US2940921A - Fixed bed reforming process - Google Patents

Description

June 14, 1960 J. B. MALLOY 2,940,921

FIXED BED REFORMING PROCESS Filed June 12, 1956 Recycle Gas Ill ,3 L5

N m Fad a 5/2 32 Fuel Gas REACTOR SEPARA T0]? 87A BIL IZER k 3 47 S Q 29 r E 114" fiefarmale Jolm 8. Mal/0y 2,940,921 FIXED BED REFORMING PROCESS .lohnB. Malloy, Lansing, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Filed June 12, 1956, Ser. No. 590,882 3 Claims. (Cl. 208-65) My invention relates to improvements'in the conventional fixed bed process for reforming naphthas in the presence of a platinum containing catalyst. More particularly, my invention is directed to means for improving the yield-octane character of product reformate produced at a given reforming severity by selective handling of C and C hydrocarbon components of the process naphtha.

The C and C hydrocarbons in reforming feed stocks are mainly paraflins. Essentially, the only favorable reaction that C -C parafiins can undergo under reforming conditions is isomen'zation. Aromatics formation occurs only to a negligible extent. The C paraflins do not contain sufiicient carbon atoms for cyclization, while unfavorable thermodynamic equilibria limit the aromatization of hexanes. Hydrocracking obviously is undesirable because scission of the carbon-to-carbon bond in these light hydrocarbons results in taking the products out of the gasoline range.

Isomerization of C and C parafi'ins however causes appreciable improvement in octane number. In a typical Mid-Continent reformer feed, the C and C paraflins have blending octane numbers (CPR-R) of about 62 and 47 respectively. When these parathns are treated under reforming conditions, the resulting isomerization improves their blending octane numbers respectively to about 80 and 61. Thus, the octane number of the light fraction of reformer feeds may be considerably improved by reforming, but, unfortunately in conventional processing, the improvement is obtained only at the expense of considerable yield loss resulting from hydrocracking. The loss may run as high as 30% to 40% by volume, particularly at the higher reforming severities. The art has recognized this problem, and the trend to higher reforming severities has been accompanied by greater reliance on prefractionation, thereby eliminating C and C s from feed stocks subjected to high severity reforming. This merely avoids the problem, however, while at the same time accepting either the loss in potential barrel octanes necessitated by blending the virgin C and C s to finished gasoline or the added cost in processing these hydrocarbons separately.

My process is designed to take advantage of the potential octane improvement which can result from isomerizing C and C paraflins in full range naphtha feed stocks but to avoid the yield loss inherent in processing C s and C s by conventional methods. According to the invention, a full range charge naphtha is processed in a plurality of fixed bed reactors, each containing a platinum type reforming catalyst, whereby the charge is contacted in successive stages with the catalyst with reheating between stages. The charge naphtha is preheated to a temperature substantially in excess of 900 F. and contacted in admixture with hydrogen recycle gas with the catalyst in the first stage under conditions providing an average bed temperature in the range of about 825 to 900 F., preferably, about 875 F. The efiluent from the first stage is separated by fractionation into a C fraction, a C to C fraction and a C7+ fraction. The C and the C fractions are reheated to a temperature in excess of 900 F. and charged to at least one subsequent stage wherein they are contacted with catalyst at elevated temperature in order to complete the normal reforming process, i.e. carry the octane of the charge to the 85-100 CFR-R range, depending upon feed quality,

Patented June 14, 19670;

catalyst activity, octane goal, and the like. The effiuent from the last reforming stage is separated into a recycle hydrogen gas fraction and a liquid reformate fraction. The C -C fraction separated from the first stage efliuent is combined with the product reformate.

The invention is best described in detail by reference to the accompanying drawing which provides a flow diagram of the process in simplified form.

To illustrate the operation, a Mid-Continent naphtha feed boiling in range of about 80 to 400 F. (about 45 CPR-R octane number) is charged to the process via line 10. Recycle hydrogen gas from line 11 is admixed with the charge in line 10. The combined charge is preheated in coil 12 of furnace 13 to a temperature substantially in excess of 900 F., preferably in the range of about 950 to 1050" F. for example, 980 F. In the drawing, a single furnace with multiple coils is shown but obviously separate heaters may be used, and the naphtha charge and recycle gas may be heated separately. The preheated charge mixture is passed by line 14 to reactor 15 which contains a bed of platinum reforming catalyst in pellet form. The catalyst comprises, for example, 0.6% platinum on an alumina gel base. The pressure of the reforming operation advantageously is about 200 to 400 p.s.i.g., but may be varied within the conventional reforming range of about 50 to 750 p.s.i.g. The hydrogen recycle rate advantageously is about 4000 cubic feet per barrel of feed but also may be varied in the conventional range of about 1000 to 10,000 s.c.f. per barrel. Since over-all space velocity for the reforming reaction usually is in the range of about 0.2 to 5.0 LHSV over the multi-reactor system, the space velocity in the first reactor 15 is high, usually in the range of about 1 to 15, preferably about 5 to 6 LHSV, depending upon the other operating conditions and the desired on-stream cycle time. Under these conditions, dehydrogenation of naphthenes to produce aromatics is substantially com pleted, and isomerization of C s and C s, because of the rapid rate of this reaction, is carried substantially to equilibrium. Because of the short contact time with catalyst at a relatively moderate temperature, occasioned by the large endothermic temperature drop, e.g. about 150 F. across the bed, practically no hydrocracking occurs in the first stage reactor 15.

The effluent from reactor 15 containing the C s and C s, which have been isomerized to about the equilibrium composition, is passed via line 16, cooler 17 and line 18 to high temperature separator 19, operated at about 200 F. Separator 19 is designed to collect C hydrocarbons as condensate, and the C fraction is taken overhead through line 20, cooler 21 and line 22 to low temperature separator 23, operated at about F.

Separator 23 is designed to collect as condensate the C fraction which is removed by line 24 to fractionator 25. The overhead from separator 23 comprises a C fraction including hydrogen gas, which is taken by line 26 to line 27. In fractionator 25, additional light com ponets boiling in the range of C are taken overhead via line 28 to line 27. The C -C fraction is removed as an intermediate cut through line 29. Heavier components comprising (3 hydrocarbons are removed as bottoms through line 30 and, in admixture with the 0 fraction in line 24a is passed via connection 31 to col lector line 27. The combined C and C7+ fractions in line 27 are passed through coil 32 in furnace 13 and from thence by means of line 33 to reactor 34. I

The reheated charge, at a temperature in excess of 900 F., is contacted with additional platinum-alumina catatylst in the reactor. The efiiuent from reactor 34 advantageously is removed through line 35 to a second reheating coil 36 of furnace 13 in which it is again re.

reactor 38.

The efiiuent from reactor 38 is passed by means of connection 391 to separator 40, after appropriate cooling (not shown). The recycle hydrogen gas fraction is separated in separator 40 is taken overhead through line 41 to recycle compressors 42 for recycle yia 1ine 11. Ex

- cess gas may be vented from the system'through' valved line 43. The liquid condensate collected in. separator 40 is passed by means of line 44 to stabilizer 45, which is operated conventionally to take overhead a C5 or C gas stream 46 and to recover 'a C or'C reformate as bottoms through 'line'47. 'The isomerized C and C hydrocarbons recovered from fractionator 25 may be handled separately, but advantageously are blended with the finished reformate in line 47. t

Although the example shows separation of a C -C fraction from the first reforming stage, the separation can be effected with advantage from this stage or any intermediate stage'prior to the last stage. Any appropriate modification'in the nature of the reaction and separation elements can be made as desired.

The following data, obtained by the analysis of several reformates by gas phase chromatographwshow the extent to which the isomerization equilibrium is reached in processing C s and'C s under platinum reforming conditions. It will be noted that a close approach'to equilibrium is reached at the condition of lowest severity shown and that the equilibrium tends to ward unfavorable displacement at'the conditions of highest severity shown. The yields are highest at the lowest condition of severity, and suifer increasing losses'of about 20 and 35percent at the successively higher severities. The equilibrium data on C isomerization is also given to show that there is no benefit to be obtained by removing Cis fronrthe system. r

Equi-' Reformates librium,

86 O.N. 91 O.N. 97 O.N.

I 1 Per'ceitl.

norma tiso. 33 {normal 32 40 40 44 Z-methylbuta 68 60 60 56 normal 24 38 35 30 2-methylpentane+2,3 di- 7 39 27 35 37 0a.--- methylbutane.

3-methylpentane 18 32 27 26 ,2dimethylbutane 19 3 3 7 In the operation of the invention, the feed is advantageously a full range naphtha, usually a virgin naphtha, although cracked components may be included, and the naphthamay be a hydrofined cracked naphtha. The feed however may be prefractionated if desired to remove a heavier fraction for separate processing. The catalyst comprises platinum on' a solidadsorbent support, most advantageously alumina, but other supports such as sintered silica-aluminaand silica stabilized with small amounts of alumina alsohave value. Thecatalyst may contain acidic promoters such a halides. The operating conditions are selected in the usualway to provide the desired degree of severity for the over-all operation. The amount of catalyst in the firstreaction stage then is correlated with the nature of thefeed and the preheating conditions (taking into account the endothermic temperature drop across the bed) to producethe desired average 'bed temperature, advantageously in the region of about 875 F., at relatively high space velocity whereby dehydrogenation and isomerization are favored, with only 4 V fractionation equipment to efiect the intermediate separations, the cost of this is. off-set to a. substantial extent by reduction in the size of the subsequent reactors, catalyst requirements, heaters and post fractionation equipment. In a particular embodiment of the invention, advantage can be taken of the intermediate fractionation facilities to separatehigh boiling aromatic components, e.g. C hyrocarbons, as; a heavy, condensate, which maybe bypassed around the subsequentreactors and blended directly with the ultimate reformateproduct. This has the advantage of further reducing the burden on the subsequent processing system since the heavier components are almost wholly converted in the first stages of the reaction. Also, the removal of aromatics tends to promote the desired reaction of dehydrocyclization of parafiins in the subsequent reactor stages since a high concentration of aromatics in the charge tends to'repress the rate of aromatics formation by parafiin dehydrocyclization, with accompanying loss in yield because of increased hydrocracking. If desired, a wider range of aromatics may be removed by selective extraction means. Thus, the invention affords in its various aspects cumulative yield advantages for any given severity level compared to conventional operation.

I claim:

l. A reforming process which comprises: admixing a full range naphtha, boiling over the range from about 80 F. to about 400 F., with a hydrogen-containing gas in an amount such thatthe resultant mixture contains between about 1,000 and 10,000. standard cubic feet of hydrogen per barrel of'na'phtha; passing said naphtha and gas mixture at an initial temperature between 900 F. and about 1050 F. to a first fixed bed of catalyst particles'comprising platinum on a solid support wherein said naphtha is subjected to moderate reforming conditions favoring dehydrogenation of naphthenes and isomerization' of pentanes and hexanes with insignificant hydrocracking, said moderate reforming conditions being defined by a pressure between about 50 and 750 p.s.i.g., a liquid hourly space velocity between about 1 and 15, and an average bed temperature in the range of about 825 to 900 F.; cooling the efiiuent from said bed and separating from thecooled effluent a hydrogen-throughbutanes' fraction, a pentanes-hexanes fraction, and a heptanes and-heavier fraction; admixing said hydrogenthrough-butanes and said heptanes-and-heavier fraction and contacting said mixed fractions with at least one additional fixed bed of catalyst particles comprising platinum on a solid support for subsequent reforming under conditions including a reheat temperature of at least 900 F. and with 'sufiicient catalyst particles to prohaving an octane number in the Iangeof'aboutSS-IOO CPR-R.

2. Process of claiinl wherein the average bed temperature of said first bed is about 875 F.-

3. Process of claim 1 wherein said pressureis between about 200 and 400 p.s.i.g.

References Cited in the file of this patent -UNITED STATES ATENTS

Claims (1)

1. A REFORMING PROCESS WHICH COMPRISES: ADMIXING A FULL RANGE NAPHTHA, BOILING OVER THE RANGE FROM ABOUT 80* F. TO ABOUT 400*F., WITH A HYDROGEN-CONTAINING GAS IN AN AMOUNT SUCH THAT THE RESULTANT MIXTURE CONTAINS BETWEEN ABOUT 1,000 AND 10,000 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF NAPHTHA, PASSING SAID NAPHTHA AND GAS MIXTURE AT AN INITIAL TEMPERATURE BETWEEN 900* F. AND ABOUT 1050*F. TO A FIRST FIXED BED OF CATALYST PARTICLES COMPRISING PLATINUM ON A SOLID SUPPORT WHEREIN SAID NAPHTHA IS SUBJECTED TO MODERATE REFORMING CONDITIONS FAVORING DEHYDROGENATION OF NAPHTHENES AND ISOMERIZATION OF PENTANES AND HEXANES WITH INSIGNIFICANT HYDROCRACKING, SAID MODERATE REFORMING CONDITIONS BEING DEFINED BY A PRESSURE BETWEEN ABOUT 50 AND 750 P.S.I.G., A LIQUID HOURLY SPACE VELOCITY BETWEEN ABOUT 1 AND 15, AND AN AVERAGE BED TEMPERATURE IN THE RANGE OF ABOUT 825 TO 900*F., COOLING THE EFFLUENT FROM SAID BED AND SEPARATING FROM THE COOLED EFFLUENT A HYDROGEN-THROUGHBUTANES FRACTION, A PENTANES-HEXANES FRACTION, AND A HEPTANES-AND-HEAVIER FRACTION, ADMIXING SAID HYDROGENTHROUGH-BUTANES AND SAID HEPTANES-AND-HEAVIER FRACTION AND CONTACTING SAID MIXED FRACTIONS WITH AT LEAST ONE ADDITIONAL FIXED BED OF CATALYST PARTICLES COMPRISING PLATINUM ON A SOLID SUPPORT FOR SUBSEQUENT REFORMING UNDER CONDITIONS INCLUDING A REHEAT TEMPERATURE OF AT LEAST 900*F. AND WITH SUFFICIENT CATALYST PARTICLES TO PROVIDE A LIQUID HOURLY SPACE VELOCITY THROUGH ALL THE FIXED BEDS IN THE PROCESS BETWEEN ABOUT 0.2 AND 5.0, SEPARATING FROM THE FINAL BED OF CATALYST PARTICLES A REFORMATE CONTAINING ALL THE HYDROCARBONS BOILING ABOVE BUTANES AND A HYDROGEN-CONTANING GAS FOR RECYCLE, AND COMBINING SAID REFORMATE CONTAINING ALL THE HYDROCARBONS BOILING ABOVE BUTANES WITH THE PREVIOUSLY-OBTAINED PENTANESHEXANES FRACTION TO OBTAIN A REFORMED NAPHTHA PRODUCT HAVING AN OCTANE NUMBER IN THE RANGE OF ABOUT 85-100 CFR-R.

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