THE AIM OF THIS PROJECT IS AN EXPERIMENTAL LABORATORY ATTEMPT AT DIRECT VINYL CHLORIDE SYNTHESIS FROM METHANE, CHLORINE AND OXYGEN IN THE GASEOUS PHASE AT HIGH TEMPERATURES AND SHORT CONTACT TIMES.
The oxychlorination of methane is an interesting way of producing hydrocarbons with carbon chains greater or equal to 2 carbons long (C2+ or C2). A study is reported of the reactions of various mixtures containing methane, oxygen and chlorinated compound (eg chlorine, methyl chloride or hydrogen chloride in a flame). For this study, a special burner has been designed with operating conditions based on the same principles used for well known autothermal processes. Partial combustion of the methane was achieved by means of a diffusion flame followed by rapid quenching with jets of inert gas. The influences of chlorinated additives and of several other parameters (reactant concentrations, conditions of admission of the reactants, flame length) on the product distribution have been pointed out, particularly concerning the methane conversion, the C2 selectivity and the formation of soot.
Experimental results show that the addition of chlorine to methane and oxygen flames improved both the methane conversion and the C2 selectivity. These results have been established under a limited range of operating conditions (geometry of the burner, flow rates, mixing of the reactants, etc) and, therefore it could not be claimed that they are the optimal ones.
Some important problems still remain which are not easy to solve. Recycling hydrogen chloride via gas phase reactions seemed impossible and could only be achieved by heterogeneous catalytic processes. Soot formation was the main drawback in such systems. Even if the quantities of carbonaceous deposits formed may be maintained at very low levels, accumulation in the reactor or in the pipes could have catastrophic consequences for the process operation. But, due to the lack of quantitative measurements in this field, it is not possible to estimate at present the real significance of this problem.
BENSON'S REACTION APPEARS VERY ATTRACTIVE AS TO ITS COMMERCIAL VIABILITY, BUT IT NEEDS TO BE COMBINED WITH A CATALYTIC OXYCHLORINATION REACTION WHICH WOULD BE VERY DIFFICULT TO SET RUNNING. IT IS PROPOSED TO ASSOCIATE A CONFINED OXYCHLORINATION-PYROLISIS REACTION TO THE BENSONS'S REACTION: THIS WOULD LEAD DIRECTLY TO VINYL CHLORIDE SYNTHESIS FROM CH4 CL2 AND O2 IN THE GASEOUS PHASE:
2 CH4 + 1/2 CL2 + 5/4 O2 ---- CH2 = CHCL + 5/2 H2O
FOR THIS REACTION H300 = - 103,7 KCAL.MOL-1
A SINGLE AS WELL AS A SYSTEM OF TWO CASCADE MATRAS AND VILLERMAUX PERFECTLY STIRRED REACTORS, CONTINUOUSLY OPERATING AT CONSTANT TEMPERATURE AND PRESSURE ARE ENVISAGED FOR THE STUDY OF THE FUNDAMENTAL KINETICS OF THE REACTION.
IN THE CASE OF THE CASCADE SYSTEM, CH4 AND CL2 WILL BE INTRODUCED INTO THE FIRST REACTOR, WHILE O2, POSSIBLY DILUTED WITH AN INERT GAS, WILL BE SENT INTO THE SECOND ONE.
TEMPERATURES WILL BE FROM 700 TO 1100 CELSIUS DEGREES, PRESSURES FROM 100 TO 1000 TON AND RESIDENCE TIMES FROM 0,5 TO 5 SECONDS.
AT LEAST A FIFTYFOLD CH4 EXCESS SHALL BE KEPT. A FLAME REACTOR OF THE TUBULAR-ANNULAR TYPE SHALL ALSO BE USED. ITS DESIGN WILL ALLOW OXYGEN TO REACT WITH THE PRODUCTS OF THE CH4 + CL2 REACTION TAKING PLACE IN A DIFFUSION FLAME. REACTION TIMES CAN ALSO BE VARIED OVER A VERY WIDE RANGE (0,1 MS TO 1 S). REAGENT FLOW RATIOS WILL BE OF THE ORDER OF THE STOICHIOMETRIC ONES FOR THE AFOREMENTIONED REACTION. SPECIAL CORROSION-WITHSTANDING MATERIALS SHALL BE USED AND THEIR POSSIBLE CATALYTIC ROLE WILL BE INVESTIGATED. THE STOICHIOMETRIC, THERMOCHEMICAL AND POSSIBLY KINETIC ANALYSES OF THE EXPERIMENTAL DATA WILL ALLOW A REACTION SCHEME TO BE PROPOSED, WHICH WILL BE INTERPRETED IN TERMS OF A RADICAL REACTION MECHANISM. A CONCLUSION WILL THEN BE DRAWN AS TO THE VIABILITY OF THE PROCESS.