Effect of SiO_(2)on loss of catalysis of inherent metallic species in CO_(2)gasification of coke from lignite

Inherent metallic species retained by coal char or coke,such as Na and Ca,behave as catalysts in gasification.The char/coke normally contains inherent SiO_(2),which can react with the inherent catalysts to form silicates,resulting in catalyst deactivation over the range of pyrolysis,carbonization and gasification,and thereby reducing the char/coke reactivity.The present authors simulated the inherent catalyst deactivation experimentally by blending a Victorian lignite with SiO_(2),briquetting the SiO_(2)/lignite blend,carbonizing the briquette,and then gasifying the coke with CO_(2).The kinetic analysis of the gasification employed a comprehensive model,which assumed progress in parallel of non-catalytic and catalytic gasification.The model quantitatively described the measured kinetics of the coke gasification with different SiO_(2)contents over a range of coke conversion up to 99.9%.The kinetic analysis revealed that the SiO_(2)deactivated substantial and entire portions of the most active catalyst and its precursor,respectively,before the gasification(i.e.,during the carbonization).The catalyst deactivation also occurred during the gasification,but mainly following a self-deactivation mechanism that involved no silicates formation.

Continuous monitoring of char surface activity toward benzene

Kinetics of thermal decomposition of benzene on lignite-derived char was investigated at 900℃ by applying a new method to continuously monitor the char surface activity.Benzene vapor was continuously forced to pass through a micro fixed bed of char with residence time as short as 7.6 ms,and then detected continuously by a flame-ionization detector.Results showed the presence of two different types of char surfaces;consumptive Type I surface and non-consumptive(sustainable)Type II surface.Type I surface of a partially CO_(2)-gasified char had an capacity of carbon deposit from benzene over 20 wt%-char and an initial activity(represented by a first-order rate constant)as high as 160 s−1.Both of them decreased with increasing carbon deposit due to consumption of micropores accessible to benzene,and finally became zero leaving Type II surface that had a very stable activity with rate constant of 4 s−1.The chars without gasification had capacities of Type I surfaces smaller by two orders of magnitude than the partially gasified char,while the Type II surfaces had activities similar to that of the partially gasified char.It was found that Type II surface converted benzene into not only carbon deposit but also diaromatics and even greater aromatics.Composition of the greater aromatics was unknown because they were deposited onto the reactor wall immediately after passing through the char bed.

Catalytic hydrotreatment of alkaline lignin and its consequent influences on fast pyrolysis

The current state of lignin has been characterized by these three:(1)as one of the main components in lignocellulosic biomass with an abundant amount;(2)not be taken seriously but treated as a waste product;(3)underutilized due to a complex and stubborn structure.However,lignin can be a rich source for hydrocarbons and aromatic compounds when gives appropriate utilization.In this work,we have studied the hydrotreatment of alkaline lignin(AL)under relatively mild conditions and further investigated the characterization of hydrogenated lignin(HL),especially the behavior during fast pyrolysis.The recovery of the HL decreased with increasing reaction temperature from 60 wt.%to 41 wt.%in the range of 150-250℃.The hydrotreated products were analyzed using Elemental Analysis,FTIR(for HL)and GC-MS(for bio-oil).The HL samples were found to have a higher hydrogen/carbon atomic effective ratio(H/C_(eff) ratio)and a higher degree of saturation than AL.Compared to the internal structure of the lignin before and after hydrotreatment,the side chain groups were removed from AL during the process.After that,from the fast pyrolysis of HL,it was observed that more light hydrocarbons and aromatic compounds were formed than that of AL.Furthermore,fast pyrolysis in the hydrogen atmosphere revealed that more volatile fractions were released compared to the Helium atmosphere.The total olefins yield was increased for HL compared AL from 1.02 wt.%to 3.1 wt.%at 250℃for 7 hours.This study of HL is instructive to some extent for the industrial utilization of lignin.