US3366702A - Preparation of unsaturated hydrocarbons by pyrolysis, and related compositions - Google Patents

Description

' pane, and butane, and of natural United States Patent ()fifice 3,366,702 PREPARATION OF UNSATURATED HYDRO- CARBONS BY PYROLYSIS, AND RELATED COMPOSITIONS Francis C. Moriarty, Findlay, Ohio, assignor to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio No Drawing. Filed May 3, 1965, Ser. No. 452,842 Claims. (Cl. 260-679) ABSTRACT OF THE DISCLOSURE The present invention comprises, in the preparation of unsaturated hydrocarbons by the pyrolysis of hydrocarbons by passing them through a heated furnace and thereafter separating out the products thus produced, the step comprising injecting an effective amount of an oxy-compound inhibitor into the process stream at a point downstream from said furnace to reduce the formation of solid deposits.

The invention further comprises gaseous hydrocarboncontainiug compositions inhibited against varnish formation comprising 10 to about 90 mole percent acetylene and derivatives, 10 to about 90 mole percent ethylene and derivatives, and 0.0001 to 0.05 mole percent of an oxycompound inhibitor. Unsaturated hydrocarbons are useful as chemical intermediates and particularly as starting materials for the formation of various polymers.

The present invention relates to the preparation of unsaturated hydrocarbons and in its preferred embodiments relates to improved processes for the preparation of acetylene and ethylene from non-gaseous hydrocarbons.

Processes for thermally cracking hydrocarbons into acetylene, ethylene, and other unsaturated gases have been described at length in the literature. (See, for example, the Wultf Process described in US. Patents 1,996,185; 2,037,056; 2,236,534; 2,236,535; 2,236,555; 2,319,679;

' of methane, ethane, progas to form acetylene and ethylene have particularly been studied. (See, for example, Tropsch and Englotf, Industrial and Engineering Chemistry, 27, page 1063 (1935), and US. Patent 1,983,- 992.) As illustrated by US. 2,236,534, FIGURE 1, such processes typically consist of a furnace in which the thermal cracking of hydrocarbons is accomplished generally at temperatures above about l,500 F. for carefully controlled contact periods generally less than about lO seconds. A rapid cooling of the efiluent from the furnace is usually essential to the attaining of the desired ethylene and acetylene products. By control of the process conditions, the percentage of acetylene and ethylene can be controlled generally within the range of about 10 to 90 mole percent of each.

The hydrocarbons fed to such processes have generally been the gaseous aliphatic hydrocarbons, i.e., methane, ethane, propane, and butane. In utilizing such feed ma terials the furnace produces a substantial amount of tars which are removed by a trap located in the efiluent stream. Even with an efiicient trap, some build-up of tars is encountered in the equipment downstream from the trap. Since the separation of the efiluent acetylene and ethylene requires a relatively complex selective absorption and stripping section, maintenance in removing tar deposits from this equipment can present a significant problem.

Current markets for petroleum products have made it economically expedient to utilize the Wullf process with much higher boiling feed stocks than the gaseous hydrocarbons commonly employed. These feed stocks, primarily heavy naphthas having boiling ranges of approximately 200 to 400 F., form substantially greater amounts of 3,366,762 Patented Jan. 30, 1968 deposits. Further, these deposits, while originally soft and tacky, solidify with time into relatively hard material which is diflicult to remove from the interior of equipment.

The present invention embodies the discovery that these deposits are primarily composed of oxygenated varnishlike materials which are apparently primarily formed from diolefins, especially diacetylenes. According to the invention, by the addition of certain inhibitors into the process stream at a point downstream from the furnace, formation of varnishes is reduced and those varnishes which form are maintained in a substantially fluid condition. By maintaining the varnishes in a fluid condition, they are prevented from depositing on equipment and are readily removed with other fluid by-products of the process.

While the process of the present invention may be practiced Without conventional tar removal, in order to minimize the amount of inhibitors required, a conventional tar placed upstream from the point of injection of the inhibitors. Most preferably, the inhibitors are injected downstream from the tar removal apparatus at a number of points so spaced as to maintain a relatively constant concentration of the inhibitor in each of the process streams in which tar formation is likely to occur.

The inhibitors to be utilized with the present invention are not narrowly critical. In general, inhibitors which prevent the formation of oxy substances, and particularly those which prevent the formation of peroxides have been discovered to be valuable. While the present invention is not to be taken as being dependent upon any mechanism by which the formation of deposits or the inhibition occurs, it is believed that the formation of peroxides greatly accelerates the formation of deposits and the solidification of such deposits.

Thus, while tertiary butyl catechol is the most preferred inhibitor for the process of the present invention, other oxy-compound inhibitors including other alkyl catechols, cresylic acid and its derivatives, butyl phenols, phenylene diamine, 2,4,6-trimethylphenol, 2,4-dimethyl-6-t-butylphenol, 2,4-dimethyl-6-isobutylphenol, 2,6-di-sec-butyl-4- methylphenol, 2,6-di-t-butyl-4-isopropylphenol, N,N'-di- (sec-butyl)-p-phenylene diamine, p-phenylene diamine, N,N'-di(tert-butyl)-p-phenylene diamine, and p-butylaminophenol are useful in the process. All such inhibitors are included within the term oxy-compound inhibitor as used herein.

The inhibitors will be utilized in whatever mole percent is found to give 'best results at reasonable cost. Generally from about 0.0001 to about 0.05 mole percent inhibitor will be injected based on the moles of product. The molecular weights of inhibitors may be chosen so as to provide desirable boiling points and other physical properties, e.g., by varying the length of the alkyl group in alkyl catechols. A mixture of different inhibitors may be desirable under some circumstances. While heavier feeds normally produce larger amounts of viscous deposits, it should be understood that the present invention is beneficial when crude oils, light and heavy naphthas, gaseous hydrocarbons and other feed stocks are utilized in the Wulif Process and analogous processes.

The preceding discussions and the following examples are intended to be merely illustrative of the invention and the claims are to be taken as including all of the variations and modifications which would be apparent to one skilled in the art.

Example I A naphtha feed stock having a boiling range of from about 250 to 350 F. is fed to a modified WuliT process according to the process of US. 2,236,534. The maximum temperature in the furnace is approximately 2,400 F. and the residence time is approximately 0.015 second. The

effluent from the furnace is quenched and immediately upon leaving the quencher, the product stream is injected with 0.01 mole percent tert-butyl catechol. Gummy varnishes, which solidify forming hard deposits on the downstream :separatory equipment, are not encountered, although such deposits are encountered when the injection of the tert-butyl catechol is discontinued.

What is claimed is:

1. In the process for the preparation of unsaturated hydrocarbons by the pyrolysis of hydrocarbons by passing them through a heated furnace and thereafter separating out the products thus produced, the step comprising injecting an effective amount of an oXy-compound inhibitor into the process stream at a point downstream from said furnace to reduce the formation of solid deposits.

2. In a Wulif-type process involving the pyrolysis of hydrocarbons at short residence times in a furnace followed by a rapid cooling of the effluent from the furnace, the step comprising injecting into the process stream after said rapid cooling from 0.0001 to about 0.05 mole of an oxy-compound inhibitor per mole of product to reduce the formation of solid deposits.

3. The process of claim 1 wherein the oXy-compound inhibitor is an alkyl catechol.

4. The process of claim 1 wherein the oXy-compound inhibitor is selected from the group consisting of cresylic acid and cresylic acid derivatives.

5. The process of claim 2 wherein the oxy-compound inhibitor is an alkyl catechol.

6. The process of claim 2 wherein the oxy-compound inhibitor is selected from the group consisting of cresylic acid and its derivatives.

7. Gaseous hydrocarbon-containing compositions inhibited against varnish formation comprising 10 to about mole percent acetylene and derivatives, 10 to about 90 mole percent ethylene and derivatives, varnish-forming materials and 0.0001 to 0.05 mole percent of an oXy-cornpound inhibitor.

8. The process of claim 7 wherein the oxy-cornpound inhibitor is an alkyl catechol.

9. The process of claim 7 wherein the oXy-compound inhibitor is selected from the gr'oup'consisting of cresylic acid and its derivatives.

10. The compositions of claim 7 wherein the oxy-compound inhibitor is tert-butyl catechol.

References Cited UNITED STATES PATENTS 2,038,630 5/1936 Bennett et al 4478 FOREIGN PATENTS 599,733 4/ 1948 Great Britain.

DELBERT E. GANTZ, Primary Examiner. J. D. MYERS, Assistant Examiner.