Process for continuous industrial synthesis of alkane-suphonicacid

1. A process for the continuous industrial preparation of alkanesulphonic acid of formula C n H 2n+1 SO 3 H from the alkane of formula C n H 2n+2 , wherein n represents an integer between 1 and 20 inclusive, said process comprising at least the following steps:

a) loading of alkanesulphonic acid C n H 2n+1 SO 3 H, wherein n is as defined above, in a reactor,

b) heating said alkanesulphonic acid at a temperature between 25° C. and 120° C.,

c) introducing a quantity of sulphur trioxide so that the molar ratio (alkanesulphonic acid)/(sulphur trioxide) is between 70/30 and 95/5,

d) introducing the alkane under a pressure between 4 MPa and 15 MPa,

e) introducing a radical initiator,

f) continuous conducting of the reaction, and simultaneously or in any order performing the following three sub-steps f1), f2) and f3):

f1) addition of sulphur trioxide in order to maintain the initial molar ratio (alkanesulphonic acid)/(sulphur trioxide) defined in step c),

f2) addition of alkane in order to maintain a molar ratio (alkane)/(sulphur trioxide) between 4/1 and 2/1, and

f3) continuous withdrawal of the alkanesulphonic acid of formula C n H2 n+1 SO 3 H, and

g) recovery of the alkanesulphonic acid of formula C n H 2n+1 SO 3 H after optional separation of unreacted reagents, and optionally any undesired by-products.

2. The process according to claim 1 , wherein the reaction temperature is between 25° C. and 70° C.

3. The process according to claim 1 wherein the reaction pressure is between 5 MPa and 12 MPa.

4. The process according to claim 1 , wherein the reactor is selected from reactors equipped with a recirculation loop, self-suction turbine reactors, reactors equipped with a venturi system, rotary bed reactors, and tubular reactors.

5. The process according to claim 1 , wherein the radical initiator is selected from azo-bis-iso-butyronitrile, inorganic or organic peroxides, mercury sulphate, palladium sulphate, caesium sulphate, K 2 P 2 O 8 , CaO 2 , halogens, wherein n is as previously defined, the initiators of formula C n H 2n+1 SO 2 —O—O—SO 2 OX, wherein n is as defined above and X is hydrogen, an alkali or alkaline earth metal, zinc or aluminium, Caro acid and its salts with one or more alkali or alkaline earth metals, and Marshall acid and its salts with one or more alkali or alkaline earth metals.

6. The process according to claim 1 , wherein alkane and sulphur trioxide are added as they are consumed and the amount of alkanesulphonic acid withdrawn, while maintaining the molar ratio (alkane of formula C n H 2n+2 )/(sulphur trioxide) between 3.5/1 and 2.5/1, and the molar ratio (alkanesulphonic acid)/(sulphur trioxide) between 70/30 and 95/5.

7. The process according to claim 1 , wherein the solvent is methanesulphonic acid, the alkane is methane, and the continuously withdrawn product is methanesulphonic acid.

8. A reaction medium comprising an alkane sulphonic acid of formula C n H 2n+1 SO 3 H, wherein n is an integer between 1 and 20 inclusive, sulphur trioxide SO 3 , and an alkane of formula C n H 2n+2 , wherein n is as previously defined, said reaction medium, in which:

the molar ratio (alkanesulphonic acid)/(SO 3 ) is between 70/30 and 95/5, and

the molar ratio (alkane)/(SO 3 ) is between 4/1 and 2/1.

9. The reaction medium of claim 8 , comprising methanesulphonic acid (CH 3 SO 3 H), sulphur trioxide SO 3 , and methane (CH 4 ) wherein:

the molar ratio (alkanesulphonic acid)/(SO 3 ) is between 70/30 and 95/5, and

the molar ratio (methane)/(SO 3 ) is between 3.5/1 and 2.5/1.