GB2295779A

GB2295779A - Catalyst and its use in aliphatic alkylation

Info

Publication number: GB2295779A
Application number: GB9524251A
Authority: GB
Inventors: Eric Benazzi; Jacques Alagy; Jean-Francois Joly; Christian Marcilly
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1994-11-29
Filing date: 1995-11-28
Publication date: 1996-06-12
Also published as: FR2727404B1; ITMI952448A1; DE19544544A1; ITMI952448A0; IT1277245B1; FR2727404A1; GB9524251D0

Description

1 2295779 The present invention relates to a catalyst comprising sulphuric

acid and HB(HSQ),, and its use in catalytic alkylation of isoparaffins (e.g. isobutane and/or isopentane) in the presence of at least one olefin having 3 to 6 carbon atoms carbon per molecule.

It is of particular interest to have fuels available with a high octane rating, that is to say comprising strongly branched paraffinic hydrocarbons, for supplying internal combustion, spark ignition engines, and particularly engines with a high compression ratio. The alkylation of isoparaffins (e.g. isobutane and/or isopentane) by at least one olefin containing 3 to 6 carbon atoms per molecule enables such products to be obtained. This reaction generally requires the use of highly acidic catalysts. particularly in order to reduce spurious reactions such as abstraction reactions of the olefin h%,dride and polymerisation, which produce weakly branched hydrocarbons with a low octane rating and unsaturated hydrocarbons. cracking reactions and dismutation reactions.

The existing processes for the production of hydrocarbons by alkylation of isobutane by olefins generally use either sulphuric acid or fluorhydric acid as the catalyst. In these processes. where the reaction medium is two-phase, the acid catalyst constitutes a liquid phase which contacted with the liquid isobutane- olefin(s) mixture to form an emulsion. For example, in the case where Stratco technology uses sulphuric acid (L.F. Albright, Chem.Eng., August 15, 1966, p.143 and L.F. Albright, Oil and Gas Journal, November 12, 1990), which is the technology most widely used, an emulsion is created at one end of a horizontal reactor by a turbine mixer supplied with the reactants and the recycled acid. In this case the continuous phase is the acid phase, as the volume ratio of acid/hydrocarbon is greater than 1. The reaction takes place almost instantly at the mixer. The olefins form alkyl sulphates which then lead to the formation of alkylated products. - The heat produced during the reaction is removed by a system of tubes inside the reactor in which an alkylate/isobutane mixture circulates, cooled by the release of a part of the isobutane at the outlet of the reactor. The separdtion of the two phases, acid and 2 hydrocarbon, is carried out in a decanter situated above the reactor. Nevertheless, secondary oligomerisation reactions followed by oxidation reactions lead to the formation of "red-oils", which are in fact highly unsaturated oligomers with a high molecular weight. On the other hand, the oxidation of these products by sulphuric acid leads to the formation of water and SO.. The "red-oils" and water which are formed during these reactions are soluble in sulphuric acid and contribute to its dilution. Thus. the concentration of fresh acid entering the unit, which is approximately 98-99% by weight. giving the acid a high oxidising capacity, will CI diminish to a titre of 92-90%. Below this value. the acid has to be extracted from lic jim to be regenerated. As a result. a constant supply of fresh acid and a ons,.1 1 f used acid is necessar to maintain an avera2e acid titre of ant c-tract on o 9)-94' iiicii ensures ofgood quality alkylated products.

c 1 1 ---hisoiiltiuous and substantial coiisuini)t!oi,, of sulphuric acid makes reaeneration L_ )t lic ancr necessary. The regeneration -)rk-.cess consists of burning the used acid and recovering the SO. formed. which is (lien oxidised to form SO- The sulphur - 1 (SO.) is contacted with a quantity of water sufficient to allow sulphuric acid riox de - 1 1 - a titre of 98-99% by weight to be obtained. which will be re-used to produce the alkylation reaction. The cost of this regeneration step amounts to approximately 3Mc of the operating costs of the alkylation process. As a result, a catalyst formulation which would enable acid consumption to be reduced would allow the profitability of alkylation units to be increased.

The present invention relates to a catalyst comprising sulphuric acid (H2SO,) and HWHSQ),, and its use in the alkylation of C,-C, isoparaffins by at least one olefin c --cfl. Said catalyst comprises (in % by weight) between 0.4 and 68.8%, preferably between 0.4 and 60% of HWHSQ), and between 31.2 and 99.6%, preferably between 40 and 99.6% Of H504. Said catalyst is such that it does not contain free sulphur trioxide (S03).

The catalyst is generally therefore an unsupported catalyst.

3 The catalyst used according to the invention has the advantage over sulphuric acid of 98-99% titre by weight, currently used in alkylation units, of having a higher or equal acidity while having a much weaker oxidising property. The use of the catalyst according to the invention thus leads to a reduction in catalyst consumption 5 and therefore to a reduction in the operating costs of alkylation units.

In particular said catalyst does not contain free sulphur trioxide, that is to say SO, unreacted with the boric acid, but can optionally contain excess free boric acid, that is to say boric acid unreacted with sulphur trioxide.

The itivention therefore envisaces the use of said catalyst in catalytic aik\,latioii of c 1 - at least one isoparaffin selected from isobutane and isopentane (that is to say isobutane and/or isopentane: 'Isobutaile or isopentane, or isobutane and isopentane). in the presence of at least one olefin containing 3 to 6 carbon atoms.

The compound HB(HSO,), In the catalyst according to the invention can be obtained by any of the methods known to the man skilled in the art. For example, and in a non-limiting manner. the preferred method according to the invention comprises reacting 1 mol of boric acid B(OH), with 3 mols of sulphur trioxide S03 and 1 mol of sulphuric acid H,SO, to obtain 1 mol of the compound HB(HSO,),.

A process for the preparation of the catalyst according to the invention generally comprises at least two steps. In a first step a solution of the desired amount of SO, in sulphuric acid is prepared. Then in a second step the desired quantity of boric acid, according to the reaction set out above, is added such as to give a solution of HB(HSO,), in WSO, The catalyst according to the present invention is conveniently used in a process which allows the alkylation of an isoparaffin by at least one olefin to be carried out under advantageous conditions. In particular, since the reaction is characterised by a strong exotherm (approximately 83.6 0/mol of converted butene if the olefin is 4 butene, and if the isoparaffin is isobutane), the use of the catalyst according to the present invention allows a good homogeneity of temperature and reagent concentration to be obtained.

In particular. the catalyst according to the present invention may be used by techniques known by the man skilled in the art. e.g. which use a reactor and a separator.

The rnixture of lsoparaffin(s)-olefin(s) is generally introduced into the reaction zone at a rate per hour expressed as ihe weight ofolefin introduced per unit weight of the -t.,ai,,,st per hour (ppli) of between 0.001 aild W h ' and preferably between 0.002 :nd h '. Said mixture can also be produ.::i inside the reaction zone. Generally.

iiiix,,ure inade in this \ay, is in iii: reaction zone under pressures and such that the mixture of li\(iro(:,lrbojis remains liquid.

The conunuous phase is either the acid phase or the hydrocarbon phase. and the reactlon rnediurn is usually, two-phase.

The reaction temperature is generally lower than +20'C, preferably less that + 15: C and in a frequently preferred inanner between +5'C and -5'C. The pressure of the reaction zone is sufficient to maintain the hydrocarbons in the liquid state in said zone.

In order to limit secondary reactions. ail excess of isoparaffin(s) with respect to the olefin(s) can be used. By, way of example. in the case of alkylation of isobutane by a butene. the isobutane can be introduced in pure form in the charge or in the form of a mixture of butanes containing. for example. at least 40% isobutane. Moreover, a pure butene or a mixture of isomeric butenes can be introduced. In all cases, the molar ratio of isobutane/butene(s) in the charge is generally between 1 and 100, preferably between 3 and 50, and in a frequently preferred manner between 5 and 15.

When the catalyst and the reaction conditions are selected carefully (in particular the temperature), the catalyst according to the invention allows the production of alkylation products of at least one isoparaffin and at least one olefin which are useful as fuels for engines and as petrol constituents, and which comprise, for example, at least 60% mol of C, paraffins and less than 1 % mol of unsaturated compounds, the C, paraffins containing 70-98% mol of trimethylpentanes.

The following examples illustrate the invention without limiting its scope.

Example 1

Preparation of the catalyst 1 in accordance with the invention g, of a in ixture comprising 80 % by weight of sulphuric acid (99.99 %) and 20% by, weight of sulphur trioxide is prepared. 5g of boric acid is then added to the 100a of the mixture to obtain 105g of an acid phase. Following the reaction of the sulphur trioxide and the boric acid in the presence of sulphuric acid, and respectively in the molar ratios 3/1/1 (that is to say 1 mol of boric acid with 3 mols of sulphur trioxide and 1 mol of sulphuric acid), an acid phase is obtained which contains HB(HSO,), in solution in WSO, and containing 31.69% by weight of HB(HSO,), and 68.31 % by weight of H,SO, Alkylation of isobutane by butene-1 with the catalyst 1 in a continuous hydrocarbon phase 40g of the catalyst 1 prepared according to the method described in Example 1 is introduced into a 500 mi steel reactor previously purged with argon. The reactor containing the catalyst is then closed and cooled to 5'C.

100 mI of isobutane is then added to the reactor containing the catalyst while stirring with a rotation speed of 2000 rpm, the reactor being cooled to 5'C by circulation 6 of a cold liquid (O'C) in the double envelope with which it is equipped. The stirring (by screw) is maintained for a duration of 30 minutes in order to homogenise the temperature.

g of a mixture comprising 10% by weight of butene-1 and 90% by volume weight of isobutane is added regularly over a total duration of 5 hours, the temperature of the reactor being maintained at 5'C over the entire duration of the introduction.

After reaction and decanting the hydrocarbon phase is drawn off from the reactor.

:sk)ia[ed. then neutralised and analysed M -.iiroinato!zrapliy In the vapour phase. its -,o,:iir)ositioii 1w weliffit 1)eliiúi ulven in below. The catalyst is then washed ilmes with lsobutane. theil lie -,.,,rboii content of the acid phase is determined.

Example 2

Preparation of the catalyst 2, not in accordance with the invention 100 g of a mixture comprising 80% by weight of sulphuric acid (100%) and 20% by weight of sulphur trioxide is prepared.

4.73g of boric acid is then added to 100g of the mixture prepared above to obtain 104.73g of acid phase. Following the reaction of the sulphur trioxide and the boric acid in the presence of sulphuric acid. and respectively in the molar ratios 3/1/1 (that is to say 1 mol of boric acid with 3 mols of sulphur trioxide and 1 mol of sulphuric acid), an acid phase is obtained which contains 29.3% by weight of the compound HB(HSO.,)4, 69.2% by weight of sulphuric acid and 1.5% by weight of sulphur trioxide.

7 Alkylation of isobutane by butene-1 with the catalyst 2 in a continuous hydrocarbon 12hase The catalytic alkylation of isobutane by butene-1 is carried out under the same experimental conditions as those described in Example 1, and the same analyses are carried out. The results are set out in Table 1 Table 1: Comparison of catalysts 1 and 2 Alkylate composlilon Example 1, Example 2 7c by, weight) Catalyst 1 in accordance Catalyst 2. not in with the invention accordance with the invention with free SO, c-C2.3 6.2 C, 93.8 85.5 C, + 3.9 8.3 Content of carbon in 1.8 4.7 1 the acid phase This table clearly shows that it is desirable to work with the catalyst according to the invention, comprising an acid phase containing sulphuric acid and the compound HB(HS04)4 and without sulphur trioxide. Indeed, the presence of the HB(HS04)4 compound in the acid phase, in the absenceOf S03 allows a catalyst 1 according to the invention to be obtained, which is more selective as shown in table 1 and which has, after 5 hours of testing, a lower carbon content, which is indicative of a lower consumption of acid phase per gram of alkylated product. These results are obtained in a continuous hydrocarbon phase.

Example 3

Preparation of the catalyst 3 in accordance with the invention 8 g of a solution of sulphur trioxide in sulphuric acid is prepared, containing 11.5 % by weight of sulphur trioxide and 88.5 % by weight of sulphuric acid. 2.97g of boric acid is then added to this solution to obtain 102.97g of acid phase. Following the reaction of the sulphur trioxide and the boric acid in the presence of sulphuric acid, and respectively in the molar ratios 3/1/1, an acid phase is obtained which contains HB(HS0j, in solution in WSO, and comprising 18. 6% by weight of HB(HSO,),, and 81.4% by weight of WSO, .',1k.\,latioil of isobutane by butene-1 with the catalyst 3 in a continuous hydrocarbon p Liase -,0,, of the catalyst 3 prepared according to he method described above is introduced,on. The reactor containing iito a -500 iTil steel reactor previously purLed with arg the catalyst is then closed. and cooled to C.

i-nl ot' isobutane is then added to the reactor containing the catalyst with stirring with a rotation speed of 2000 rpm. the reactor being cooled to 5'C by circulation (-M a cold liquid (O'C) in the double envelope with which it is equipped. The catalytic acid phase + isobutane systern is kept stirred (by screw) for a duration of 30 minutes in order to homogenise the temperature.

c, of a mixture comprising by 10% by, weight of butene-1 and 90% by volume c, weight of isobutane is added regularly, over a total duration of 5 hours, the temperature of the reactor being maintained at 5'C over the entire duration of the introduction.

After reaction and decanting the hydrocarbon phase is drawn off from the reactor and isolated, neutralised and analysed by chromatography in the vapour phase, its composition by weight being given in Table 2. The catalyst is then washed several tirnes with isobutane, then the content of carbon present in the acid phase is determined.

9 Example 4

Preparation of the catalyst 4. not in accordance with the invention Catalyst 4 comprises by 100 g of a solution of sulphuric acid at 99% by weight.

Alkylation of isobutane by butene-1 with the catalyst 4 Catalytic alkylation of isobutane by butene-1 is repeated, under the same experimental conditions as those described in Example 3. The results are set out in Table 2.. they are obtained in a continuous hydrocarbon phase.

Table 2: Comparison of catalysts 3 and 4 Alkylate composition Example 3 Example 4 (% by weight) Catalyst 3, in Catalyst 4, not in accordance with the accordance with the invention invention cl-cl 5.4 9.1 C, 91 ') 82.9 c) + 3.4 8.0 Content of carbon in 1.9 4.0 the acid phase This table clearly shows that it is desirable to use the catalyst according to the invention, comprising an acid phase containing sulphuric acid and the compound H13(1-IS04)4 and without sulphur trioxide. Indeed, the presence of the HB(HS04)4 compound in the acid phase allows a catalyst 3 according to the invention to be obtained which is more selective as shown in Table 2 and which has, after 5 hours of testing, a lower carbon content, which is indicative of a lower consumption of acid phase per gram of alkylated product.

Example 5

Preparation of the catalyst 5 in accordance with the invention This relates to the same catalyst, in accordance with the invention, as is described in example 1 of the present invention.

Alkylation of isobutane by butene-1 with the catalyst 5 in a continuous acid phase 100g of the catalyst 5 prepared according to the rnethod described in example I is introduced into a 250 i-nl steel reactor. pre% lously purged with argon. The reactor containing the catalyst is then closed. and:ooied to 5'C.

ini of isobutane is then added to the reactor containing the catalyst while stirring takes place, with a rotation speed of 2000 rpin. said reactor being cooled to 5'C by circulation of a cold liquid WC) in the double envelope with which it is equipped.

The stirring (by screw) is maintained for a duration of 30 minutes in order to homogenise the temperature.

17 g of a mixture comprising 30% by weight of butene-1 and 70% by volume weight of isobutane is added regularly over a total duration of 1 hour, the temperature of the reactor being maintained at 5'C over the entire duration of the introduction.

After reaction and decanting, the hydrocarbon phase is drawn off from the reactor and isolated, neutralised and analysed by chromatography in the vapour phase, its composition by weight being given in Table 3. The catalyst is then washed several C times with isobutane, and the content of carbon present in the acid phase is determined.

Preparation of the catalyst 6. not in accordance with the invention The catalyst 6 comprises 100g of a solution of sulphuric acid of 99.5 % by weight.

Alkylation of isobutane by butene-1 with the catalyst 6 in a continuous acid 12hase 100g of the catalyst 6 is introduced into a 250 mI steel reactor previously purged with argon. The reactor containing the catalyst is then closed, and cooled to 5'C.

mi of isobutane is then added to the reactor containing the catalyst while stirring takes place, with a rotation speed of 2000 rpm, said reactor being cooled to 5'C by circulation of a cold liquid WC) in the double envelope with which it is equipped.

The stirring (by screw) is maintained for a duration of 30 minutes in order to horno-enise the temperature.

17 g of a mixture comprising 30% by weight of butene-1 and 70% by volume c -tl weiglit of isobutane is added regularly over a total duration of 1 hour. the temperature of the reactor being maintained at 5'C over the entire duration of the introduction.

After reaction and decanting the hydrocarbon phase is drawn off from the reactor and isolated, neutralised and analysed by chromatography in the vapour phase, Its composition by weight is given in Table 3. The catalyst is then washed several times with isobutane, and the content of carbon present in the acid phase is determined.

12 Table 3: Comparison of catalysts 5 and 6 Alkylate composition Example 5 Example 6 (% by weight) Catalyst 5 in accordance Catalyst 6, not in with the invention accordance with the invention Cl-C- 2.6 6.9 C, 94.3 85.8 C, + 3.2 7.3 Content of carbon in 1.7 3.5 the acid phase This table shows that in a continuous acid phase, it is also advantageous to use a catalyst comprising an acid phase containing sulphuric acid and the compound HB(HS04)4. Indeed, the presence of the HB(HS04)4 compound allows a catalyst 5 according to the invention to be obtained which is more selective as shown in Table 3 and which has. after 1 hour of testing, a lower carbon content, which is indicative of a lower consumption of acid phase per gram of alkylated product.

13

Claims

Claims

4.

7.

8.

A catalyst comprising sulphuric acid and the compound of formula HB(E[S0j, , said catalyst containing (by % weight) between 0.4% and 68.8% of HB(HS04)4 and between 31.2% and 99.6% of sulphuric acid, and wherein said catalyst does not contain sulphur trioxide.

A catalyst according to claim 1, wherein the compound of formula HB(M04)4 has been obtained by reacting boric acid with sulphur trioxide and sulphuric acid in a molar ratio of 1:3A respectively.

Use of a catalyst according to either of claims 1 and 2 in the catalytic alkylation of at least one isoparaffin selected from isobutane and isopentane in the presence of at least one olefin containing 3 to 6 carbon atoms.

Use according to claim 3, in which the catalytic alkylation is carried out at a temperature lower than +20'C, and at a pressure sufficient to maintain the hydrocarbons in the liquid state during the reaction.

Use according to claim, in which the reaction temperature is lower than + 15'C.

Use according to any one of claims 3 to 5, in which alkylation is carried out such that the continuous phase is the hydrocarbon phase.

Use according to any one of claims 3 to 5, in which the alkylation is carried out such that continuous phase is the acid phase.

A catalyst according to claim 1 substantially as herein described.

14 9. Use according to claim 3 substantially as herein described.