Thermodynamic Study on the Formation of Acetylene during Coal Pyrolysis in the Arc Plasma Jet

Abstract

Based on the principle of minimizing the Gibbs free energy, the composition of C-H-O-N-S equilibrium system about acetylene formation during the pyrolysis in arc plasma jet for four kinds of different rank-ordered coals such as Datong, Xianfeng, Yangcheng, and Luan was analyzed and calculated. The results indicated that hydrogen, as the reactive atmosphere, was beneficial to the acetylene formation. The coal ranks and the hydrogen, oxygen, nitrogen, and sulfur in coal all could obviously affect the acetylene yield. The mole fraction of acetylene is the maximum when the ratio value of atom H/C was 2. The content of oxygen was related to the acetylene yield, but it does not compete with CO formation. These agreed with the experimental results, and they could help to select the coal type for the production of acetylene through plasma pyrolysis process.

Production of Acetylene and Acetylene-based Chemicals from Coal

“…On the basis of thermodynamic modeling of the reactions of Chinese coals, a hydrogen atmosphere would give the highest acetylene yield, followed, in order of decreasing yield, by argon and nitrogen. 45 However, the yields reported in this work, ≈10%, 45 are significantly lower than conversions of 35−40% reported by other authors. 33,47,56,58 Use of an argon−hydrogen mixture substantially increased acetylene yields relative to reaction in pure argon, for example, from 15% to 40%.…”

“…46 Rather, a coal of about 80% carbon and 12% oxygen gives a better acetylene yield. 45 Other work has suggested 25−44% volatile matter and <9% oxygen [on a dry ash free (daf) basis] as optimum. 47 Coals in this volatile matter range have produced acetylene yields of 17−22%.…”

“…The mineral matter content would affect the energy requirement per unit acetylene yield, since the minerals will be heated right along with the carbonaceous part of the coal. 41 With respect to the heteroatoms, oxygen forms primarily carbon monoxide, especially above 1227 °C; 54,55 sulfur produces primarily carbonyl sulfide, especially between 727 and 1527 °C, along with some hydrogen sulfide and carbon disulfide; 45,54 and hydrogen cyanide represents the main nitrogen-containing product. 33,45,55,56 Tests with a series of four British coals showed that carbon monoxide formation was quite close to the amount that would have been predicted on the basis of oxygen content of the coals, 57 confirmed by a study on six Chinese coals.…”

“…41 With respect to the heteroatoms, oxygen forms primarily carbon monoxide, especially above 1227 °C; 54,55 sulfur produces primarily carbonyl sulfide, especially between 727 and 1527 °C, along with some hydrogen sulfide and carbon disulfide; 45,54 and hydrogen cyanide represents the main nitrogen-containing product. 33,45,55,56 Tests with a series of four British coals showed that carbon monoxide formation was quite close to the amount that would have been predicted on the basis of oxygen content of the coals, 57 confirmed by a study on six Chinese coals. 49 Addition of nitrogen to the reactor increases the yield of hydrogen cyanide at the expense of acetylene, 33 suggesting that, as in formation of carbon monoxide, there is a competition for available carbon.…”

“…Thermodynamic modeling indicates that two properties impact acetylene yield: the volatile matter content, which has a positive effect, and the oxygen content, which diminishes acetylene formation with concomitant increase in carbon monoxide yield . Both of these parameters decrease with increasing rank.…”