oil is neutralized with caustic soda, for instance a twenty per cent caustic soda solution, which both neutralizes residual acid and removes the phenols from the oil.

The thus sweetened oil is separated from the aqueous layer and chargedto a fractionating still and carefully fractionated, there being recovered products, such as motor benzene, pure benzene, toluol and xylol of standard quality.

All grades of benzene thus normally recovered contain varying amounts of thiophene and, since r the varying amounts of thiophene contained in the benzene assumes importance.

Many procedures for removing thiophene from benzene have been the use of much larger quantities of sulphuric acid of 66 B. gravity, or even more concentrated sulphuric use of oleum (fuming sulphuric acid).

of the benzene, or the cost of equipment and maintenance is excessive.

The present process provides a procedure for removing thiophene from benzene either completely, or to an extent wherein any residual thiophene is so small in amount as to be undetectable by the most sensitive reactions therefor.

In accordance with the presentinvention, the

The absorbent oil,

acid, or by the" "motor benzene, the "pure benzene, the light oil referred to above herein, or other fractions of the light oil, are treated for the removal of thlophene. The motor grade benzene is a grade that is suitable as motor fuel. The"pure benzene is what is referred to as industrially pure. Both grades of benzene contain thlophene, the amounts of which depend upon the quality of the coal from which the benzene has been obtained. Thus some of these benzenes and/or light oils are found to contain only from about 0.001 per cent to 0.002 per cent thlophene, while others contain upwards of 0.03 per cent of thlophene, or more. Even such small amounts of thiophene as the 0.001 per cent mentioned above have proved objectionable and have rendered the benzene unacceptable for the purposes indicated above here- In accordance with the present invention, thiophene and thiophene compounds are removed from aromatic hydrocarbons by a process that is simple and relatively inexpensive. In the process of the present invention, a solution consisting of an alkali, water, and an alcohol, is added to the hydrocarbon solution, containing thlophene or its homologues, either in the kettle of a still before distillation or at the top of the fractionating column during distillation. On distilling, the major 4. been concentrated can be withdrawn from the still.

As a further modification of the process, it may be noted that the process may be carried out by adding the alkali-water-alcohol solution to the thiophene-containing hydrocarbon and refluxing until the distillate from the condenser is free from thlophene, then distilling.

An example is given below to show the results which have been obtained in the application of the present process to the removal of thiophene from nitration grade benzene, together with comparative results obtained by straight fractionationand by azeotropic distillation with methanol. The thlophene concentrations were obtained by a colorimetric method using isatin, which was described by W. L. Glowacki, The Determination and Examination of Light Oil in Gas," American Gas Association (1941), pages 33 and 34. All the distillations were made in a still equipped with a packed fractionating column. This was equivalent to forty-three theoretical plates measpart of the distillate from the top of .the column is free from thlophene.

The alkali employed in the present process may be sodium hydroxide or potassium hydroxide and the alcohol may be any aliphatic alcohol as methyl, ethyl, propyl, Or the like. It is preferred to use an alcohol boiling below the boiling points of the hydrocarbon and thiophene in any particular case. In addition to the foregoing alcohols, there may be employed also secondary alcohols, such as isopropyl alcohol, or tertiary alcohols, such as tertiary butyl alcohol.

The alkali employed in the present process should be present at least in equimolecular amounts with the thiophene present, although usually a larger amount is preferable, and enough alcohol should be used to carry the aromatic hydrocarbon over in the form of the azeotrope with the alcohol. In case complete removal of thicphene should not be required for a, particular application of the benzene, the amount of alcohol added during distillation may be reduced.

The process ofthe present invention may be carried out in a variety of ways. The two following examples of the procedure are given by way of illustration, as representing two effective modes of operation, although it will be understood that the process is not limited to these specific pro cedures, as other modifications will become suggested to one skilled in this art. The illustrative examples of the procedure are:

1. The hydrocarbon containing the thlophene is charged into the kettle of a still provided with a fractionating column. As soon as the still is operating uniformly with total reflux, flow of the alkali-water-alcohol solution into the top of the fractionating column is started, so that it runs down countercurrent to the flow of vapors. Distillate can then be taken off the still.

2. The hydrocarbon containing the thlophene is charged into the kettle of the still, together with the alkali-water-alcohol solution and the distillate taken ofi the top of the fractionating column.

In either case, after a large proportion of the aromatic compound in the feed has been distilled oil, a residue in which the thlophene has ured at total reflux.

. Inoperating the presentprocess, 500 cc. of nitration grade benzene were charged into a still and 138 cc. of sodium hydroxide-.water-methanol solution were fed in at the top of the fractionating column during removal of the first 15.8 per cent (by volume) of the benzene as dis tillate. The said solution contained 5 per cent caustic soda and equal volumes of methanol and water. tion were added 25 cc. of methanol plus 1 cc. of water, and 300 cc. more of methanol were added to the column after 25 per cent by volume of distillate was off.

In the straight fractionation 400 cc. of the benzene were distilled. In the azeotropic distillation with the methanol-water solution, 400 cc. of benzene, 350 cc, of methanol, and 2 cc. of water were charged. The comparative results are indicated in the folowing table:

Method Azcotropic Distil- Plescnt Improved Straight Process Fractionation ggig g gfigi Distillate, gl ggl Distillate, i i ggf Distillate, 5 3: per cent a 5 per cent H q per cent g by vol. an y v01. by vol. f h r per cent of char per cent 0 char 8 per cont 0 c by wt. 5 by wt. g by 5. 8 0 5. 2 0. 0005 5. 3 0 10.8 0 11.0 .002 11.0 0 15. 8 0 16. 5 004 18. 9 0 25. 0 0 22. 0 005 32. G 0 35. 2 0 32. 0 Over .005 39. 5 0 47. 2 0 46. 5 0. 002 57. 2 0 53. 4 001 70. 7 0 60. l .003 80. 7 0 71. 2 004 85. 7 0 75. 9 Over .005 91. 0 Over .005 l Organic sulphur compounds other than thlophene have been removed or reduced in concentration by use of the present process.

In practicing the present invention, the ratio of water to the alcohol employed can be varied To the still at the start of the distilla umn or interference with its efiiciency due' to such precipitation of the alkali.

We claim:

1. The process of removing thiophene from benzene, which comprises fractionating the benzene in the presence of a caustic soda-meth- 'anol-water solution containing the caustic soda in at least equimolecular amounts with the thiophene present in the benzene, the methanol in an amount large enough to carry over the benzene as its azeotrope with the methanol, and the water in an amount from between one per cent by volume of the methanol to substantially equal volume with the methanol.

2. The process of removing thiophene from aromatic hydrocarbons, which comprises fractionating the hydrocarbons in the presence of a potassium hydroxide-methanol-water solution containing the potassium hydroxide in at least equimolecular amounts with the thiophene present in the hydrocarbon, the methanol in an amount large enough to carry over the hydrocarbon as its azeotrope with the methanol, and the water in an amount from between one per cent by volume of the methanol to substantially equal volume with the methanol.

3. The process of removing thiophene from aromatic hydrocarbons, which comprises fractionating the aromatic hydrocarbons in the presence of an alkali-water alcohol solution containing an alkali of the group consisting of sodium hydroxide and potassium hydroxide in at least equimolecular amounts with the thiophene present in the aromatic hydrocarbons, and enough of an aliphatic alcohol 'to carry over the aromatic hydrocarbons in the form of its azeotrope with the alcohol, the said alcohol having a boiling point below that of the hydorocarbon to be separated.

4. The process of removing thiophene from aromatic hydrocarbons, which comprises fractionating the aromatic hydrocarbons in the presence of an alkali-water-alcohol solution containing a alkali of the group consisting of sodium hydroide and potassium hydroxide in at least equimolecular amounts with the thiophene present in the aromatic hydrocarbons, an aliphatic alcohol in an amount large enough to carry over the aromatic the alcohol, the said alcohol having a boiling point below that of the hydrocarbons to be separated, and enough water to maintian the alkali continuously in solution.

5. The process of removing thiophene from aromatic hydrocarbons, which comprises fractionating the aromatic hydrocarbons in the presence of an alkali-water-alcohol solution containing an alkali of the group consisting of sodium hydroxide and potassium hydroxide in at least equihydrocarbons as its azeotrope wtih separated, and the water in an amount from between one per cent by volume of the alcohol to substantially equal volume with the alcohol.

6. The process of substantially removing thioprises fractionating the aromatic hydrocarbons in the presence of an alkali-water-alcohol solution containing an alkali of the group consisting of sodium hydroxide and potassium hydroxide in at least equimolecular amounts with the thiophene present in the aromatic hydrocarbons and analiphatic alcohol having a. boiling point below that of the aromatic hydrocarbon to be separa ed.

ing point below that separated.

8. The process of removing organic sulphur compounds present in coal tar and coke oven light oils from aromatic hydrocarbons which com- PHILIP J. wrLsoN, JR.

JOSEPH H. WELLS.

PAULINE SOMMERFELD. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS