483 / 2018-09-09 10:24:00

Conversion of Biomass-derived Levulinic Acid (Esters) to Liquid Fuel and Chemicals

全体主题 > 生物质液体燃料

As a potential renewable substitute for fossil resources, biomass has been converted to food, heat, electricity, liquid fuel and platform chemicals, which are the bases of human society. As the most abundant bio-based raw material, lignocellulose can be fractionated to three main components: cellulose, hemicellulose and lignin through various pretreatment methods. Cellulose and hemicellulose are degraded to sugars by acid catalyzed hydrolysis/alcoholysis and further converted to levulinic acid (LA) and levulinate esters (LE) including methyl levulinate (ML) and ethyl levulinate (EL), which are very important platform molecules for the production of liquid fuel, fuel additives, essences, building blocks and other downstream value-added chemicals.
In this study, LA and LE are adopted as off the shelf starting materials for the preparation of heterocyclic, alicyclic compounds and their derivatives. Besides the atom-economic preparation of gamma-valerolactone (GVL), the synthesis of a series of LA/LE derivatives, including methyl 4-methoxypentanoate (MMP), ethyl levulinate dimer (ELD), saturated ethyl levulinate dimer (SELD), 5-methylthiophene-2-thiol (MTT) and the condensation products of LA derived α-angelicalactone (AL) with 5-chloromethylfurfural, (5-CMF) or 2,5-diformylfuran (2,5-DFF).
Firstly, GVL was synthesized from EL under a solvent-free condition with the catalysis of a Cu-Cr oxide, which was in-situ activated by molecule H2. The yield of GVL was up to 95% with a catalyst loading of 1 wt%, H2 pressure of 4 MPa at 250 oC after 4 h. The catalyst was reused without any reactivation processes and provided excellent recyclability.
Considering that methanol could be decomposed on the Cu-Cr catalyst, an atom-economic method for GVL synthesis was developed. ML was used as starting material and an extremely low amount of methanol was introduced as in-situ hydrogen donor. A 90% yield of GVL was obtained with the addition of 0.23 equivalent of methanol at 250 oC after 4 h. As the in-situ generated methanol during ML cyclization was also effectively utilized for H2 supply, this system was proved to be more atom-economical than previous research.
Secondly, the ring-opening reaction of GVL in methanol in the presence of HUSY and CaCO3 was studied, in which GVL was converted to a novel molecule MMP with a conversion of 58% and a selectivity up to 87% at 250 oC in 4 h under 4 MPa of N2. MMP was reported as a by-product for GVL ring-opening reaction with a selectivity lower than 10%, which could be applied as building block, fuel additive and essence. By studying the ring-opening chemistry of gamma-butyrolactone as a model compound under same conditions, insoluble carbonates such as CaCO3 was proved to promote the generation of methoxyl anions, thus inhibited the generation of pentenoates and improved the selectivity to MMP.