The Study On Pyrolysis And Thermochemical Conversion Characteristic Of Cornstalk In Methanol

Using renewable biomass resources has been becoming a hot research field considering environmental protection and fossil resource crisis since the 20th century. In this paper, the pyrolysis kinetics of representative biomass—cornstalk in northwest China was studied, Also pyrolysis characteristics of the corn stalks at low-temperature under high-pressure and high temperature under atmospheric pressure, and the properties of pyrolysis gasification of residual were investigated. The thermal chemical conversion of corn stalks has been studied by the methanol in supercritical reaction over different alkaline catalysts, the research of the effects of temperature, liquid ratio and catalyst dosage on the products yield during the thermal chemical conversion has been carried out, the results shows that:1)The pyrolysis process of corn straw can be divided into three stages, predehydration (～150℃), pyrolysis phase (150℃～400℃) and the slow decomposition of residue (>400℃). The Cornstalk pyrolysis process of weight loss occurs mainly in the second phase, the effect of heating rate on the cornstalk pyrolysis temperature is not obvious.2)At different heating rates, the corn straw pyrolysis heating rate has a linear relationship with the temperature corresponding to the maximum weight loss rate. The study of corn straw pyrolysis process should be carried out under the same heating rate to eliminate the influence of different heating rate, and the temperature corresponding to the maximum weight loss rate is 309℃. Therefore, pyrolysis characteristics of corn stalks should be carried out under the same heating rate.3)Below 309℃is low temperature pyrolysis zone; over 309℃is high temperature pyrolysis zone. The order of reaction at low temperature pyrolysis is 1, pyrolysis activation energy is 25KJ/mol; The order of reaction at low temperature pyrolys is 2, pyrolysis activation energy is between 16KJ/mol and 25KJ/mol.4)Cornstalk pyrolysis at low temperature high pressure is not conducive to the formation of CO but the formation of H2, CH4 and CO2, the heating value of purified clean fuel is 8860.64 kJ/m3. The combustible components, in the gas products especially the H2 during the cornstalk pyrolysis at high temperature under atmospheric pressure, with increasing temperature, are increased.5)The residue of corn biomass pyrolysis (700℃), at 700℃～900℃, the calorific value of steam gasification up to 9508.90 KJ/m3, the content of H2 in the gasification gas is up to 55%, CO is up to 26%. The ratio of H/C in high temperature gases produced by gasification is about 2, the both content of H2 and CO in the gasification gas is up to 80%.6)Reaction temperature, liquid ratio and amount of catalyst is the liquefaction of corn stalk impact. In comparison, biomass liquefaction reaction temperature is the main factor.7)The CaO, K2CO3, Na2CO3 and KOH enhance the thermochemical conversion of corn stalks. Based on the purpose of producing the liquid product, the catalytic capacity from strong to weak is: KOH>CaO> K2CO3>Na2CO3; Based on the purpose of conversion rate of raw material, the catalytic capacity from strong to weak is: K2CO3>KOH>Na2CO3> CaO.8)Based on the purpose of producing the liquid products, the optimum conditions to produce maximize the liquid over four basic material as the catalyst are: liquid ratio was 50/5, the temperature range is 280℃~ 290℃, CaO% 2.5% ~ 5.0%, K2CO3% 5.0% ~ 10.0%.9)Alkaline catalyst can effectively increase the degree of thermochemical conversion of corn stalks, but its catalytic ability does not has a linear relationship with its degree of alkaline strength.