Catalyzed Hydrogenolysis Of Lignin Into Phenolic Chemicals

With more and more people given attention to the problem of environmental protection and with the increasing shortage of petrol and coal resources, exploitation and utilization of lignocellulosic biomass resources become the inevitable trend of social development. Lignin is one of the major components of plant skeleton construction. The content of lignin is only below cellulose, lignin is the nature’s most abundant renewable aromatic compounds. Phenolic compounds can be obtained from Lignin degradation, so the lignin is a potential source of phenolic compounds. Considering the lignin can produce a large number of free radicals in the process of pyrolysis, and the free radicals can have condensation reaction with itself, then affect pyrolysic conversion rate. The introduction of the hydrogen atoms can combine with these free radicals, and thus effectively reduce condensation reaction between free radicals. Therefore hydrogenation cracking is an important direction of lignin degradation. The challenge of extract phenolic compounds from lignin is to find the moderate technological process to ensure high yield of lignin depolymerization product and high selectivity of the target product.In this paper, lignin will be extracted from wheat straw with the method of high boiling alcohol solvent. Glycerol has many advantages for as the solvent. For example, it has high boiling point, low saturated steam and it has a high solubility for lignin. After explore the effect of various factors on lignin extraction, the best condition were determined: the temperature is 180 ℃, reaction time is 3 h, ratio of solid to liquid 1:12, Na OH dosage is 10% of straw, glycerol concentration is 90%. Under this condition, the lignin extraction yield is 47%.The lignin will be degraded with the way of catalyzed hydrogenolysis. The react is conducted in hydrogen atmosphere, the solution is methanol, the catalyst is Na OH cooperate with another selective hydrogenation catalyst. Through analysis the effect of temperature, time, liquid-solid ratio, dosage of Na OH, types of hydrogenation catalyst on lignin degradation yield and the selectivity of product. The optimum condition for lignin degradation is: the temperature is 230 ℃; the reaction time is 9 h; the volume ratio of methanol to water is 1:1; solid-liquid ratio of 1:12; atmosphere: hydrogen, at the beginning the atmosphere pressure is 1 MPa, when achieve the required temperature, maintain 4 MPa; the catalyst is Na OH cooperate Pd/C; the stirring speed: 360 r/min. Under this condition, lignin degradation rate is 89%, the rate of oil production is 59%, the rate of single benzene ring derivatives is 57%, the yield of single phenol ring derivatives is 45.4%. Alkaline environment is an important condition for lignin hydrogenolysis, Pd/C play an important role to improve the content of single phenol ring derivatives.