Efficient synthesis of lactic acid from cellulose through the synergistic effect of zinc chloride hydrate and metal salts.

The chemocatalystic conversion of cellulose, the main component of lignocellulosic biomass, to building-block chemicals in water under mild conditions, is an ideal but highly challenging process due to the robust crystal structure of cellulose. It is also the key to establishing a sustainable biomass-based chemical process. Here, we present a highly efficient and selective chemocatalytic hydrolysis of cellulose using ZnCl ₂ ·3H ₂ O hydrate as the pretreatment reagent and water-compatible metal salts - ErCl ₃ as the catalyst, into lactic acid (LA), which is an important chemical building-block widely utilized in the food industry and in the production of chemicals and biodegradable plastic. With 94.0 % conversion of cellulose, an impressive LA yield of 84.6 % was achieved at 170 °C after 4 h under ambient air pressure in water. High yields of LA were also obtained from other carbohydrates, such as fructose (68.3 %), glucose (52.7 %), starch (54.4 %), and inulin (67 %). A series of experiments demonstrated that Er(III) combination with water catalyzed cascading steps of soluble cellulose into LA after ZnCl ₂ ·3H ₂ O hydrate disrupted the hydrogen bonds in the cellulose, Zn(II) played an indirect role by promoting LA formation through inhibition of side reactions. A plausible mechanism was proposed for the chemocatalytic conversion of cellulose to LA.
Competing Interests: Declaration of competing interest We hereby affirm that we do not possess any financial or personal affiliations with individuals or organizations that may exert undue influence on our work. Furthermore, we assert that there are no professional or personal interests of any kind in any product, service, and/or company that could be perceived as impacting the stance presented in, or the evaluation of, the manuscript entitled "Efficient synthesis of lactic acid from cellulose through the synergistic effect of zinc chloride hydrate and metal salts”.
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