US3167498A - Process for the hydrogenation of hydrocarbons in the gasoline boiling range - Google Patents

Description

United States atet PROCESS FUR Tim HYDRGGENATKON OF HY- DRGCARBONS IN THE GASOLENE BQEILHJG RANGE Walter Kriinig, Leverlrusen, Joachim Ester, Dormagen, and Hans-Joachim Miiller, Leverlrusen, Germany, assignors to Farhenfahriiren Bayer Alrtiengesellschaft, lireverlruscn Germany, a corporation of Germany No Drawing. Filed Dec. 6, 1962, Ser. No. 242,589 Claims priority, application Germany Dec. 8, 1961 3 Claims. (Cl. 2655-143) This invention relates to a process for the hydrogenation of hydrocarbons in the gasoline boiling range.

When mineral oils, particularly crude oils or their fractions or residues (especially fractions in the gasoline boiling range) are subjected to pyrolysis at temperatures above 600 C., a gasoline is obtained in addition to gaseous cracking products. This gasoline (cracked gasoline or pyrolysis gasoline) contains considerable quantities of unsaturated hydrocarbons, which are partly diolefinic hydrocarbons. it is frequently desirable to remove from the pyrolysis gasoline not only the diolefinic hydrocarbons, which have a strong tendency to form gum, but also the monoolefines while conserving the aromatic compounds. This is particularly the case when it is desired to isolate aromatic compounds from the pyrolysis gasoline, ecause the isolation of pure aromatic compounds is greatly impaired by the presence of olefinic hydrocarbons. To this is added the fact that it is frequently desirable or even necessary not only to remove all the olefines but also to convert the organic sulfur compounds in the Starting materials into hydrogen sulfide and hydrocarbons as far as possible. When purifying the hydrocarbon mixture by hydrogenation for the purpose of isolating the aromatic compounds it is necessary .to ensure that there will be practically no hydrogenation of the aromatic hydrocarbons in the course of removing the olefines and the sulfur compounds.

A process which may also be used on the technical scale for removing olefines and sulfur compounds from pyrolysis gasolines comprises the steps of removing the strongly resinifying components almost completely by hydrogenation under pressure at about 200 to 250 C. over catalysts, e.g., cobalt molybdate catalysts, then evaporating the pretreated product in a stream of hydrogen, hydrogenating the remaining monoolefines in the gas phase at about 300 to 350 C. over catalysts, for example cobalt molybdate catalysts, and removing the sulfur compounds to a large extent.

A disadvantage of this method lies in the fact that the second hydrogenation stage, in which the monoolefines are saturated and the sulfur compounds are split by hydrogenation, is carried out in the gas phase. This involves a considerable expenditure of energy for the evaporation of the prehydrogenated starting material and the condensation of the completely hydrogenated product.

It is an object of the present invention to avoid the aforementioned disadvantages. A further object is to provide a process for the hydrogenation of undesired unsaturated compounds contained in hydrocarbons of the gasoline boiling range which is economical and which does not need much operational supervision. Still more objects will appear hereinafter.

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It has now been found that these objects can be attained and that the above-mentioned undesirable components contained in hydrocarbons of the gasoline boiling range, e.g., acetylenes, monoolefines, diolefines and organic sulfur compounds may be removed from the hydrocarbons by hydrogenation, without hydrogenation the aromatic compounds by allowing the hydrocarbons to trickle in the liquid phase at temperatures below C. over noble metal catalysts in a first hydrogenation stage, the noble metals being situated on macroporous carrier materials which have an inner surface area of less than about 100 m. g. and a water absorption capacity of at least 10%, and the resulting product of hydrogenation may be hydrogenated in a second stage again as liquids in a trickle phase at temperatures between about to 250 C., again using noble metal catalysts.

Selective hydrogenation of cracked gasoline has already been disclosed in Belgian patent specification 589,804. However, the method described there involves mainly the removal of diolefinic hydrocarbons, whereas the monoolefines have to be removed by hydrogenation in the gaseous phase. Thus the method according to the invention achieves the possibility of carrying out the second hydrogenation stage also in the liquid phase. This not only saves the energy that would be required for evaporating and condensing the starting material again in the second hydrogenation stage but additional energy is saved by the fact that the hydrogenation in the second stage can also be carried out by trickling the hydrocarbon fraction in the liquid phase through a bed of solid hydrogenation catalyst in a practically stationary atmosphere of hydrogen, whereas circulating hydrogen would have to be used for hydrogenation in a gaseous phase. In addition, the plant required for the new process is simpler and less expensive than in the known process.

In the known methods of hydrogenating monoolefines in the gaseous phase there is always the danger that minute quantities of diolefines may be present in the hydrogenation product of the first stage, and these diolelines may cause deposition of polymers in the subsequent heating to relatively high temperatures, particularly when the material has to be evaporated. The new process according to the invention is much less sensitive, since it is not necessary to employ such high temperatures in the second stage and mainly because the hydrogenation product from the first stage does not have to be evaporated. There -is therefore always sufficient liquid hydrocarbon to ensure that even if small amounts of polymers should be formed, they will be kept in solution.

The hydrogenation temperature in the first stage should not be higher than 100 C. and should preferably be below 75 C. It is very advantageous to take steps to ensure that at least approximately the first quarter of the reaction chamber is kept at a temperature below 50 C. The process can be carried out for example by introducing the feed at the lower temperature, e.g., 20 to 35 C. into the reactor and then to raise the temperature gradually to the higher temperatures, e.g., 75 C. Since the hydrogenation process is exothermic, this can be easily arranged. The process is carried out in a substantially stationary hydrogen atmosphere. It is generally not necessary to keep the hydrogen in circulation. It is suflicient to release small quantiti s of hydrogen at the end of the reaction chamber and thereby to remove any impurities contained in the hydrogen used. Hydrogen pressures of 10 to 50 atmospheres may be used in general. On the other hand, it may be advantageous to use higher pressure, for example up to 150 to 200 atmospheres. The hydrocarbons may be charged into the process at a rate of 1 to 10, preferably 2 to 6 or 8 kg. ,per liter of reaction space that means the room filled with catalyst. The metals that may be used for the noble metal catalysts are mainly the noble metals of the 8th group of the periodic system of elements such as specially palladium and platinum, which may be precipitated on the carriers in quantities of 0.1 to by weight, preferably 0.5 to 2% by weight. The carriers should be absorptive but have only a small internal surface. Suitable carriers fortthe process according to the invention are, for example, Weekly roasted clays that have only a small content of iron or are free from iron, sintered aluminum oxide and sintered magnesium oxide. The capacity of the carriers for water absorption should be at least 10% and the internal surface less than 50 to 100 m. /.g If carriers are used which have pores with a relative large diameter such as pores above about 100 A. up to about 500 A. then it might be of advantage to use carriers with the higher inner surfaces that means up to 100 m. /g. while it might be more advantageous to use carriers with a lower inner surface if the pores of the carriers are smaller. It has been found advantageous to subject the noble metals on the carriers before they are used for hydrogenation to a treatment with gases containing hydrogen sulfide and then to treat the sulfurized catalyst with hydrogen. The hydrogenation product obtained should be substantially free from diolefines, i.e., the diolefine content should be less than about 1% by weight. Preferably the final hydrogenation temperature in this stage should be so chosen that there will be practically no desulfurization of the starting material, because it has been found that the activity of the catalyst might be im paired if any marked desulfurization takes place.

Temperatures of about 125 to 250 C., preferably about 150 to 230 C. are employed in the second hydrogenation stage. Thereby it might be again preferable to introduce the product to be hydrogenated at the lower temperatures into the hydrogenation unit and to raise the hydrogenation temperature in the hydrogenation reactor gradually to the higher temperatures, preferably above 150 C., e.g., 180 to 230 C., whereby most of the hydrogenation may be carried out at the higher temperatures In this temperature range, there is substantial hydrogenation of the monoolefines and splitting up of the organic sulfur compounds. It has been found that under these conditions of hydrogenation there is practically no damage to the catalyst by the hydrogen sulfide released by hydrogenating desulfurization, as opposed to the first hydrogenation stage where the catalyst may be damaged if the temperature is too high.

Pressures of about 50 to 300 atmospheres, preferably about 75 to 150 atmospheres have been found to be suit able. Again this stage may be carried out in a practically stationary hydrogen atmosphere and it is sufiicient to depressurize a small quantity of hydrogen at the end of the reaction chamber after the reaction products have cooled down, mainly in order to remove from the system the compounds accompanying the hydrogen. The rate of throughput may be about 0.5 to 10 kg. per hour per liter of reaction space, preferably about 1 to 5 or 8 kg. The metals most suitable for the noble metal catalysts are again the noble metals of the 8th group of the periodic system of elements such as especially palladium and platinum, although ruthenium, rhodium and iridium may also be used or mixtures of these metals. The noble metals are precipitated on the carriers in quantities of about 0.1 to 5% by weight, preferably about 0.5 to 2%. It has been found again advantageous to subject the noble metals on the carriers before they are used for hydrogenation to a treatment with gases containing hydrogen sulfide and then to treat the sulfurized catalyst with hydrogen. Although in the first hydrogenation stage the carriers should have a small internal surface, in this stage it is in general advantageous to use carriers with a larger internal surface, e.g. above 50 m. /g., e.g., up to 500 m. /g. and higher, preferably between and 300 m. g. The whole carrier may be made of such a material having a large internal surface. Alternatively, one may use a carrier with a small internal surface on to which about 5 to 20% of a suitable material is applied which has a large internal surface when it has been fixed. Aluminum oxide is particularly suitable as carrier, and small quantities of silicic acid may be added. Very suitable as carriers are as well co-precipitates of aluminum oxide with other oxides such as chrome oxide. Furthermore, there can be used natural occurring bauxites especially those poor in silicic acid which are preferably thermically pretreated. Basic carriers such as magnesium oxide, calcium oxide, barium oxide and carbonates of the alkaline earth metals are also suitable. Other oxides may also be used as carriers, for example titanium, zirconium, thorium and others. Suitable raw materials for the process of the invention are, e.g., cracked gasolines obtained in the pyrolysis of hydrocarbons at temperatures above 600 C., e.g., up to 900 C. or 1400" C. The liquid hydrocarbons in the gasoline boiling range, i.e., in the boiling range of about 30 to 200 C., which contain the unsaturated compounds should preferably be free from hydrogen sulfide and from readily decomposable organic sulfur compounds, although the presence of small quantities or organic sulfur compounds which do not decompose easily, for example thiophenes, is not a disadvantage. It is generally advisable to remove any hydrogen sulfide dissolved in the hydrocarbons by allowing the hydrocarbons to trickle down a tower in countercurrent against an ascending gas which is free from hydrogen sulfide and does not react with the hydrocarbons. Alternatively, small quantities of low. boiling fractions, e.g., C or C hydrocarbons, may be removed by distillation and these low boiling fractions will carry the hydrogen sulfide with them. It has been found advantageous to redistil the hydrocarbons with the exclusion of air immediately before they are used in the hydrogenation stage in such a manner that a residue of a few percent remains. This residue contains the resins that may be formed when the hydrocarbons have been stored for a long time.

It is also advisable to redistil these raw. materials before they are used in the first hydrogenation stage because they frequently contain lubricating oils in which inorganic products are dissolved. If the new process is used for isolating aromatic compounds from the raw materials it is advisable to remove, from the whole quantity of cracked gasoline, the fraction which contains the aromatic compounds and only to use this fraction for the two hydrogenation stages. Since these fractions frequently are ageing rapidly, that means that they are forming gum, it might be advantageous to add to these fractions inhibitors, especially phenolic inhibitors such as 2,6-ditert.butyl-phenol. But alternatively, it may frequently be advantageousto use first the whole of the redistilled cracked gasoline in the first hydrogenation stage and to remove the required aromatic fractionfrom the product of the first hydrogenation stage and then to use only this aromatic fraction in the second hydrogenation stage. This has the advantage that the fractions of the first hydro genation stage which are not fed to the second hydrogenation stage are sufiiciently freed from resinifying diolefinic constituents so that they may be used as fuels for internal combustion engines or the like. The hydrogen gas used in the hydrogenation stages should preferably contain at least 50% hydrogen but preferably 70% or more.

In the combination of the first and second hydrogenation stage, the hydrogenation conditions in the first stage should be so chosen within the given limits that the diolefines in the raw material are removed to such an extent that the hydrogenation product does not contain more than 1% by weight of diolefines. As already mentioned earlier, desulfurization to any significant extent should be avoided. In the second hydrogenation stage, the conditions of hydrogenation should be so chosen that the monoolefines and sulfur compounds are removed to the extent required. In general, hydrogenation will be carried out until the bromine number of the hydroenation product is less than 1, preferably less than 0.1 g. Br/ 100 g. of product and desulfurization has proceeded to at least 70% and preferably 90%. The hydrogenation conditions may be varied by varying the reaction temperature or the rate of increase of the reaction temperature, the hydrogen pressure and the rate of throughput of the hydrocarbon fraction that is to be treated. More vigorous hydrogenation conditions are obtained at higher temperatures, higher hydrogen pressures and lower rates of throughput. The most favourable conditions for the particular material being treated may easily be determined by preliminary experiment.

It has surprisingly been found that there is practically no hydrogenation of aromatic compounds either in the first hydrogenation stage or even in the second hydrogenation stage, in which the conditions of hydrogenation are much more vigorous and in which the monoolefines are practically completely hydrogenated.

Example 1 The raw material for carrying out the process was a cracked gasoline obtained from pyrolysis of a predominantly aliphatic gasoline at about 750 C. This gasoline was first redistilled in such a manner that there was a residue of 3 rug/100 cc. The redistilled gasoline was then introduced into the first hydrogenation stage. The catalyst carrier was sintered aluminum oxide which had an absorptive capacity of 35 cc. water per 100 cc. dry material and an internal surface of 5 m. g. Palladium was precipitated on this carrier in quantities of 0.5% by weight by saturation with palladium chloride and subsequent reduction of the salt with hydrazine hydrate. The catalyst was filled into a reaction tube which was 6 meters long and had an internal diameter of 40 mm. The hydrocarbon fraction, together with hydrogen, was introduced into the upper part of the vertical reaction tube and trickled down over the catalyst in an atmosphere of hydrogen. The inlet temperature of the hydrocarbon fraction was 30 C. and the temperature at the outlet of the reaction tube was 65 C. After about /3 of the reaction tube the temperature of the feed had reached 50 C. The temperature can also be regulated in such a manner that the temperature at the outlet of the reactor tube is, e.g., 80 C. The pressure in the reaction space was 40 atmospheres and the rate of throughput of raw material was 5 kg. per liter of reaction space and per hour. The product leaving at the bottom of the reactor was collected in a separator which was kept at a fixed level. 5 liters of gas per kg. of starting material were released from the separator.

The reaction product from the first stage was then introduced into the second hydrogenation stage after it had been heated to 190 C. In this second stage, the material again trickled down in a reaction tube of the same kind as used in the first hydrogenation stage over the catalyst in a substantially stationary hydrogen atmosphere. The temperature in the reaction tube was gradually raised and was at the end of the reaction tube 220 C. The pressure employed was 100 atmospheres. The product leaving the reactor was cooled down to 30 C. and collected in a separator in which the liquid product was separated from the remaining waste gas. The quantity of gas released from the separator was again 50 liters per kg. of starting material. A sintered aluminum oxide with an internal surface of 200 m. g. was used as carrier for the catalyst in the second hydrogenation stage. As

described for the first hydrogenation stage, 2% by weight of palladium was deposited on the carrier. After deposition of the palladium and drying, the catalyst was treated at 70 C. with hydrogen sulfide and then with hydrogen at 300 C. under atmospheric pressure.

The hydrogen-containing gas for the two hydrogenation stages contained hydrogen. The remainder of the gas was composed mainly of methane and nitrogen. The quantity of carbon monoxide in the hydrogen gas was reduced to below 5 p.p.m. by methanization.

The analytical data for the starting material and hydrogenation product of the first and second stage are as follows:

Feed crude Product of gasoline hydrogena- Product of (redistilled) tion Stage I hydrogen a- =Feed for =Feed for tion Stage II hydrogenahydrogena tion Stage I tion Stage II Bromine number, g./ g 65. 5 28. 8 0.08 Dienes, wt. percent 13. 7 0. 79 Sulfur, wt. percent 0. 016 0.015 0. 0014 Gum before aging, rug/100 cc 3.0 3 0 3. 0 Benzene, wt. percent 23.0 22 7 22. 6 Toluene, wt. percent 20.0 20 1 20.0 C aromatic compounds,

wt. percent 12. 8 17 5 17. 3

Example 2 For the process of this example there was used as raw material a pyrolysis gasoline as described in Example 1. From this pyrolysis gasoline there was separated by distillation a fraction boiling between 70 and C. which contained practically the whole amount of benzene and toluene contained in the pyrolysis gasoline. To this fraction of the pyrolysis gasoline there was added immediately as inhibitor 2,6-di-tert.butyl-phenol in an amount of 40 rug/kg. Thereafter, the fraction was hydrogenated in a first hydrogenation stage as described in Example 1. As catalyst there was used a carrier consisting of sintered aluminum oxide which had an absorptive capacity of 50 cc. water per 100 cc. dry material and which had an inner surface of S0 m. g. The pores of this carrier had an average diameter of about A. On this carrier palladium was precipitated in an amount of 1.5% by weight. The catalyst was then treated at 70 C. with gaseous hydrogen sulfide and was subsequently reduced at 300 C. with hydrogen.

The reaction product obtained from this first hydrogenation stage was heated to C. and introduced at this temperature in the second hydrogenation stage. The hydrogenation was carried out in the same manner as described in Example 1. The catalyst was prepared by using as carrier a bauxite poor on silicic acid which was activated by heat treatment at 450 C. On this carrier 1.8% by weight of palladium were deposited. The analytical data of the starting material and of the hydrogenation products of the first and second stages are as follows:

In the second hydrogenation stage there can be used with similar results a catalyst which consists of aluminum oxide having an inner surface of 200 m. /g. on which 0.5% by weight of platinum were deposited. Furthermore, there can be used with practically similar results the following catalysts whereby again the aforementioned aluminum oxide is used as carrier and on which the following noble metals have been deposited:

(l) 1.0% by weight of rhodium,

-(2) 1 A mixture of 1.5% by weight of palladium +0.15%

by weight of platinum,

'(3) Arnixture of 1.5% by weight of palladium +0.15%

by Weight of iridium.

We claim: 7

1. In a process for the selective hydrogenation of monoand diolefins in a gasoline boiling range hydrocarbon containing the same and aromatic hydrocarbons, the improvement which comprises, in a first hydrogenation stage trickling the hydrocarbon in the liquid phase through a fixed bed of solid hydrogenation catalyst at a temperature below 100 C., said hydrogenation catalyst comprising a noble metal catalyst on a macro-porous support having an internal surface of less than 100 m. g. and a water absorption capacity of at least 10%, and thereafter in a second hydrogenation stage trickling the hydrocarbon in the liquid phase through a fixed bed of solid noble metal hydrogenation catalyst at a temperature between about 125 and 250 C.

2. Improvement according to claim 1 in which said hydrocarbon contains organic sulfur compounds which are split in said second hydrogenation stage.

3. Improvement according ,to claim 1 in which said noble metal hydrogenation catalyst used in said second hydrogenation stage comprises a noble metal on a carrier having an internal surface of more than m /g.

4. Improvement according to claim 3 in which said noble metal hydrogenation catalyst used in said second hydrogenation stage comprises a noble metal catalyst on a carrier having an internal surface between about and 300 mP/g.

5. Improvement according to claim 1 in which said catalyst comprises noble metal catalysts on carriers which havebeen precontacted with hydrogen sulfide and then hydrogen.

6. Improvement according to claim 1 in which said second hydrogenation stage is effected at a temperature between and 230 C.

7. Improvement according to claim 1 in which the hydrocarbon from the first hydrogenation stage is introduced into the second hydrogenation stage at a temperature of about 25 C. and which includes raising the temperature during the hydrogenation in the second hydrogenation stage to be between about 180 and 230 C.

8. Improvement according to claim 1 in which said noble metal is palladium.

References Cited in the file of this patent UNITED STATES PATENTS 2,365,751 Drennan Dec. 26, 1944 3,075,915 Kronig et al Jan. 29, 1963

Claims (1)

1. IN A PROCESS FOR THE SELECTIVE HYDROGENATION OF MONO- AND DIOLEFINS IN A GASOLINE BOILING RANGE HYDROCARBON CONTAINING THE SAME AND AROMATIC HYDROCARBONS, THE IMPROVEMENT WHICH COMRPISES, IN A FIRST HYDROGENATION STAGE TRICKLING THE DYDROCARBON IN THE LIQUID PHASE THROUGH A FIXED BED OF SOLID HYDROGENATION CATALYST AT A TEMPERATURE BELOW 100*C., SAID HYDROGENTATION CATALYST COMPRISING ANOBLE METAL CATALYST ON A MACRO-POROUS SUPPORT HAVING AN INTERNAL SURFACE OF LESS THAN 100M.2/G. AND A WATER ABSORPTION CAPACITY OF AT EAST 10%, AND THEREAFTER IN A SECOND HYDROGENATION STAGE TRICKLING THE HYDROCARBON IN THE LIQUID PHASE THROUGH A FIXED BED OF SOLID NOBLE METAL HYDROGENTATION CATALYST AT A TEMPERATURE BETWEEN ABOUT 125 AND 250*C.