The effect of the initial water of lignite on its liquefaction reactivity
In this paper, the effect of different initial water content of lignite on its direct liquefaction reactivity was studied. The results show that: initial water content in lignite can be used as hydrogen supplier and promote direct liquefaction reaction inducing higher total conversion rate, higher oil yield and lower pre-asphaltene / asphaltene yield, when the water content of lignite is of 20 ~ 30%. And the maximum of total conversion rate and oil yield is achieved 85.12% and 51.72%, respectively, when the water content of lignite is 25.33%. While the gas product yield and the pre-asphaltene /asphaltene yield is relatively lower, which is of 11.16% and 3.93%, respectively. This can be of practical significance to optimize the coal pre-treatment technology of direct liquefaction industry.
A new process for catalytic liquefaction of coal using dispersed MoS2 catalyst generated in situ with added H2O
Abstract We have found that adding a proper amount of water can dramatically improve conversion of a sub-bituminous coal in solvent-free liquefaction under at 350°C using ammonium tetrathiomolybdate (ATTM) as precursor to dispersed MoS 2 catalyst H 2 pressure. However, adding water to catalytic reactions at 400°C decreased coal conversion, although water addition to the non-catalytic runs was slightly beneficial at this temperature. We further examined the effect of water in solvent-mediated runs in addition to “dry” tests and explored a temperature-programmed liquefaction (TPL) procedure to take advantage of the synergetic effect between water and dispersed Mo catalyst precursor at low temperatures for more efficient coal conversion. The TPL using ATTM with added water at 350°C, followed by water removal and subsequent reaction at 400°C gave good coal conversion and oil yield. Model reactions of dinaphthyl ether (DNE) were also carried out to clarify the effect of water. Addition of water to ATTM substantially enhanced DNE conversion at 350°C. The combination of data from one-step and two-step tests of DNE and coal at 350–400°C revealed that water results in highly active MoS 2 catalyst in situ generated at 350°C, but water does not promote the catalytic function or reaction once an active catalyst is generated. Using ATTM coupled with water addition and removal and temperature-programming may be an effective strategy for developing a better coal conversion process using dispersed catalysts.
Temperature-staged catalytic coal liquefaction
Abstract An investigation has been made of the liquefaction of a bituminous and a subbituminous coal under conditions where reaction is conducted in successive stages of increasing temperature and in the presence of a dispersed sulphided Mo catalyst. This sequence has been found to lead not only to high coal conversion but to greatly increase the selectivity of the liquefied products to oils at the expense of asphaltenes. These gains are made with marginal increases in the production of light hydrocarbon gases. Although no systematic attempt has yet been made to determine the specific influence of reaction parameters upon liquefaction behaviour, preliminary results show that there is substantial potential for further improvement through the suitable choice of solvent and reaction conditions in the two stages. The reasons for the effectiveness of temperature staged liquefaction are discussed in terms of the balance between hydrogenation and condensation reactions. Examination of the liquefaction residues by optical microscopy has provided strong supporting evidence to show that the staged reaction sequence favours hydrogenative processes. Moreover, the microscopic examination has proved to be a powerful diagnostic technique, showing, for example, that the first stage temperature should be lower for the subbituminous than the bituminous coal, and providing insight into the processes of catalysed liquefaction.