Bacterial cellulose (BC) was produced by Acetobacter xylinum KJ1 in a modified airlift-type bubble column bioreactor, which had a low shear stress and high oxygen transfer rate (k L a). Saccharified food wastes (SFW) were used as the BC production medium due to its low cost. An aeration rate of 1.2 vvm (6 L/min) was tentatively determined as the optimal aeration condition in a 10 L spherical type bubble column bioreactor, by analysis of the oxygen transfer coefficient. When 0.4% agar was added, the BC production reached 5.8 g/L, compared with 5.0 g/L in the culture without the addition of agar. The BC productivity was improved by 10% in the addition of 0.4% agar into the SFW medium. Then, by conversion of a linear velocity of 0.93 cm/sec, from the relationship between the linear velocity and oxygen transfer rate, 1.0 vvm (30 L/min) was determined as an optimal aeration condition in a 50 L spherical type bubble column reactor. Using SFW medium, with the addition of 0.4% agar, and air supplied of 1.0 vvm, 5.6 g/L BC was produced in the 50 L spherical type bubble column bioreactor after 3 days of cultivation, which was similar to that produced in the 10 L bioreactor. In conclusion, the addition of agar, a viscous polysaccharide, into SFW medium is effective for the production of BC, and this scale-up method is very useful for the mass production in a 50 L spherical type bubble column bioreactor by decreasing the shear stress and increasing the k L a.
H2O2 was used in the final stage of a multistage bleaching process to increase ISO brightness by 2-3%, because of the poor selectivity and bleachability. However, concerns about the environmental load of the bleaching process have led to the efficient use of oxygen-derived compounds, with a concomitant decrease in the quantity of chlorine-derived compounds consumed. In this study, thermomechanical pulp (TMP) and unbleached kraft pulp (UKP) were bleached with H₂O₂ and ultrasonicated in order to increase the bleaching efficiency, and the effects of some bleaching conditions such as treatment time, treatment concentration, and temperature were determined. The best bleaching efficiency of pulp was obtained using H₂O₂ with ultrasonication (at 20 kHz) of the pulp mixture at 45 °C for 30 min. The ISO brightness of the bleached pulp increased up to 1.9%, although the bleached pulp yield was slightly reduced to 1.5%. Magnesium sulfate was used as a bleaching stabilizer to increase the bleached pulp yield and viscosity. As a result, the bleached pulp yield and viscosity increased by 2.1% and 10%, compared with fully bleached pulp at the end of the process, respectively, despite a decrease in ISO brightness.
Gas
grafting with fatty acid chloride (FAC) is a simple and ultrafast
paper treatment, which produces only hydrochloric acid as a byproduct.
In this study, poly(vinyl alcohol) (PVOH)-coated paper was treated
by gas grafting with palmitoyl chloride, and the effects of temperature,
time, and concentration of palmitoyl chloride on discoloration were
investigated. The grafting efficiency expressed by the water absorption
capacity (Cobb size) and the amount of grafted FAC increased with
increasing temperature, reaction time, and concentration of palmitoyl
chloride. However, discoloration of PVOH was inevitable at high temperature
and long reaction time, and under excessive FAC dosage. PVOH was converted
into polyene via dehydration by the acid catalyst at high temperature.
Calcium carbonate applied to PVOH coating for preventing discoloration
of the PVOH-coated paper could neutralize gaseous hydrochloric acid.
Unfortunately, the hydrophobicity decreased slightly with an increase
in the calcium carbonate blending ratio due to the additional consumption
of FAC. The grafting efficiency could be improved without discoloration
if the blending ratio was appropriately controlled based on the specific
surface area of the calcium carbonate particles.
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