FR2571981A1 - Catalyst system for the production of hydrocarbons which are rich in light olefins from carbon monoxide and hydrogen - Google Patents

Abstract

Catalyst system for the production of hydrocarbons from a gaseous mixture of CO and H2, comprising one or more transition metals associated with at least one oxide, the oxide(s) being chosen from those of the rare-earth metals.

Description

The invention relates to the production of hydrocarbons by passage of synthesis gas, that is to say of
CO and H21 hot on a catalyst based on one or more transition metals. It aims, more particularly, at a new catalytic system, containing such metals and making it possible to carry out the process of converting CO + H2 into hydrocarbons containing many olefins in C2 to C4.

 The synthesis of hydrocarbons from mixtures of CO with H2, or FISCHER-mROPSCH synthesis, has been practiced for more than 60 years, and has given rise to numerous variants, especially with regard to the composition of the catalysts used. Nevertheless, there is always progress and modifications to be made in order to meet industrial needs, which - moreover - may vary over time and according to regions. One of the questions which arise at present is the obtaining of gases which are as rich as possible in the olefins from C2 to C4; we know in fact the interest currently present in ethylene, propylene and butylene, so useful both for the production of polymers and for many syntheses of organic compounds.

However, it appears that obtaining, by the process
Fischer-Tropsch, hydrocarbon gas containing more than about 20% light olefins is hardly easy. In fact, on conventional catalysts, such as Ni or Co, supported by alumina or silica, at 2500 ° C. under atmospheric pressure, generally only about 7 to 17% of these olefins are reached in the mixture obtained. , and more than 50% methane is formed, constituting much less interesting.

Over the past decade, efforts to resolve this problem have made it possible to reach approximately 50% of C2 to C4 olefins using special catalysts such as Mn + Fe, but at the cost of relatively high temperatures and pressures.

 The present invention provides the advantage of allowing the conversion of CO + H2 mixtures into hydrocarbons, mainly from C2 to C4 with a high proportion of olefins in this margin, the reaction being able to be carried out at a moderate temperature, under low pressure, generally close to atmospheric pressure. Another unforeseen advantage of the invention lies in the formation of much smaller amounts of CO2 than in the known technique; indeed, the selectivity for CO2 is - with the catalytic system according to the invention - most often limited to around 10 to 20%, whereas it generally reaches up to 40 to 50% in the old processes. This factor is important , especially for the stability of the catalyst, because at least part of the CO2 can come from the reaction 2CO = C02 + C which consumes CO at the expense of hydrocarbons and leaves a carbon deposit on the surface of the catalyst, thus causing the aging of the latter.

 The catalytic system according to the invention, constituted by one or more transition metals associated with at least one oxide, is characterized in that the oxide or oxides are chosen from those of the rare earth metals. Thus, the new catalyst according to the invention comprises one or more of the transition metals associated with a rare earth oxide: more particularly suitable the metals with atomic numbers 21 to 30 in the Periodic Table of the elements with oxides of the series lanthanides, or atomic numbers 57 to 71.

 From the point of view of accessibility, the very practical systems include Fe, Ni or / and Co, that is to say metals of group VIII of the Classification, with oxides of La, Ce or / and Pr.

 The association of the rare earth oxide with the metal can be carried out by the addition of the metal to the oxide used as a support for this metal. It can also take place by adding rare earth to the transition metal1 the assembly being fixed on a conventional support, for example activated carbon, alumina, silica, various alumina silicates, titanium oxide or the like, having preferably a specific surface area as large as possible.

 The various modes of incorporation of the active elements of a catalyst into a support being known in the art, there is no need to describe them here. All these modes are applicable to the system according to the invention.

 When the new catalytic system consists of one or more rare earth oxides supporting the transition metal (s), the content by weight of these, as a whole, can vary between 0.01 and 30%, and preferably between 0.5 and 15%. Thus, for example, an excellent catalyst is formed by the incorporation of 1 to 12% by weight of Fe, Ni or / and Co in lanthanum oxide and / or cerium oxide.

 In the case where the metal and the oxide are deposited jointly on a conventional support, in particular on carbon with a large specific surface, the metal content can be approximately 0.01 to 30% by weight of the total, or better from 0.5 to 15%; the proportion of rare earth oxide is then from 0.01 to 30% of the whole, and preferably from 0.1 to 10% by weight. Examples of such catalytic systems consist of activated carbon with a specific surface of the order of 1000 m 2 / g containing 1 to 12% by weight of Fe; Ni or / and Cot as well as 0.5 to 8% of oxide of La or / and Ce.

 The physical state of the catalyst influences its properties; it depends on the heat treatment or / and the reduction applied to the system after the incorporation of the metal, generally in the form of a salt in solution, in the chosen support. The catalyst according to the invention can therefore be subjected to a prior calcination, preferably at a temperature of 200 to 500 C. it is advantageously reduced to hydrogen, before use, between 2000 and 5000C.

 As regards the reaction itself, of conversion of the CO + H2 mixtures into hydrocarbons, it is carried out in the manner known per se, that is to say under normal conditions of the Fischer-Tropsch synthesis. In particular, can it be driven at temperatures of 1000 5000C and especially between 2000 and 4000C. As indicated above, an advantage of the catalytic system according to the invention lies in the possibility of obtaining gases rich in C2-C4 olefins, at moderate temperatures, in particular 2300 to 3300C.

 As in the known technique, it is possible to operate under very variable pressures, namely between 1 and 1000 bars, and especially under 1 to 30 bars. But here too, an advantage of the invention makes it possible to operate at atmospheric or low pressure.

 In the embodiment of the invention where one or more oxides of rare earth elements serve as a support for the transition metal, it is good that the specific surface of the oxides is high, but it is sufficient that it is 1 at 20 m2 / g (BET). On the other hand, if a conventional support is used for fixing the transition metal and the rare earth oxide, in particular activated carbon, a greater specific surface is required, in particular from 20 to 1500 m2 / g, preferably 500 to 1300 m2 / g.

 The invention is illustrated by the following nonlimiting examples.

EXAMPLES 1 to 6
Six nickel-based catalysts, supported by different oxides, are prepared by impregnating the oxide with an aqueous solution of Ni nitrate. The oxide, thus impregnated, is dried in air and in an oven for 12 h at 1200C.

it is then reduced in situ with hydrogen for 10 hours at 3O00C, except for Example 3 where this reduction is carried out at 4000C.

An equimolecular mixture of H2 + CO is then passed over the catalyst at 2500C (except 2700 in Example 6) under a pressure of 1.013 bar, at a volumetric speed, ho -1 rary, VVH, of 1000 h
The results obtained are reported in Table I below, in which it is indicated
the weight% of Ni in each catalyst
the nature of the support
the activity of the catalyst in mol. CO-transformed by
hour, per gram of Ni
analysis of hydrocarbons formed
the rate of CO2 formation.

TABLE I
EXAMPLES n 1 2 3 * 4 5% Ni 3 12 12 1.7 5 11
Support oxide La203 La 203 La203 CeO2 SiO2 A 2 3
Its SBET surface
m / g 10 10 10 40 10 10
Activity (x 102) 4.7 2 1.5 1.7 5.9 3.4
Gas (excluding CO2)% C1 31 27 25 46 53 58 C2-C4 59 58 67 54 40 35
C5 + 10 15 8 0 7 7% Olefins in
C2-C4 51 70 65 70 19 22% Olefins C2-C4
in the total of hy
drocarbons 30 40.6 44.0 37.8 7.6 7.7
CO2 / (CO2 + H2O) 0.12 0.18 0.14 0.36 -
* - reduction to 400 C against 300 C in the other examples **
- reaction at 2700C - against 2500C in the other examples.

It can be seen that the operations according to the invention, ie examples 1 to 4, provided a gas much richer in C2 - C4 olefins (30 to 44%) than the prior art of examples 5 and 6 (maximum 7.7% ), despite the very moderate temperature and atmospheric pressure. The test with a support for CeO2 - example 4 - is also interesting in that it did not give hydrocarbons with more than 4 carbon atoms at all.

EXAMPLES 7 to 11
Tests similar to those of Examples 1 to 6 were carried out, but with cobalt nitrate instead of that of nickel. The activity is therefore expressed in moles of CO converted per gram of Co per hour.

The results are collated in Table II.

(The supports have a specific surface of 10 g / m2 BET).

TABLE II
Examples nO 7 8 9 10 11% Co 10 10 10 10 10
Support oxide La203 La203 CeO2 SiO2 SiO2
Reduction temperature 2500 4000 2500 2500 4000
Activity (x102) 0.7 0.1 1.1 3.5 7.0
Gas (excluding CO2)
C1 44 55 23 60 62
C2-C4 48 45 53 34 35
C5 8 traces 24 6
Olefins in C2-C4 73 84 70 50 39
Total olefins
hydrocarbons 35 37.8 37.2 17 13.7
CO2 / (CO2 + H2O) 0.23 0.43 0.23 -
As with nickel, we find, for cobalt supported by oxides of La or Ce, (examples 7 to 9) much higher proportions of C2-C4 olefins than in the case of silica ( examples 10,11).

EXAMPLES 12 to 14
Examples 12 and 13 illustrate the second embodiment of the invention, in which the transition metal, together with a rare earth oxide, is incorporated into a conventional support. The metal here is Co, the rare earths La or Ce, and the activated carbon support, known under the name of Arcticicbone, having a specific surface of approximately 1200 m2 / g. Example 14, comparative, relates to the same Acticarbone supporting cobalt, without rare earth.

The procedure (reaction at 250oc) is the same as in the previous examples: the support is impregnated with a Co salt and a La or Ce salt; The results are gathered at
Table III.

TABLE III
EXAMPLES 12 13 14% Co 10 10 10% rare earth 4 Ce 4 La
Activity (for Co) (x102) 1.8 3.7 0.3
Gas (excluding CO2)
% C1 47 46 96
C2-C4 38 38 4
C5 + 15 16% olefins in C2-C4 80 71 0% olefins in total
hydrocarbons 30.4 27 0
CO2 / (CO2 + H2O) 0.14 0.11 0.10
The influence of rare earths is remarkable in examples 12 and 13 compared to 14. La and Ce, at the rate of 1 atom for 6 atoms of Co, are sufficient to produce approximately 30% of light olefins, while without these elements, there are no olefins at all.

We also note that the activity is greatly increased by the presence of rare earth.

Claims (10)

Claims  1. Catalytic system for the production of hydrocarbons from a gaseous mixture of CO and H2, comprising one or more transition metals associated with at least one oxide, characterized in that the oxide or oxides are chosen from those of the metals of rare earths.  2. Catalytic system according to claim 1, ca characterized in that the transition metal has an atomic number from 21 to 30 and the oxide is that of a lanthanide with atomic number 57 to 71.  3. System according to claim 2, characterized in that the metal is Fe, Ni or / and Co and the oxide is that of La, Ce or / and Pr.  4. System according to one of claims 1 to 3, characterized in that the rare earth metal oxide serves as a support for the transition metal whose content is 0.01 to 30% by weight.  5. System according to one of claims 1 to 3, characterized in that the transition metal and the rare earth are incorporated together with a conventional support, in particular with activated carbon, silica, alumina, silicates d alumina or / and titanium oxide.  6. System according to claim 5, characterized in that it contains at the same time, by weight, 0.01 to 30% of transition metal and 0.01 to 30% of rare earth oxide.  7. System according to claim 6, characterized in that the content of transition metal being from 0.5 to 15%, that of rare earth oxide is from 0.1 to 10%.  8. System according to claim 7, characterized in that it contains 1 to 12% of Fe, Ni or / and Co together with 0.5 to 8% of oxide of La or / and Ce.  9. Process for converting a mixture of CO with H2 into hydrocarbons, by passing over a catalyst based on one or more transition metals, at a temperature of 100 "to 500" C at 1 to 1000 bars of pressure , characterized in that the catalyst consists of the system according to one of claims 1 to 8.  10.Application of the process according to claim 9 to the production of hydrocarbons with a high content of olefins of 2 to 4 carbon atoms.