US2746996A - Catalytic cracking of high boiling tar acids - Google Patents

Description

May 22, 1956 M. B. NEUWORTH CATALYTIC CRACKING OF HIGH BOILING TAR ACIDS Filed June 18, 1953 FLUE GAs SOLIDS LIFT I2 OATALYsT REGENERATION 4 24 GAs I 22,532 HYDROCARBON I I FDTAR VAPORS PRODUCT OARBON RECOVERY DEPOSITION HYDROCARBON Low BOILING DISTILLATE NEUTRALS INERT DII-UENT NONDISTILLABLE lo RESIDUE HEATER 22 REACTION 32 VESSEL G I REGYCLE HIGH BOILING TAR ACIDS A B HIGH BOILING 49 'figfif z g INERT TAR ACIDS DILUENT ff 48 FLUE 42 HIGH BOILING "Q I GAs 6o HEATER 56 TAR ACIDS 54 I GAS cATALYsT 3 ,LOw BOILING VESSEL PRODUCT TAR ACIDS RECOVERY LOW BOILING NEUTRALS 58 52 NONDISTILLABLE AIR RESIDUE JNVENTOR MARTIN B. NEUWORTH HYDROOARBON VAPORS United States Tatent CATALYTIC CRACKING OF HIGH BOILING TAR ACIDS Martin B. Neuworth, Pittsburgh, Pa., assignor to Pittsburgh Consolidation Coal Company, Pittsburgh, Pa, a corporation of Pennsylvania Application June 18, 1953, Serial No. 362,517 Claims priority, application Great Britain August 6, 1952 7 Claims. (Cl. 260--621) like. In conventional processing, tar acids are separated into a low boiling fraction and a high boiling fraction. The commercially valuable tar acids comprising phenol, cresols, xylenols and mono-ethyl phenol, boil below 230 C. All other tar acids can be characterized as high boiling tar acids. Thus the term high boiling tar acids comprehends any and all tar acids boiling above 230 C. and encompasses, for example, polyethyl and higher alkylated phenols, polycyclic phenols, polyhydric phenols and the like.

Low boiling tar acids are generally in greater demand than high boiling tar acids. It is therefore desirable to convert the tar acids boiling above 230 C. into the less complex and more valuable materials boiling below 230 C.

The primary object of the present invention is to provide a new method of making low boiling tar acids from high boiling tar acids.

According to my invention, tar acids boiling above 230 C. are passed in the vapor phase at a temperature of about 700 to 850 F. over a silica-alumina catalyst that has deposited thereon a layer of carbon constituting at least five per cent of the weight of the catalyst. The reaction is preferably carried out at atmospheric pressure, although the partial pressure of the tar acids may be reduced by the addition of an inert diluent gas, such as nitrogen, flue gas or the like.

Prior processes have been proposed for dealkylating four-carbon atom alkyl sidechains from alkyl substituted phenols using silica-alumina catalysts in the liquid phase. These liquid phase processes merely effect the removal of a readily removable substituent, namely, a four-carbon atom sidechain. However, it should be pointed out that I four-carbon atom sidechains are virtually unknown in raw tar acids, probably because the conditions required for preparing the raw tar are sufiiciently drastic in themselves to dealkylate any existing sidechains containing as many as four-carbon atoms.

Silica-alumina is well known commercially as a catalyst for converting hydrocarbons, and especially petroleum hydrocarbons, in the vapor phase. These reactions convert a portion of the feedstock to carbon which is deposited upon the catalyst, substantially diminishing its activity. This drastic reduction in activity necessitates regeneration of the catalyst before the carbon content reaches five per cent of the weight of silica-alumina. Regeneration consists of substantially completely burning off the deposited carbon to restore the catalyst activity.

Fresh silica-alumina exhibits a high activity and a low selectivity towards high boiling tar acids, i. e., with fresh silica-alumina catalyst, high conversions are effected (high activity) but very little of the converted material is in the form of the desired products (low selectivity); instead, most of the converted material is carbon, high boiling residue and gas. Hence, if pure silica-alumina (i. e., no carbon coating) were employed as a catalyst for high boiling tar acids, substantial quantities of the tar acids would be converted, but the principal products would be carbon, gas and high boiling residue instead of the desired low boiling tar acids.

I have discovered that high boiling tar acids can be converted into low boiling tar acids in high yields by contacting vaporized tar acids at about 700 to 850 F. with a silica-alumina catalyst coated with at least five per cent of carbon. High conversions are accompanied by corresponding high selectivity in my new process.

For a better understanding of my invention and its objects and advantages, reference should be had to the following description and accompanying drawings in which:

Figure l is a schematic representation of an apparatus for carrying out my new process on a continuous basis; and

Figure 2 is a schematic representation of an apparatus for carrying out my new process in a batchwise manner.

In Figure 1 a moving bed solids contacting unit is provided which comprises a reaction vessel 10, a catalyst regeneration vessel 12 and a carbon deposition vessel 13. A bed of silica-alumina catalyst containing at least five per cent by weight of carbon on its surface is maintained in the reaction vessel 10. Spent catalyst is withdrawn from the bottom of vessel 10 and carried through a solids lift 14 to the regeneration vessel 12. Regenerated catalyst is withdrawn from the vessel 12, conducted to the carbon deposition vessel 13, and then returned to the reaction vessel 10.

A tar acid fraction whose minimum boiling point is greater than 230 C. is introduced in the vapor phase into the reaction vessel 10 through conduit 18. The temperature of the catalyst in the reaction vessel is maintained at about 700 to 850 F. The high boiling tar acids may be preheated to the reaction temperature by a heater 20. If desired, an inert diluent gas, such as nitrogen, flue gas or the like may be added through conduit 22 to the high boiling tar acids in order to reduce their partial pressure. In general, from zero to ten parts of inert diluent should be employed. The liquid hourly space velocity (LHSV) for the reaction is preferably 0.1 to 5.0.

The catalyst in the reaction vessel 10 comprises silicaalumina which has carbon on its surface amounting to at least five per cent of the weight of silica-alumina. Suitable catalysts for the purposes of this invention can be purchased commercially or can be prepared by processes well known in the art. In general, these catalysts consist essentially of l to 50 per cent alumina and 99 to 50 per cent silica; the preferred catalysts for the present invention are those consisting essentially of 1 to 20 per cent alumina and 99 to per cent silica. The carbon on the catalyst may be deposited by treating fresh silica-alumina at elevated temperatures with hydrocarbonaceous materials that will react to form coke on the catalyst particles, as will be more fully described below.

During the cracking of the high boiling tar acids in the reaction vessel 10, additional carbon is deposited upon the catalyst from the decomposition of a portion of the feed material. The selectivity of the catalyst for the desired low boiling tar acids increases with the carbon content of the catalyst. However the catalyst activity gradually decreases with increasing carbon content. Ultimately, the increased carbon deposition reduces the catalyst activity to an uneconomic level and regeneration is required in order to restore the catalyst to a higher activity level. While the precise value of the carbon content at this uneconomic level will vary with the treated materials, it generally is of the order of 20%.

Regeneration is conducted in the regeneration vessel 12 where air is introduced through a conduit 24 to burn the carbon from the catalyst. Gaseousproducts of cornbustion are removedtrom the system through a conduit 26. These gases can be employed satisfactorily as inert diluents for the feed tar acids if desired. I V

The substantially carbon-free catalyst is conducted through a valved conduit 15 to a carbon deposition vessel 13 Where a fresh coating of carbon amounting to at least five per cent of the Weight of silica-alumina is deposited. This deposition of carbon may be effected by passing a low cost hydrocarbon distillate from a conduit 25 through the regenerated silica-alumina in vessel.13 at a temperature of 70$) to 850 F, and thence to discharge through conduit 27. The distillate is decomposed and the decomposition is continued until the desired amount of carbon is deposited. The freshly coated catalyst is returned to reaction vessel through valved conduit 16.

vaporized products of the cracking reaction pass from the reaction vessel 10 to a product recovery system 28 through a product conduit 30. Generally the product is separated into fixed gases, such as ethylene and propylene, low boiling tar acids, low boiling neutral compounds and nondistillable residue. The unconverted high boiling tar acids are separately recovered and can be recycled to the reaction zone through a conduit 32.

Figure 2 illustrates a fixed bed apparatus for the cracking of high boiling tar acids according to my invention. A reaction vessel 40 is provided in which a fixed bed of catalyst is maintained. The catalyst is silicaalumina which has carbon deposited thereon amounting to at least five per cent of the weight of silica-alumina. The operation of the apparatus is cyclic, with each reaction phase being interspersed with a catalyst regeneration phase. During the reaction phase, high boiling tar acids in the vapor form are introduced through a valved conduit 42 into the catalyst vessel 40 which is maintained at a temperature of 700 to 850 F. The high boiling tar acidsmay be preheated to the reaction temperature in a 'preheater 46. The partial pressure of the high boiling tar acids may be reduced by dilution with an inert diluent gas which is introduced through a conduit 43. Vaporized products of the cracking reaction are collected through conduit 52 and sent to a product recovery system 54. Products are separated into. gases, low boiling tar acids, low boiling neutral compounds and undistillable residue. Unconverted high boiling tar acids can be recycled to the reaction vessel through a conduit 56.

As the cracking reaction proceeds, a portion of the high boiling tar acids is converted to carbon which is deposited upon the catalyst. The continued carbon deposition gradually decreases the catalyst activity and necessitates catalyst regeneration when the activity falls below a predetermined level which is relatable to the carbon content. In order to regenerate catalyst in the system illustrated in Figure 2, the flow of high boiling tar acids into the reaction vessel 40 is terminated by closing conduit 42. Air is introduced through a valved conduit 58 into the vessel 40 to burn carbon from the catalyst. Gaseous products of combustion are discharged from the system through a valved conduit 60. The air may be diluted with an inert gas, such as nitrogen, flue gas or the like, in order to prevent excessive temperatures from developing in the vessel 40 through the combustion of carbon.

Gaseous products of combustion may be used to dilute feedstock for the reaction phase or as a diluent for combustion air in the regeneration phase. When the catalyst is satisfactorily regenerated, conduits 58 and 60 are closed. The regenerated catalyst is then prepared for a subsequent reaction phase by coating it with at least five per cent by weight of carbon. For this purpose hydrocarbon distillate is introduced into vessel 40 through valved conduit 49 and withdrawn through valved conduit 59.

The process of Figure 2 can be made continuous by providing two or more catalyst vessels arranged in parallel. By operating the catalyst vessels alternately in a cyclic manner, the system can be continuously onstream with respect to the high boiling tar acids. 7

The results of carrying out the cracking of high boiling tar acids in accordance with my new process are tabulated in Table I. The tar acid feed was a 230300 C. boiling range distillate fraction of tar acids obtained from tars derived from low temperature carbonization of bituminous coal. Partial pressure of the feedstock was reduced by diluting it with nitrogen gas. The silicaalumina contained about 88 per cent by Weight of silica and about 12 per cent by weight of alumina. The catalyst was prepared by passing high boiling tar acids in vapor form through a bed of the fresh silica-aiumina at a temperature in the range of 700-850 F. until the carbon deposition on the catalyst amounted to more than live per cent of the Weight of the fresh silica-alumina.

The process was operated according to the method illustrated in Figure 2, i. a, batchwise with respectto the catalyst which was maintained in the fixed bed. The tar acids passed downwardly through the catalyst vessel. The abbreviation VMSV means vapor minute space velocity, i. e., the volume of vapor per volume of catalyst per minute. Its numeral value is expressed then as min- Table I.230300 C. tar acids Run 1 1 2 3 4 Temperature, F 800 800 800 700 VMSV i0. 4 7. G 6.8 Partial Pressure, atm i). 51 O. 35 0. 36 Conversion (Wt. Percent of Feed) 2 32 53 30 Yield Wt. Percent of Converted Feed:

Tar Acids 080-230 C.) 47.2 47.1 37.9 39.4 Neutrals (180230 C.) 3 8. 8 10. 9 13.4 10. 3 Residue (B. P. above 300 C.) 12. 7 6. 5 8. 9 6. 4 Gus 7. 5 6. 7 8.3 3.4 Carbon 23. 8 28. 8 31. 2 40. 9

K Run Number 1 was conducted with a raw distillate ta'r acid fraction which had not been freed of tar bases prior to the cracking treatment. gggser runs were conducted with tar acids which had been freed of 1 Any materials boiling in the range 230 to 300 C. are reported as unconverted feed.

3 Neutrals as reported in Table I are those compounds which remain undissolved in caustic soda during the separation procedure set forth in Ind. dz Eng. Chem. 32, 1614 (1940).

The results reported in Table I establishedthat my new process is eifective for converting high boiling tar acids (i. 'e., those boiling above 230 C.) into low boiling 'tar acids (i. e., those boiling below 230 C.). Low boiling neutral oils in the products from my process also can be be marketed at an advantage over the high boiling tar acid feedstock. v

In general, the rate of conversion increases with the temperature and also with the contact time between the feed material and the catalyst.

It should be noted that my new process will operate to crack tar acids which have not been freed of tar bases. This is surprising in view of the fact that tar bases are well known as a catalyst poison. For example, in run 1, taracids which had not been freed of 'tar bases were converted at a rate of 25 percent; the preliminary removal of the tar bases, run 2, increased the conversion to 32 percent under otherwise similar conditions,

I have found that the rate of carbon laydown can be reduced by using an inexpensive neutral hydrocarbon distillate fraction as diluent for the high boiling t'ar acids. Particularly 1 have found that an effective diluent is 'the neutral oil derived from the tars produced by low 'temper ature carbonization of bituminous coal.

Results of two runs "employin neutral "oil as "diluent are reported in Table II. In runs 5 and 6, 45 parts by weight of 230-300 C. tar acids were mixed with 100 parts by weight of 160-300 C. low temperature carbonization tar neutral oil. The mixture was passed downwardly at LHSV of 1.10 through a fixed bed of silica-alumina which had at least five percent of its weight of carbon deposited thereon.

Comparison of run 5 using neutral oil with run 4 shows that the neutral oil results in increased conversion of 230-300 C. tar acids without altering'the yield of low boiling tar acids (180-230" C.) at 700 F. Comparison of run 6 and runs 2 and 3 shows that the addition of neutral oils to high boiling tar acids results in increased conversion without substantial change in the production of low boiling tar acids (180230 C.) at 800 F.

A blank run was carried out in which neutral oil alone was passed through silica-alumina catalyst. The carbon laydown from the neutral oils alone was greater than that of the mixture of tar acids and neutral oils under similar conditions of temperature and contact time. Hence, the neutral oil and the high boiling tar acids appear to cooperate to reduce carbon laydown to a value which is less than the sum of the carbon laid down by each material independently.

It is thus possible to convert the high boiling tar acids in a raw tar distillate fraction into low boiling tar acids without the necessity of first separating the tar acids from the neutral oils of the tar fraction. Accordingly not only can the costly step of preliminarily recovering high boiling tar acids free of neutral oils be obviated, the overall recovery of valuable low boiling tar acids is thereby increased. Examples of this operation are set forth hereinafter in Table III.

To illustrate my new process as a continuous operation, low temperature carbonization tar acid oil was vaporized and passed co-currently through a downwardly moving bed of silica-alumina catalyst having various carbon contents. The tar acid oil feedstock was a 230- 300 C. distillate fraction of raw tar produced by low temperature carbonization of bituminous coal. Tar acids content of the feedstock was 33.6 percent by weight; neutral oils accounted for substantially all of the rest of the feedstock. Temperature was 800 F.; LHSV was 0.86 hr.- partial pressure of the tar acid oil was reduced to 0.92 atmosphere by dilution with nitrogen. Results of these experiments are tabulated in Table HI.

Table III Run No 7 8 Average Carbon Content of Catalyst, Wt. Percent 5 11.5 Conversion of 'Iar Acids in Feedstock, Wt. Percent... 72.9 34. 7 Yield of Tar Acids (B. P. range 180-230 C.) Wt. Percent of Converted Tar Acids 13. 2 43. 2 Yield. Wt. Percent of 'Iar Acid Oil Feedstock:

Light Oil to 160 C 3. 6 1. 6 160230 C. Distillate 8. 6 9.0 230-300 C. Distillate 64. 6 83. 8 Water 3. 4 1. 2 Carbon 18.6 2. 1 Gas 1.2 1.3 Tar Acids Content of 130-230 C D tillate, Wt. Percent 38.1 57. 0

As shown in Table III, it is possible to convert tar acids boiling above 230 C. into tar acids boiling below 230 C. in a continuous moving bed process. Moreover it is possible to convert these tar acids boiling above 230 C.

into tar acids boiling below 230 C. without first sepa rating the tar acids from the tar acid oil in which they occur. As much as 50 Weight per cent and more of the converted tar acids are those commercially valuable tar acids boiling below 230 C.

The data in Table III also indicate the substantial improvements in product distribution which results with increased carbon on the catalyst. As the carbon content of the catalyst increases: (1) the conversion rate decreases; (2) carbon is laid down at a reduced rate; (3) the conversion of feedstock to low boiling distillate increases; (4) the tar acids content of the low boiling distillate increases; and (5) the amount of distillate available. for recycle increases. v

The foregoing description of the preferred embodiment of my'invention discloses silica-alumina catalysts consisting of silica and alumina. However, it is to be understood that silica-alumina catalysts as commercially obtainable maycontain minor amounts of other oxides such as magnesia, boria and zirconia. Since it is essential for the purpose of this invention that the catalyst be principally silica and alumina, the amount of other oxides should preferably be kept below ten per cent by weight.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of converting tar acids boiling above 230 C. into tar acids boiling below 230 C. which comprises passing a mixture boiling above 230 C. and containing tar acids and neutral oils in the vapor phase at a temperature of 700 to 850 F. through a catalyst consisting essentially of 1 to 50 weight per cent alumina and 99 to 50 weight per cent silica, said catalyst having carbon deposited thereon in an amount which is at least five per cent by weight of the silica and alumina, and collecting the vaporized products.

2. The method of converting tar acids boiling above 230 C. into tar acids boiling below 230 C. which comprises passing a mixture boiling above 230 C. and containing tar acids and neutral oils in the vapor phase at a temperature of 700 to 850 F. through a catalyst consisting essentially of 1 to 20 weight per cent of alumina and 99 to per cent silica, said catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the silica and alumina, and collecting the vaporized products.

3. The method of treating tar acid oil containing tar acids and neutral oils derived from the tar produced by low temperature carbonization of bituminous coal and boiling above 230 C. which comprises passing said tar acids in the vapor phase at a temperature of 700 to 850 F. through a silica-alumina catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the catalyst, and recovering the product vapors.

4. The method of treating a 230 to 300 C. boiling range distillate fraction of raw tar containing tar acids and neutral oils which has been derived from the tar produced by low temperature carbonization of bituminous coal, which comprises passing said distillate fraction in the vapor phase at a temperature of 700 to 850 F. through a silica-alumina catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the catalyst, and collecting the resulting vapors.

5. The method of treating tar acids boiling above 230 C. which comprises passing said tar acids in admixture with neutral oil in the vapor phase at 700 to 850 F. through a bed of silica-alumina catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the catalyst, and collecting the product vapors.

6. The method of converting tar acids boiling above 230 (3. into tar acids boiling below 230 C. which comprises passing the vapors of the tar acids boiling above 230 C. in admixture with neutral oil vapors through a reaction zone containing a bed of silica-alumina catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the catalyst, maintaining the temperature of said reaction zone between about 700 and 850 F., collecting the product vapors, withdrawing high carbon content catalyst from said reaction zone, regenerating said withdrawn catalyst by burning the carbon deposited thereon, thereafter depositing a fresh layer of carbon on the regenerated catalystin an amount equal to at least five per cent by weight of the catalyst, and returning the resulting carbon coated catalyst to said reaction zone to repeat the above steps.

7. The method of converting tar acids boiling above 230 C. into tar acids boiling below 230 C. which comprises passing a mixture boiling above 230 C. and con E taining tar acids and neutral oils in the vapor form through a reaction zone containing a bed of silica-alumina catalyst having carbon deposited thereon in an amount equal to at least five per cent by weight of the catalyst, maintaining the temperature of said reaction zone between about 700 and 850 F., collecting the product vapors, withdrawing high carbon content catalyst from said reaction zone, regenerating said withdrawn catalyst by burning at least a portion of the carbon deposited thereon, and returning regenerated catalyst having a layer of carbon thereon amounting to at least five per cent of the weight of the catalyst to said reaction zone to repeat the above steps.

References Cited in the file of this patent UNITED STATES PATENTS 2,372,018 Ruthruff Mar. 20, 1945 2,394,978 Brandon Feb. 19, 1946 FOREIGN PATENTS 874,911 Germany Sept. 4, 1952

Claims (1)

1. 6. THE METHOD OF CONVERTING TAR ACIDS BOILING ABOVE 230* C. INTO TAR ACIDS BOILING BELOW 230* C. WHICH COMPRISES PASSING THE VAPORS OF THE TAR ACIDS BOILING ABOVE 230* C. IN ADMIXTURE WITH NEUTRAL OIL VAPORS THROUGH A REACTION ZONE CONTAINING A BED OF SILICA-ALUMINA CATALYST HAVING A CARBON DEPOSITED THEREON IN AN AMOUNT EQUAL TO AT LEAST FIVE PER CENT BY WEIGHT OF THE CATALYST, MAINTAINING THE TEMPERATURE OF SAID REACTION ZONE BETWEEN ABOUT 700 AND 850* F., COLLECTING THE PRODUCT VAPORS, WITHDRAWING HIGH CARBON CONTENT CATALYST FROM SAID REACTION ZONE,

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