Immobilization Of Pectinase On Cellulosic Materials And Its Application Intreatment Of Specific DCS In Papermaking

In order to reduce water consumption, economize on raw materials and reduce pollution,it is demanded that the whitewater in papermaking process should be increasingly recycled.Consequently, dissolved and colloid substances accumulate in the system, leading to seriousproblems. In this dissertation, immobilized enzyme was used to deal with pectic substances,one of the major contributions to anionic trash. Pulp fiber in papermaking and regeneratedcellulose beads were utilized as carrier for pectinase via simple, facile and inexpensivemethods, respectively. The preparation and the properties of the resultant enzymes werestudied. Besides, they were tested for reducing cationic demand of practical DCS.Pulp fiber was oxidized using NaIO4and then pectinase was coupled on it through Schiffbase reaction. Oxidized pulp fiber by25.0g/L NaIO4for30min was chosen for its relativelyhigh aldehyde content and minor degradation. The enzymatic activity of immobilizedpectinase on pulp fiber reached65U/g when immobilization pH value, temperature and timewere of7.0,20℃and15min, respectively. The immobilized pectinase showed higherthermo stability in a wider temperature range of40–70℃than its free type and its optimalpH shifted from8.0to8.8. About60%of the original activity was maintained after theimmobilized pectinase was used6times. When employed in DCS treatment of papermakingindustry, it reduced the cationic demand by37%, meaning almost all of the polygalacturonicacid depolymerized. Moreover, it still decreased the cationic demand by15%after operatingrepeatedly for6batches.Polyethyleneimine is a common used additive in papermaking process. It was used tocoat pulp fiber to produce PEI-coated fiber, which was then employed to immobilize acidicpectinase through ionic adsorption. Immobilized pectinase with higher activity could beobtained if the pulp fiber was thoroughly washed after being coated with PEI and noglutaraldehyde was added for crosslinking. When PEI concentration, enzyme concentrationand pH of enzyme solution were0.01%(w/v),0.25%(v/v) and7, respectively, the resultantimmobilized enzyme exhibited the highest enzymatic activity as about670U/g. The PEIloading and protein loading under the condition were1.1mg/g and36.4mg/g, respectively. Higher thermo and pH stabilities than those of the free enzyme were achieved afterimmobilizing the enzyme on PEI-coated pulp fiber with its optimal pH shifting from3.5to4.0. Furthermore, the bound pectinase depolymerized pectin with a higher rate. Its loweractivatioin energy meant that the catalytic rate was less sensitive to temperature. On top ofthat, the immobilized pectinase effectively decreased the cationic demand of DCS inpapermaking under the practical industrial conditions and still maintained activity afteroperating repeatedly for7batches.Porous cellulose beads were prepared through a simple dripping method after dissolvedin LiCl/N, N-Dimethylacetamide. The resultant microspheres exhibited good spherical shapewith a diameter of1-2mm. Their morphology, pore structure, and physical properties werecharacterized. The regenerated cellulose was shown to have a three-dimensional porousstructure, which led to a BET surface area of as large as108m2/g. This may be useful asadsorbents or carriers. Besides, the resultant bead cellulose remained cellulose Ⅰ structureand good thermo stability. The regenerated cellulose maintained Iβtype with substaintaillylower crystalinity. Finally, the cellulose beads were tested in adsorption of pectinase. It wasrevealed that the adsorption was a favorable spontaneous process. Moreover, analysis resultsshowed that the adsorption was in well agreement with Langmuir isotherm with a capacity of7.39mg/g, which meant that pectinase adsorption was a monolayer sorption. It can also beconcluded from the kinetics study that the adsorption followed a pseudo-second-order kineticmodel in the overall process, indicating that chemisorptions were the rate controllingmechanism. This will provide information for the potential utilization of the regeneratedcellulose microspheres as support for enzyme in biotechnology and biochemistry field.Pectinase was immobilized on regenerated cellulose beads using physical adsorption andcolavent binding, respectively. By adsorption, the optimum immobilization temperature, timeand pH of the immobilized pectinase on regenerated cellulose beads were20℃,2h and7.0,respectively, under which the enzyme showed high protein loading and enzymatic activity of2.9mg/g and178U/g of the immobilized biocatalyst, respectively. On the other hand, thecolavently immobilized pectinase showed6.7mg/g and100U/g. Compared with the free pectinase, both kinds of the immobilized enzyme showed higher thermo and pH stabilities andeffectively lowered the cationic demand of slurry filtrate by36%. Besides, the immobilizedenzyme obtained through chemical reaction had better reusability. Furthermore, theregenerated cellulose beads maintained good mechanical strength after several batches andcould be resued as support.