Study On The Preparation Of Wood Vinegar From Biomass Waste By Hydrothermolysis Process

Biomass energy has the enormous potential to be used in diverse fields for the lower proportion in Chinese current energy consumption structure.It is well known that biomass energy is renewable,wide distribution,low-cost,etc.,with the disadvantages of loose structure,low-energy density,etc.,for which the efficient conversion and utilization of biomass is limited.Recently,hydrothermolysis technology is considered as the most promising technology for the efficient conversion and utilization of biomass because of the mild operating condition.Besides,there are the acids,phenols,ketones,etc.,in posthydrothermolysis liquid product(PLP)so that hydrothermolysis technology may be a new approach for wood vinegar preparation.In the study,the various formulas for the solid/liquid ratio,temperature and retention time were conducted according to Box-Behnken design.Cotton stalk(CS)was used as the raw material to prepare the crude PLPs in an autoclave reactor under designed formulas.Afterwards,the refining process was conducted for the crude PLPs.The yield and pH of the refined PLPs were measured and used as the response values.The effects of solid/liquid ratio,temperature and retention time on the yield and pH of the the refined PLPs were investigated using response surface.Subsequently,the refined PLPs at the optimal formulas of yield and pH,respectively,were prepared,of which the chemicals were determined using gas chromatograph-mass spectrometer.The comparison of the chemicals in the wood vinegar and resulted refined PLPs was conducted to evaluate whether hydrothermolysis technology could be used for wood vinegar preparation.The results indicate that the temperature plays the most significant role among the three factors.The main organic chemicals in the refined PLPs prepared under the optimal formulas of yield and pH,i.e.,yield: 0.05w/w,280.00°C,0min and pH: 0.05w/w,251.43.00°C,0min,respectively,were similar with those in the conventional wood vinegar,even with more content.Secondly,based on the above results,the effects of the main factor,hydrothermolysis temperature(180-280°C),on the typical properties,yield and organic compounds of the refined hydrothermolytic acids(RHTA)prepared from CS were further investigated.The refraction index of RHTAs showed an excellent correlation to the pH of RHTAs.With the increase in the temperature of 180-230°C,the yield of RHTA increased continuously and reached the maximum(65.2%)at 230°C.Subsequently,the yield of RHTA firstly decreased and then increased as the temperature increased from 230°C to 280°C.Phenolic compounds was the dominant component in RHTA above 260°C.Furthermore,on the basis of the above conclusions,the effect of the oxidation processing on the typical properties,yield and organic compounds of the refined hydrothermolytic oxidation acid(RHOA)at different temperature were investigated by adding hydrogen peroxide.The results show that with increasing temperature from 180°C to 280°C,the pH of RHOAs increase consecutively while the refraction index decreased continuously.As temperature increasing from 180°C to 230°C,the yield of RHOAs firstly increased to 58.8% at 200°C,and then decreased to the minimum(50.0%)at 230°C.When the temperature further increased to 280°C,the yield of RHOAs increased to the maximum(68.0%)at 260°C and then decreased.In comparison with the chemical compounds in the RHTAs at 200-280°C,the identical the acids and phenols with more content existed in the RHOAs at lower temperature,while the contents of the ketones and furan derivatives in the RHOAs showed no significant variation.Above all,the oxidation processing could alleviate the conditions of the post-hydrothermolysis acid preparation and enrich the acids and phenols during hydothermolysis process.