The Effect Of Hydrogen On Initial High Reactivity Of Coal Liquefaction

In this paper, the requirement and approach of hydrogen entering into coal liquefaction in initial high-activity stage in coal liquefaction is systematically studied by experiment when selecting Yanzhou coal as object of study. Firstly, the change of coal conversion rate of coal liquefaction with time is studied in normal coal liquefaction conditions. In this course, it is found that a initial high-activity stage exists in the course of coal liquefaction. Accordingly, the effect of different atmospheres on the high-activity of coal liquefaction is analyzed. Secondly, the rule of solubility when hydrogen is dissolved in two kinds of liquefaction solvents and the effect of hydrogen pre-dissolving is studied in detail. Finally, the impact of ammonium molybdate and high dispersed iron catalyst on initial high-activity stage is investigated. The main conclusions are as follows:In normal liquefaction, most of the reactions in the process are founded to have finished in the first 5mins. The conversion rates can reach 90.49% and 72.36% of the highest conversion rates respectively in the same conditions when coal liquefaction is carried out. It demonstrates that the reactions of the first 5mins of coal liquefaction contribute a lot to the total conversion rate. In this stage, the reactivity of the reactions is high and the reaction rate is quick. In addition, most of the reactions have been completed.When the reaction conditions are 450℃,7Mpa of hydrogen or nitrogen initial cold pressure, the total conversion rates under nitrogen atmosphere is a little higher than those under hydrogen atmosphere in the initial high-activity stage of coal liquefaction without catalysts whether in naphthalene or tetrahydronaphtha-lene solvents. At the same time, the distributions of liquefied products are almost the same. The result demonstrates that hydrogen hardly participates in coal liquefaction under this condition.In a certain range, the solubility of hydrogen in tetrahydronaphthalene and naphthalene increases linearly with the increase of equilibrium pressure and temperature. According to the dissolving rates of hydrogen in naphthalene and tetrahydronaphthalene, the dissolution process can be divided into three stages: quick dissolving stage, slow dissolving stage and dissolving equilibrium stage. The result which is especially noticeable is that the dissolved quantity can reach to as much as 78.54% of the maximum dissolved quantity. It is indicated that the dissolving process shouldn't be the main reason for the failure of hydrogen participating in coal liquefaction effectively in the initial high-activity stage.According to the comparison and analysis of TG and DTG curves of coal samples before and after adding catalysts, the effect of high dispersed iron catalyst or ammonium molybdate catalyst on pyrolysis of raw coal is relatively small. Under nitrogen atmosphere, the total conversion rate of initial high-activity stage won't rise by adding the two kinds of catalyst into the reaction system both in naphthalene and tetrahydronaphthalene liquefaction solvents. Under hydrogen atmosphere, the addition of high dispersed iron catalyst can promote hydrogen participating in coal liquefaction, increase the total conversion rate and make the distribution of liquefied products lighter both in naphthalene and tetrahydronaphthalene liquefaction solvents.In the initial high-activity stage, the hydrogenation is prior to polycondensation when the hydrogen donating ability is strong enough and the amount of solvent is enough. In the liquefaction process, the resource of activated hydrogen contains:hydrogen in coal, hydrogen and solvent. Among the contributions of them to initial high-activity stage in coal liquefaction, solvent is most important, hydrogen in coal follows and hydrogen is least. In all, when all the three kinds of hydrogen resource exist, the highest total conversion rate can be reached with a proper catalyst.