US2039441A - Treatment of hydrocarbon gases - Google Patents

Description

Patented May 5, 1936 UNITED STATES PATENT OFFICE TREATMENT OF HYDROCARBON GASES Jacque C. Morrell, Chicago, 111., assignor to Universal Oil Products Company, corporation of Delaware Chicago, 111., a

No Drawing. Application January 19, 1933. Serial No. 652,575

7 Claims.

- used as constituents of gasoline so that the overall yield of motor fuel from the cracking process may be treated directly or after removal of the hydrogen sulfide contained therein. The gases to be treated by the process may also be produced by subjecting natural or other hydrocarbon gases to elevated temperatures and pressures to crack them and increase their content of unsaturated hydrocarbons.

In cracking heavy hydrocarbon oils to produce lower boiling fractions, the yield of gasoline is limited by the fact that as more severe conditions particularly of temperature and time are imposed, the gas and coke yields increase out of proportion to the yield of gasoline and a point may be reached where the gasoline yield actually decreases while that of the less desirable products, gas and coke, sharply increases. Apart from their use as fuel, the gases resulting from cracking operations have heretofore been looked upon as an undesirable by-product so that a process for increasing the yield of desired gasoline fractions and at the same time decreasing the yield of gas will have economic value.

In one specific embodiment the present invention comprises the treatment of gases from cracking plants with solutions of zinc chloride alone or in combination with halogen acids such as hydrogen chloride to controllably produce polymers from the olefins in the gases, such polymers being of a character suitable for use as con-v stituents of gasoline and of particular value in improving its anti-knock value.

The composition of the gases from cracking processes varies over wide ranges in respect to paraflins and olefins and sulfur derivatives of hydrocarbons, the composition depending upon the type of charging stock cracked and the severity of cracking conditions. The following analysis is typical of the gases produced in the cracking of heavy distillates and residues in present day commercial plants:

Per cent Hydrogen 12 Methane Ethan Ethylene Propane Propylene Butanes Butylenes Pentanes Amylenes Miscl. heavier hydrocarbons The olefins, however, may run as high as 40% and over as a result of intensive cracking operations at high temperatures for the production of arcmatics or high anti-knock gasolines and even higher if oils are cracked with the primary object of gas production. The latter type of gases may produce the higher yields of desirable liquid products.

Olefin-containing gases may be subjected to the action of zinc chloride solutions according to the process of the invention in a number of ways; The simplest method of operation consists in bubbling the gases through a stationary pool of zinc chloride solution, the concentration of which is varied to produce the desired rate and character of polymerization. In this method of operation liquid hydrddarbon polymers will accumulate on the surface of the aqueous solution and some may be carried on in unaffected residual gases to be later recovered by absorption.

Another alternative method of operation consists in passing the gas stream upwardly countercurrent'to descending solutions of zinc chloride, the stream being subdivided by passage over relatively inert spacing material such as Raschig rings, crushed firebrick, silica fragments, fullers earth, clays, etcetera, or towers containing regularly spaced trays of the perforated or bubble type may be employed.

A still further alternative mode of operation, which may be operated in conjunction with the two mentioned above may consist in atomizing Cit In all cases of treatment it is comprised within the scope of the invention to re-use the chloride solutions insofar as their polymerizing effectiveness may indicate. If the solution becomes contaminated with partly soluble polymers or addition compounds with the zinc chloride it may be subjected to any suitable regenerating steps to bring it back to a condition for use.

It is to be understood, of course, that the gases to be treated may originate or be led directly from a concurrently operating cracking process.

Obviously, no entirely general rules can be laid down for obtaining the best results with all gases, not only because of the variations in the percentage of olefins which they contain, but also on account of variations in the types of olefins as to whether they are normal or iso compounds and because 01' the variation in the relative propor-' tions of these different types. However, a consideration of the general mechanism of the reactions furnishes some guidance for predetermining the best conditions of operation in any case though the exact determination of conditions is usually a matter of trial.

As exemplifying the type of reaction which results in the formation of simple polymers from a mono-olefin, the case of isobutylene may be considered. When isobutylene is treated with a concentrated'zinc chloride solution in a relatively large volume, say by weight of the isobutylene, varying percentages of di-, triand tetrabutylene are formed. There is evidence to support the assumption that hydrochloric acid resulting from partial hydrolysis of the zinc chloride adds directly to isobutylene to form a butyl chloride which then reacts with further amounts of iso-butylene to form an octyl chloride as an intermediate product, this then decomposing with loss of hydrochloric acid to form octylene, and allowing the hydrochloric acid to react further in the same cycle. There is evidence also in support of the view that intermediate addition compounds are formed between olefins and zinc chloride, a compound of this character having the formula CsHio.2ZnCl2, being formed by the direct addition of one molecule of amylene to two of zinc chloride. Such compounds are readily decomposed by water, which may account for the observed fact that a certain concentration of solution is desirable to insure the desired polymerization reactions. Whatever the exact course of the reactions may be it is nevertheless an observed fact that liquid products boiling within gasoline range and possessing unusually high anti-knock value can be produced from the olefins in cracked gases by the use of zinc chloride solutions of regulated strength which are contacted with the gases in any suitable manner.

While elevated temperatures are sometimes desirable, the temperature used must not be high enough to cause too extensive polymerization. In some cases it suffices to merely pass the fixed gases from an oil cracking process through a stationary pool of concentrated zinc chloride solution, at ordinary temperatures and pressures. In other cases, elevated temperatures and pressures are desirable, particularly if the percentage of readily polymerizable olefins is relatively low.

Control of the extent and action 01 the p ymerizing reactions may be to some extent a matter of adjustment of the amount of moisture and hydrochloric acid present. In the operation of the process moist hydrochloric acid or hydrogen chloride may be injected into the stream of gases, or either hydrochloric acid or water may be introduced into treating equipment so that aqueous hydrochloric acid is present as a liquid phase, or hydrochloric acidmay be a constituent of the polymerizing salt solution in any desired quantity.

An example of results obtainable by the use of the process may be given in connection with a gas having the composition shown in the preceding table. This gas, produced at a rate of 1,000 cubic feet per barrel of charging oil to a cracking plant may be passed at atmospheric temperature and pressure upwardly countercurrent to a solution of zinc chloride of approximately 80 to 85% concentration. The gas mixture may be saturated with water vapor and contain in addition a small percentage of hydrochloric acid gas, say, about 0.3% by volume of the gas mixture.

By this operation there may be recovered from two to two and one-half gallons of 51 A. P. I. gravity liquid boiling within the range of 120 to 410 F. and consisting for the most part of hexylenes. octylenes and decylenes and some higher homologs, resulting from the formation of dimers from the corresponding olefins of one-half their molecular weight. The resulting liquid product may have an octane number or anti-knock value exceeding that of benzol. In the case under discussion the gasoline yield from oil charged to the cracking plant may be increased from a total of 60 to 65% by the incorporation of these polymers with the gasoline normally produced. Furthermore, owing to the high anti-lmock value of the polymers the octane number of the gasoline may be increased from '75 to 80, which constitutes a further advantage. Good results may be obtained with zinc chloride in aqueous solution at an elevated temperature of approximately 400 F. and a pressure of 400 pounds per square inch. Under these conditions employing a gas from a cracking process containing 35% of olefins, approximately three gallons of liquid product of high anti-knock value may be obtained per thousand cubic feet of gas. The anti-knock value of the liquid thus obtained frequently exceeds that of benzene and is highly desirable as a motor fuel blending agent.

The examples given herein are merely illustrative of the many possibilities of the process and are not to be considered as limitations thereof.

I claim as my invention:

1. A process for the treatment of oleflnic gases to polymerize the gaseous olefin hydrocarbons and. convert the same into liquid hydrocarbons, which comprises subjecting the said gases in the absence of any substantial quantity of normally condensible hydrocarbon vapors to the action of a concentrated aqueous solution of zinc chloride at a temperature and pressure such that the zinc chloride is in aqueous solution during the polymerization of the olefins.

2. A process for the treatment of olefinic gases to polymerize the gaseous olefin hydrocarbons and convert the same into liquid hydrocarbons, which comprises subjecting the said gases in the absence of any substantial quantity of normally condensible hydrocarbon vapors and while in heated condition to the action of an aqueous solution of zincchloride at a temperature and pressure such that the zinc chloride is in aqueous solution during the polymerization of the olefins.

3. A process for the treatment of olefinic gases 30 Y substantial quantity of normally condensible hy- 4. A process for the treatment of gaseous hydrocarbons from a cracking process to polymerize the olefin hydrocarbons contained therein for the purpose of producing liquid hydrocarbons suitable for high anti-knock motor fuel or a blending agent therefor, which comprises subjecting the said gases in the absence of any substantial quantity of normally condensible hydrocarbon vapors and while in heated condition to the action of an aqueous solution of zinc 'chloride at a temperature and pressure such that the zinc chloride is in aqueous solution during the polymerization of the oleflns.

5. A process for the treatment of gaseous hydrocarbons from a cracking process to polymerize the olefin hydrocarbons contained therein for the purpose of producing liquid hydrocarbons suitable for high anti-knock motor fuel or a blending agent therefor, which comprises subjecting thesaid gases in the absence of any carbon vapors and while in heated condition under superatmospheric pressure to the action drocarbon vapors and while in heated condition under superatmospheric pressure to the action of an aqueous solution of zinc chloride at a temperature and pressure such that the zinc chloride is in aqueous solution during the polymerization of the'olefins.

6. A process for the treatment of gaseous hydrocarbons from a cracking process to polymerize the oleiln hydrocarbons contained therein for the purpose of producing liquid hydrocarbons suitable for high anti-knock motor fuel or a blending agent therefor, which comprises subjecting the said gases in the absence of any substantial quantity of normally condensible hydroot a concentrated aqueous solution of zinc chloride at a temperature and pressure such that the zinc chloride is in aqueous solution during the polymerization of the oleflns.

7. A process for the treatment of oleflnic gases to polymerize the gaseous olefln hydrocarbons and convert the same into liquid hydrocarbons, which comprises subjecting the said gases in the absence 'of any substantial'quantity of normally con-