US2289716A - Catalytic motor fuel production - Google Patents

Description

July 14, 1942. R. -F. MARscHNER OA'LLYMO MOTOR FUEL PRODUCTION 'Filed oct. 19, 19:59

Patented July 14, 1942y UNITED 'STATE CTALYTIC MOTOR FUEL PBOIUCTION Robert F. Marschner, Chicago, Ill., asslgnor to Standard Oil Company, Chicago, Ill., a corporation of Indiana vApplication October 19, 1939, Serial hlm-300,229

1|)v Claims. (Cl. 196-v-49) This invention relates to the production of high quality motor fuel by catalytic processes and it pertains more particularly to the prepa-ration of aviation gasoline in an improved system employing catalytic dehydro-aromatization, catalytic cracking and catalytic hydrogenation.

Motor fuelproduced by catalytic cracking may be objectionable for aviation purposes because of itsy higholenic content and its consequent high acid heat. The acid heat test is a common method for determining the unsaturated content of gasoline and is described, for example in volume IV of Science of Petroleum, page 2430 According to this test the acid heat number is expressed as th'e number of degrees F. rise in temperature, following the addition of 30 cc. of 66 B. sulfuric acid to 150 cc. of fuel to be tested .in a Dewar ask. Themixture is thoroughly agitated and the temperature e during a three minute Aperiod following the ad ition of the acid a low acid heat.

Benzol is objectionable as a motor fuel in many instances because of its low total heat content. However, benzol and alkyl substituted benzols have excellent antiknock properties. An object of the invention is to provide a motor fuel which 'contains substantial quantities of aromatics, which is characterized by a high octane number and which simultaneously meets rigid specifications with regard to total heat content.

Afurther object of the invention .is to provide an improved aviation gasoline which'will meet rigid volatility specifications and in which the various componentsof different boiling range areV chemically constituted to obtain maximum overall antiknock propertiesy and to insure the most elcient' engine performance. A further object is to provide a motor fuel with good lead response, i. e., one in which theaddition of small amounts of lead tetraethyl will produce 4relatively large' increases in octane number.

A further object is to provide a new combina# tion of catalyst conversion systems with means for producing the hydrogen in one part of the system and utilizing said hydrogen in another part of the system. A further object is to provide an improved method for treating the components of a petroleum oil or oil fraction whereby maximum yields of high quality gasoline are obtained in each step with a minimum degradation to gas and coke.

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tively and efliciently to utilize catalytic .cracking in a combination system involving dehydroaromatization and hydrogenation. A further object is to provide an improved process wherein the hydrogenation step is applied only to a particular and relatively small fraction of the materials which have previously undergone catalytic conversion steps. Other objects will be apparent as the detailed description of the invention proceeds.

'Ihis invention is based on the discovery that certain naphtha, gas oil or heavy oil fractions fis expressed as the acid heat. `An object of my invention is to catalytically produce a high knock -catalytically produced gasoline prior to hydrorating motor fuel l'which will be characterized by require different conversion conditions than do other fractions and that heavy fractions produced by dehydro-aromatization are particularly amenable to catalytic cracking. I have found that it is unnecessary to hydrogenate the entire gasoline fraction from catalytic cracking in order to obtain a finished gasoline of desired low acid heatk and high lead response and an important feature of my invention is the fractionation of genation so that only the small fraction is subjected to hydrogenation. Furthermore, only partial hydrogenation of this fraction is necessary and even desirable. I have found that the desired A further object of the invention is more effecchemical constitution of the individual hydrocarbons which make up nished gasoline is best obtained if: (a) the C4 and C5 fractions are kept out of the charging stock to the dehydro-aromatization unit; (b) the naphtha fractions are subjected to dehydro-aromatization; (c) the heavier fractions together with heavy products from dehydro-aromatization are subjected to catalytic cracking; and (d) the light catalyticallyjcracked naphtha (which may include light aromatized naphtha) is partially hydrogenated without hydrogenating the hea y fractions. Referring more specifically to the partial hydrogenation, I have found that catalytically cracked gasoline contains two types of oleilns: the unsubstituted ole- -ns and the branched chain, substituted or isoolens. I have found that the unsubstituted oleilns are hydrogenated much more easily than the substituted olefns. Thus the two hexenes cm-Ld-cmcm and blending octane number, but the-second hydrogenates much more easily than the first.

Furthermore, the lighter parains such as isoand n-pentanes show exceptionally high lead response, making hydrogenation of these cuts desirable. On the other hand hydrogenation of the heavy cuts is undesirable, even if carried out partially, since the less branched parafhns, although showing a high lead response,`have extremely low octane numbers, causing an excessive fall in O. N. upon hydrogenation.

Partial hydrogenation of the lighter fraction of catalytically cracked gasoline, when effected to the extent of 20% to 90%, preferably about 6075%, selectively leaves unhydrogenated the substituted olefins (to which much of the clear octane number of the gasoline may be attributed) and give a product of low acid heat which will have an increased lead tetraethyl response.

Complete hydrogenation of a cut boiling at ISO-160 lowers the O. N. from 81 to 72, whereas hydrogenation of 225250 cut lowers the O. N. from 80 to 62. This O. N. lowering is even greater in such fractions as the 350-400 cut.

The partial hydrogenation may be effected with the impure hydrogen produced in the system itself and the utilization of this hydrogen in the finished motor fuel results in increased gasoline yield. Not only may impure hydrogen be used for securing this partial hydrogenation, but the catalysts employed may likewise be of only mod-- erate activity. They are therefore less expensive and are longer-lived than catalysts ordinarily employed for absolutely complete hydrogenation of olefins to parafiins.

In practicing my process I fractionate the charging stock into a C5 and lighter fraction, a naphtha fraction and a heavy fraction. The C4 and Cs hydrocarbons may -be yblended directly with finished gasoline, any excess being withdrawn from the system. The naphtha is catalytically dehydro-aromatized to increase its knock rating and to supply hydrogen. The heavy fraction is c'atalytically cracked and fractionated. Lightv naphtha produced by catalytic cracking (which may have an end point of about 150 to 250 F. and which may include light naphtha produced by dehydru-aromatization) is then partially hydrogenated with the hydrogen produced in the dehydro-aromatization step. The heavy cracked naphtha, which may have an initial boiling point of about 150 to 250 F. and an end point of at least 350 to 400 I` is blended with the finished gasoline without hydrogenation. By means of this integrated catalytic system I obtain maximum yields of high octane number gasoline which when properly fractionated and blended not only meets motor fuel requirewents but which meets the rigorous requirements of aviation gaso- The invention will be more clearly .understood from the following detailed description read in conjunction with the accompanying drawing which forms a part of this specification and which is a simplified schematic flow diagram of my improved conversion system.

My invention is not limited to any particular feed; it may carbonaceous materials, by the catalytic conversion of carbon monoxide and hydrogen or by any other known method. Preferably the original charge is straight-run or parainic hydrocarbon of wide boiling range and a relatively low octane number. In 'the preferred embodiment of the in- 'be either straight-run or crackedV or it 4may be produced by the hydrogenation ofl vention I will describe the conversion of straightrun charge obtained from East Texas crude.

The catalyst employed for the naphtha reforming or dehydro-aromatization step is preferably an oxide of a VI group metal mounted on active alumina or activated alumina (a form of alumina obtained as a scale in 'aluminum ore purification) or alumina gel. About 2 to 10% of molybdenum oxide on alumina or about 8 to 40% of chromium oxide on alumina have been found to give excellent results. The minor ingredient of the catalyst is preferably an oxide or sulde of'molybdenum, chromium, tungsten or uranium or any mixture thereof mounted on bauxite, precipitated alumina, activated alumina" or any other suitable catalyst support. Magnesium, aluminum or zinc chromites, molybdenites, etc. may be employed. Vanadium and cerium oxides have been found to be eiective for this conversion. Oxides of copper, nickel, manganese, etc. may be included to' facilitate regeneration or to supplement or promote catalyst activity. It should be understood, however, that the present 4invention is not limited to any particular catalyst but is `applicable to the use of any dehydroaromatization catalyst known to the art.

The catalyst may be made by impregnating "activated alumina or other support with molybdic acid, ammonium molybdate or any other cata.- lyst compound decomposable by heat. Also the aluminum and molybdenum oxides may be coprecipitated as a gel or the separate oxides may be mixed together as a paste, dried, extruded under pressure or pelleted and heated to a temperature of about 1000 to 1200 F. Since the preparation of the catalyst forms no part of the present invention it will not be described in further detail. t

For the catalytic' cracking step the catalyst is preferably an lactivated hydrosilicate of alumina or an active silica gel impregnated with a metal oxide, although it should be understood that cracking catalysts of any known type may be used. So-called natural catalysts may be made by treating fullers earthjor other natural clays with acid or with aqueous solutions of chlorides or sulfates of magnesium, aluminum, manganese, etc. the ,treated catalyst then being washed, dried and pelleted. An acid-treated clay of the type commonly marketed as Super-Filtrol has been found to be an excellent catalyst for cracking and is an example of the so-called "activated clay commonly used in the decolorizing of lubricating oils, which activated clays are also good cracking catalysts.

Synthetic cracking catalysts may be prepared by depositing on silica gel oxides of such metals as aluminum, cerium, beryllium, thorium, zir-l conium, cadmium, copper, boron, titanium, manganese, magnesium, etc. Natural or artificial zeolites may be used as cracking catalysts when the alkali metals therein have been replaced by oxides of the metals hereinabove listed, particularly aluminum, copper, cadmium, manganese, magnesium, etc. 'Ihe catalyst may be used in granular or pelleted form and it may for instance be made into a thick slurry or paste, molded, pelleted or extruded by conventional means, dried at about 300 to 400 F. and nally heated to about 800 to 1200 F. or higher. The preparation of the cracking catalyst forms no part of the present invention and it will not -be described in further detail.

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rality of beds in vertical towers or chambers.

The moving catalyst may be charged to the top of a tower or tube either continuously or intermittently, the spent catalyst being withdrawn from the base of the tube at substantially the same rate; in this case the reaction takes place continuously and under substantially constant conditions of temperature and pressure, the regeneration being eifected outside of the conversion zone. The powdered catalyst may be fed into a rapidly moving stream of vaporized naphtha and hydrogen, separated therefrom after reaction is completed and separately regenerated by oxygen while suspended in flue gas. Any of these specific catalyst reactors or their equivalents may be used in practicing the invention, but they will not be described in further detail.

Referring specifically to Figure 1, a crude East Texas petroleum is passed from a heater or pipe still (not shown) through line I to fractionator I I` from which a butane-pentane fraction is withdrawn overhead through line I2, a naphtha fraction is Withdrawn through line I3 and 'a heavy fraction such as gas oil is withdrawn through line I4 lubricating oils or tarry fractions being withdrawn through line I5.

The naphtha fraction may be supplemented by other naphthas from outside sources introduced through line I6. Generally speaking, the boiling range of this fraction will be in the general range of from about 150 to 350 F. and it will contain predominantly hydrocarbons ranging from about 6 to 12 or 14 carbon atoms per molecule. This naphtha fraction is passed by pump I1 through coils I8 of `furnace I9 and thence through transfer line to catalyst chamber 2 I.

Hydrogen from line 22 may be passed by compressor 22a through line 23 for admixture with charging stock in line I3 or it may be passed through separate coil 24 in furnace I9 and then introduced into transfer line 20 or directly into catalyst chamber 2l.

The reaction in the catalyst chamber is preferably effected at a space velocity of about 0.04 to 10, preferably about 0.2 to 2-fvolurnes of liquid naphtha per volume of catalyst space per hour at a temperature of about 875 to 1075 F., preferably about 950 450 pounds per square inch, preferably about 200 pounds per square inch, and in the presence of about .4 to 8 mols of hydrogen to 1 mol of-naphtha, preferably Iabout 3 mols of hydrogen per mol of naphtha. 1

Reaction products and vapors leave reaction chamber 2I through line 25, are passed through heat exchanger 25 and cooler 21 and are then introduced into hydrogen separator 28 which is preferably maintained at substantially reaction pressure but at a temperature of about to 105 F. Separated hydrogen is withdrawn through line 29 (any excess or unduly low grade hydrogen being vented through line 30) and boiling range (so-called polymers) are withdrawn through line 31 and removed from the system through line 38 or preferably introduced through line 39, together with gas oil from line I4, into the coils 40 of pipe still 4I. Outside gas oil may be introduced into line I4 thru line Ila when crudes containing high proportions of.

naphtha are charged to -fractionator II. The charging stock is heated in coils 40 to a temperature of about 875 to 925 F. under 'a pressure of about atmospheric to 50 pounds per square inch and is then introduced by transfer line 42 to catalytic cracking chamber 43. Space velocity in the cracking' chamber is preferably about 0.5 to 2 volumes of liquid feed per volume of catalyst space per hour, and the average cracking temperature is preferably about 850 to 950 F.

Products from the catalytic cracking step are withdrawn through line 44 and introduced into fractionating column 45 which is provided with suitable reflux and reboiler means. Hydrogen and hydrocarbon gases are taken overhead through line 46. A light cracked naphtha fraction with an end point preferably within the range of 150 to 250 F. is withdrawn through line 41. Heavy cracked naphtha .is withdrawn through 48 and gas-oil and heavier fractions are removed from the base `of the column through line 49; these heavier fraction may either be removed from the system through line 5i] or returned by pump 5I and line 52 to line I4 for further cracking. It should be understood, of course, that any number of side streams may be taken from this fractionator and that suitable side stream strippers or other expedients may be employed forobtaining the desired boiling range, flash point, end point, volatility, etc. of each fraction. Instead of employing only a single gasoline F., at a pressure of about 50 to passed by pump 3| to hydrogen storage 32.

Liquid from separator 28 is withdrawn through line 33, heated in exchanger 26 and introduced into fractionator 34 fro-m which gases are taken overhead through line 35 and aromatic gasoline is withdrawn as a side stream through line 36. Products boiling above the gasoline or motor fuel storage tank l may employ a number of tanks, particularly when motor fuel and aviation fuel of different grades are desired.

An important feature of the invention is the segregation of the light cracked naphtha for subsequent partial hydrogenation. As hereinabove pointed out, the partial hydrogenation of this particular fraction does not materially lower its octane number` while lit markedly lowers its acid heat and markedly improves its response to lead tetraethyl. This light cracked naphtha of about to 250c F. end point, withdrawn through line 41 is -passed through coils 53 of furnace 54 and then introduced through transfer line 55 to hydrogenation reactor 56. Hydrogen may be introduced from storage tank 32 and line 51 either through line 58 with incoming charging stock or through separating heating coil 59 which discharges into transfer line 55` or into the hydrogenation chamber 5G. Pump 60 and compressor 5I are provided in lines 41 and 51, respectively, for maintaining the necessary hydrogenation pressure which may vary from 50 pounds or lower to upwards of 3,000 pounds, depending upon the catalyst temperatures, space velocities,

etc. employed in the hydrogenation reactor.

The hydrogenation catalyst may be of any type known to the art. Oxides or suliides of VI group metals such as molybdenum, tungsten,-

metals supported 'on pumice, silica or preformed porcelain may be employed. In the case of the VI group oxides or sulfides the hydrogenation conditions may be about the same as those used and other operating conditions will be controlled to bring about only partial hydrogenation, i. e. a saturation of about 20% to 90% or preferably about 60 to 75% of the oleflns in the cracked light naphtha. The pressure for such hydrogenation Amay be from about 200 to about 3000 pounds per square inch. The space velocity may be higher than that used in dehydrogenation, for instance about 1 to 5 volumes of charging stock per volume of catalyst space per hour. The temperature may be somewhat lower than that used for dehydrogenation, i. e. of the order of 550 to 850 F.

When catalysts such as nickel are employed dehydrogenation may be effected at lower pressures, ranging from atmospheric to 50 pounds. The temperatures may be from about 350 to 450 F. and space velocities may be of the order of 8 or 10 volumes of liquid charged per volume of catalyst space per hour. The hydrogenation step per se is, of course, well known in the art and I modify this Well-known process by employing sufficiently higher space velocity or sufficiently lower temperature or pressure to obtain only partial instead of complete saturation of the olefins in the light cracked naphtha.

Products from the hydrogenation reactor 56 are passed by line 62 through cooler 63 to hydrogen separator 64. If the hydrogen is sufiiciently pure for reuse it may be returned by pump 65 and line 66 to storage tank 32. The hydrogenated products are Withdrawn from the base of the separator through line 61 and are further fractionated if such fractionation is necessary before being passed to the proper gasoline storage tank.

If the gases in line 46 do not contain appreciableamounts of hydrogen they may be passed directly to line l2. Butanes and pentanes from `lines I'2, 35 and 46 may then be passed through cooler 68 to separator, stabilizer or depropanizer tower 68, from which propane and lighter gases are taken overhead through line 10 and pentane, together with some butanes are withdrawn as a liquid through line 1|. Excess butanes and pentanes may be vented through line 1| a.

If the gases in line 46 contain sufficient hydrogen for recovery such gases may be compressed by compressor 12 land introducedv through line 13 and cooler l14 to hydrogen separator 15, the hydrogen passing by line 16 to line 66. vLiquid from separatoris preferably introduced Iby line 11 to tower 69. When the gases from separator 64 for dehydrogenation, except that space velocity contain substantial quantities of hydrocarbons v such gases may be passed by line 18 to line 13 for separately recovering hydrogen and hydrocarbons as hereinabove described.

'I'he final gasoline is composed of two or more of the following products: (a) aliphatic Ce hydrocarbons (containing also C4 and Cc hydrocarbons) from line 1|; (b) aromatic hydr-ocarbons from line 36; (c) partially saturated branched chain aliphatic light naphtha from line 61; and (d) heavy cracked naphtha from line 48. Various blends of gasoline may be produced from these products, either for ordinary motor fuel or for aviation fuel. Such fuels will be characterized .'by a low acid heat, a very high octane number, a relatively high total heat content and a good 'lead tetraethyl response. The overall chemical compositions of such fuels will differ from any heretofore produced 'because the heavy fraction thereof will be more highly olenic than the light fractions and beca-use of the aromatic and branched chain structures whichresult from the various conversion steps.

Instead of employing separate fractionating columns 34 and 45, as hereinabove described, I may eliminate fractionator 34 with its associated lines 35, 3B, 31, etc. and pass the products from line 33 through line 19 to line 44 for fractionation in column 45. This effects considerable savings in investment costs. Furthermore, by fractionating materials from line 33 and line 44 in a common fractionating column I mayl hydrogenate the undesirable cracked olens which are present in the light aromatic gasoline fractions along with the olens present in the light cracked gasoline fraction, thereby increasing the overall heat content and markedlyl improving the lead response of the finished gasoline. In this modification the heavier-than-gasoline aromatic products are withdrawn through line 49 and they may either be returned by line y52, line I4 as hereinabove Aciescribed, or they may be returned by lines 52 and to crude fractionator I l.

While I have described in detail a preferred embodiment of my invention it should be understood that I do not limit myself to such details since many alternatives and modifications Will be apparent to those skilled ln the art.

I claim:

1. The method of producing high quality aviation fuel from petroleum hydrocarbons containing fractions of the naphtha .boiling range and fractions boiling above the naphtha boiling range, which method comprises separating hydrocarbons of the naphtha boiling range from heavier hydrocarbons, dehydro-aromatizing the hydrocarbons of the naphtha boiling range to produce an aromatic gas-oline fraction and a heavy fraction, catalytically cracking the combined heavierthan-naphtha fraction and the heavy fraction from the dehydro-aromatization step, separating the catalytically cracked products into a light cracked gasoline and a heavy cracked gasoline fraction, respectively, partially hydrogenating the light cracked gasoline fraction and blending the aromatic gasoline with the hydrogenated light cracked gasoline and the heavy cracked gasoline, respectively, to form a `blended aviation fuel oi' low acid heat and high antiknock. f

2. The method of claim 1 which includes the further step of separating butanes, pentanes and lighter hydrocarbons from the naphtha fraction prior to dehydro-aromatization, removing lighter hydrocarbons from said separated butanes and pentanes and blending said butanes and pentanes with the aromatic gasoline fraction, hydrogenated light cracked gasoline fraction and heavy cracked gasoline fraction, respectively, to form an aviation fuel of improved volatility, knock rating and lead response.

3. The method of claim 1 which includes the step by hydrogenating at least a part of the light aromatic gasoline simultaneously with the hydrogenation of the catalytically cracked gasoline.

4. The method of making high quality gasoline from a charging stock containing naphtha and gas oil which method comprises catalytically dehydro-aromatizing said naphtha to produce hydrogen, aromatic gasoline and an aromatic oil heavier than gasoline, catalytically cracking said gas oil in the presence of said aromatic oil heavier-than-gasoline, separating the catalytic cracking products into a light gasoline fraction and a hydrogenating said light cracked gasoline fraction to effect saturation oi' at least but' not more than 90% of the olens contained therein vwith hydrogen produced in the dehydro-aromatization step and blending the hydrogenated product with the aromatic gasoline and the heavy cracked gasoline fractions, respectively. t

5. The method of lowering the acid heat of catalytically cracked gasoline without unduly impairing its octane number and tetraethyl lead response, ,which method comprises fractionating `said cracked gasoline into a, light fraction having an end point of 150 to 250 F. and a heavy fraction, respectively, hydrogenating said light fractionto eieot at leastA 20% saturation but not more than 90% saturation of the-olens contained therein and blending the partially hydrogenated light yfraction with the unhydrogenated heavy fraction.

6. The method of lowering lytically cracked gasoline .without unduly impairing its octane number and tetraethyl lead response, which method comprises partially hydrogenating a light fraction of saidv catalytically cracked gasoline having an end point of 150 to 250 F. to effect about 60% to 75% saturation of acid heat of catal the olefins contained therein and blending the partially hydrogenated light fraction with an unhydrogenated heavy fraction of said catalytically cracked gasoline. 7. An integrated process for making low acid heat, high octane number gasoline from petroleurn charging stocks containing hydrocarbons of the naphtha and gas oil boiling ranges, which method comprises dehydro-aromatizing a naphtha fraction of the charging stock for the production of an aromatic gasoline .fraction 'catalytically cracking a gas oil 'fraction of said charging stock, fractionating the products of the cata,- lytic cracking step to obtain a light naphtha fraction having an end point of about 150 to 250 F., partially hydrogenating said light nwphtha fraction to saturate at least 20% butnot more than 90% of the oleiins contained therein anda mended aviation fuei of1ow acid heat and high i antiknock.

'8. An integrated process for making low acid v heat,` high octane number gasoline from charging stocks containing n'aphtha and gas oil, which method comprises dehydro-aromatizing a naphtha fraction of said charging stock to produce hydrogen, a gasoline fraction and a fraction heavier than gasoline, catalytically cracking the fraction heavier than gasoline with a gas oil fraction from the charging stock, separating the catalytically cracked products into a light cracked gasoline fraction having an end point of 150 to 250 F. and a heavier fraction, hydrogenating the light cracked gasoline fraction to an extent sufficient to saturate yat least 20% but not more than 80% of the oleiins contained therein, effecting said hydrogenation with hydrogen produced in the dehydro-aromatization step and blending the hydrogenated cracked fraction with the gasoline produced by dehydro-aromatization to form a blended motor fuel of low acid heat and high antiknock properties. i

9. The method of claim 8 wherein the hydrogenation is effected under conditions for obtaining saturation of at least 60% but not more than '15% of the oleiins in the catalytically cracked gasoline fraction.

10. A' hydrocarbon conversion process which.

comprises catalytically dehydro-aromatizlng A naphtha to produce hydrogen, a gasoline fraction and a fraction heavier than gasoline, catalytically cracking the heavier-than-gasoline fraction, sep- -arating a cracked gasoline having an end `point of to 250 F. from the products of the catalytic cracking step and partially hydrogenating the ROBERT F.. MARSCI-INER.

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