US2934490A - Two-pass hydroforming - Google Patents

Description

United States Patent TWO-PASS HYDROFORMIN G Donald Dnnwody Dnnlop, Baton Rouge, La., and Charles E. Hemminger, Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application January 30, 1957, Serial No. 637,232

5 Claims. (Cl. 208-65) The present invention relates to improvements in hydroforming. More particularly the present invention relates to a process involving hydroforming of a Wide boiling range naphtha in an operation in which the naphtha components or fractions are treated separately under conwhich involves dehydrogenation of naphthenes to form the corresponding aromatics, isomerization of paraffins and carbocyclic compounds, some aromatization of parafiins and .hydrocracking of the highest boiling parafiins. The process results in the production of sufiicient hydrogen to supply the requirements of the hydroforming operation, in most cases.

Heretofore and'prior to the present invention others have proposed separately treating, in blocked operation, otherwise separate fractions of the original feed naphtha, under difierent conditions. For example, it has been proposed previously to hydroform a whole naphtha and separate from the product a so-called heart cut which is either recycled for further treatment in the hydroforming step or treated in a second zone operated under the same or dilierent conditions than the whole naphtha. The purposes of retreating a heart out fraction of the hydroformed naphtha include aromatization of cyclic compounds'which, in the first pass through the hydroforming were merely isomerized as, for example, where an allrylated 'cyclopentane was isomerized to form an alkylated cyclohexane in the first step. During the second treatment, the isomerized hydrocarbon is treated, by dehydrogenation, to form benzene, toluene or xylene, depending on the number of side chain carbon atoms present in the substituted cyclopentane. Another purpose of retreating the heart cut, according to prior art practice, was to supply heat to the reaction zone and this may be accomplished by recycling the reheated heart cut obtained from the product recovery equipment which recycled cut, of course, possessing a much higher heat capacity than the recycle gas, which in prior practice also been reheated and recycled for this purpose. The recycling of heated product not only supplies heat to the-hydroforming step but also permits reduction of the quantity of hydrogen-containing recycle gas that must be returned to the reaction zone. This reduction in the amount of hydrogen recycled to the hydroforming zone for reasons of equilibrium considerations favors the dehydrogenation of the naphthenes and is therefore, within limits, a preferred procedure.

jThe present invention, in brief compass, involves a process in which a'wide naphtha fraction boiling, say from about '170" F. and 340+ F., is first hydroformed under mild conditions hereinafter more fully explained. At this point it will simply be stated that the hydroforming operation of this wide "boiling range fraction is hydroformed under conditions such that the product obtained will have an F-l octane rating of from about to 80,. The product from this low severity hydroforming step is then subjected to fractional distillation and the fraction boiling within the range of from about 175 to 290 F. is subjected to a second stage of hydroforming under severe conditions, hereinafter also more fully explained, to produce a product having an octane quality corresponding to form about to 99 or higher. The higher boiling material obtained from the first stage of the process, namely, the stage carried out under mild hydroforming conditions is recovered by distillation of the product and after admixture with a heavy second stage product is subjected to thermal reforming in the pres.- ence or absence of hydrogen and the product is subjected to distillation to recover a fraction boiling inzthe C to about 346 F. boiling range and a second product which boils about 340 F. The C to 340 P. fraction thus produced possesses a high octane quality because it contains substantial amounts of aromatic hydrocarbons and also possesses good volatility characteristics so that it forms a valuable constituent which may be included in the premium gasoline pool. Referring again to the product obtained from the second-pass hydroforming of the to 290 P. fraction the product obtained therefrom is subjected to distillation and the material boiling above about 320 F. is recovered from this distillation and mixed with the heavy or high boiling fraction recovered from the first-pass hydroforming stage as pro.- viously indicated and the mixture is subjected to thermal reforming conditions in the absence or presence of hydrogen. A fraction boiling substantially within the range of from about C to 320 F. is recovered fromthe fractional distillation .of the second stage high severity process and this material possesses both high octane quality and good volatility characteristics and'therefore may be delivered to the premium gasoline pool. i

The procedure indicated above serves to correct a number of problems that have arisen in prior practice. Among these are: (1) By hydroforming the C to 175 P. fraction a loss of yield due to hydrocracking results and in the present invention this fraction is not hydro? formed. (2) One-pass hydroforming at high severity results in excessive cracking off of paraffin chains attached to the higher boiling n-aphthenes and excessive cracking of the high boiling parafiins so that excessive dry gas and C hydrocarbon yields result. (3) Subjecting the Whole naphtha including the high boiling material boiling above about 340" F. to severe hyroforming results inthe formation of as much as 5 weight percent heavy polymer based on the original feed and this polymer is not only useless as a constituent of gasoline but more importantly it decomposes on the catalyst causing excessive coke formation and rapid decrease in activity of the catalyst. These insufiiciencies are corrected, according to the present in,- vention, by the two-stage operation in which the original feed comprising wide boiling range naphtha is subjected to mild conditions of hydroforming and only the intermediate fraction is subjected to severe conditions of hydroforming. The high boiling material recovered'from the first stage of the present process is thermally reformed usually in the presence of hydrogen to crack oil or de alkylate the high boilingaromatics. This may be carried out in the absence of hydrogen. These high boiling alkylated aromatics, it has been found, cause excessive carbon formation in a gasoline motor particularly where the alkyl chains are branched and at the same time, of course, they possess poor volatility characteristics.

The main object of the present invention is to subject a virgin naphtha preferably, but also a cracked naphtha, a synthetic naphtha or various mixtures of these naphthas to hydroforming in the multi-stage oper- Patented Pr- 26, 6(1

a hydroforming operation under Conditions which will' minimize very substantially the amount of polymers which are formed during the conventional hydroforming oper- 'ation.

Another object of the present invention is to produce a product by hydroforming, coupled with dealkylation of high boiling alkylated aromatics in an integrated operaation wherein excess hydrogen produced during hydroforming may be utilized during the dealkylation step to produce a motor fuel conducive to engine cleanliness. A still further object of the present invention is to operate the combination process described herein in such a manner as to cause a minimum amount of cracking of C paraffins thus avoiding polymerization of unsaturates normally formed during such cracking. A still further object of the invention is to effect hydroforming of the mid-boiling fractions of the feed naphtha at a time when they are more refractory and heat stable and are therefore adapted for 'treatment' under severe hydroforming conditions without excessive degrada tion thereof.

Other and further objects of the invention will appear in the following more detailed description and claims.

In the accompanying drawing there is shown diagram- 'matically an apparatus layout in which a preferred modification of the invention may be carried into effect.

- Referring in detail to the drawing, 1 represents a naphtha feed line by means of which a naphtha of wide boiling range is introduced into the present system which feed naphtha is mixed with recycled hydrogen-containing gas from line 2 and this mixture is then charged to heating means 3, such as a furnace, wherein it is heated to a-temperature of about 850 F., thence withdrawn from said heating means via line 4 and charged to the top of a vessel 5 containing a fixed bed of catalyst C. The catalyst in bed C contains a small amount of platinum and also chlorine or some other halogen and is hereinafter more fully identified. The conditions in vessel 5 are set forth hereinafter. The product is withdrawn from reactor 5 through line 6 and to a cooling means 7 wherein it is cooled to about 100 F. to condensenormally liquid constituents, thence withdrawn from the cooling means and conducted to a separator 9 via line 8. A hydrogencontaining gas is withdrawn overhead through line 10 and at least a portion of this gas is recycled to line 2 for further use in the system. The remainder is withdrawn 3 from the system; The liquid product is withdrawn through line 11 and in the usual manner it is subjected to distillation to recover the following: (1) Normally gaseous material containing less than 4 carbon atoms which are withdrawn overhead via line 13 and utilized in the manufacture of chemicals, as a fuel or otherwise utilized; (2) a C to 175 F. fraction withdrawn overhead through line 14 and conducted to gasoline pool (not shown); (3) a fraction boiling substantially within the range of from about 175 to 290 F. withdrawn as a-side stream through line 15, thence charged with hydrogen in line 16 to a furnace or other heating means 17 where it is heated to a temperature of about 925 to 1000 F., withdrawn through line 18 from said heating means and subjected to a second stage of hydroforming in a retort 19 in which is disposed a fixed bed of a platinum-containing catalyst C. Under conditions more fully set forth hereinafter, the desired hydroforming converslon reaction occurs and the product is withdrawn from hydroformer 19 through line 20 and after cooling in 21 it is passed to separator 23 via line 22 from which product is withdrawn through line 24 and conducted to a second fractional distillation column 25 wherein the product is subjected to distillation to recover the following: (1) a normally gaseous material containing C -C; 75 Octane rating, CPR. 75

. 4 hydrocarbons which is withdrawn overhead through line 26 and utilized in any known manner to recover, for some useful purpose, such as suggested hereinbefore as to the utilization of the overhead from distillation column 12; (2) a fraction boiling within the approximate range of C to 175 F. which is withdrawn through line 27 and delivered to gasoline storage pool; (3) a second side stream withdrawn through line 28 which boils substantially within the range of from about 175 to 320 F. which preferably is delivered to storage or a pool containing premium quality motor fuel constituents; (4) and, a fraction withdrawn from the bottom of column 25 via line 29 boiling above 320 F. which is combined with the heavy bottoms withdrawn from fractional distillation column 12 via line 30 which latter fraction boils above 290 F. and which latter stream is mixed with the material in line 29 in line 30. The mixture is 1 charged to a furnace 31 and heated to a temperature up to 1100" F., thereafter withdrawn from the furnace through line 31 and charged to a thermal reforming reactor 32. Hydrogen-containing gas withdrawn, say, from recycle gas line 33, is mixed with the oil in line 29 and heated with the latter in furnace 31. The thermally reformed product is withdrawn from the bottom of reactor 32 and subjected to distillation in column 34. From column 34 a fraction boiling within the range of from about C to 340 F. is recovered through line 35 and this fraction may be delivered to the premium gasoline pool while a second stream boiling above 340 F. is withdrawn through line 36 and delivered to a gasoline storage pool. Overhead through line 37 and from the bottom of column 34 through line 38 there is recovered normally gaseous material and heavy bottoms respectively both of which may be utilized in any suitable manner forming no part of the present invention.

In order to give more information the following'specific example is set forth as to the operating conditions in the several parts of the present combination process and the results attainable.

Conditions in hydrofarmer 5 Catalyst composition,

wt. percent Eta A1 0 98.9, C1 0.5, Pt 0.5 Temperature, F. (average) 850 Pressure, p g 200 Oil residence time, seconds 20 Recycle gas rate, s.c.f./bbl 5000 Concentration of hydrogen in recycle gas, vol. percent Inspection of feed to hydroformer 5 Boiling range, F to 340 Vol. percent naphthenes 45 Vol. percent paraffins 45 Vol. percent aromatics 10 Wt. percent sulfur 0.0001 Octane rating, CFR 45 Inspection of product from hydroformer 5 Boiling range, F 70 to 390 Vol. percent naphthenes 20 Vol. percent paraflins 45 Vol. percent aromatics 35 Wt. percent sulfur Nil Octane rating, CFR 75 Inspection of feed to hydroformer 19 Boiling range, F to 290 Vol. percent naphthenes 25 Vol. percent parafiins 45 Volnpercent aromatics 30 Wt. percent sulfur.... Nil

Conditions hydrbf f same as in s Concentration of hydrogen in recycle gas,

' vol. percent 85 Inspection of the product from hydroformer I9 Boiling range, F 70 to 430 Vol. percent naphthenes Nil Vol. percent parafiins 8 Vol. percent aromatics 92 h Wt. percent sulfur Nil Octane rating, CFR 'l00+0.5 cc. TEL

Inspection of feed tothermal reformer 32 Boiling range, F 290 to 430 Vol. percent naphthenes Nil Vol. percent paraflins -5 Vol. percent aromatics 95-100 Wt. percent sulfur Nil Octane rating, CFR 100 with 1.5 cc. TEL Conditions in reactor 32 Temperature, F 1100 Pressure, p.s.i.g. 1000 Reaction time, sec 100 Gas rate, s.c.f./bbl 1000 Concentration of hydrogen in gas, percent 85 Inspection of the product from thermal reformer 32 Boiling range, F 70 to 400. Vol. percent naphthenes 0. Vol. percent paraffins 0-5. Vol. percent aromatics 95-100.

Wt. percent sulfur Nil.

Octane rating, CFR Isooctane +1.5 cc. to

isooctane+3 cc. TEL.

1 Fuel rated equivalent to isooctane plus 1.5 to 3.0 cc. TEL in F-l engine.

It will be understood that the foregoing specific example is merely illustrative and does not impose any limitation on the invention. Thus good results are attainable in the reaction vessels under the conditions listed below. It is pointed out that with the passage of time, the catalyst decreases in activity and the temperature must be increased in both reactors as much as 65 F. after which the catalyst must be regenerated. The catalyst may be regenerated every 4 to 6 months by first treating with diluted (2% O and thereafter with straight air containing C1 Conditions in reactor Catalyst composition, wt. percent Pt 0.05-2, C1 0.5-2, remainder A1 0 Temperature, F 850 to 900. Pressure, p.s.i.g 100 to 500. Oil residence time, seconds 15 to 50. Recycle gas rate, s.c.f./bbl 2000 to 6000. Concentration of hydrogen in recycle gas, vol. percent 70 to 95.

Conditions'in reactor Catalyst None Temperature, F 950-1200 Pressure, p.s.i.g 500-2000 Reaction time, seconds 30-200 Gas rate, s.c.f./bbl 500-2000 Concentration of hydrogen in gas, percent -90 Other modifications of the invention will be apparentto those skilled in the art, e.g., other catalysts, such as molybdena on alumina in both stages of hydroforming utilizing the fluidized catalyst technique. Steam may be included in the feed to the thermal treatment.

While the herein described invention has potential disadvantages in that it may require two hydroforming reactors and two fractional distillation columns, these disadvantages are more than offset by the following advantages of the present process emphasizing mild catalytic hydroforming attainable by operating at lower temperatures and higher rates of oil followed by more severe reforming plus thermal treatment of the heavy or high boiling reformer products.

(1) The hydrogen purity in the off gas from the first reactor is very high, especially where the catalyst contains platinum.

(2) Omission of the 0 to 175 F. fraction from the herein described treatments.

(3) Very little cracking of the C paraffins results in the low severity operation.

(4) Increase in the naphthene dehydrogenation rate because of rejection of diluting light products before second pass processing.

(5) Feed to a high severity operation is considerably more stable at the high severity conditions resulting in a higher yield octane ratio.

(6) Less polymerization results in the mild, low severity hydroforming operation.

(7) The thermal reforming of high boiling material which contains a relatively large amount of alkylated aromatics to form a product of high octane quality boiling in the motor fuel boiling range serves to increase the overall yield of desired product. I

(8) The removal of heavy or high boiling material from the hydroformed product of the first stage herein decreases the rate of carbon build up on the catalyst, serving to extend the on-stream period, less frequent catalyst regeneration and hence catalyst life.

(9) Improvement in the aromatics distribution effected by the thermal treatment, i.e., more benzene and toluene formed for blending in front ends of motor fuel.

Numerous modifications of the present invention may be made by those who are familiar with the present art.

What is claimed is:

1. The method of treating, in an integrated procedure,

- involving a combination of interrelated treatments, a

naphtha to yield a motor fuel of improved octane quality and volatility which comprises subjecting a naphtha boiling in the range of from about to 340 F. to a mild hydroforming treatment in which temperatures within the range of from about 850 to 900 F. are employed and the naphtha residence time in the hydroforming zone is from 15 to 50 seconds, in the presence of a catalyst and added hydrogen, recovering a product of moderately improved octane quality, separating from said product a fraction boiling in the range of from about to 290 F., subjecting said fraction to a more severe hydroforming treatment, in the presence of a catalyst and added hydrogen, said more severe hydroforming treatment emplaying a temperature within therange of about 925- 1900, F., a pressure of about 100 to 300 p.s.i.g., and an oil residence time'of from'lOO to 200 seconds, separat v ing from the respective products of the said mild and severe hydroforming treatments, a product boiling above about 290 F. and containing substantial amounts of alkylated aromatics, subjecting said alkylated aromatics to a thermal treatment to cause dealkylation of said alkylated aromatics to form a naphtha of increased volatility adapted for blending with hydroformed products to improve the aromatics distribution in the resulting motor fuel.

2. The method of claim 1 in which the catalyst is platinum, further characterized in that the method is carried out in a blocked operation.

- 7 3. The method set forth in claim 2 in which the ther-' mal reforming 'of the high boiling alkylated aromatics is carried outin the presence of added hydrogen.

'.4.The'method set forth in claun 1' 'n 'which'the catalyst in the hydroforming stages is molybdenum oxide carried on a1umin'a,further characterized in that the method is carried 'out in a blocked operation.

5.'The method of claim 1 in which the thermal reforming was carried out at elevated temperatures but not exceeding about 1100 F.

References Cited in the file of this patent V UNITED STATES PATENTS Hemrninger Nov. 18, 1958

Claims (1)

1. THE METHOD OF TREATING, IN AN INTEGRATED PORCEDURE, INVOLVING A COMBINATION OF INTERRELATED TREATMENTS, A NAPHTHA TO YIELD A MOTOR FUEL OF IMPROVED OCTANE QUALITY AND VOLATILITY WHICH COMPRISES SUBJECTING A NAPHTHA BOILING IN THE RANGE OF FROM ABOUT 170* TO 340*F. TO A MILD HYDROFORMING TREATMENT IN WHICH TEMPERATURES WITH IN THE RANGE OF FROM ABOUT 850 TO 900*F. ARE EMPLOYED AND THE NAPHTHA RESIDENCE TIME IN THE HYDROFORMING ZONE IS FROM 15 TO 50 SECONDS, IN THE PRESENCE OF A CATALYST AND ADDED HYDROGEN, RECOVERING A PRODUCT OF MODERATELY IMPROVED OCTANE QUALITY, SEPARATING FROM SAID PRODUCT A FRACTION BOILING IN THE RANGE OF FROM ABOUT 175* TO 290* F., SUBJECTING SAID FRACTION TO A MORE SEVERE HYDROFORMING TREATMENT, IN THE PRESENCE OF A CATALYST AND ADDED HYDROGEN, SAID MORE SEVERE HYDROFORMING TREATMENT EMPLOYING A TEMPERATURE WITHIN THE RANGE OF ABOUT 9251000*F., A PRESSURE OF ABOUT 100 TO 300 P.S.I.G., AND AN OIL RESIDENCE TIME OF FROM 100 TO 200 SECONDS, SEPARATING FROM THE RESPECTIVE PRODUCTS OF THE SAID MILD AND SEVERE HYDROFORMING TREATMENTS, A PRODUCT BOILING ABOVE

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