Mechanism Study And Catalytic Oxidation Of Starch In Old Corrugated Cardbard Pulping Wastewater Over Phosphomolybdic Acid

The recycling efficiency of old corrugated cardbard(OCC)is getting higher due to the rapid development of express paper packaging and the raised public awareness of environmental protection.Usually,the raw materials of corrugating medium and cardboard are completely made from OCC secondary fiber,and the mechanical strength of pulp fiber decreases gradually with the OCC waste paper cycle-index increases.Generally,the strength of corrugating medium and cardboard is enhanced by enzyme modified starch via surface sizing in paper mills.However,enzyme modified starch will dissolve into water during pulping process due to its non-ionic properties,leading to pulp rot and amine nitrogen odor,further resulting in microorganisms propagating,which seriously affect the cleaning of pulp and paper system and product quality.At present,the pulping waste water with high concentration of starch is generally sent to produce biogas energy for anaerobic fermentation.Only part of the value is recycled resulting in huge waste of valuable starch resources.To understand the physicochemical properties and resource utilization feasibility of waste starch objectively,the contents of starch,metal ions and acid radical ions in OCC pulping wastewater were analyzed and characterized in present study.Molybdophosphoric acid was used to catalyze and oxidize starch simulacra to produce monosaccharide and glycolic acid.The feasibility of molybdophosphoric acid catalytic system applied to OCC pulping wastewater was evaluated,which would provide a theoretical basis in achieving the resource utilization of waste starch.The main conclusions are listed as follows:(1)The content of waste starch in OCC pulping wastewater was 4.5?4.8 g/L,the contents of Na⁺,K⁺,Mg²⁺ and Ca²⁺ were 49.53,19.88,40.88 and 1645.98 mg/L,and the contents of Cl-and SO₄2-were 115.84 and 300.51 g/L,respectively.The molecular weight(Mw)of nonionic waste starch was 2.79×104.(2)The high yield of monosaccharide and glycolic acid reached up to 93.57 wt%under the starch concentration of 5 g/L and the phosphomolybdic acid amount of 20 wt%at 145? for 120 min,the pH was 2.The acid hydrolysis of starch could be accelerated due to the bifunctionalization of phosphomolybdic acid,and the isomerization of glucose to mannose also can be catalyzed.Both hexose can react with[2+4]retro-aldol,which was beneficial to produce glycolic acid with high selectivity.(3)The nonlinear least square regression method was used to fit the experimental and predicted values of the kinetic factors by using MATLAB software.The kinetic parameters such as reaction rate and activation energy of starch degradation under different conditions were obtained,and the parallel first-order cascade kinetic model was established.r₁=5.05×10⁹C_SC_H+^0.34e^-87620/RT;r₂=9.28×10⁹C_SC_H+^0.28e^-90040/RT r₃=5.55×10¹7C_SC_H+^0.33e^-157790/RT;r4=9.75×10¹1C_SC_H+^0.28e^-107750/RT(4)The phosphomolybdic acid catalytic oxidation system was applied to handle waste starch in OCC pulping process.When the reaction time was 60 min,the highest yield of monosaccharide and glycolic acid was 56.34 wt%and 10.12 wt%,respectively.It was not difficult to found that the yield of monosaccharide and glycolic acid was lower than that of starch simulacra,which may due to the factors such as microbial fermentation and residence time in actual production system.In summary,the starch dissolved in OCC waste paper pulping process could not be utilized directly on account of the characteristics of small Mw and non-ionic property.Polybdophosphoric acid catalytic oxidation system is an effective approach to catalyze and oxidize strarch to high value-added platform chemicals,which paves significant theoretical basis for developing the resource utilization technology and solving the contamination of waste starch.