Solid-state hydrolysis of cellulose and methyl α- and β-d-glucopyranosides in presence of magnesium chloride

Advancing Lignocellulosic Biomass Fractionation through Molten Salt Hydrates: Catalyst-Enhanced Pretreatment for Sustainable Biorefineries

Developing a process that performs the lignocellulosic biomass fractionation under milder conditions simultaneously with the depolymerization and/or the upgrading of all fractions is fundamental for the economic viability of future lignin-first biorefineries. The molten salt hydrates (MSH) with homogeneous or heterogeneous catalysts are a potential alternative to biomass pretreatment that promotes cellulose's dissolution and its conversion to different platform molecules while keeping the lignin reactivity. This review investigates the fractionation of lignocellulosic biomass using MSH to produce chemicals and fuels. First, the MSH properties and applications are discussed. In particular, the use of MSH in cellulose dissolution and hydrolysis for producing high-value chemicals and fuels is presented. Then, the biomass treatment with MSH is discussed. Different strategies for preventing sugar degradation, such as biphasic media, adsorbents, and precipitation, are contrasted. The potential for valorizing isolated lignin from the pretreatment with MSH is debated. Finally, challenges and limitations in utilizing MSH for biomass valorization are discussed, and future developments are presented. Cellulose Avicel®PH-101 ZnCl2 ⋅ 4H2O, ZnBr2 ⋅ 4H2O, LiCl ⋅ 8H2O, LiBr ⋅ 4H2O H2SO4, (0.2 M); H3PW12O40 (0.067 M); H4SiW12O40 (0.05 M) T (145-175 °C); Time (30-120 min) Organic solvent (MIBK) LA (94 %) and HMF (3.4 %) Dissolution time: ZnBr2 ⋅ 4H2O<>2O<>2 ⋅ 4H2O<>2O; The highest conversion of pretreated cellulose and yield of glucose were obtained with ZnBr2 ⋅ 4H2O (88 % and 80 %, respectively).

Analysis of the Catalytic Effects Induced by Alkali and Alkaline Earth Metals (AAEMs) on the Pyrolysis of Beech Wood and Corncob

The catalytic pyrolysis of beech wood and corncob was experimentally investigated considering six additives containing alkali and alkaline earth metals (Na2CO3, NaOH, NaCl, KCl, CaCl2 and MgCl2). Thermogravimetric analyses (TGA) were carried out with raw feedstocks and samples impregnated with different concentrations of catalysts. In a bid to better interpret observed trends, measured data were analyzed using an integral kinetic modeling approach considering 14 different reaction models. As highlights, this work showed that cations (Na+, K+, Ca2+, and Mg2+) as well as anions (i.e., CO32−, OH−, and Cl−) influence pyrolysis in selective ways. Alkaline earth metals were proven to be more effective than alkali metals in fostering biomass decomposition, as evidenced by decreases in the characteristic pyrolysis temperatures and activation energies. Furthermore, the results obtained showed that the higher the basicity of the catalyst, the higher its efficiency as well. Increasing the quantities of calcium- and magnesium-based additives finally led to an enhancement of the decomposition process at low temperatures, although a saturation phenomenon was seen for high catalyst concentrations.

Emerging heterogeneous catalysts for biomass conversion: studies of the reaction mechanism

The development of efficient catalysts to break down and convert woody biomass will be a paradigm shift in delivering the global target of sustainable economy and environment via the use of cheap, highly abundant, and renewable carbon resources. However, such development is extremely challenging due to the complexity of lignocellulose, and today most biomass is treated simply as waste. The solution lies in the design of multifunctional catalysts that can place effective control on substrate activation and product selectivity. This is, however, severely hindered by the lack of fundamental understanding of (i) the precise role of active sites, and (ii) the catalyst-substrate chemistry that underpins the catalytic activity. Moreover, active sites alone often cannot deliver the desired selectivity of products, and full understanding of the microenvironment of the active sites is urgently needed. Here, we review key recent advances in the study of reaction mechanisms of biomass conversion over emerging heterogeneous catalysts. These insights will inform the design of future catalytic systems showing improved activity and selectivity.

Thermochemical behavior of tris(2-butoxyethyl) phosphate (TBEP) during co-pyrolysis with biomass

Co-pyrolysis of plastic waste and wood biomass to recover valuable chemicals is a cost-effective waste-recycling technology. However, widely used organophosphate ester additives in plastic, such as tris(2-butoxyethyl) phosphate (TBEP), can form diverse phosphorus (P)-containing species. These P-containing compounds can pose new environmental challenges when the biochar is reused. In this study, a mixture of TBEP and lignin was used to simulate the feedstock of plastic waste and wood biomass, and the thermochemical behavior of TBEP in slow pyrolysis (20 K min(-1)) and fast pyrolysis at 400-600 °C was investigated. The results show that low temperature in fast pyrolysis favors the enrichment of P in char. Up to 76.6% of initial P in the feedstock is retained in the char resulting from 400 °C, while only 51% is retained in the char from 600 °C. Slow pyrolysis favors the formation of stable P species regardless of the temperature; only 7% of the P retained in the char is extractable from char from slow pyrolysis, while 20-40% of P can be extracted from char resulting from fast pyrolysis. The addition of CaCl2 and MgCl2 can significantly increase the fraction of P retained in the char by the formation of Ca, Mg-P compounds. Online TG-FTIR-MS analysis suggests that TBEP undergoes decomposition through different temperature-dependent pathways. The P-containing radicals react with the aromatic rings produced by the pyrolysis of lignin to form Ar-P species, which is an important factor influencing the distribution and stabilization of P in char.

Comparative Performance of Three Magnesium Compounds on Thermal Degradation Behavior of Red Gum Wood

The effect of basic magnesium carbonate (BMC), magnesium hydroxide (MH), and magnesium chloride hydrate (MCH) on thermal degradation of red gum wood was studied using cone calorimetry, Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, and X-ray diffraction (XRD) characterization. The results showed common fire retardation actions of the three compounds by releasing incombustible gas and/or water vapor to dilute combustible gas in the flaming zone, and by converting to MgO, which had a satisfactory protective wall effect on the wood. Individually, BMC absorbed heat from the wood at the pre-decomposition stage and, thus, slowed down wood pyrolysis process. It slightly increased the char yield by charring in both the charring stage and the char calcination stage. MH lost water at about 270°C, close to the temperature at which wood thermally degraded. MH rendered wood char quickly, and the compact char layer impeded further carbonization and burning of inner wood. MCH promoted charring with Mg²⁺ as a Lewis acid, and increased wood char yield. MCH also released Cl· free radical and HCl at 167°C, which easily coordinated with combustion reaction radical, and slowed down, even inhibited, the combustion chain reaction.

Influence of inorganic salts on the primary pyrolysis products of cellulose

Processing bio-oil with the help of currently existing petroleum refinery infrastructure has been considered as a promising alternative to produce sustainable fuels in the future. The feasibility of bio-oil production and upgrading processes depend upon its chemical composition which in turn depends on the biomass composition and the process conditions of the fast pyrolysis reactions. The primary goal of this paper was to investigate the effect of mineral salts including mixtures of salts in the form of switchgrass ash on the chemical speciation resulting from primary pyrolysis reactions of cellulose and to gain an insight of the underlying mechanisms. Various concentrations of inorganic salts (NaCl, KCl, MgCl(2), CaCl(2), Ca(OH)(2), Ca(NO(3))(2), CaCO(3) and CaHPO(4)) and switchgrass ash were impregnated on pure cellulose. These samples were pyrolyzed in a micro-pyrolyzer connected to a GC-MS/FID system. Effects of minerals on the formation of (a) low molecular weight species - formic acid, glycolaldehyde and acetol, (b) furan ring derivatives - 2-furaldehyde and 5-hydroxy methyl furfural and (c) anhydro sugar - levoglucosan are reported exclusively. Further, the effect of reaction temperature ranging from 350 to 600 degrees C on the pyrolysis speciation of pure and ash-doped cellulose is also reported. The pyrolysis speciation revealed the competitive nature of the primary reactions. Mineral salts and higher temperatures accelerated the reactions that led to the formation of low molecular weight species from cellulose as compared to those leading to anhydro sugars.

Zinc chloride mediated degradation of cellulose at 200 degrees C and identification of the products

The effect of ZnCl(2) on the degradation of cellulose was studied to develop conditions to produce useful feedstock chemicals directly from cellulosic biomass. Cellulose containing 0.5 mol of ZnCl(2)/mol of glucose unit of cellulose was found to degrade at 200 degrees C when heated for more than 60 s in air. The major non-gaseous products of the degradation were identified as furfural, 5-hydroxymethylfurfural and levulinic acid. The maximum yields for furfural and 5-hydroxymethylfurfural are 8% and 9%, respectively, based on glucose unit of cellulose. These yields are reached after 150 s of heating at 200 degrees C. A cellulose sample containing 0.5 mol of ZnCl(2)/mol of glucose unit of cellulose and 5.6 equivalents of water when heated for 150 s at 200 degrees C produced levulinic acid as the only product in 6% yield. The ZnCl(2) mediated controlled degradation of cellulose at 200 degrees C is shown to produce useful feedstock chemicals in low yield.