Competitive adsorption of vanillin and syringaldehyde on a macro-mesopore polymeric resin: modeling

Review on the oxidative catalysis methods of converting lignin into vanillin

Vanillin plays an important role not only in food and flavouring, but also as a platform compound for the synthesis of other valuable products, mainly derived from the oxidative decarboxylation of petroleum-based guaiacol production. In order to alleviate the problem of collapsing oil resources, the preparation of vanillin from lignin has become a good option from the perspective of environmental sustainability, but it is still not optimistic in terms of vanillin production. Currently, catalytic oxidative depolymerization of lignin for the preparation of vanillin is the main development trend. This paper mainly reviews four ways of preparing vanillin from lignin base: alkaline (catalytic) oxidation, electrochemical (catalytic) oxidation, Fenton (catalytic) oxidation and photo (catalytic) oxidative degradation of lignin. In this work, the working principles, influencing factors, vanillin yields obtained, respective advantages and disadvantages and the development trends of the four methods are systematically summarized, and finally, several methods for the separation and purification of lignin-based vanillin are briefly reviewed.

Synthesis, adsorption and molecular simulation study of methylamine-modified hyper-cross-linked resins for efficient removal of citric acid from aqueous solution

A series of methylamine-modified hyper-cross-linked resins were fabricated from chloromethylated polystrene-co-divinylbenzene by two continuous reactions (Friedel-Crafts alkylation and amination). The BET surface area and pore volume of the as-prepared resins took a positive correlation to the reaction time and temperature during alkylation reaction while lessened during amination process. When running batch adsorption experiments for adsorption of citric acid, the methylamine-modified resin named HM-65-2 showed higher adsorption capacity of 136.3 mg/g and selectivity of 6.98 (citric/glucose) than the precursor resins. The pseudo-second-order rate model fitted better than the pseudo-first-order model, implying the adsorption sites distributed on the resins surface tended to be heterogeneous. Subsequently, the interactions between citric acid and the resin were investigated by means of molecular simulation. Simulation result showed the addition of nitrogen-containing groups significantly enhanced the adsorption performance of citric acid. Lastly, the dynamic column experiments were performed to obtain the suitable operating conditions for the citric acid adsorption.