Coal Liquefaction

Is a renaissance of coal imminent?—challenges for catalysis

“…Fischer-Tropsch synthesis is a nonselective process that produces a wide range of compounds containing from 1 to 4100 carbon atoms. 15 The reaction is a surface polymerisation. However, there is still a large debate about the reaction mechanism.…”

“…The chain terminates by hydrogenation. 15 The Schulz-Flory distribution can be used to predict selectivities assuming that all hydrocarbon species regardless of chain length add a carbon atom with equal probability, the so-called chain growth probability a. Thus, only C 1 compounds can be produced with 100% selectivity for a = 0.…”

“…However, for intermediate products, only certain maximum values are possible. 15 Catalysts active for Fischer-Tropsch synthesis are Ni, Fe, Co and Ru. Since Ni is also very active for hydrogenation, the selectivity to undesired methane is too high and since Ru is too expensive, only Fe and Co are possible for commercial application.…”

“…The first viable process was the German Bergius-Pier process developed in 1925. 15 For optimum catalyst performance, the process had two stages (Fig. 7).…”

“…In the second stage, an Ni-Mo/Al 2 O 3 catalyst is used in a fixed bed reactor. 15 The yield achievable during direct coal liquefaction considerably depends on the rank and the chemical structure of the coal used. The long-term continuous operation of a process development unit at DMT in Germany, where a wide range of coals has been processed, demonstrated that the oil yield reaches a maximum of about 60% near the transition of subbituminous to bituminous coal, i.e., at about 13% oxygen and 80% carbon in the dry ash-free coal.…”