Catalytic Conversion Of Wheat Stalk Into Levulinic Acid

Levulinic acid（LA） is an important biobased bulk chemical. Using wheat stalk as the raw material to produce LA is very meaningful to achieve integrative and high efficient application for biomass. In this article, wheat stalk powder（WSP） was as the raw material. The effects of acid treatment, base treatment, oxidation treatment and ultrasound treatment on the result of WSP treatment were investigated. The process of WSP treatment was optimized in order to remove lignin in WSP. This article preparaed magnetic immobilized solid acid catalyst SO3H/SiO2/Fe3O4 and the catalyst was analysed. LA was produced from pretreated wheat stalk powder（PWSP） over this catalyst. According to LA yield, the reaction conditions were optimized and selected by orthogonal experiments. The repeatability of the catalyst was investigated and LA was separated. Finally, the mechanism of producing LA was studied.Firstly, the treatment of WSP was studied. Hemicellulose content was decreased by acid treatment and lignin content was decreased by base treatment. Hemicellulose and lignin were decreased by oxidation treatment. Ultrasound treatment can effectively destroy the hydrogen bonds in cellulose molecules, but also can make the WSP become more loose. The optimum conditions of treatment were the alkaline H₂O₂ solution containing 1 mol·L-1 NaOH and 1.5 % H₂O₂, the ratio of alkaline H₂O₂ to ethanol of 1:1, reaction time 3 h, reaction temperature 80 oC, WPS dosage 5 g, the ratio of solid to liquid of 1: 20, WSP and liquid after 5 min ultrasound treatment. Under these conditions, the removal rate of lignin from WSP reached 88.0%.Secondly, PWSP was as the raw material. The influences of reaction time, reaction temperature, catalyst dosage and PWSP dosage on LA yield were investigated. The optimize production conditions to produce LA were reaction time 45 min, reaction temperature 200 oC, water 80 mL, catalyst dosage 0.24 g, PWSP dosage 1.2 g. Under these conditions, LA yield was 16.24 %.Finally, when the catalyst was reused for fourth times, LA yield reached 85% of use for fresh catalyst. After actived,the catalyst recovers great catalytic effect, the LA yield reached 96% for fresh catalyst. Ethyl acetate can effectively purify LA.