US 2998457 A
Description (OCR text may contain errors)
Aug. 29, 1961 T. H. PAuLsEN PRODUCTION oF PHENoLs Filed Nov. 19, 1958 B n?. num m,
United States atent Otiee 2,998,457 Patented Aug. 29, 1961 2,998,457 PRODUCTION F PHENOLS Thorwell H. Paulsen, Ashland, Ky., assignm` to Ashland Orl & Refining Company, Ashland, Ky., a corporation of Kentucky Filed Nov. `19, 1958, Ser. No. 775,050 8 Claims. (Cl. 260-621) This invention relates to the treatment of coal tar byproducts for the recovery of phenols therefrom. it is directed particularly to the catalytic removal of methyl and hydroxyl radicals from xylenols which are produced asl residual by-products in the distillation of coal tar light o1 s.
In a copending patent application Serial No. 728,620, tiled April l5, 1958, now U.S. Patent No. 2,951,886, issued September 6, 1960, of which this application is a continuation-in-part, a process is disclosed and claimed for recovering benzene of high purity from coal tar light oil by subjecting it to catalytic cracking conditions in the presence of hydrogen at a temperature above approximately 1200 F. By this process toluene and xylene which are present with benzene in coal tar light oil are demethylated into benzene, while parafiins, and thiophenes, and other sulfur compounds which also contaminate the coal tar light oil are destructvely removed. By the use of a catalyst comprising 10-15% chromia on a high purity, lo-w sodium content, gamma type lalumina support, formation of coke and gas, which would otherwise be expected from the high cracking temperature, is very low. By this means coal tar light oil or crude benzene, which in itself is of limited utility, is readily converted into benzene of high purity for which there is great chemical demand.
An important objective of the present invention is to provide an equally convenient means for converting into useful products mixed xylenols which are produced as residual by-products in the recovery of crude benzol or coal tar light oil from coal tar. As was the case with crude benzol, the xylenols at present are of limited market value. Because of the contaminating constituents of these crude products, relatively pure chemicals cannot be obtained from them at reasonable cost. However, the
present invention provides a xylenols into relatively pure demand has long continued.
Briefly, the present invention is based upon the discovery that the methyl and hydroxyl groups attached to the benzene rings in the isomers constituting a typical mixed xylenol derived from coal tar can selectively be cracked therefrom, and the sulfur impurities such as thiophenes as well as paraiiinic compounds which are present can be removed by subjecting the mixed xylenols to hydrocracking conditions in the presence of a specific catalyst and that the formation of gas and coke from destructive decomposition in such operation may be held to an inconsequentially low figure even at temperatures above l200l250 F.
More specificaly, the present invention is based upon the discovery that the xylenols in a mixed xylenol product derived from coal tar may be converted and thereby up-graded into a product containing phenols in admixture with benzene, toluene, xylene, and cresols, by catalytic hydrodealkylation in a rapid and convenient manner and at relatively low equipment cost. According to the process of the present invention, mixed xylenols are subjected to catalytic cracking in the presence of hydrogen at temperatures of from approximately 10501250 F. or higher in a single pass, with high yield.
While temperatures of the order heretofore have been known to produce destructive effects upon benzenoid hydrocarbons, this adverse effect appears chiefly to have process for converting crude chemicals for which a high been caused by the nature of the catalysts previously used. However, I have found that a catalyst consisting of approximately 10-15% by weight of chromia oxide on a high purity, low sodium content, gamma type alumina support is capable, in the presence of hydrogen, of causing selective demethylation and dehydroxylation of mixed xylenols and of promoting concurrent conversion of sulfur-bearing and paraliinic impurities with little or no coking effect. A particular catalyst which enables such results to be obtained is commercially available from the Girdler Corporation, Louisville, Kentucky, under their trade designation G-4l. X-ray defraction patterns show the chromia oxide to be present in the form of hexagonal crystals as distinguished from chromia aluminum co-gel catalysts which have also been available but which are incapable of providing similar results. The total chromia content of the commercial product is calculated as 11.8% Cr203 by weight, the remainder of the product being the Specified high purity, low sodium content, gamma type alumina. In use the catalyst is employed in the form of tablets, for example, 3/16 x da" in size, forming a fixed bed through which the feed stock and hydrogen are passed continuously.
The process of this invention is effected by contacting a charge of mixed xylenols with the catalyst and hydrogen at a temperature of the order indicated at a suitable operating pressure, for example, 500 p.s.i.g., and for a short contact time, for example 5 to 100 seconds depending upon the operating condition of temperature and pressure and preferably about l5 to 25 seconds. At temperatures of the order of 1040" F., a substantial proportion of benzene, toluene, and xylene are produced from the mixed xylenols but, in a single pass treatment, a substantial proportion of the mixed xylenols remains unconverted. However, at temperatures of 1235 F. or higher substantially all of the mixed xylenols are usefully demethylated, and phenol constitutes a substantial percentage of the products of conversion in conjunction with benzene, toluene, xylene, and cresols. Thus, for single pass operation, a temperature of approximately 1235 1250 F. is preferred. Phenol readily may be recovered from the mixed products of conversion by fractional distillation. Therefore, mixed xylenols, for which there heretofore has been a limited market, constitutes a source of a very valuable product.
In the conventional high temperature coking of coal, as has ben practiced in the past, the mixed xylenol content of the coal tar is relatively low in comparison with the crude benzol and cresol content. However, in the more recently developed low temperature process of coal carbonization, mixed xylenols constitute a large part of the coal tar. Thus, mixed xylenols for which there is no substantial demand even in the limited quantities -produced in conventional coke oven operation, become such a drug on the market as to affect the economic utilization of the more modern, low temperature coal carbonization process. However, by the process of the present invention mixed xylenols may be converted into phenols and benzene of high purity, for both of which a great demand exists and is likely to increase.
In the practice of the process since demethylation occuring in the charge stock is accompanied by heat liberation, the feed is preferably held at a temperature somewhat lower than the preferred l2351250 F.; for example, the feed temperature may be approximately 1150 F. Control of the feed temperature thereby provides a convenient means of limiting peak temperature at the contact zone.
Within the contact zone demethylation and dehydroxylation occur rapidly but selectively. Even at the high temperature at which cracking is conducted, there is little destructive cracking of the hydrocarbons into coke or normally gaseous products `and little undesirable polymerization. It is to be noted that neither demethylation nor dehydroxylation of the xylenol is complete, as shown by the substantial percentage of phenol and some cresol in the end product, as well as the substantial percentages of toluol and xylene. Sulfur impurities are converted into hydrogen sulfide and paraflinic impurities are cracked to gas.
Following the catalytic treatment, the mixed products of conversion from the hydrocracker are condensed to liquid, and the gaseous products are separated from the liquid products by means of a ilash drum and absorber. Dry gas products may be used for plant fuel, while the liquid products are stabilized by removal of entrained or absorbed gas. The liquid products are then subjected to fractionation for the separation of benzene, toluene, and xylene from the phenol and cresol as desired.
One method of practicing the invention continuously oii a 'commercial scale as an adjunct to petroleum retining operations is illustrated in the accompanying diagram, according to which the hydrogen employed for the hydrocracking operation is furnished as hydrogen off-gas from a catalytic reformer. This is supplied through line l to a gas compressor 2. Xylenol-containing feed stock is supplied through line 3 to a feed pump 4. Hydrogen gas and the charge stock, commingled in line 5, pass through a heater 6 wherein the temperature is elevated sufliciently to inaugurate or support selective cracking or to provide the desired autocatalytic effect; for example` the feed stock may be preheated to a temperature of ll50 F. or more depending upon the weight/hourly/space velocity in the reactor. It will also be understood that the reactor may be provided with a coolant system for temperature control.
The hot feed stream passes through line 7 to reactor 8 wherein a suitable pressure, for example approximately 500 p.s.i.g., is maintained, as provided by the compressor 2 and feed pump 4. The reactor contains a fixed bed of catalyst as described, through which the feed material is passed. Flow rate preferably is adjusted to provide a contact time or time of residence within the reactor of approximately 15 to 25 seconds. As will be understood by those skilled in the art, the reactor pressure may be varied yfrom approximately 100 to 1000 p.s.i.g., the 500 p.s.i.g. pressure disclosed herein being an operating pressure which is practical to employ.
A weight/hourly/space velocity of approximately 0.5 to 2.0 pounds of xylenol feed per pound of catalyst per hour is suitable. The molar ratio of hydrogen to hydrocarbon may he from approximately 2:1 to 10:1; a ratio of approximately :1 has been found to provide very satisfactory results. These ratios, of course, may be varied to accommodate variations in the composition of the feed stock; for example, mixed xylenols produced in the low temperature carbonization of coal may consist of approximately 97% xylenols `and `3% C9 phenols with little or no cresol, while mixed xylenols from coal tar fractions produced by other processes may contain significant quantities of cresol and varying percentages of parainic and substituted phenolic constituents.
The reactor output passes through line 9 and a cooler 10 into a condenser 11 wherein the liquid product s condensed. The output stream then passes through line 12 into a Hash drum 13 which may be maintained for example at a pressure of approximately 490 p.s.i.g. and a temperature of 100 F. Gases non-condensible from the ash drum conditions of temperature and pressure are liberated from the stream at this point.
Gases from the ilasli drum 13 pass through line 14 into an absorber 15 which may be held at a pressure of approximately 450 p.s.i.g. and a temperature of 100 F. The absorber operates in conjunction with a stabilizer 16 and a recirculating cresol product stream may be passed into the absorber as lean oil through line 17. Liquid product collected in the flash drum, as withdrawn through line 18 therefrom, is commingled with fat oil from the absorber in line `19. In this manner valuable liquid product contained in the ash drum vapor is recovered in the absorber while the dry gas from the `absorber is withdrawn through line 21 for use as plant fuel. The stabilizer may be operated for example at a temperature of approximately 155 F. and .a pressure of 75 p.s.i.g. The necessary heat of vaporization for the stabilizer is supplied by reboiler 22 with the vapors returning -to the stabilizer through line 23. Also, the stabilizer overhead, withdrawn through line 24, operates in conjunction with a reux system comprising condenser 25 and receiver 26, the liquid reflux collecting in the receiver at a temperature of approximately F. and being recirculated to the stabilizer by pump 27.
The stabilizer bottoms are withdrawn through line 28 and may be passed into a Ifractionation system comprising three or more fractionating columns which may be of conventional design. For example, the fractionating system shown comprises fractionating columns 30, 311: and 32. The first fractionator 30 fractionates out a mixture of benzene, toluene, and xylenols while the bottoms product of this tower is then pumped to the second fractionator, 31, where the phenol product is separated as overhead. The bottoms product of tower 31 is then pumped to the third fractionator, 32, which produces cresol overhead while the bottoms product is a heavy oil which may be used for fuel if desired. In the system shown, a portion of the cresol overhead is withdrawn from the output stream by means of pump 33 'which feeds to absorber lean oil line 17. A coolant 34 is installed `ahead of the pump 33, which cools the product to a temperature of approximately 100F. n
The -following table illustrates the results obtained in the catalytic conversion of a typical mixed xylenol product under diterent sets of operating conditions A, B, and C.
Isomer distribution of feed and products-typical runs Feed Run A Run B Run C Wel lit ourl /space velocity 1.0 0.8 0.8 Hyrogiieln-hysclroearbon, mol ratto... 4:1 5.1 Tempirature, F. ;t .f 1040 1150 Li ul recovery perce i100 wt. perce';i1t) i...E .t.. 100 89. 0 86.0 79.0 Isonier anal also qu w .perceu Benning, toiuene, xy'fiene 24.1 1c. i 42. a Phenol 0.3 2. 5 (i. 9 20. 7 Crcsols 0.8 10. 1 1S). 4 18. 3 Xylen S .5 50. 9 48.8 6. 3 Ga Pheno .4 3. 6 1. 0.3 Water. 4. 5 3. 7 5. tl Residual. 4. 1 2. 7 5.6 Loss 0.2 0.8 0. 9
l Dlstlllatlon at 50 mm.
'Ilie xylenol feed material treated according to the above examples was a commercial stock having 8" API gravity. The operating pressure in each of runs A, B, and C above was 500 p.s.i.g.
It will be noted from this data that the yield of liquid product is high, as is the yield in terms of phenol in run C where the operating temperature was 1235 F. The unusual and unexpected result provided by the present invention is that a catalyst possessing such a high degree of catalyst activity is nevertheless selective in its action and does not destructively degrade the useful components of the feed.
While the invention has been disclosed principally in relation to the recovery of useful products from mixed xylenols, the invention is also useful for other types of charge stocks such as mixed cresols and the like. Moreover, it will be noted that the process of this invention, utilized in conjunction with the process disclosed in the aforesaid copending application Serial No. 728,620, enables large quantities of benzene and phenol to be produced of a quality and purity not otherwise obtainable from coal tar lfractions. Thus, by conventional distillation of coal tar, whether obtained from the high temperature or low temperature carbonization of coal, to recover light oil and residual mixed xylenols, and by catalytic hydrodealkylation of the respective separated fractions as disclosed in this and the copending application, high quality benzene is obtained from the former and from the latter a mixture which readily may be separated into its phenol, benzene, toluene, and cresol components.
Having described my invention, I claim:
1. A method of treating mixed xylenols derived from coal tar which method comprises, subjecting the mixed xylenols to catalytic hydrocracking conditions in the presence of hydrogen and a catalyst consistin-g of approximately 10 to 15% by weight of chromia on a high purity low sodium content gamma type alumina support at a temperature in the range from approximately 1040 F. to approximately 1250 F., at a pressure in the range from about 100 to 1000 p.s.i.-g., and for a period of time Ifrom about to about 100 seconds, to demethylate and dehydroxylate at least some of the xylenols and to destructively crack sulfur and paratinic impurities therein to gas.
2. The process of claim 1 wherein the hydrocracking temperature is approximately 1235 F.
3. The process of claim 1 wherein the catalytic hydrocracking operation is conducted n the presence of hydrogen off-gas obtained from a catalytic reformer.
4. The process of claim 1 wherein the catalyst consists of approximately 11.8% chromia on said support.
5. The process of claim 1 wherein the chromia is in the form of hexagonal crystals.
6. The process of claim 1 wherein the hydrocracking operation is conducted by passing a stream of said xylenols through a fixed bed of the said catalyst.
7. A process for obtaining phenol from xylenols which process comprises, subjecting the xylenols to catalytic cracking conditions in the presence of hydrogen and a catalyst consisting of approximately l0 to 15% by weight of chromium oxide on a high purity low sodium content gamma type alumina support, at a temperature in the range from approximately 1200 F. to approximately 1250 F., at a pressure in the range from about to 1000 p.s.i.g., for a period of time from about 5 to about 100 seconds, and separating phenol from the liquid product resulting from the treatment.
8. A process for selectively splitting methyl and hydroxyl groups from xylenols in a xylenol-containing feed stock to form simpler products therefrom, said process comprising, contacting said xylenol-containing feed stock in the presence of hydrogen with a catalyst consisting ot approximately 10 to 15% by weight of chromia, the balance of the catalyst composition being high purity low sodium content gamma type alumina, at a temperature of from approximately 1040 F. to approximately 1235 F., at a weight hourly space velocity of from about 0.5 to about 2.0, and at a pressure in the range from about 100 to about 1000 p.s.i.=g.
References Cited in the lle of this patent UNITED STATES PATENTS 1,208,833 Ramage Dec. 19, 1916 2,398,687 Winans Apr. 16, 1946 2,636,843 Arnold et al. Apr. 28, 1953 2,705,733 Nonnemacher et al. Apr. 5, 1955 2,773,917 Coonradt et a1. Dec. 11, 1956 2,780,661 Hemminger et al. Feb. 7, 1957 OTHER REFERENCES Russel: Alumina Properties, Tech. Paper No. 10, page 5 (1 page), published by Aluminum Company of America, Pittsburgh, Pa. (1953).
Grossinsky et al.: German application 1,001,998, published February 7, 1957.