Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 1: Experiments and development of a mechanistic model

New Perspectives into Cellulose Fast Pyrolysis Kinetics Using a Py-GC × GC-FID/MS System

Cellulose pyrolysis is reportedly influenced by factors such as sample size, crystallinity, or different morphologies. However, there seems to be a lack of understanding of the mechanistic details that explain the observed differences in the pyrolysis yields. This study aims to investigate the influence of particle size and crystallinity of cellulose by performing pyrolysis reactions at temperatures of 673–873 K using a micropyrolyzer apparatus coupled to a GC × GC-FID/TOF-MS and a customized GC-TCD. Over 60 product species have been identified and quantified for the first time, including water. Crystalline cellulose with an average particle size of 30–50 × 10^–6 m produced 50–60 wt % levoglucosan. Predominantly amorphous cellulose with an average particle size of 10–20 × 10^–6 m resulted in remarkably low yields (10–15 wt %) of levoglucosan complemented by higher yields of water and glycolaldehyde. A detailed kinetic model for cellulose pyrolysis was used to obtain mechanistic insights into the different pyrolysis product compositions. The kinetics of the mid-chain dehydration and fragmentation reactions strongly influence the total yields of low-molecular weight products (LMWPs) and are affected by cellulose chain arrangement. Levoglucosan yields are very sensitive to the activation of parallel cellulose decomposition reactions. This can be attributed to the mid-chain reactions forming smaller chains with the levoglucosan ends, which remain in the solid phase and react further to form LMWPs. Direct quantification of water helped to improve the description of the dehydration, giving further indications of the dominant role of mid-chain reaction pathways in amorphous cellulose pyrolysis.

Heat-induced conversion of multiscale molecular structure of natural food nutrients: A review

Thermal process is the most important way of treating foods. Heat energy inputted into the natural food system induces the depolymerization of multi-scale structures of matrix, and causes the intramolecular and intermolecular interactions of different nutrients. It attacks and breaks the original polymeric molecule structures and the functional properties of macronutrients such as carbohydrates, proteins and lipids. Micronutrients such as vitamins and other novel functional ingredients are also thermally converted. The heat-induced conversions of nutrients are slightly or totally with discrepancy in simple-, simulated- and real-food systems, respectively. Thus, this review aims to extensively summarize the heat-induced structural characteristics, thermal conversion pathways and pyrolysis mechanism of nutrients both in simple and complex food matrices. The structural change of each nutrient and its thermal reaction kinetics depend on the molecule structure and polymeric characteristic of the unit substances in the system.

Investigation of the relevance between biomass pyrolysis polygeneration and washing pretreatment under different severities: Water, dilute acid solution and aqueous phase bio-oil

Washing pretreatments of rice straw were performed using three different solutions, namely water, dilute hydrochloric acid solution (HCl solution, pH = 2.9), and aqueous phase bio-oil (APBO, pH = 2.9). The raw and pretreated samples were pyrolyzed at 550 °C in a fixed bed reactor. Results showed that among the three pretreatments, washing with APBO had the highest removal efficiency of alkali metal and alkaline earth metals (AAEMs). Among the pyrolysis products, bio-oil from APBO washed sample had the highest mass, energy, and carbon yields, lowest water content of 36.9%, highest HHV of 17.2 MJ/kg, and highest relative content of anhydrosugars of 31.2%. Its biochar had the lowest ash content of 27.3% and highest specific surface area of 98.6 m²/g, and its non-condensable gases had the highest HHV of 11.9 MJ/m³. Therefore, APBO washing was effective in improving the quality of biomass and its subsequent pyrolysis products.

Mechanistic investigation of CO generation by pyrolysis of furan and its main derivatives

A large amount of furan and its derivatives are contained in the biomass pyrolysis products, which mainly lead to the formation of combustible CO with an increase in the pyrolysis temperature; in this study, to illuminate the reaction mechanisms involved in the evolution of CO during the pyrolysis of furan and its main derivatives, quantum chemical theory has been adopted with the GGA-RPBE method, and nine possible reaction pathways have been investigated for the pyrolysis of furan, furfural (FF), furfuryl alcohol (FA) and 5-hydroxymethylfurfural (5-HMF) to generate CO. According to the calculation results, the optimal path for the pyrolysis of furan and its main derivatives to generate CO is as follows: at first, a ring opening reaction of furan occurs to form an aldehyde group, and then, decarbonylation occurs to form CO. Furthermore, the side chain functional groups on the furan ring can promote the ring opening reaction of the furan ring. In addition, the reaction energy barriers of the rate-determining step for the pyrolysis of furan, furfural, furfuryl alcohol and 5-hydroxymethylfurfural (5-HMF) to form CO have been determined as 343 kJ mol⁻¹, 330 kJ mol⁻¹, 317 kJ mol⁻¹ and 363 kJ mol⁻¹, respectively.

Quantum chemical theory has been used to study the furan and its derivatives pyrolysis reaction, nine possible reaction pathways has been studied. Results show that decarbonylation of CO after ring opening is easier than direct decarbonylation.

Detailed kinetics of substituted phenolic species in pyrolysis bio-oils

A comprehensive kinetic model for the pyrolysis and combustion of substituted phenolic species, key components of fast pyrolysis bio-oils.

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

Biomass pyrolysis by solid acid catalysts is one of many promising technologies for sustainable production of hydrocarbon liquid fuels and value-added chemicals, but these complex chemical transformations are still poorly understood. A series of well-defined model SiO₂ -supported alumina catalysts were synthesized and molecularly characterized, under dehydrated conditions and during biomass pyrolysis, with the aim of establishing fundamental catalyst structure-activity/selectivity relationships. The nature and corresponding acidity of the supported AlO_x nanostructures on SiO₂ were determined with ²⁷ Al/¹ H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations. Operando time-resolved IR-Raman-MS spectroscopy studies revealed the molecular transformations taking place during biomass pyrolysis. The molecular transformations during biomass pyrolysis depended on both the domain size of the AlO_x cluster and molecular nature of the biomass feedstock. These new insights allowed the establishment of fundamental structure-activity/selectivity relationships during biomass pyrolysis.