Synthesis of Cumene from Lignin by Catalytic Transformation

Cumene is an important intermediate and chemical in chemical industry.In this work,directional preparation of cumene using lignin was achieved by a three-step cascade process.The mixture aromatics were first produced by the catalytic pyrolysis of lignin at 450℃ over 1% Zn/HZSM-5 catalyst,monocyclic aromatics with the selectivity of 85.7 wt% were obtained.Then,the catalytic dealkylation of heavier aromatics resulted in benzene-rich aromatics with 93.6 wt% benzene at 600℃ over Hβ catalyst.Finally,the cumene synthesis was performed by the aromatic alkylation,giving cumene selectivity of 91.6 C-mol% using the[bmim]Cl-2AlCl₁₃ ionic liquid at room temperature for 15 min.Besides,adding a small amount of methanol to the feed can efficiently suppress the coke yield and enhance the aromatics yield.The proposed transformation potentially provides a useful route for production of cumene using renewable lignin.     

Mechanistic studies on the effect of veratryl alcohol on the lignin peroxidase catalyzed oxidation of pyrogallol red in reversed micelles

The lignin peroxidase (LiP) catalyzed oxidation of pyrogallol red (PR) in the absence and presence of veratryl alcohol (3,4-dimethoxybenzyl alcohol, VA) was carried out in bis (2-ethylhexyl) sulfosuccinate sodium (AOT)/ polyoxyethylene lauryl ether (Brij30) reversed micelles to elucidate the role of VA. Results indicated that VA could accelerate the LiP catalyzed oxidation of PR, especially at low H₂O₂ concentrations. Unlike in bulk aqueous medium, the protection of LiP by VA in the present medium was relatively unsubstantial, even at high H₂O₂ concentrations. Analysis of data from a series of experiments showed that the enhancement of the PR oxidation caused by VA was mainly due to the indirect oxidation of PR by VA^+∙ from the LiP catalyzed oxidation of VA. It was also found that at the same protector concentration (40 μM), VA (the physiological substrate of LiP) was less effective than PR (a phenolic compound) in protecting LiP from the H₂O₂ derived inactivation. This novel phenomenon deserves further study.      

木质纤维素中C-O键选择性活化和高效转化制化学品

高效转化来源丰富且可再生的木质纤维素制备化学品和燃料对建立可持续发展社会具有重要意义。木质纤维素利用的一条理想途径是将其主要成分纤维素、半纤维素和木质素在温和条件下高选择性地催化转化为关键平台化学品。本文综述了近年报道的有关纤维素、半纤维素和木质素或其模型分子中C–O键选择性活化生成葡萄糖、葡萄糖衍生物(包括葡萄糖苷、六元醇和葡萄糖酸)、木糖、阿拉伯糖和芳香化合物的新催化剂和新策略,阐述了决定催化性能的关键因素。本文还讨论了相关反应机理以深入理解C–O键选择性活化。纤维素由葡萄糖单元通过β-1,4-糖苷键连接而成,通过水解反应,选择性切断这些糖苷键可以获得葡萄糖或其低聚物。鉴于葡萄糖在水热条件下不稳定,发展纤维素温和条件下水解的酸催化剂至关重要。众多研究表明,均相酸催化剂(如无机酸,杂多酸等)具有强Br?nsted酸,在该水解反应中显示高的催化活性。另一方面,拥有强酸性基团-SO3H的固体酸也表现出优异的水解糖苷键性能,但是-SO3H官能团易于流失,限制了这类固体酸催化剂的循环使用。最近研究显示,一些催化剂尤其是碳材料上引入能够与纤维素形成氢键的官能团时,其催化纤维素水解性能显著增强。设计合成这类具备酸性位和氢键位协同效应的稳定固体酸催化剂是纤维素水解转化的一个颇具前景的研究方向。以醇替代水为溶剂实施纤维素醇解制葡萄糖苷是高效活化糖苷键的有效策略。杂多酸被证实为该醇解反应的高性能催化剂。在相同反应条件下,醇解产物葡萄糖苷较水解产物葡萄糖更为稳定,因此可以获得高的葡萄糖苷收率。开发稳定可重复利用的固体酸催化剂是纤维素醇解的关键。耦合水解与加氢或氧化反应可以直接将纤维素转化为相对稳定且具有广泛用途的多元醇或有机酸。目前已有一系列双功能催化剂被报道,这些催化剂通常组合了具备水解功能的液体酸或固体酸和具备加氢或氧化功能的贵金属或过渡金属(譬如Ru, Pt, Ni和Au)。其中杂多酸盐或含有磺酸官能团的固体酸负载Ru或Au双功能催化剂显示出优异的生成六元醇或葡萄糖酸的催化性能。半纤维素由葡萄糖、甘露糖、木糖、阿拉伯糖、半乳糖等单糖单元通过糖苷键连接而成,糖苷键选择性活化可生成各种单糖混合物。硫酸可以有效水解半纤维素,但是同时也易于催化所生成的单糖深度转化为呋喃及其衍生物。较之硫酸,酸性较弱的有机酸特别是二元羧酸(例如马来酸、草酸等)具有较高的单糖选择性。固体酸如酸性树脂,分子筛等亦可催化半纤维素水解反应,但树脂类催化剂中官能团的流失问题有待解决。木质素是由含甲氧基等取代基的苯丙烷单元通过一系列化学键连接而成的复杂大分子,其芳香单元间包括β-O-4,α-O-4和4-O-5等三种主要连接方式,选择性切断这些C–O键可获得高附加值的芳香化合物。水解和氢解是两类普遍用以活化木质素及其模型化合物C–O键的反应。酸和碱均可催化木质素及其模型化合物水解,但是通常需要苛刻条件获取高转化率。近期研究显示,通过对木质素Cα-OH预氧化,再以HCOOH/HCOONa实施水解反应,可以成功实现温和条件下有机溶剂提取木质素及其模型化合物的高效转化。另一方面,均相金属络合物(如Ni, Fe和Ru)或多相负载型金属催化剂(如Ni, Cu, Mo, Pt, Ru, Pd或Ru等)均可有效催化木质素及其模型化合物中C–O键氢解,获得芳烃化合物。在部分多相催化剂体系中,除C–O键活化断裂外,还伴随芳环深度加氢反应,产生较多环己烷衍生物。因此,设计合成具备氢解功能同时抑制过度加氢功能的催化剂是获得芳烃化合物的关键。     

Effects of chemical composition,mild alkaline pretreatment and particle size on mechanical,thermal, and structural properties of binderless lignocellulosic biopolymers prepared by hot-pressing raw microfibrillated Phoenix dactylifera and Cocos nucifera fibers and leaves

We developed value-added, high-strength lignocellulosic biopolymers by exploiting high-lignin biomass waste of palms. Lignocellulosic biopolymers were prepared by hot-pressing microfibrillated raw and alkaline pre-treated date and coconut fibers and leaves powders consisting of (≤53–≤106 μm) particles in the range 140–180 °C. The obtained biopolymers were subjected to three-point bending strength, water resistance, structural morphology (SEM), thermal stability (TGA/DTG), spectroscopy (FTIR), and crystallinity (XRD) analyses. Findings showed that raw fiber-based and alkaline-pretreated biopolymers exhibited bending strength, water resistance, and thermal stability (~200 °C) superior to those of leaf-based biopolymers. Furthermore, lignocellulosic biopolymers prepared from smaller particles showed enhanced bending and thermal properties, compared to those prepared from large particles. By mechanical and thermal properties, the optimum results were observed for biopolymers pre-treated with 1 wt% NaOH, except for coconut leaf-based biopolymers. Results were correlated to chemical composition and particle size of milled lignocellulosic biomass, allowing for efficient lignin condensation.     

Hydrolysis kinetics of benzyl phenyl ether in high temperature liquid water

The application of high temperature liquid water(HTLW) to decomposition of lignin as efficient and green solution for phenolic compounds recovery was studied.Benzyl phenyl ether(BPE),the lignin model compound,was treated at temperatures ranging from 220 to 250℃.BPE undergo hydrolysis in HTLW,and main products were phenol and benzyl alcohol with the minimum selectivities of 75.7%and 82.8%,respectively.Lower temperature led to higher selectivity in 220-250℃temperature range.The kinetics on BPE hydrolysis was studied and the activation energy was determined as 150.3±12.5 kJ/mol with the first-order kinetic equations.Based on products distribution,the reaction mechanism for decomposition of benzyl phenyl ether was proposed.The investigated process provides insights into the design of a commercial method for utilization of lignin.     

迭代法在相思树近红外光谱分析中的应用

以相思树样本的克拉森木素含量为研究对象,利用多波长下的近红外光谱数据建立了若干个预测木素含量的子数学模型.使用加权平均值公式给出了木素含量的首次近似值.根据木素含量实验值与近似值之间所具有的较强线性关系,给出了建立近红外光谱数据预测模型的迭代法.模型的预测精度随迭代次数的增加而提高.本迭代法有望用于其它树木某些化学成分...     

Catalytic degradation of lignin model compounds in acidic imidazolium based ionic liquids: Hammett acidity and anion effects

Ionic liquids based on the 1-methylimidazolium cation with chloride, bromide, hydrogen sulfate, and tetrafluoroborate counterions along with 1-butyl-3-methylimidazolium hydrogen sulfate were employed to degrade two lignin model compounds, guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether. The acidity of each ionic liquid was approximated using 3-nitroaniline as an indicator to measure the Hammett acidity (H₀). While all of the tested ionic liquids were strongly acidic (H₀ between 1.48 and 2.08), the relative acidity did not correlate with the ability of the ionic liquid to catalyze β-O-4 ether bond hydrolysis. The reactivity of the model compounds in the ionic liquids is dependent not only on the acidity, but also on the nature of the ions and their interaction with the model compounds.     

Gas- and solid/liquid-phase reactions during pyrolysis of softwood and hardwood lignins

Pyrolytic reactions of Japanese cedar (Cryptomeria japonica, a softwood) and Japanese beech (Fagus crenata, a hardwood) milled wood lignins (MWLs) were studied with thermogravimetry (TG) and by pyrolysis in a closed ampoule reactor (N₂/600 °C). The data were compared with those of guaiacol/syringol as simple lignin model aromatic nuclei. Several DTG peaks were observed around 300-350, 450, 590 and 650 °C. The first DTG peak temperature (326 °C) of beech was lower than that (353 °C) of cedar. This indicates that the volatile formation from cedar MWL is slightly delayed in heating at 600 °C. The gas-phase reactions via GC/MS-detectable low MW products were explainable with the temperature-dependent reactions observed for guaiacol/syringol in our previous paper. The methoxyl groups became reactive at ∼450 °C, giving O-CH₃ homolysis products (catechols/pyrogallols) and OCH₃ rearrangement products (cresols/xylenols). The former homolysis products were effectively converted into gaseous products (mainly CO) at >550-600 °C. However, the GC/MS-detectable tar yields, especially syringyl unit-characteristic products, were much lower than those from guaiacol/syringol. Thus, contributions of higher MW intermediates and solid/liquid-phase reactions are more important in lignin pyrolysis. From the results of stepwise pyrolysis of char + coke fractions at 450 and 600 °C, the methoxyl group-related reactions (450 °C) and intermediates gasification (600 °C) were suggested to occur also in the solid/liquid phase. This was consistent with the DTG peaks observed around these temperatures. These solid/liquid-phase reactions reduced the tar formation, especially catechols/pyrogallols and PAHs. Different features observed between these two MWLs are also focused.     

Thermal reactivities of catechols/pyrogallols and cresols/xylenols as lignin pyrolysis intermediates

Thermal reactivities of lignin pyrolysis intermediates, catechols/pyrogallols (O-CH₃ homolysis products) and cresols/xylenols (OCH₃ rearrangement products), were studied in a closed ampoule reactor (N₂/600 °C/40-600 s) to understand their roles in the secondary reactions step. Reactivity tends to be enhanced by increasing the number of substituent groups on phenol and this effect was greater for -OH than for -CH₃. Thus, catechols/pyrogallols were more reactive than cresols/xylenols and syringol-derived products were more reactive than corresponding guaiacol-derived products. Catechols/pyrogallols were effectively converted into CO (additionally CO₂ in the case of pyrogallols) in the early stage of pyrolysis. In contrast, cresols/xylenols were comparatively stable and produced H₂, CH₄ and demethylation products (cresols and phenol) after prolonged heating. All intermediates except phenol and 2-ethylphenol formed coke during a long heating time of 600 s (second stage coking). Based on the present results, the roles of intermediates in tar, coke and gas formation from guaiacol and syringol are discussed at the molecular level, focusing on their differences. Molecular mechanisms of gas formation from pyrogallols and demethylation of cresols/xylenols are also discussed.     

THERMAL CHARACTERIZATIONS OF WOOD FLOUR/STARCH CELLULOSE ACETATE COMPOUNDS

Thermogravity analysis (TGA) and differential scanning calorimetric (DSC) analysis, as well as dynamic thermal analysis (DMA), were carried out to study the interfacial interaction between wood flour (WF) and starch/cellulose acetate (SCA) blend. It was found that the main components in the compounds, namely, starch, cellulose, and cellulose acetate, started to decompose at around 330°C, a characteristic temperature for breaking glycoside-linked glucose units. Complexation of lignin in WF with amylose in SCA occurred during compounding, which gave rise to new crystallites that have a melting point of around 160°C. Hydrogen bonding is believed to play a key role in the crystallization. With increasing WF content, both the glass transition temperature and softening temperature increase as a result of the restricted molecular chain mobility imposed by rigid cellulose filaments. In addition, the DMA data revealed that amylose can occur as linkages in the crystallites. All these observations indicated that the interfacial adhesion between SCA and WF is relatively strong, even in absence of a coupling agent.