Hydrocarbons synthesis from syngas by very high pressure plasma
Résumé
Experimental studies related to chemical processes based on the use of very high pressure plasma are scarce. In the domain of chemical synthesis enhanced by plasma, the influence of pressure has not been yet reported in literature for conversion of syngas into hydrocarbons. This may be attributed to the difficulties of ignition and sustaining a stable electric discharge at pressures higher than 1 MPa. Yet, the use of high pressure plasma could constitute a new route to synthesize hydrocarbons in gaseous phase. Thus, this paper presents experimental results of hydrocarbons synthesis from a syngas having a H2:CO ratio of 2.2:1, i.e. close to the one commonly met in the classical Fischer-Tropsch process, in a tip-tip non-thermal arc discharge reactor at very high pressure (in the range 0.5-15 MPa) supplied by a high-voltage DC power supply without any catalyst. The molecular synthesis is here studied through the influence of two process setting parameters: operating pressure and supplying current. The results show that C1-C3 molecules can be synthesized by this way and their concentration significantly varies with the two studied parameters. The best results in terms of products concentration after 60 s treatment were obtained: (i) for 12 MPa pressure at 0.35 A current, with concentration of C1 and C2 + C3 around 6000 ppm and 90 ppm respectively, (ii) for 0.2 A current at 0.5 MPa pressure, with concentration of C1 and C2 + C3 around 4500 ppm and 5000 ppm respectively. In addition, the energy efficiency of the process was evaluated, based on the determination of specific energies as they are defined in the classical Fischer-Tropsch process. The results demonstrate that the optima in terms of chemical conversion and energy efficiency coincide together.