Influence of biochar on the pyrolysis characteristics of bioslurry
Bioslurry is a slurry fuel prepared by mixing biochar and bio-oil produced through pyrolysis of biomass,which can be used for combustion,pyrolysis,and gasification,possessing great significance for the development of cost-effective utilizations of biomass.The easy coking phenomenon of bio-oil heating is a major problem faced by bio-slurry,while biochar,which comes with bioslurry,is a promising adsorbent and catalyst that can be used to adsorb the coking-prone components of bio-oil and to catalyze their cracking.Biochars with different physicochemical struc-tures were prepared to investigate the effect of biochar on the pyrolysis characteristics of bioslurry.The thermogravi-metric analyzer(TG)and pyrolysis-gas chromatography-mass spectrometry(Py-GCMS)were used to investigate the effect of biochar on the coking of bio-oils subjected to heat in the bioslurry system as well as the effect of adsorption and catalytic effect of biochar on the pyrolysis of bio-oils,respectively.The experimental results showed that the bio-oil was more prone to coking at low heating rates when being warmed up to the same temperature.The biochar could selectively adsorb the coking-prone components of the bio-oil,thus reducing the coking of the bio-oil that was not ad-sorbed by the biochar,which was conducive to the improvement of the stability of the reactor operation.The compari-son of the theoretical and actual coking rates of the bio-oil and biochar mixtures without interaction showed that the theoretical values of the CO2-activated biochar/bio-oil mixtures at 700 ℃ were slightly higher than the actual values,which indicated that the biochar could play a catalytic cracking role for the bio-oil.The coking of bio-oil inside the pores of biochar was affected by both adsorption and catalysis of biochar.Py-GCMS examination results showed that biochar was able to catalyze the conversion of components of bio-oil to phenolics,and the phenolics content of the bio-oil pyrolysis product catalyzed in situ was 65.13％,which was lower than that of the non-in situ catalyzed one(69.01％).This might due to the poor mass transfer of its generated volatile matter to the outside world,which was converted into carbon accumulation within the pores of the biochar,covering some active sites on the biochar,which would reduce the catalytic effect of biochar on bio-oil to a certain extent.Overall,in bioslurry,biochar can catalyze the cracking of coking-prone aromatic compounds in bio-oil.The adsorption effect can make the coking-prone compo-nents more coking in the pores,reduce the coking of unabsorbed bio-oil,and facilitate the catalytic conversion by en-hancing the contact between the bio-oil and the active sites on the one hand,and reduce the catalytic effect on the oth-er hand due to the generation of more carbon deposits that cover the active sites.
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