Investigation On Syringaldehyde Mediated Electrochemical Delignification Of Poplar Kraft Pulp

Traditional chlorine pulp bleaching can generate toxic substances ofenvironmental damage. In order to improve the environment, to achieve theharmonious development of man and nature, people trying to find a bleaching waywhich cause lesser extent of environmental pollution and hazards. Chlorine freebleaching technology can solve this problem, and it can achieve the low pollution andless damage to the environment pulp bleaching. Recently, people explore some ofenvironmentally friendly bleaching technology: Bio-bleaching technique,electrochemical delignification, technique and photochemical bleaching technology etc.Electrochemical delignification technology is a delignification technology whichcomminutes electrochemical technique and pulp delignification technology. Inelectrochemical bleaching technology, the electrochemically mediated delignification(EM) is one of new pulp bleaching methods. Previous researchers had studied theoptimization of catalytic mediator and selection of electrode in the processing.In thisthesis, we do some related research of electrochemically mediated delignification onthe basis of our group`s previous research. Synthetic mediator for the electrochemicalmediator delignification process is expensive, and serious loss and other issues, so wetry to used natural small molecules electrochemical delignification of pulp as amediator of natural mediator. We used poplar kraft pulp as raw material to establishnatural mediator electrochemical delignification system. At the same time, we studiedon delignification conditions, subsequent bleaching and related mechanism of theestablished electrochemical delignification system.In this paper, We have done experiments and research on electrochemicallymediated delignification (EM) which used Syringaldehyde as a natural mediatorsubstances, which includes selection of natural mediator, the optimization of reactionmedium in electrochemically mediated delignification, and investigation of the affectfactors the electrochemically natural mediated delignification, simultaneously we havedone research on follow-up bleachability of pulp which were processed byelectrochemically natural mediated delignification and a preliminary study on law offree radicals in electrochemically natural mediated delignification four parts.First of all, on the basis of previous researchers’ study of phenolic compounds ofplant small molecules which used in laccase mediator system, This thesis proposed the concept of using natural small molecular phenolic compounds which was ubiquitous inplants as the electrochemical delignification catalytic mediator,and we also wanted tofind a natural mediator substances with electrochemical catalytic effect.Afteranalysis,we had choosed some phenolic compounds of plant small molecules withcatalytic potentia lwhich includes: syringic alcohol, syringaldehyde, acetosyringone,coumaric acid and vanillin as alternative mediator. After screening and testing, we hadcome to conclusion that syringaldehyde can used as natural mediator substances inelectrochemically mediated delignification (EM). Since the entire reaction system insolution, we requiring a mediator substance which can be well dissolved in the solution,this chapter also discussed the composition of the solution, obtained that when Vethanol:Vtotalis1:4, treatment effect is best.Secondly, on the basis of the study in the previous chapter, we used poplar kraftpulp as raw material, ruthenium titanium coated electrode as anode, the stainless steelas cathode, and syringaldehyde (C9H8O3) as a natural mediator to study the process ofelectrochemically mediated delignification. After researched and analyzed the mainlyinfluencing factors on effect of delignification, We got a more suitable delignificationconditions when syringaldehyde was used as natural mediator substances:syringaldehyde concentration1.0mmol/L, voltage1.8V，Temperature45°C，pH4.0to5.0, Sodium sulfate0.05mol/L, time5.5h. Under these conditions, the pulp Kappanumber decreased from18.5to13.5, the viscosity decreased from1185mL/g to1109cm3/g, Under these conditions,the pulp achieve a good effect of delignification.Once more, we processed the pulp separately for hydrogen peroxide bleaching (P)and chlorine dioxide bleaching (D) as follow-up bleaching treatment on the basis ofelectrochemically mediated delignification treatment (EM), so that we formed TCFbleaching process and ECF bleaching process after EM. Poplar wood kraft pulpbleaching effect was investigated after treated by the two subsequent bleachingprocesses. After treated under the conditions of EQP hydrogen peroxide bleachingprocess, the whiteness of pulp reached81.2%ISO. This Illustrated the pulpelectrochemically mediated delignification treatment had good hydrogen peroxidefollow-up bleachability.As for EpD0D, when the amount of chlorine dioxide in D0sectionand D section was1.5%,after EpD0D chlorine dioxide bleaching the pulpbrightness reached84.1%ISO, while the viscosity is still maintained above880cm3g-1.Finally, we do preliminary study on produce law of syringaldehyde intermediateswhen used syringaldehyde as natural mediator substances in electrochemically mediated delignification voltage. Influencing factors include temperature, pH valueand other factors. In addition, we also conducted a preliminary study on affection ofthe composition of reaction medium to the law of natural mediator substancessyringaldehyde change into syringaldehyde intermediates. The results show that:Oxidation potential and reduction potential of syringaldehyde are1.28V and1.33V, thedifference between oxidation potential and reduction potential is the small, so we couldgot that syringaldehyde have a certain capability of reaction reversibility. In theelectrochemical catalytic system, an appropriate increase in cell voltage, temperature,and a suitable pH value can effectively reduce the time of syringaldehyde intermediatereach a high concentrations, and improve the efficiency of produce syringaldehydeintermediates. If we added ethanol in the electrolyte to improve the solubility ofsyringaldehyde, generation rate and the highest concentration can effectively improved,which was conducive to delignification. The reaction between syringaldehydeintermediate and pulp was very quickly, the rate-limiting step of entire electrochemicalmediator delignification was the generation of oxidative syringaldehyde mediatorintermediates in delignification process.