Radical and(photo)electron transfer induced mechanisms for lignin photo-and electro-catalytic depolymerization

As one of the three major components of woody biomass,lignin is a kind of natural organic polymer and the only abundant natural renewable resource with aromatic nucleus.Chemical catalysis induced depolymerization is an important and effective approach for lignin utilization.In particular,photocatalysis and electrocatalysis show great potential in accurately activating C-O/C-C bonds,which is a critical point of selective cleavage of lignin.In this contribution,we focus on radical and(photo)electron transfer induced reaction mechanisms of the photo(electro)catalytic depolymerization of lignin.Primarily,the general situation of Carbon-centered radicals and active oxygen species mediated lignin conversion has been discussed.Then the mechanisms for(photo)electron transfer mediated lignin depolymerization have been summarized.At the end of this review,the challenges and opportunities of photo(electro)catalysis in the applications of lignin valorization have been forecasted.

Co@CoO:An efficient catalyst for the depolymerization and upgrading of lignocellulose to alkylcyclohexanols with cellulose intact

The depolymerization and upgrading of lignin from raw biomass,while keeping cellulose intact is important in biorefinery and various metal-based catalysts have been used in reductive catalytic fractionation,a key method in"lignin-first"strategy,Recently,we found that a core-shell structured Co@CoO catalyst with CoO shell as the real active site had excellent performance in the hydrogenolysis of 5-hydromethylfurfural to 2,5-dimethylfuran due to its unique ability to dissociate H_(2)and yield active H^(δ-)species(Xiang et al.,2022).In this work,we report a one-pot depolymerization and upgrading of lignocellulose to alkylcyclohexanols,a flavour precursor,with intact cellulose over this unique core-shell structured catalyst,Co@CoO.Lignin model compounds(β-O-4,4-O-5,α-O-4)were first used to clarify the activity of Co@CoO catalyst.Then,the one-pot conversion of various organosolv lignin(birch,pine and poplar)to alkylcyclohexanols was realized with the mass yield of alkylcyclohexanols up to25.8 wt%from birch lignin under the reaction condition of 210℃,1 MPa H_(2),16 h.Finally,the corresponding woody sawdusts were used as feedstocks and found that the Co@CoO catalyst indeed preferentially depolymerized and upgraded the lignin part and obtained the same alkylcyclohexanols products with the retention of cellulose-rich pulp.The collected alkylcyclohexanols were further esterified to obtain valueadded esters,which can be used as flavors.This work will inspire the design of new efficient metal oxide catalysts in lignin fractionation and depolymerization to high-value-added chemicals with intact cellulose.

Lignin depolymerization for phenolic monomers production by sustainable processes

Biomass wastes(almond shell and olive tree pruning) were used in this work as raw materials for the extraction of high purity lignin by different delignification methods. A pretreatment stage was carried out to remove the major hemicelluloses content in the solid feedstocks. Afterward, two sulfur-free pulping processes(soda and organosolv) were applied to extract the largest fraction of lignin. The extracted lignin contained in the liquors was isolated using selective precipitation methods to design a tailor-made technique for obtaining high-purity lignin(in all cases more 90% of purity was reached). Soda process allowed the extraction of more lignin(around 40%–47%) than organosolv process(lower than 20%) regardless of the lignocellulosic source employed.Once the different lignin samples were isolated and characterized, they were depolymerized for the obtaining of small phenolic compounds. Three main streams were produced after the reaction: phenolic enriched oil, residual lignin and coke. After the purification of these fractions, their quantifications and characterization were conducted.The most abundant product of the reaction was residual lignin generated by the undesirable repolymerization of the initial lignin with yields around 30%–45%. The yield of the stream enriched in phenolic oil was higher than 20%. Coke, the lowest added-value product, presented a yield lower than 12% in all the cases. Lignin from organosolv presented higher phenolic oil yields, mainly due to their lower molecular size. This parameter was, thus, considered a key factor to obtain higher yields.

Catalytic depolymerization of calcium lignosulfonate by NiMgFeO_x derived from sub-micron sized NiMgFe hydrotalcite prepared by introducing hydroxyl compounds

A new method for regulating the synthesis of Ni Mg Fe hydrotalcites(NMF LDHs) with the addition of hydroxyl compounds was proposed. A series of NMF LDHs were prepared by the above method, and then were calcined to obtain the Ni Mg FeOx(NMFOx) samples. The NMFOxsamples were characterized by XRD,SEM, TG-DTG, XPS and CO2-TPD, respectively. The catalytic performance of NMFOxfor depolymerizing calcium lignosulfonate(CLS) was evaluated by hydrothermal reaction. The results showed that the addition of hydroxyl compounds favored reducing the particle sizes of NMF LDHs. For the depolymerization of CSL, the yield of liquid product increased from 45% to 75.8% with the addition of NMFOx-ethanol(NMFOxET). The liquid products were mainly phenolics, aromatics, ketones and esters. The total selectivity of oxy-containing compounds was over 90.6%, among them, the phenolics were approximately 35.2%. The valence of Ni and Fe, crystalline phase and basicity almost remained unchanged. The NMFOx-ET samples were recycled for the depolymerization of CLS, moreover, the NMFOx-ET samples had high activity and stability after 4 cycles.

Depolymerization of Poly(bisphenol A carbonate) in Subcritical and Supercritical Toluene

The depolymerization of poly（bisphenol A carbonate）（PC） in subcritical and supercritical toluene was studied. The experimental parameters, which influence the depolymerization reaction such as temperature （570-633 K）, pressure （4.0-7.0 MPa）, reaction time （5-60 min）, and toluene to PC weight ratio （3.0-11.0）, were investigated, and the reaction products were determined by CrC, GC/MS and FT-IR spectrometer. It was found that the main product of the depolymerization reaction was bisphenol A（BPA）. BPA accounted for over 55.7% of the depolymerization products at reaction temperature 613 K, pressure 5.0-6.0 MPa, reaction time 15 min and toluene/PC weight ratio of around 7.0.

Oxidative depolymerization of lignin improved by enzymolysis pretreatment with laccase

A new lignin depolymerization approach for improving the yield of aromatic monomers（YAM） by enzymolysis pretreatment was investigated, in which lignin was pretreated with laccase followed by oxidative depolymerization. It was found that lignin depolymeirzation was enhanced significantly by enzymolysis. The oxidative depolymerization contributed to 21.37% of YAM after the enzymolysis pretreatment,whereas the conventional oxidative depolymerization only gave 14.10% of YAM. The addition of ethanol in enzymatic pretreatment process improved the efficiency of enzymolysis, which effectively improved the solubility of pretreated lignin and depolymerization degree（DD） of lignin. The enzymolysis pretreatment increased the content of syringyl（S） style aromatic monomers, which hindered the recondensation among polymerized products. As lignin has low solubility in acidic aqueous solution, ethanol was added into enzymolysis system to improve the efficiency. However, the enzymolysis of lignin should be carried out for a limited period of time to prevent the inactivation of laccase.

Mathematical Modeling and Inverse Analysis for Microbial Depolymerization Processes of Xenobiotic Polymers

Microbial depolymerization processes of xenobiotic polymers are discussed. A mathematical model is formulated and inverse problems for a time factor and a molecular factor of a degradation rate are described. Experimental outcomes are introduced in inverse analyses. Once the time factor and the molecular factor are obtained, the microbial depolymerization process is simu-lated. Numerical techniques are illustrated and numerical results are presented.

A Bifunctional Brønsted Acidic Deep Eutectic Solvent to Dissolve and Catalyze the Depolymerization of Alkali Lignin

Lignin is an abundant renewable macromolecular material in nature,and degradation of lignin to improve its hydroxyl content is the key to its efficient use.Alkali lignin(AL)was treated with Brønsted acidic deep eutectic solvent(DES)based on choline chloride and p-toluenesulfonic acid at mild reaction temperature,the structure of the lignin before and after degradation,as well as the composition of small molecules of lignin were analyzed in order to investigate the chemical structure changes of lignin with DES treatment,and the degradation mechanism of lignin in this acidic DES was elucidated in this work.FTIR and NMR analyses demonstrated the selective cleavage of the lignin ether linkages in the degradation process,which was in line with the increased content of phenolic hydroxyl species.XPS revealed that the O/C atomic ratio of the regenerated lignin was lower than that of the AL sample,revealing that the lignin underwent decarbonylation during the DES treatment.Regenerated lignin with low molecular weight and narrow polydispersity index was obtained,and the average molecular weight(Mw)decreased from 17680 g/mol to 2792 g/mol(130°C,3 h)according to GPC analysis.The lignin-degraded products were mainly G-type phenolics and ketones,and small number of aldehydes were also generated,the possible degradation pathway of lignin in this acidic DES was proposed.

Numerical Simulation of Microwaveassisted Depolymerization of Kraft Lignin

Kraft lignin has the potential to replace traditional fossil resources for the preparation of high-value chemicals because it is rich in aromatic rings and active functional groups.An effective method for the pyrolysis of kraft lignin into chemicals/fuels is microwave-assisted depolymerization.A simulation model is urgently needed to illustrate the coupling effect and mechanism of lignin conversion during the depolymerization process.In this study,COMSOL Multiphysics was used to simulate the microwave-assisted depolymerization process.The results showed that microwave power had a significant effect on the electric field and temperature distribution in the microwave cavity,while the reaction time had little effect on the electric field.The effect of the nitrogen flow rate on the electric field and temperature was negligible.The intensity of the electric field,heating rate of lignin,and final temperature of lignin depolymerization increased with increasing microwave power.

DEPOLYMERIZATION AND KINETICS OF DEPOLYMERIZATION OF POLYETHYLENE TEREPHTHALATE USING DIBUTYLTIN OXIDE CATALYST

Depolymerization of poly（ethylene terephthalate） （PET） was performed in the tubular bomb microreactor which contained the solution of PET in methanol and dibutyltin oxide at the temperature ranging from 433 K to 473 K, the reaction time from 5 to 45 min and the catalyst-to-PET ratio of 0.3%-2% by weight. The optimal condition for PET depolymerization catalyzed by dibutyltin oxide is the temperature of 443-453 K, the reaction time of 20-25 min and 0.8% by weight of catalyst. By using differential methods, the activation energy for the depolymerization process was found to be 154.05 kJ/mol in the temperature range from 433-463 K.

Depolymerization of <i>α</i>- &<i>β</i>-Chitosan by <i>e</i>-Beam Irradiation

α- and β-chitosan with molecular weight of 190,000 and 800,000 respectively, were depolymerized by e-beam irradiation with various doses. The radiation yield of scission (Gs) and degradation rate of the chitosans were identified. The synergistic chemical degradation in the presence of hydrogen peroxide is more effective at lower doses. Mw of β-chitosan was dramatically decreased from 800,000 to 21,030 at the irradiation dose 5 kGy, on the other hand, that of α-chitosan was decreased much more gradually from 190,000 to 36,000. The values of Gs at 10 kGy in the solution without H2O2 and with H2O2 were respectively 6.09 × 10-5 mol/cal and 30.6 × 10-5 mol/cal for α-Chitosan, and 8.18 × 10-5 mol/cal and 43.8 × 10-5 mol/cal for β-chitosan. It was obviously effective on depolymerization by using the combination of e-beam and H2O2. α-Chitosan molecules are likely to adopt a diffuse conformation in the solution and make the different morphologies depending on the concentration.

Production of Bio-Phenols for Industrial Application:Scale-Up of the Base-Catalyzed Depolymerization of Lignin

Objective of this study was the investigation on the up-scaling of base-catalyzed depolymerization (BCD) of lignin to pilot plant dimension. The cleavage process was carried out in dilute alkaline solution at temperatures up to 340°C and a pressure of 25 MPa in a continuously operated tubular flow reactor with throughputs up to 20 kg/h. Investigations included the proof of the feasibility of the scale-up as well as a parameter study on the cleavage of hardwood Organosolv lignin and softwood Kraft lignin within the established pilot plant. Yields and molecular compositions of the isolated product fractions BCD-oil (liquid phenolic fraction) and BCD-oligomers (solid phenolic fraction) are similar to those described in technical lab scale, showing a good scalability. Here, BCD-oils rich in phenolic monomers such as guaiacol, catechol and/or syringol were obtained with a content of up to 13.3 wt% and 14.5 wt% from Organosolv lignin and Kraft lignin, respectively. Formation of BCD-oligomers strongly depends on temperature and residence times within the reactor.

团聚物与凸起结构柔性振动筛板碰撞解聚特性

为了促进潮湿细粒煤团聚物的解聚,提出将凸起结构筛板用于物料的筛分。首先,采用挤压壁面法构建了潮湿细粒团聚物模型,仿真分析了团聚物在不同筛板上的碰撞解聚过程及解聚程度;其次,通过单因素和响应面分析法研究了凸起结构参数对团聚物碰撞解聚程度的影响性能,对凸起结构参数进行了优化;最后,通过筛分试验对比了物料在普通筛板和凸起结构筛板的解聚性能。结果表明:凸起结构能提高潮湿细粒团聚物的解聚程度,其参数对团聚物的解聚性能有显著影响;平均垂直应力σyy、液桥断裂百分比DR、平均偏心距离Ad和膨胀速度Ue随凸起结构下底a、上底b的增加呈非单调变化,与高h的变化呈正比;响应面分析得到凸起结构各参数对解聚程度的影响显著性依次为h>b/a>a;通过对凸起结构参数优化,团聚物的解聚程度最高可提升13.4%。

药渣木质素定向解聚制备高密度航油合成原料

以三叉苦药渣木质素为原料,在低共熔溶剂(ChCl-MeOH-AlCl_(3)·6H_(2)O)与催化剂(Cu(OAc)_(2)/邻菲罗啉)耦合作用下解聚生成高密度航油合成原料,考察不同反应温度、时间、固液比、催化剂添加量与氧气含量对木质素催化氧化解聚效果的影响。结果表明:在固液比1∶30 g/mL,木质素、Cu(OAc)_(2)、邻菲罗啉的质量比1∶1∶1,3 MPa氧压,60℃条件下反应3 h后,木质素选择性解聚生了芳香醛酮类高密度航油合成原料,木质素转化率达到80.84%,香草乙酮与香草醛收率分别为16.69%和34.39%。

木质素抑菌性能强化改性方法研究进展

综述了木质素的结构特征,说明了木质素对革兰氏阳性菌和革兰氏阴性菌的抑菌机理,即酚羟基能促进细胞周围pH值的降低,从而可以破坏细胞膜,使蛋白质变性,抑制微生物细胞的呼吸系统和电子传递酶系统活性,达到抑菌作用,而分子量降低可以提高木质素酚羟基含量,亲水性提高则可有效提高木质素水溶性。结合国内外研究现状,介绍了提高木质素抑菌活性的主要方法:解聚法、分级法、木质素的提取方法和木质素-银络合物法,阐述了不同方法改性木质素如何提高其抑菌活性,并对提高木质素抑菌活性研究进行展望。

环状对苯二甲酸乙二醇酯低聚体的沉淀分离提纯与开环聚合

通过低溶液浓度下聚对苯二甲酸乙二醇酯(PET)的解聚成环(CDP)反应可制备环状对苯二甲酸乙二醇酯低聚体(CET),但解聚粗产物组成复杂,影响CET高值化应用。本研究对PET解聚产物进行选择性沉淀分离提纯,研究了沉淀温度、沉淀剂种类等对CET收率的影响,并考察了纯化CET的热性能和开环聚合行为。结果表明:以乙醇为沉淀剂时,选择性沉淀得到的CET中线性低聚物和催化剂残留量随温度降低而减少,沉淀温度为30℃时线性低聚物和催化剂残留量较低;以正己烷等饱和烷烃为沉淀剂,沉淀温度为30℃时,可得到不含线性低聚物组分的CET,且以正己烷为沉淀剂,CET收率最高(72.69%)。纯化CET在不加催化剂或添加1%(质量分数)三氧化二锑催化剂、320℃下开环聚合8 min,可分别制得特性黏数为0.56 dL/g和0.64 dL/g的PET。

木质素光催化解聚研究进展

综述了近年来用于木质素解聚的光催化剂种类,分析了木质素光催化解聚机理及策略,还对光催化与多种技术耦合的解聚方法进行了介绍,并展望了木质素光催化解聚研究领域所面临的挑战及发展方向。