关于举办海外名师—美国威斯康星大学麦迪逊分校Xuejun Pan教授 发布者:魏巍   发布时间:2018-06-29   浏览次数:854

报告题目一Solid-state depolymerization to produce uncondensed lignin for valorization

报 告 人Prof. Xuejun Pan (University of Wisconsin-Madison)

报告时间201872日(周一)上午9:00

报告地点:逸夫工程馆105楼会议室


报告题目二:Isomerization of glucose to fructose catalyzed by a weak Lewis base in water

报告人:Prof. Xuejun Pan (University of Wisconsin-Madison)

报告时间:201874日(周三)上午9:00

报告地点:逸夫工程馆105楼会议室

  

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化学与化工学院

2018629

  

Solid-state depolymerization to produce uncondensed lignin for valorization

  

Xuejun Pan, PhD

Professor

Biological Systems Engineering, University of Wisconsin-Madison

  

Abstract:

This study demonstrated that lignin could be efficiently depolymerized in the solid state with minimal condensation and separated from biomass with high purity by dissolving and hydrolyzing cellulose and hemicelluloses, using an acidic lithium bromide trihydrate (ALBTH) system under mild conditions (with 40 mM HCl at 110 °C). The benzodioxane structure was identified and confirmed for the first time in an acid-depolymerized lignin. Reactions using lignin model compounds confirmed the formation of the uncondensed moieties and revealed the synergy between LiBr and acid in inducing the crucial intermediate α-benzyl carbocations, which then led to cleavage of the β–O–4-aryl ether bonds to produce Hibbert’s ketones, demethylation to produce benzodioxanes, and condensation reactions. Unlike in the LMC reactions, the condensation of the real lignin in biomass under ALBTH conditions was greatly diminished, possibly due to lignin’s remaining in the solid state, limiting its mobility and accessibility of the a-benzyl carbocation to the electron-rich aromatic sites for condensation. Preliminary results indicated that, because of its uncondensed nature, the ALBTH lignin was a good lignin feedstock for hydrogenolysis. This study provided a new approach to effectively isolate depolymerized lignin from lignocellulose in a less condensed form for boosting its downstream valorization.


Isomerization of glucose to fructose catalyzed by a weak Lewis base in water

  

Xuejun Pan, PhD

Professor

Biological Systems Engineering, University of Wisconsin-Madison

  

Abstract:

This study demonstrated that glucose could be isomerized to fructose in the concentrated aqueous solution of lithium bromide (LiBr) alone without any additional catalyst under mild conditions. The isomerization mechanisms were studied via isotopic labeling experiments. It was verified for the first time that not only the cation (Li+) but also the anion (Br‾, a weak Lewis base) in the system catalyzed the isomerization of glucose to fructose. The Br‾ catalyzed the isomerization through the proton transfer mechanism via enediol intermediate, while the Li+ did through the intramolecular hydride shift mechanism from C2 to C1. The estimation using quantitative 13C-NMR analysis indicated that Br‾ catalyzed approximately 85% of the isomerization, while Li+ was responsible for the rest 15%. It was found that 31% of fructose was produced from glucose under the optimum reaction conditions (120 °C for 15 min in LiBr trihydrate). The outcomes of this study provided not only better understanding and insights of the sugar transformations to fructose and subsequently to furan-based platform chemicals in LiBr trihydrate but also an alternative approach to produce fructose from glucose.

Biography

Dr. Pan is a Professor in the Department of Biological Systems Engineering at University of Wisconsin-Madison. He earned his Bachelor, Master and PhD degrees in Chemical Engineering at Tianjin University of Science and Technology, China, and a PhD degree in Applied Bioscience at Hokkaido University, Japan. Dr. Pan conducted postdoctoral researches at Georgia Tech, University of Minnesota, and University of British Columbia, successively.

  

Dr. Pan’s areas of interest include (1) pretreatment and fractionation of lignocellulosic biomass; (2) enzymatic and chemical saccharification of lignocellulose; (3) chemical and biological conversion of lignocellulose to chemicals and liquid fuels; (4) high-value utilization of cellulose, hemicellulose and lignin; and (5) fundamental understanding of physical and chemical changes of plant cell wall during biorefining.

  

Dr. Pan has published 90+ peer reviewed journal articles, 6 book chapters, and 3 US patents. Total citation >6500, h-index 37, and i10-index 64. He was elected as Fellow of International Academy of Wood Science in 2013 and won Alfred Toepfer Faculty Fellow Award in 2011 and NSF Career Award in 2009.