Haibo Xie

Preparation of lignin/glycerol-based bis(cyclic carbonate) for the synthesis of polyurethanes

A bis(cyclic carbonate) was obtained via glycidylation of lignin-based bisphenol followed by cycloaddition with CO2. Further polyaddition between the bis(cyclic carbonate) and diamines led to the synthesis of polyurethanes. The structure and thermal properties of these polyurethane materials were elucidated by NMR, FT-IR, GPC, XRD, TGA and DSC.

Tungsten Carbide: A Remarkably Efficient Catalyst for the Selective Cleavage of Lignin C−O Bonds

A remarkably effective method for the chemoselective cleavage of the C-O bonds of typical β-O-4 model compounds and the deconstruction of lignin feedstock was developed by using tungsten carbide as the catalyst. High yields of C-O cleavage products (up to 96.8 %) from model compounds and liquid oils (up to 70.7 %) from lignin feedstock were obtained under low hydrogen pressure (0.69 MPa) in methanol. The conversion efficiency was determined to a large extent by solvent effects and was also affected by both the electronic and steric effects of the lignin model compounds. In situ W2 C/activated carbon (AC)-catalyzed hydrogen transfer from methanol to the substrate was proposed to be responsible for the high performance in methanol solvent. The conversion of 2-(2-methoxyphenoxy)-1-phenylethanol showed that the catalyst could be reused five times without a significant loss in activity for C-O bond cleavage, whereas the selectivity to value-added styrene increased markedly owing to partial oxidation of the W2 C phase according to X-ray diffraction, Raman spectroscopy, and transmission electron microscopy characterization. 2 D-HSQC-NMR spectroscopy analysis showed that W2 C/AC exhibited high activity not only for β-O-4 cleavage but also for the deconstruction of more resistant α-O-4 and β-β linkages, so that a high yield of liquid oil was obtained from lignin. Corn stalk lignin was more liable to be depolymerized than birch lignin owing to its loosened structure (scanning electron microscopy results), larger surface area (BET results), and lower molecular weight (gel-permeation chromatography results), whereas its liquid oil composition was more complicated than that of birch wood lignin in that the former lignin contained more p-hydroxyphenyl units and the former contained noncanonical units.

Effects of Extraction Methods on Structure and Valorization of Corn Stover Lignin by a Pd/C Catalyst

With the significant development of efficient pretreatments of lignocellulosic biomass towards using carbohydrate compositions for biofuel production, the valorization of associated lignin products into valuable chemicals has gained much attention. Four lignins obtained by pretreatment of corn stover with emerging ionic liquid‐based mixed organic electrolytes (ILOE) and alkaline twin‐screw extrusion (ATSE) pretreatment technologies were characterized by gel permeation chromatography (GPC), FTIR, HSQC, 31P NMR spectroscopy, and SEM. These lignins were valorized by using Pd/C under various conditions, followed by an elucidation of the relationship between the lignin structure and valorization efficiency and selectivity. The pretreatment/separation methods have a significant effect on lignin structure and subsequent valorization efficiency. HSQC spectra revealed that corn stover lignin consisted of β‐O‐4, β‐5, β‐1 linkages, and cinnamyl alcohol end groups. The extracted lignins (EL) showed less carbohydrates and β‐O‐4 units than those of enzymatic hydrolytic lignins (EHL). The yields of bio‐oils were 61.7 % and 57.9 % for ATSE‐EL and ILOE‐EL, and 34.2 % and 45.1 % for ATSE‐EHL and ILOE‐EHL under optimal and comparative conditions, respectively. Part of the syringyl (S) units were converted into guaiacyl or p‐hydroxyphenyl (H) units by release of methoxyl groups on the aromatic ring through hydrogenolysis, which led to a decreased proportion of S units and an increased proportion of H units in oil compared with in lignin.

Synthesis of cellulose acetate propionate and cellulose acetate butyrate in a CO 2 /DBU/DMSO system

The reversible reaction of the hydroxyl groups in cellulose with CO2 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) results in a rapid and effective derivative dissolution of cellulose in DMSO, by which a series of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) with various degrees of substitution (DS) were synthesized controllably without adding external catalysts. Wherein DBU not only achieves the dissolution of cellulose, but also acts as an efficient organocatalyst for the subsequent cellulose derivatization. The DS of CAB and CAP can be tuned by changing the feed molar ratio of propionic (butyric) anhydride/acetic anhydride and the reaction temperature. The structural and thermal properties of the products were characterized by several analytical techniques including NMR, FT-IR, and TGA. The CO2/DBU/DMSO dissolution system provides a new platform for controllable synthesis of mixed cellulose esters with high efficiency under mild conditions.

Capturing CO2 to reversible ionic liquids for dissolution pretreatment of cellulose towards enhanced enzymatic hydrolysis

To overcome the natural recalcitrance of cellulose for glucose production in aqueous media catalyzed by enzyme, in this study, a dissolution pretreatment strategy was developed by using in situ formed CO2-based reversible ionic compounds (RICs)/DMSO mixed organic electrolytes under mild conditions. The influences of the constitution of RICs, CO2 pressure, dissolution pretreatment time on the physic-chemical structure of cellulose were investigated systematically by FTIR, XRD, SEM, AFM towards in-depth understanding of the correlations between the pretreatment conditions, micro-scale structure and enzymatic saccharification of cellulose. The results showed that the tetramethyl guanidine (TMG) based RICs solvent system [TMGH]2+[O2COCH2CH2OCO2]2-/DMSO (XRICs  = 0.1, XRICs: the mole fraction of the formed RICs in the mixture) presented the best performance, which was evidenced by 100% glucose yield after the dissolution-regeneration pretreatment strategy under mild conditions (T = 60 °C, Pco2 = 2.0 MPa, t = 2 h). Furthermore, the solvent system have good recyclability and usability.

Vanillin derived a carbonate dialdehyde and a carbonate diol: novel platform monomers for sustainable polymers synthesis

Vanillin has been regarded as one of the important biomass-based platform chemicals for aromatic polymers synthesis. Herein, novel symmetric bis(4-formyl-2-methoxyphenyl)carbonate (BFMC) and bis(4-(hydroxymethyl)-2-methoxyphenyl)carbonate (BHMC) polymeric monomers have been synthesized in high yields using vanillin as a raw chemical, which have been submitted for polymer synthesis via well-established polymeric strategies. A new class of poly(carbonate ester)s oligomers with amide moieties in their side chain can be prepared by using the BFMC as one of monomers via the Passerini three compound reaction (3CR). A new class of poly(carbonate ester)s oligomers and poly(carbonate urethane)s can be prepared via reactions between BHMC with dicarboxylic acid chlorides and diisocyanates, respectively. Their structure have been confirmed by 1H NMR, 13C NMR and FTIR, and the gel permeation chromatograph (GPC) analysis shows that the Mn of poly(carbonate ester)s oligomers ranges from 3100 to 7900 with PDI between 1.31 and 1.65, and the Mn of poly(carbonate urethane)s ranges from 16 400 to 24 400 with PDI ranging from 1.36 to 2.17. The DSC analysis shows that the poly(carbonate ester)s oligomers have relative low Tg ranging from 37.4 to 74.1 °C, and the poly(carbonate urethane)s have Tg ranging from 97.3 to 138.3 °C, mainly correlating to the structure of dicarboxylic acid chlorides and diisocyanates used.

Preparation of Novel Aromatic-Aliphatic Poly(ketone ester)s through Condensation of Biomass-Derived Monomers

Abstract: Novel unsaturated and saturated monomers with a hydroxyl group and a carboxylic group via aldol condensation reaction of lignin‐derived aromatic aldehydes with levulinic acid were prepared through organocatalysis and hydrogenation, respectively. The catalytic process was optimized and the structure of the monomers were full characterized. The as‐prepared monomers were ready for the subsequent condensation polymerization to achieve a serial of novel full biobased poly(ester ketone)s. The chemical‐physical properties of the poly(ester ketone)s were evaluated. This provides a green upgrading strategy to prepare sustainable synthetic polymers from building blocks available on a large scale using a catalytic biorefinery approach.

Fast dissolution pretreatment of the corn stover in gamma-valerolactone promoted by ionic liquids: Selective delignification and enhanced enzymatic saccharification

The dissolution of corn stover was investigated in gamma-valerolactone (GVL) assisted by ionic liquids. An enhanced subsequent enzymatic saccharification was reached with a total reducing sugar yield of 0.69 g.g-1 and a glucose of 0.38 g.g-1 within 24 h. The treatment effects on the physical-chemical features of corn stover in terms of the natural recalcitrance to the subsequent biological digest were systematically investigated using composition analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The structures of the associated enzymatic hydrolysis lignin (EHL) and ionic liquid extracted lignin (IEL) were characterized by gel permeation chromatography (GPC), fourier transform infra-red spectroscopy (FTIR), phosphorous nuclear magnet resonance spectrometry (31P NMR), and heteronuclear single quantum coherence spectroscopy (HSQC) for an in-depth understanding of the delignification process and the basic structural information for further lignin valorization.