|Title of Invention||
A PROCESS FOR THE PURIFICATION OF HYDROCHLORIC ACID BY PRODUCT OF THE SYNTHESIS OF METHANE SULPHONIC ACID
|Abstract||The invention relates to the purification of the hydrochloric acid by-product of the synthesis of methanesulponic acid. The methanesulphonyl chloride entrained by the gaseous HCl by-product is removed using an amount of water ranging from 0.01 to 20%, relative to the mass of HCl to be treated. The water is injected into the HCl gas flow and the temperature is lowered to 15°C or below.|
The present invention relates to a process for the purification of the hydrochloric acid by-product of the synthesis of methanesulphonic acid (referred to hereinbelow as MSA).
The synthesis of MSA from methyl mercaptan and chlorine according to the reaction:
CH3SH + 3 Cl2 + 3 H2O -► CH3S03H + 6 HCl
produces a large amount of hydrochloric acid by-product. The HCl gas flow separates from the reaction medium, entraining some of the volatile compounds/ and this entrainment is proportionately larger when the reaction is carried out at 100°C. By means known per se, the chlorine and the methyl mercaptan are readily eliminated from the hydrochloric acid. The water is not a hindrance since the aim is to recover a 33% solution of HCl in water.
However, during the reaction which leads to methanesulphonic acid, a relatively volatile intermediate is produced, methylsulphonyl chloride CH3S02C1 (MSC) , which, on working up the gaseous HCl with water, converts into methanesulphonic acid, thereby contaminating the i hydrochloric solution and making it unsuitable for a certain number of applications.
The entrainment of MSC is considerable since the contact between the HC1 and the MSC takes place at high temperature. The excess MSC is readily removed using the known standard techniques such as, for example, washing the hydrochloric effluent with the MSA produced in the reaction and preferably purified. Nevertheless, appreciable amounts of MSC are entrained by the HC1 since the operations do not take place at low temperature, but in the region of room temperature. It is known that depending on the temperature (see Table I), the MSC content of the hydrochloric acid takes increasing values.
In a usual process for the synthesis of MSA, the HC1 flow is at a temperature in the region of 20°C. It thus contains from 5000 to 9000 ppm of MSC, which lead to a 33% hydrochloric solution containing from 1500 to 2500 ppm of MSA,
The aim of the present invention is to provide a process which makes it possible to reduce the MSC content in the HC1 gas as much as possible, without making it necessary to use extremely low temperatures or ) highly sophisticated and expensive techniques.
According to the invention, there is provided a process for the purification of hydrochloric acid byproduct of the synthesis of methanesulphonic acid, which comprises injecting water into the hydrochloric acid (HCl)gas flow, in order to remove methanesulphonyl chloride entrained by the HC1 gas, the amount of water ranging from 0.01 to 20%, relative to the mass of HCl to be treated and the temperature being reduced to 15°C or below.
The cooling and water injection operations can be carried out simultaneously or successively. In the latter case, the water is preferably injected first and cooling carried out thereafter.
In accordance with the process according to the invention, the lowering of the HCl gas temperature to below or equal to 15°C, preferably approximately between
~5 and + 5°C, makes it possible to decrease the MSC content considerably. Thus, for example, a gas cooled from 21°C to 0°C may have its MSC content of 8830 ppm reduced to 1245 ppm, i.e. an efficacy of 86% or a reduction factor equal to 7.
In accordance with a second characteristic of the process according to the invention, an aerosol of pure water may be injected into the hydrochloric gas in an amount corresponding to a few per cent of the mass of HC1 to be treated (0.01 to 20%, preferably 5 to 10%).
The aggregation effect between the hydrochloric acid and the water which results therefrom makes it possible to trap out most of the residual MSC, which can be returned to the MSA synthesis reactor. Thus, with 10% water relative to the HCl, an MSC content of 1245 ppm may readily be reduced to 120 ppm, i.e. for the process an overall purification efficacy of 98,6% or a reduction factor equal to 73.6. The process according to the invention makes it possible not only to purify the HCl but also to recover more than 17 tonnes of MSC per 1000 tonnes of MSA produced.
The invention is further illustrated by way of example with reference to the accompanying drawing and following Example.
The apparatus illustrated in the accompanying drawing is designed to treat 60 litres/hour of hydrochloric gas (about 90 g/h) and is made of glass with connecting pipes made of polytetrafluoroethylene(PTFE). Pure MCS may be used as the fluid for saturating the HC1.
A stream (2) of HC1 gas is passed through a saturator (1) containing liquid MSC and the exiting stream of HC1 charged with MSC is conveyed via pipes (3) and (4) to a treatment column containing three main parts, namely:
- a gas injector (5) containing a water-spraying system (mini hydro-injector) supplied at (6) by a syringe pump or by a peristaltic micropump,
- a heat-exchange zone (7) comprising a coil (8 and 9) through which a coolant liquid runs, and
- a retention zone (11) separated from the rest of the column by a splash head (12) made of rock wool packed to a thickness of 5 centimetres and prewashed with concentrated hydrochloric acid, rinsed with distilled water and dried with ether before being inserted.
After passage through the heat-exchange zone (7), the hydrochloric acid and the condensates are conveyed via a pipe (10) to a retention zone (11). The condensates leave via a pipe (13). The hydrochloric acid crosses the splash head (12) and is conveyed via a pipe
(14) to a column (15) for working up the purified HC1 gas with water. This standard column (15), supplied with water via a pipe (16), is thermostatically regulated and operates in batchwise mode in order to produce at (17) hydrochloric acid with a titre of about 33%.
The same column may be used to control the MSC titre of the contaminated HCl to be treated, by circulating the flow of HCl gas charged with MSC directly from the saturator (1) to the column (15) via pipes (3) and (18).
Anhydrous hydrochloric acid gas was diffused into liquid MSC whose temperature was set so as to charge the HCl with the desired amount of MSC vapour. After passing into the treatment column, the hydrochloric gas was worked up with water so as to obtain a solution at a concentration of 33% by mass. The MSC entrained by the HCl was hydrolysed into MSA, which was assayed according to the known analytical techniques.
The results obtained are given in the table below.
1. Process for the purification of
hydrochloric acid by-product of the synthesis of
methanesulphonic acid, which comprises injecting water
into the hydrochloric acid (HC1) gas flow in order to
remove methanesulphonyl chloride entrained by the HC1
gas, the amount of water ranging from 0.01 to 20%
relative to the mass of HC1 to be treated and the
temperature being reduced to 15°C or below.
2. Process according to claim 1, in which the
temperature of the HCl gas flow is lowered to a value of
approximately between -5 and +5°C.
3. Process according to claim 1 or 2, in
which 5 to 10% of water, relative to the mass of HCl to
be treated, is used.
4, Process for the purification of hydrochloric acid by-product of the synthesis of methanesulphonic acid, substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||1668/MAS/1998|
|PG Journal Number||26/2007|
|Date of Filing||27-Jul-1998|
|Name of Patentee||ELF ATOCHEM S.A|
|Applicant Address||4 & 8 COURS MICHELET LA DEFENSE 10 F-92800 PUTEAUX.|
|PCT International Classification Number||C01B07/7|
|PCT International Application Number||N/A|
|PCT International Filing date|