Molten salt pyrolysis of biomass: the mechanism of volatile reforming and pyrolysis

Abstract A novel reactor with a short shrinking volatile catheter directly inserted into molten salt was applied to fast pyrolysis of cotton stalks and pyrolysis volatiles reforming in molten salt (Li2CO3-Na2CO3-K2CO3) at the temperature range of 450 to 850°C with conventional pyrolysis as comparison. Simultaneously, the possible mechanism of biomass pyrolysis in molten salt was proposed according to the characteristics of products and the volatiles reforming under variant conditions. Compared with conventional pyrolysis, molten salt pyrolysis produced more gas, especially CO and H2 at 750 to 850°C. It can be further revealed by experimental results of volatiles reforming in molten salt that syngas yield gradually increased with the increase of temperature. Besides, molten salt intensified the decomposition of acids/esters, producing a large amount of CO. It also promoted the conversion of methoxyphenol to alkylphenol and then to phenol, along with CH4 formation, and the evolution of multi-ring PAHs mainly naphthalene and acenaphthylene into small PAHs mainly alkylphenol and phenol. Eventually, high temperature around 850°C was recommended to produce high quality syngas for molten salt pyrolysis of biomass. The syngas yield reached 72 vol.% and the low heating value surpassed 14 MJ/Nm3.