FR2502142A1 - - Google Patents

Abstract

A process for the preparation of methane by hydrogenolysis of a batch which consists of hydrocarbons having at least two carbon atoms per molecule, characterised in that it is carried out in the presence of a catalyst which contains the following constituents: a carrier from the group comprising the aluminium oxides, silicon dioxide-aluminium oxides, silicon dioxide-magnesium oxide, carbon and silicon dioxide, 0.5 to 50 % by weight of at least one metal of the group iron, nickel and cobalt and 0.01 to 20 % by weight of at least one so-called additional metal from the group chromium, molybdenum, tungsten, titanium, zirconium and hafnium.

Description

 The present invention essentially relates to a process for obtaining a gas with a high calorific value, and in particular relates to a process for the manufacture of gases containing more than 95%, by volume, of methane, by hydrogenolysis, in the presence of a specific catalyst of hydrocarbon cuts having a boiling point below about 400 ° C.

 It is known to obtain industrially, from hydrocarbon cuts, in the presence of hydrogen, hydrocarbons having a lower molecular weight than that of the starting material. This transformation can be carried out both thermally and catalytically.

 But it is less easy to be able to transform economically and commercially hydrocarbons having more than two carbon atoms per molecule into methane with very high yields.

 One of the aims of the present invention is a process for the conversion of hydrocarbons having at least two carbon atoms per molecule into lower hydrocarbons and especially high purity methane.

 The process is characterized in particular by the use of a specific catalyst specially adapted for the very selective production of high purity methane by hydrogenolysis of hydrocarbons having more than two carbon atoms per molecule.

The type of catalyst used in the present invention is characterized not only by a very selective behavior in carrying out this reaction, but also by a very high stability and lifetime
Reactions aimed at lowering the molecular weight of hydrocarbon cuts, known as destructive hydrogenation, hydrocracking or hydrogenation cracking, etc. are generally conducted under high pressures with hydrocarbon products having a high molecular weight; they have been known since the works of Bergius, then those of IG Farda Industrie.

 2is this work was particularly intended for obtaining cuts lighter than the treated filler (fuels or liquid species) by subjecting bituminous coals to pressures of 20 to 30 MPaO Later, the oil industry adapted this technique to the conversion of low-value heavy products into lighter products, such as diesel, naphtha, gasoline, LPG, etc., with a much higher market value.

 The object of the present invention is to produce the complete and deep hydrogenolysis of hydrocarbons, and to obtain most of the methane as a product from feeds such as those listed above.

 To do this, use is made of a catalyst having, as hydrogenolysing agent, one or more metals of group VIII of the periodic table of the elements and in particular the elements selected from the group consisting of iron, cobalt and nickel.

 The group VIII metal or metals are deposited on a suitable support, and according to the invention, one or more metal elements (or a derivative thereof) chosen from among chromium, molybdenum and tungsten are to be added thereto. titanium, zirconium and hafnium.

 Indeed, it has been found that the catalysts jointly containing on the one hand at least one Group VIII metal and on the other hand at least one additional said element chosen from chromium, molybdenum, tungsten, titanium and zirconium. hafnium, very considerably increased their selectivity in the hydrogenolysis reaction, selectivity resulting in obtaining a very pure methane, and also had a significantly longer life. As a result, regeneration of the catalyst at the end of the cycle is facilitated and leads to the production of a regenerated catalyst having substantially recovered its initial activity and selectivity.

 It will be noted here that the methane thus produced can be used as gaseous fuel with a high heating value, or for various other industrial uses, for example for the synthesis preparation of products such as carbon disulfide, hydrogen cyanide, carbon tetrachloride and the like. carbon, chloroform, etc ...

hence the economic interest of a process and a catalyst according to the invention for obtaining methane under satisfactory economic conditions.

The reaction consists in reacting the hydrocarbon or the hydrocarbons constituting the raw material to be converted, with hydrogen and in the presence of a suitable catalyst; under appropriate pressure and temperature conditions, the carbon-carbon bond is cut off and hydrogen bonded to the released bond; It must be pointed out that this hydrogenolysis reaction is very exothermic, as can be seen in the few examples that follow.
C2H6 + H2 = 2H4C + 65,000 Joules / mol
C3H8 + 2H2 = 3H4C + 121,000 Joules / rnol
C4H10 + 3H2 = 4H4C + 173,000 Joules / mol
etc ....

 This exothermicity causes a significant increase in temperature through the catalytic bed, and can cause rapid deactivation of the catalyst by deterioration of the solid and also, as a consequence of the accelerated drop of selectivity that ensues, the formation of: a deportation of products more or less coked on the catalyst surface resulting in a very fast deactivation.

 Indeed this important exothermicity directs the transformation towards the production of carbon and hydrogen by thermal dissociation of hydrocarbons.

 To avoid this rapid rise in temperature through the catalyst bed, it is essential to take special and appropriate precautions to effectively remove the bieleur released by the reaction.

 For example, it is possible to use reactors commonly used in hydrocracking reactions, allowing a dissipation of the calories produced, and for example, a multitube reactor with an external cooling, or a series of small reactors, with intermediate heat exchangers a multi-stage reactor with interstage cooling devices etc. As the evacuation agent for the formed calories, the gases produced by the reaction can be used after cooling. This can be achieved by ensuring a high recycling rate of these gases of at least 10/1 (molar (recycle gas with respect to the total charge).

 The Group VIII metals used in the catalyst preferably do not belong to the noble metals of this group (platinum-family metals) because the hydrogenolysing power of the noble metals is less "deep" which manifests itself by a methane yield much lower than that obtained with at least one of the metals of the group formed by iron, nickel and cobalt and preferably with nickel. However, small amounts of platinum group noble metals can be used as the second additional element, as discussed below.

These Group VIII metals are deposited on a suitable support
quat, preferably not having acidic characteristics, by
for example, alumina, silica-alumina, silica-magnesia, coal,
and silica, etc.

Preferably, a silica having a specific surface is used.
between 50 and 400 m2 per gram and preferably between
2
100 and 300 m 2 / g, having a total pore volume of between 0.40 and
1.20 cm3 / g and preferably between 0.45 and 0.80 cm3 / g, the diameter
average of the pores being generally between 5 and 15 rpm avoiding
that the pores have a diameter of less than 2 nm.

A particularly suitable catalyst contains nickel
associated with silica Silica does not combine with nickel or
nickel oxide and such a catalyst, to which a metal is added
additional as taught above is particularly effective for the methane cracking of paraffinic or cycloparaf molecules
finiques.

 The content (expressed as metal element) of iron, and / or cobalt and / or nickel is preferably between 0.5 and 50% by weight relative to the total mass of the catalyst ready for use. The additional metal content (expressed as metal element) chosen from chromium, molybdenum, tungsten, titanium, zirconium and hafnium is generally between 0.01 and 20% by weight and preferably between 0.1. and 10% by weight and more particularly between 0.3 and 0.8%. When nickel is used, the preferred nickel content is between 15 and 25% by weight.

 In addition, as the second additional metal, the catalyst may contain small amounts of platinum-family noble metals, for example between 0.01 and 5 wt.% Platinum or palladium, or iridium, or rhodium, etc., and preferably between 0.01 and 1 7 by weight (expressed as metal element).

 The catalyst is generally prepared by impregnating the chosen support with an aqueous solution containing the element or elements that are to be deposited on the support.

The impregnation can be unique if the selected metals are introduced in one go, using a single solution containing them. But we can also introduce the active elements separately in several times by successive impregnations, using various solutions each containing one of the elements constituting catalysis1: rç
In the case of successive impregnations, each impregnation is generally followed by drying at about 100-110 ° C. under dry air for 2 hours, and then the solid is calcined under air.
dry, at a temperature between 250a and 5000C for two hours. The solid is then allowed to cool, under dry air, until
the ambient temperature, and the impregnation is then carried out
next.

The support may, for example, remain in contact with the
impregnation solution for a time of between 0.5 and 6 hours, and preferably between 12 hours.

For the examples which follow, a catalyst is prepared whose support is a silica having a surface of
150 m 2 / g, a pore volume of 0.50 cm / g, an average pore diameter
of 14 nm, and having no porosity represented by pores having a diameter less than 5 nm
100 g of this support, in the form of beads 2 mm in diameter, were impregnated at room temperature with 50 cm 3 of a nickel nitrate solution containing 40% by weight of nickel. We leave the
solid and the solution in contact for two hours then we put the
solid impregnated in an oven where it is dried under a stream of dry air at a temperature of 110 C for 2 hours.

 The dry catalyst is then placed in an oven where it is gradually brought to 4500 (in 1 hour) under a dried air stream on activated alumina, and it is left for 2 hours at this temperature.

 The product obtained is then impregnated with 50 cm 3 of a solution containing 17% by weight of molybdenum in the form of ammonium paramolybdate. Then we proceed as we did after the introduction of nickel.

 The calcined catalyst is then reduced in the reactor under a current of hydrogen at a temperature which may be between 200 and 5000 ° C and for a period of between 1 and 6 hours and which, in the present example, has been reduced to a temperature of 300 ° C for a period of 2 hours.

The finished catalyst contains
20% by weight of nickel and
0.5% by weight of molybdenum.

 Then, the hydrocarbon feedstock can be introduced together with hydrogen, in an amount sufficient to convert all the introduced hydrocarbons into methane, and with a diluent gas, which may be methane, to eliminate the calories produced by the reaction. .

 The quantity of hydrogen introduced is limited to the necessary (theoretical) ZmeK austrict for the total hydrogenolysis of hydrocarbons to methane and for the hydrogenation of olefins to paraffins, and aromatic hydrocarbons to cycloparaffins, in the case where those are present in the charge. The process still requires large quantities of hydrogen but nuclear batteries can provide cheap at night by electrolysis of water.

 It is preferred in the present invention to carry out the transformation at temperatures between about 340 and 5000 ° C, and preferably between 350 and 4000 ° C; in any case, it is avoided to use temperatures higher than 6000, because the reactions leading to the formation of coke then become quite important.

 In case of fouling of the catalyst surface by formation of coke, it is possible to regenerate the catalyst by removing coal deposition by controlled combustion using an oxygen-containing gas.

 This oxidation phase is followed, after a scanning with an inert gas, of a reduction period, in the presence of hydrogen.

This reduction is conducted in the same way as indicated above.

 In the reaction medium, a total pressure of between 0.1 and 10 .mu.m and preferably between 3 and 6 .mu.E is maintained.

 During the reaction, the rate of passage of the reaction mixture through the catalyst bed is between about 0.1 and 10 volumes of filler per volume of catalyst per hour and preferably between 0.5 and 4 volumes of filler by volume of catalyst. catalyst and per hour.

 The amount of recycle gas to be introduced is adjusted so as to avoid excessive increases in temperature at any point in the catalyst bed.

 As the recycle gas, part of the methane obtained can advantageously be used.

3
EXAMPLE 1 10 cm of the previously prepared catalyst are placed in a reactor.

 After purging the reactor at room temperature with a gas (methane or nitrogen), the catalyst is reduced with hydrogen at a temperature of 450 ° C. for 2 hours.

 The temperature of the catalytic bed is then raised to 3700 ° C. and the pressure to 5 MPa, the flow rate of hydrogen being 43 l / h.

A feed having the following weight composition is then introduced:
Paraffins in C6 32 7
Methylcyclopentane 28%
Cyclohexane 35%
Benzene 5 7
100
S content = about 1 ppm
N content = about 1 ppm
This charge is introduced with a flow rate of 20 cm3 / h, together with nitrogen introduced at a rate of 150 l / h. This nitrogen is used to evacuate the calories produced during the reaction.

H
The space velocity is 2 and the molar ratio is 10.3. HC
The weighted composition of the hydrocarbon product at the outlet of the reactor is as follows (after 50 hours)
C1, 96.20
C2 0.30
C3 0.20
C4 0.30
C5 0.20
C6 1.20
C7
Methylcyclopentane 0.55
0.85 Cyclohexane
Benzene 0.20
Molecular Weight Medium 16.5
The overall conversion rate is 97.2 7
cc.me follows
C6 96.2%
C7 100,
Methylcyclopentane 98,
cyclohexane 97.6
96.9 benzene
The selectivity of the transformation into methane is 98.9%
Example 2 (Comparative) In this example, the reaction temperature was set at 320 ° C, all other operating conditions remaining unchanged.

 The hydrocarbon product leaving the reactor only contains 11.4% by weight of methane and the selectivity of the transformation into methane is only 34.8%.

Example 3 In this example, the evolution of two catalysts as a function of time was compared. One of the catalysts is that used in Example 1, (20% by weight of nickel and 0.5% of molybdenum) which is called A, the second contains only 20% of nickel and is called A .

 The conditions of the test are the same as in Example 1.

The results obtained are given in Table I.
TABLE I

<tb><SEP> Hours <SEP> of <SEP> On <SEP> 50 <SEP> 100 <SEP> 250 <SEP> 500
<tb> Catalyst <SEP> A <SEP> - <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.2 <SEP> 96.3 <SEP> 96.1 <SEP> 95 6
<tb> (in <SEP> weight)
<tb><SEP> Selectivity <SEP> 98.9 <SEP> 98.8 <SEP> 98.7 <SEP> 98.5
<tb> Catalyst <SEP> A '<SEP> - <SEP> Methane <SEP> to <SEP> the <SEP> output
<tb><SEP> (in <SEP> weight) <SEP> 96.4 <SEP> 96.2 <SEP> 90.4 <SE> 78.5
<tb><SEP> Selectivity <SEP> 98.8 <SEP> 98.7 <SEP> 95.9 <SEP> 87.2
<Tb>
Example 4
According to the method used for the preparation of catalyst A, the following catalysts B to F.

All these catalysts contain 20% by weight of nickel, and differ by the additional element
catalyst B contains 0.5% (weight) of chromium
the "C" contains 0.5% tungsten
the "D" contains 0.5% titanium
the "E" contains 0.5% zirconium
and the "F" contains 0.5% hafnium
With these catalysts, long-term tests were carried out.

 Table II presents the results obtained.

TABLE II

<tb><SEP> Hours <SEP> of <SEP> On <SEP> 50 <SEP> 100 <SEP> 250 <SEP> 500
<tb> Catalyst <SEP> B <SEP>% <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.3 <SEP> 96.3 <SEP> 96.2 <SEP> 95 9
<tb><SEP> Selectivity <SEP> 99.1 <SEP> 99.1 <SEP> 99 <SEP> 99
<tb> Catalyst <SEP> C <SEP>% <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.5 <SEP> 96.3 <SEP> 96.2 <SEP> 95 8
<tb><SEP> Selectivity <SEP> 99 <SEP> 98.9 <SEP> 98.8 <SEP> 98.4
<tb> Catalyst <SEP> D <SEP>% <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.4 <SEP> 96.2 <SEP> 96.3 <SEP> 95 9
<tb><SEP> Selectivity <SEP> 98.8 <SEP> 98.7 <SEP> 98.9 <SEP> 98.3
<tb> Catalyst <SEP> E <SEP>% <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.6 <SEP> 96.4 <SEP> 96.4 <SEP> 95 9
<tb><SEP> Selectivity <SEP> 98.7 <SEP> 98.5 <SEP> 98.8 <SEP> 98.4
<tb> Catalyst <SEP> F <SEP>% <SEP> Methane <SEP> to <SEP><SEP> Exit <SEP> 96.1 <SEP> 96.1 <SEP> 96.3 <SEP> 95 6
<tb><SEP> Selectivity <SEP> 98.4 <SEP> 98.5 <SEP> 98.6 <SEP> 98.3
<Tb>

Claims (5)

 1 / Process for the production of methane by hydrogenolysis of a charge  consisting of hydrocarbons having at least two carbon atoms per  molecule, characterized in that one operates in the presence of a catalyst  containing  (a) a support selected from the group consisting of aluminum  mines, silica aluminas, silica magnesia,  coal and silica.  (b) at least one metal selected from the group consisting of  iron, nickel and cobalt, and  (c) at least one additional metal chosen from the group  consisting of chromium, molybdenum, tungsten,  titanium, zirconium and hafnium.  2 / A method according to claim 1 characterized in that the catalytic  contains 0.5 to 50 per cent by weight of iron, cobalt or nickel and 0.01 to  20% by weight of additional metal.  3 / A method according to claim 2 wherein the catalyst contains  15 to 25% by weight of nickel and 0.3 to 0.8% by weight of addition metal  nel.  4 / A method according to one of claims 1 to 3 wherein the support  catalyst is silica.  5 / A method according to claim 4 wherein the silica has a surfa  2  this specific between 50 and 400 m- per gram and a volume  total porosity between 0.40 and 1.20 cm3 / g, the average pore diameter being between 5 and 15 nm, substantially no pore n having  a diameter less than 2 minutes 6 / A method according to one of claims 1 to 5 wherein the catalyst additionally contains 0.01 to 5 7 of a metal selected from the group consisting of platinum, iridium, palladium and rhodium.  7 / A method according to one of claims 1 to 6 wherein is operated at a temperature between 340 and 500 C. 8 / A method according to one of claims 1 to 7 wherein, the ready-to-use catalyst, undergoes, before being contacted with the feedstock, a treatment with hydrogen.