Degradation of vinyl ester resin and its composites via cleavage of ester bonds to recycle valuable chemicals and produce polyurethane.

Vinyl ester resins (VER) and its composites are widely used in chemical industry and municipal engineering. However, its dense three-dimensional network structure makes its degradation and recycling a great challenge. Herein, a novel, efficient and green degradation system gamma-valerolactone (GVL)-H2O/p-toluene sulfonic (PTSA) was developed to degrade VER and its composites. VER was completely degraded in the GVL-H2O/PTSA at 210 °C and 0.6 MPa. By combing SEM-EDS, IR, NMR, GPC and MALDI-TOF-MS analysis, it was clarified that VER swelled well in GVL, allowing the transfer of PTSA and H2O through the resin matrix. The ester bonds in VER were cleaved via hydrolysis with H2O catalyzed by the sulfonic acid of PTSA, and high value-added polymer products, i.e., copolymer of styrene and methacrylic acid (SMAA) and bisphenol-A diglycidyl ether (DGEBA), were recycled, which accounted for ca. 87.0 wt% of raw VER. DGEBA can be recycled to prepare a new PU material. The GVL-H2O/PTSA system was also effective for degrading UPR and VER-containing composites. This work provides a practical strategy for chemical degradation and recovery of thermoset VER resins.

A novel mechanocatalytical reaction system driven by fluid shear force for the mild and rapid pretreatment of lignocellulosic biomass.

Pretreatment is the initial stage of lignocellulosic biorefinery process, but is limited by the time-consuming processes, harsh conditions and/or undesirable products. Herein, a mild (<60 °C) and highly efficient pretreatment strategy is developed. The novel mechanocatalytical reaction system driven by fluid shear force helps to exfoliate cellulose from lignocellulose, and the heat generated by the shear process can be used to precipitate and recover the dissolved cellulose from the precooled NaOH/urea solution. The regenerated cellulose shows satisfying crystal structure (cellulose II), significantly decreased crystallinity and nearly tripled enzymolysis glucose yield. Almost 90% of lignin and hemicellulose could be rapidly separated. The separated lignin shows a nearly native structure with 64% ß-O-4 linkage, which is even higher than the ball-milling lignin (60%). This research provides a theoretical guidance for the mild pretreatment of lignocellulosic biomass, which will push the application of mechanocatalytical reaction system in biorefinery processes on a large scale.

Chemical recycling of waste poly-p-phenylene terephthamide via selective cleavage of amide bonds catalyzed by strong Brönsted base in alcohols.

Poly-p-phenylene terephthamide (PPTA) is widely applied in bulletproof products and composite materials because of its high strength, high modulus, high temperature resistance and creep resistance. The PPTA molecule with highly symmetrical and regular structure is linear structure formed by the alternating connection of benzene ring and amide bond, and the amide bonds between the molecular chains form strong hydrogen bonds. Therefore, the dissolution and depolymerization of PPTA is very challenging. In this work, an efficient catalytic system was developed for the controllable degradation of waste PPTA, and the high-value added monomers terephthalic acid (TPA) and p-phenylenediamine (PPD) were recovered. The results show that the amide bonds of PPTA can be selectively cleaved by the strong Brönsted base catalysts in alcohols, especially in the NaOH/n-butanol system. Under the optimal degradation conditions (5 wt% NaOH in n-butanol, 180 °C, 6 h), the percentage degradation of PPTA is 100%, and the yields of TPA and PPD are 92.0% and 91.5%, respectively. In addition, it is found that the wettability of n-alcohols on PPTA monofilament and the addition of a small amount of water have important influences on the degradation of PPTA. The work elucidates the degradation mechanism of PPTA, and reveals the important factors affecting the depolymerization of PPTA.

Effect of Coordination Environment Surrounding a Single Pt Site on the Liquid-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural.

As the frontier in heterogeneous catalyst, a monomer and positively charged active sites in the single-atom catalyst (SAC), anchored by high electronegative N, O, S, P, etc., atoms, may not be active for the multispecies (O2, substrates, intermediates, solvent etc.) involved liquid-phase aerobic oxidation. Here, with catalytic, aerobic oxidation of 5-hydroxymethylfurfural as an example, Pt SAC (Pt1-N4) was synthesized and tested first. With commercial Pt/C (Pt loading of 5 wt %) as a benchmark, 2,5-furandicarboxylic acid (FDCA) yield of 97.6% was obtained. Pt SAC (0.56 wt %) gave a much lower FDCA yield (28.8%). By changing the coordination atoms from highly electronegative N to low electronegative Co atoms, the prepared Pt single-atom alloy (SAA, Pt1-Co3) catalyst with ultralow Pt loading (0.06 wt %) gave a much high FDCA yield (99.6%). Density functional theory (DFT) calculations indicated that positively charged Pt sites (+0.712e) in Pt1-N4 almost lost the capability for oxygen adsorption and activation, as well as the adsorption for the key intermediate. In Pt1-Co3 SAA, the central negatively charged Pt atom (-0.446e) facilitated the adsorption of the key intermediate; meanwhile, the nearby Co atoms around the Pt atom constituted the O2-preferred adsorption/activation sites. This work shows the difference between the SAC with NPs and the SAA during liquid-phase oxidation of HMF and gives a useful guide in the future single-atom catalyst design in other related reactions.

Superior nitrogen-doped activated carbon materials for water cleaning and energy storing prepared from renewable leather wastes.

The fabrication of nitrogen-doped activated carbons (N-ACs) from leather solid wastes (LSW), a huge underutilized bioresource, by different activation methods was investigated. N-AC prepared by KOH activation (named KNAC) exhibited superior physical and chemical properties with much higher BET surface area (2247 m2 g-1) and more abundant hierarchical micropores than those activated by nano-CaCO3 (CNAC) or by direct carbonization (NNAC). KOH activation decreased the total nitrogen content in KNAC, but it increased the ratio of surface nitrogen species. KOH activation also significantly promoted the conversion of nitrogen species in the carbon material to pyridinic N. Potential applications of the prepared N-ACs were evaluated, and they were tested as adsorbents to remove phenols from water and as the anodes of lithium batteries. The high surface area, abundant micropores, and plentiful surface pyridinic N guaranteed KNAC a superior nitrogen-doped activated carbon that could serve as an excellent adsorbent to remove phenols (282 mg/g) from waste water as well as an outstanding electrode material with a high and stable charge/discharge capacity (533.54 mAh g-1 after 150th cycle). The strategy of LSW conversion to versatile N-ACs turns waste into treasure and could promote the sustainable development of our society.

A Highly Stable Copper-Based Catalyst for Clarifying the Catalytic Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation.

Identification of the active copper species, and further illustration of the catalytic mechanism of Cu-based catalysts is still a challenge because of the mobility and evolution of Cu0 and Cu+ species in the reaction process. Thus, an unprecedentedly stable Cu-based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu0 and Cu+ in the dehydrogenation of methanol to methyl formate by combining isotope-labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu0 sites promote the cleavage of the O-H bond in methanol and of the C-H bond in the reaction intermediates CH3 O and H2 COOCH3 which is formed from CH3 O and HCHO, whereas Cu+ sites cause rapid decomposition of formaldehyde generated on the Cu0 sites into CO and H2 .

Conversion of Xylose to Furfuryl Alcohol and 2-Methylfuran in a Continuous Fixed-Bed Reactor.

An efficient process was designed for the synthesis of furfuryl alcohol and 2-methylfuran from xylose using a continuous fixed-bed reactor over a catalyst combining Hß zeolite and Cu/ZnO/Al2 O3 in γ-butyrolactone (GBL)/water as solvent. The cooperative effect of Hß zeolite and GBL facilitated the dehydration of xylose and enhanced largely the furfural yield. The production of furfuryl alcohol and 2-methylfuran can be simply tuned by changing the hydrogenation temperature for furfural over the Cu/ZnO/Al2 O3 catalyst. The yield for furfuryl alcohol reached 87.2 % at 150 °C whereas a yield of 86.8 % was achieved for 2-methylfuran at 190 °C.

Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy.

The basic ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) could efficiently catalyze the conversion of 2-amino-2-deoxy-d-glucose (GlcNH2) into deoxyfructosazine (DOF) and fructosazine (FZ). Mechanistic investigation by NMR studies disclosed that [C2C1Im][OAc], exhibiting strong hydrogen bonding basicity, could coordinate with the hydroxyl and amino groups of GlcNH2via the promotion of hydrogen bonding in bifunctional activation of substrates and further catalyzing product formation, based on which a plausible reaction pathway involved in this homogeneous base-catalyzed reaction was proposed. Hydrogen bonding as an activation force, therefore, is responsible for the remarkable selectivity and rate enhancement observed.

In situ NMR spectroscopy: inulin biomass conversion in ZnCl2 molten salt hydrate medium-SnCl4 addition controls product distribution.

The dehydration of inulin biomass to the platform chemicals, 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA), in ZnCl2 molten salt hydrate medium was investigated. The influence of the Lewis acid catalyst, SnCl4, on the product distribution was examined. An in situ(1)H NMR technique was employed to follow the reaction at the molecular level. The experimental results revealed that only 5-HMF was obtained from degradation of inulin biomass in ZnCl2 molten salt hydrate medium, while the LA was gradually becoming the main product when the reaction temperature was increased in the presence of the Lewis acid catalyst SnCl4. In situ NMR spectroscopy could monitor the reaction and give valuable insight.

Direct conversion of chitin biomass to 5-hydroxymethylfurfural in concentrated ZnCl2 aqueous solution.

The direct conversion of chitin biomass to 5-hydroxymethylfurfural (5-HMF) in ZnCl2 aqueous solution was studied systemically. D-Glucosamine (GlcNH2) was chosen as the model compound to investigate the reaction, and 5-HMF could be obtained in 21.9% yield with 99% conversion of GlcNH2. Optimization of the reaction parameters including the screening of 8 co-catalysts was carried out. Among them, AlCl3 and B(OH)3 improved 5-HMF yield, whereas CdCl2, CuCl2 and NH4Cl had no effect. CrCl3, SnCl4 and SnCl2 showed negative effects, i.e. lower yields. Consequently, the optimal reaction conditions were found to be 67 wt.% ZnCl2 aqueous solution, at 120 °C without co-catalyst. The reactions were further studied by in situ NMR, and no intermediate or other byproducts, except humins, were observed. Finally, the substrate scope was expanded from GlcNH2 to N-acetyl-D-glucosamine and various chitosan polymers with different molecular weights, 5-HMF yield from polymers were generally lower than that from GlcNH2.

Efficient catalytic system for the conversion of fructose into 5-ethoxymethylfurfural.

DMSO can improve the selectivity of 5-hydroxymethylfurfural (HMF) in the conversion of carbohydrates. However, one of the bottlenecks in its application is product separation. Thus a one-pot synthesis of 5-ethoxymethylfurfural (EMF) rather than HMF from fructose in ethanol-DMSO was investigated. Phosphotungstic acid was used as an effective catalyst. The yield of EMF can be reached as high as 64% in the mixed solvent system of DMSO and ethanol within 130 min at 140 °C. Ethyl levulinate (LAE) was detected as the main by-product, the yield of which increased with the reaction time, temperature and the amount of catalyst. In addition, the existence of water could significantly reduce the yield of EMF and increased the yield of LAE. Most importantly, it was discovered that EMF could be much more efficiently extracted from the reaction solvent system by some organic solvents than HMF.

Conversion of carbohydrates into 5-hydroxymethylfurfural catalyzed by ZnCl2 in water.

The incompletely coordinated zinc ions in the concentrated aqueous ZnCl(2) solution catalyze the direct conversion of carbohydrates into 5-hydroxymethylfurfural, and a moderate HMF yield up to 50% can be achieved.