CA1165264A - Process for the regenerative catalytic reforming of light hydrocarbons - Google Patents

Abstract

A B S T R A C T

PROCESS FOR THE REGENERATIVE CATALYTIC REFORMING
OF LIGHT HYDROCARBONS

A process for the regenerative catalytic reforming of light hydrocarbons in which the light hydrocarbons are contacted under reforming conditions with a reforming catalyst comprising a platinum group metal on an alumina carrier and having an apparent bulk density of at least 0.6 g/cm3.

Description

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PROCESS FOR THE REGE~ERATIVE CATALYTIC REFORMI~G
OF LIGHT HYDROCARBO~S

This invention relates to a process for the regenerative reforming of light hydrocarbons to produce gasoline, benzene and other selected aromatics. Reforming is the operation of modifying the structure of the molecules of straight-run gasoline fractions (approximate boiling ranges between 30 and 200 C), often a naphtha (boiling range approximately 100-160 C), under strictly controlled conditions in order to improve its ienition quality. It can be achieved thermally or with the aid of a catalyst. The present process is concerned with catalytic reforming.
The main reactions occurring in catalytic refor~ing processes are:
(a) dehydrogenation of cyclohexane and alkyl cyclohexanes to aromatics;
(b) dehydroisomerization of alkyl cyclopentanes to aromatics (i.e. isomerization of five-ring to six-ring naphthenes followed by dehydrogenation of the six-ring naphthenes to aromatics);
(c) isomeriæation of normal to branched paraffins;
(d) dehydrocyclization of paraffins to aromatics;
(e) hydrocracking of paraffins and - to a minor extent -of naphthenes to lighter saturated paraffins and hydrodealkyl-ation of aromatics;
(f) isomerization of aromatics.
Reactions (a), (b), (c), (d) and (e), which involve the con-version of paraffins and naphthenes, result in an increase inoctane number. Reaction (f) affects the distribution of aromatics in the reforming product, and is of importance from the point of view of manufacturing aromatics for the chemical industry. React-ions (a), (b) and (d) produce hydrogen, even to such an extent that the reforming process has become the most important source of hydrogen in refineries, the gas being used in such processes "

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as hydrocracking, hydrodesulphuri~ation, hydrodemetallization, and the like.
The first successful catalytic reforming processes, using platinum catalysts, were non-regenerative; that means that because of the long catalyst life periodic regeneration of the catalyst in the ref;nery itself was not necessary. In recent years the severity of the reforming operation has increased, reducing catalyst life, and thus making regeneration desirable.
Depending on the operational conditions, the process can be semi-regenerative, requiring infrequent catalyst regeneration, i.e.about 1 to 2 times a year, or fully regenerative, requiring more frequent catalyst regeneration. The flllly regenerative processes require a spare reactor, the so-called swing reactor, to take the place of any reactor to be regenerated but they guarantee a con-tinuous and constant production of hydrogen. ~he semi-regenerative processes do not require a swing reactor, but during regener-ation of the catalyst the whole reforming unit has to be shut down, thus interrupting a refinery's hgdrogen production for - several days. The severe conditions applied in the frequent regenerations of the fully regenerative process preclude the use of the very active bimetallic reforming cat~lysts, e.g. Pt-Re or Pt-Ge catalysts. Therefore, the slightly less active but more stable monometallic catalysts are preferred ~r fully-regenerative reforming processes. Obviously these monometallic catalysts can be applied in semi-regenerative reforming processes too, if so desired.
As active metal monometallic catalysts contain a metal from the platinum group, i.e. ruthenium, rhodium, palladium, osmium, iridium or platinum, platinum being preferred and ruthenium and osmium being least active. Combinations of two or more of these noble metals may also be present, although the word "monometallic" would ~eem to exclude this. "Monometallic", however, should be read here as to mean containing only platinum group metal(s), whereas "bi-metallic" usually, and also in the present application, means also 1652S.~

containing a non-noble metal, prefera~ly germanium, rhenium, tin or lead, in addition to the platinum group metal(s).
The carrier material of the reforming catalyst is usually alumina. Where some hydrocracking to enhance octane number, i.e.
ignition quality, is desirable, the incorporation of an acidic promoter such as fluorine or chlorine can be effected. Other acidic promoters include silica, zirconia, boria, molybdena, chromia and the like.
The reforming conditions generally are a temperature between ~50 and 550C, preferably between 500 and 530C, a liquid hourly space velocity between 1 and 5 volumes of feed/volume of catalyst/hour, a pressure between 1 and 50 kg/cm2, preferably between 10 and 30 kg/cm , and a hydrogen/feed molar ratio between 0.5 and 15, preferably between 3 and 15. ~owever, when it is desired to favour the dehydrocyclization reaction of paraffins to aromatics, the preferred pressure lies between 1 and 10 kg/cm2, and more preferably between 2 and 5 kg/cm2, and then the hydrogen/feed molar ratio is preferably between 0.5 and 5.
The temperature of the catalyst bed is changed with time in order to obtain a product with constant quality, e.g. as in-dicated by the octane number of the C5 fraction of the product.
The semi-regenerative processes apply a relatively high pres-sure, e.g. above 13 kg/cm , whereas the fully regenerative proce~ses employ a relatively low pressure, e.g. below 13 kg/cm2.
Catalyst life ends at the point at which the catalyst is no longer able to produce a reformate at temperatures equal to or lower than the maximum temperature as allowed by the material strength of the reactors. When this point is reached, or almost reached, the catalyst is regenerated. A typical effective re-forming catalyst regeneration procedure including carbon removal, halogenation and reduction steps i8 described below, assuming that the catalyst contains a halogenide, e.g. fluoride or chloride.
Carbonaceous deposits or "coke" are removed by contacting the catalyst with an oxygen-containing gas at increased temperatures, ~ 16526~

preferably from about 370 to 510 C. The halogen content of the catalyst is replenished and the platinum group metal is re-dispersed in a halogenation procedure which preferably includes contacting the substantially carbon-free catalyst with a gas containing oxygen at a partial pressure of 0.100 to 0.175 at-m~spheres absolute, steam at a partial pressure of 0.07 to 0.35 atmospheres absolute, and a lo~er halogen (fluorine or chlorine) at a partial pressure of 0.0035 to 0.0175 atmo6pheres absolute, said gas being at a temperature from 425 to 540C and preferably at about 480 C. This treatment forms a platinum group metal-halogen complex or compound and redisperses the active metal on the support. The lower halogen may be added to the oxygen-con-taining gas as free halogen, as a hydrogen halide or an organic halogen-containing compound, e.g. trichloroethylene.
Suitable carrier gases for halogenation include, for example, synthesis gas, nitrogen, air or mixtures thereof, as long as the gas does not contain a known catalyst poison such as carbon mon-oxide. Halogenation is suitably conducted at gas flow rates from about 3 to about 15 standard cubic metres per hour per kg (Nm3/h/kg) of catalyst and preferably from 6 to 12 Nm3/h/ke at pressures from 1 to 35 atmo~pheres absolute.
After the desired quantity of halogen has been added, the catalyst is generally purged with an inert gas such as nitrogen to remove oxygen and water and then contacted with a hydrogen-containing gas at elevated temperatures to reduce the platinum complex. Advantageously reduction i8 effected at temperatures in the range from 320 to 480C, but temperatures from 370 to 430 C are preferred. Gas flow rates from 3 to 15 Nm3/h/kg of catalyst and preferably from 6 to 12 Nm3/h/kg of catalyst, and pressures from 1 to 35 atmospheres absolute are suitable for reducing the catalyst.
As already mentioned, the monometallic catalysts are, though resistant to frequent regenerations, not the most active re-forming catalysts known, and therefore the yield of high octane 526~

components is open to improvement, while retaining the resistance of the catalyst to frequent regenerations.
According to the invention this is achieved by employing a high density carrier material, instead of the low denaity car-riers used up to now.
The invention therefore relates to a process for the regener-ative catalytic reforming of light hydrocarbons to produce gasoline, benzene and ~ther selected aromatics, which comprises alternately:
(a) contacting the hydrocarbon under reforming conditions ` 10 with a monometallic reforming catalyst comprising a platinum group metal on an alumina carrier, and (b) regenerating the catalyst by contacting it under regenerati~n conditions with an oxygen-containing gas, in which process the catalyst has an apparent bulk density of at least o.6 g/cm3.
Prior art catalysts have in general a bulk density of about 0.5 g/cm3, and it was thought that a low density was advantageous for dispersing a certain mass of the expensive platinum over as large a volume as possible. Also, a low density used to correspond to a high specific pore volume and thus often a high specific surface area. Recently, however, alumina carrier materials have become available which combine a high density and a high specific surface area. This implies that per unit reactor volume more catalytic functions, i.e. re metals, can be acco = dated and the same holds for the acidic functions, i.e. the halogens, if preaent. The weight percentage of the expensive platinum loaded on the catalyst may therefore be decreased a little, reducing the cost of the catalyst calculated on a weight basis.
Generally, the catalyst density lies below 0.95 g/cm , and preferably the catalyst has an apparent bulk density of 0.7 to 0.9 g/cm3. This range of densities includes catalysts with desirable qualities as regards specific pore volume, specific surface area, attrition resistance, crushing strength and sintering reaistance.
Apparent bulk denaities may be determined in the ~ollowing manner.

, ' , ) lB5264 Catalyst is poured into a standard cylinder of about 200 ml to overflowing. The cylinder i~ made of 1 to 1.5mm thick stainless steel and has an approximate inside diameter of 55 mm and height of 80-go mm. Its volume has been calibrated to the nearest milli-litre. After filling the cylinder the top is gently levelled andthe cylinder weighed. The net catalyst weight divided by the volume of the cylinder equals the apparent bulk density.
In order to provide the catalyst with an acidic function, apart from the already present metal function, a halogen can be added, as already said. Preferably, the catalyst contains chlorine and/or fluorine in an amount of 0.01-8% by weight and in particular the catalyst contains chlorine in an amount of 0.05-5% by weight.
All weight percentages are based on the total weight of the catalyst.
The catalyst contains a platinum group metal, preferably 0.1 to 3.0% by weight. These amounts may vary somewhat according to the nature of the metal, e.g. when palladium is used somewhat more metal is needed than when platinum i6 used. In particular the catalyst contains platinum in an amount of 0.1-0.3% by weight. This range lies below the amounts of platinum normally contained in low-density monometallic reforming catalysts, which constitutes an additional economic advantage, apart from the performance ad-vantage of the catalyst according to the invention.
The surface area of reforming catalysts declines as a result o~ repeated regenerations. The catPlyst of the process according to the invention preferably ~as, in fresh condition, a specific surface area of 190-220 m /g. It will be noted that this range lies somewhat higher than the usual values of low-density mono-metallic reforming catalysts.
The invention will now be illustrated with the aid of the following Example.
EXAMPLE
A monometallic Pt-catalyst was prepared by conventional methods using a special commercial high-density alumina. Its .~ .

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properties are listed in Table A. For comparison's sake the properties of a conventional, commercial monometallic reforming catalyst are tabulated too. Both catalysts contained chlorine as the sole halogen.
TABLE A

Reforming catalyst High- Low density density 3 _ apparent bulk density g/cm 0.757 0.520 Pt-content ~Ow o.244 0.375 Cl-content %w 1.11 0.90 specific surface area n2lg 197 185 specific pore volume cm3/g 0.47 0.55 particle size cm 0.16 0.16 particle shape extrudates beads Both catalysts were tried in a catalytic, fully-regenerative reforming unit, comprising five reactors of which four were on line while the fifth was in the regeneration mode. First, all five reactors were loaded with the low-density catalyst, and operated in the conventional way. Then, the high-density catalyst was introduced into three reactors, while the remaining two retained their low-density catalyst. This loading allowed the unit to run with two reactors of low-density and two reactors of high-density catalyst for 73.5% of the operating time and with one reactor of low-density and three reactors of high-density catalyst for 26.5%
of the operating time. These figures also reflect, inter alia, the non-equal regeneration times of the high-density and the low-density catalysts.
As much as possible the same conditions were applied in all runs. All data presented hereinafter have been normalized to a typical reactor inlet temperature (R.I.T.) and a typical weighted average bed temperature (W.A.B.T.). The re~ults of the reforming 1 1~526~
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experiments during test operations of several months are presented in the following three experiments.
Experiment 1 The maximum throughput of feed of the reforming unit before and after the introduction of the high-density catalyst, at the same, relatively low, severity was compared. The severity is mainly determined by the reactor operating pressure (R.O.P.), a high pressure corresponding to a low severity. The results are shown in Table B.
TABLE B

introduction o . dense catalyst before after .
catalyst s~stem reactors with low-density catalyst 4 reactors with highsdensity catalyst _ 3 feed characteristics paraffins/naphthenes/
aromatics ~ov 45.6/45.2/9.2 45.6/45.2/9.2 ASTM 90Zv distillation point C 138 130 o~erating conditions ~2/feed ratiomol/mol 4.9 3.6 R.O.P. bar 17.2 17.2 , R.I.T. C 525 527 W.A.B.T. C 499 ' 503 through~ut m3/day 747 922 C5 yield %v 79.5 79-2 R.O.N. of C5 i 99 The throughput increased by 23.4%, using the high-density catalyst. The proportion of the C5 -components of the reformate decreased by not more than o.24%, and the research octane number ~ 16~P6Q

(R.O.N.) of the C5 -fraction remained the same. The R.C.N. was determined according to the ASTM-D 908 test method. The ASTM 90%v distillation point is the temperature at which 90~ by ~olume of a given quantity of feed has been recovered, when distilling the feed according to the ASTM-D 86 test method.
Experiment 2 The yield of C5 -products and their R.O.N. were compared at constant R.I.T. and constant throughput, using both catalysts.
The catalyst systems used were the same as used in Experiment 1.
The results are shown in Table C:
TABLE C
introduction o ~ dense catalyst before after feed characteristics paraffins/naphthenes/
aromatics %v 51.8/36.7/11.55i.8/36.7/11.5 ASTM 90%v distillation point C 138 138 throu~hput m3/day 747 747 operatin~ conditions H2/feed ratiomol/mol 4.0 4.0 R.O.P. bar 17.2 17.2 R.I.T. C 510 51o W.A.B.T. C 491 493 Cr+ yield %v 81.2 78.2 R.O.N.of CS_ 95.1 97.8 Under the conditions of this experiment the reduced yield of C5 components was offset by the raise in octane number.
Ex~eriment 3 The heat duty of the total reforming unit was compared at conBtant throughput and constant target octane number, using the low and the high-density catalysts. The catalyst systems, the feed characteristics and the throughput were the same as in Experiment 2.
The results are shown in Table D:

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TAB~E D
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introduction bf dense catalyst before after o~erating conditions H2/feed r~tiomol/mol 4.0 4.0 R.O.P. bar 17.2 17.2 R.I.T. C 522 511 W.A.B.T. C 503 494 C, yield %v 78.2 78.1 R.O.N. of C, 98 98 heat duty kJ/m3 2,331 2,219 , Using the dense catalyst, about 4.8% less heat has to be provided to keep the four reactors at a temperature sufficient to yield reformate with a R.O.N. value of the C5 components of 98.
These three experiments show that the high-density catalyst provides three benefits over the low-density catalyst: 1. higher throughput at the same severity; 2. higher octane product at the ~ame R.I.T. and feed rate; 3. energy savings for the same octane and feed rate by running at lower R.I.T.'s~
Depending on circumstances, the refiner will opt ~or one or more of these possibilities.
After many regenerations the high-density catalyst maintained its advantages over the low-density catalyst.

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the regenerative catalytic reforming of light hydro-carbons to produce gasoline, benzene and other selected aromatics, which comprises alternately:
(a) contacting the hydrocarbon under reforming conditions with a monometallic reforming catalyst comprising a platinum group metal on an alumina carrier, and (b) regenerating the catalyst by contacting it under regeneration conditions with an oxygen-containing gas, in which process the catalyst has an apparent bulk density of at least 0.6 g/cm3.

2. The process of claim 1, characterized in that, the catalyst has an apparent bulk density of 0.7 to 0.9 g/cm3.

3. The process of claim 1, characterized in that, the catalyst contains at least one element selected from the group comprising chlorine and fluorine in an amount of 0.01-8% by weight.

4. The process of claim 3, characterized in that, the catalyst contains chlorine in an amount of 0.05-5% by weight.

5. The process of claim 1, characterized in that, the catalyst contains 0.1 to 3% by weight of a platinum group metal.

6. The process of claim 5, characterized in that, the catalyst contains platinum in an amount of 0.1-0.3% by weight.

7. The process of claim 1, characterized in that, the catalyst in fresh condition has a specific surface area of 190-220 m2/g.

8. A process for the regenerative catalytic reforming of light hydro-carbons in which the light hydrocarbons are contacted under reforming conditions with a reforming catalyst comprising, a platinum group metal on an alumina carrier and having an apparent bulk density of at least 0.6 g/cm and not more than 0.95 g/cm3.

9. The process of claim 8, characterized in that the catalyst has an apparent bulk density of 0.7 to 0.9 g/cm3.

10. The process of claim 8, characterized in that, the catalyst contains 0.05-5% by weight of chlorine.

11. The process of claim 8, characterized in that, the catalyst contains 0.1-0.3% by weight of platinum.

12. The process of claim 8, characterized in that, the reforming conditions comprise a temperature between 450 and 550°C, a liquid hourly space velocity between 1 and 5 volumes of feed/volume of catalyst/hour, a pressure between 1 and 50 kg/cm2 and a hydrogen/
feed molar ratio between 0.5 and 15.

13. The process of claim 8, characterized in that, the reforming catalyst is regenerated by contacting it with an oxygen-containing gas at a temperature of from 370 to 510°C.