Biological Enzyme Control Of Dissolved And Colloidal Substances In Mechanical Pulp

Preconditioning refiner chemical alkaline peroxide mechanical pulp?P-RC APMP?is a kind of high yield pulp?HYP?which is developed on the basis of alkaline peroxide mechanical pulp?APMP?.APMP has many advantages such as low energy consumption,high yield,less pollution load and good strength.During the process of P-RC APMP,pulping and bleaching can take place at the same time which can save the equipment investment.In recent years P-RC APMP has developed rapidly,and become the the important high yield pulp in the pulp and papermaking industry worldwide.Compared with the bleached chemical pulp,P-RC APMP contained high dissolved and colloidal substances?DCS?which can affect the brightness,strength and filtration performance,etc.The DCS mainly come from lipophilic extracts and carbohydrate substance,such as fatty acid,resin acid glyceride and pectins.These substances have anionic groups,and exist in the slurry system as DCS accumulation,which can result serious problems of wet chemistry in papermaking process.In this work,DCS from homemade white water of P-RC APMP system were treated by different enzymes to solve the problem of anionic trash,and reduce the adverse impact of DCS in P-RC APMP systems.Analysis of characteristic parameters and chemical composition of DCS in P-RC APMP of fast-growing poplar were conducted.The results showed that the conductivity,the charge demand and the Zeta potential of DCS mainly depended on dissolved substances?DS?.The CODcr value of DCS was higher,while the CODcr value of DS was lower.The solid content of DS was 54.4% of the total solid content of DCS.DCS contained a large number of metal ions,the Na+content was highest,followed by K⁺,Ca²⁺ and Al³⁺.The ash content of DCS was 14.9%.The components of MTBE extractives in DCS were numerous and complex.There were up to more than 10 kinds only for the acids and esters in MTBE extractives,in which the content of palmitic acid was up to 5.372 mg/L.The main carbohydrates in DCS were mannose,galactose and glucose,in which glucose content was higher.Three kinds of enzymes?lipase,laccase and pectinase?were selected to treat DCS,and the optimal treatment conditions were obtained.The physicochemical properties and composition of DCS were analyzed before and after enzyme treatm.The results showed that lipase treatment could reduce the esters content in DCS obtained from P-RC APMP.The optimal treating conditions of lipase were the enzyme dosage of 50 U/L,30-40°C and p H 7-8 for 3 h.Laccase treatment could reduce the lignin and ester contents in DCS.Laccase is less effective than lipase in reducing ester content.The optimal treating conditions of laccase were 40°C,p H 7.5 and the laccase dosage of 100 U/L for 3 h,in which the maximum of lignin decrease obtained.Pectinase could degrade pectic acid content in DCS.The positive charge requirement of DCS and the anionic trash in P-RC APMP slurry decreased after pectinase treatment.The optimal treating conditions of pectinase were the pectinase dosage of 150 U/L,45°C and p H 4.0 for 2 h.The electrical conductivity,cation charge demand and lignin content of DCS varied in different degrees after three kinds enzymes treatment.Effect of pectinase treatment was best compared to lipase and laccase.