Dehydration Of Cellulose Research Articles

An alternative to petrochemicals: biomass electrovalorization.

Replacing petrochemicals with refined waste biomass as a sustainable chemical source has become an attractive option to lower global carbon emissions. Popular methods of refining lignocellulosic waste biomass use thermochemical processes, which have significant environmental downsides. Using electrochemistry instead would overcome many of these downsides, directly driving chemical reactions with renewable electricity and revolutionizing the way many chemicals are produced today. This review mainly focuses on two furanic platform chemicals that are produced from the dehydration of cellulose, 5-hydroxymethylfurfural and furfural, which can be electrochemically reduced or oxidized to replace fuels and monomers that today are obtained from petrochemicals. Critical parameters such as electrode materials and electrolyte pH are discussed in relation to their influence on conversion efficiency and product distribution.This article is part of the discussion meeting issue 'Green carbon for the chemical industry of the future'.

Facile construction of bio-based high fire-safety cellulose fabrics with well wearing performance

The design of flame-retardant cellulose fabrics suffered from deterioration on wearing performance and environmental issue. Here, we developed facile construction of bio-based high fire-safety cellulose fabrics (lyocell) that exploited the bio-based flame-retardant coating (APD) by adenosine triphosphate (ATP) and dicyandiamide (DCD) via ionic reaction. The rich phosphorus/nitrogen elements of APD enabled the excellent fire safety of APD/Lyocell. Specifically, the APD/Lyocell2 had a higher limiting oxygen index (LOI) value of 29.3 %, a lower peak of heat release rate (PHRR, decreasing by 66.6 %), and a reduced total heat rate (THR, lowered by 56.5 %) with respect to pure lyocell fabrics. Interestingly, the APD/Lyocell2 exhibited well flame-retardant durability via passing the vertical burning test after 100 rubs. The satisfactory flame-retardant behaviors of APD/Lyocell derived from the excellent synergistic effect on the gaseous-solid phases, where APD could release more non-flammable gasses and generate phosphoric acid, polyphosphoric acid, etc. to accelerate itself and cellulose dehydration into char residues during combustion. More importantly, the wearing performance of APD/Lyocell fabrics, such as handle, air permeability and tensile strength, etc. almost remained after treatment. The ease of operation and use of bio-based coating made it a promising option to obtain the practical lyocell fabrics with flame-retardancy.

Hydrolysis–Dehydration of Cellulose: Efficiency of NbZr Catalysts under Batch and Flow Conditions

Niobium oxide supported on ZrO2 and mixed oxide of NbOx-ZrO2 was prepared and characterized. Mechanical treatment was followed by the microwave heating procedure of catalysts with more advanced textural parameters. The amount of Lewis (LAS) and Brønsted (BAS) acid sites rose with the increasing Nb content in the catalysts. The catalytic properties of samples of niobia-zirconia (NbZr samples, NbZr catalysts) were studied in a cellulose hydrolysis–dehydration reaction at 453 K under an inert Ar atmosphere in a batch reactor. Glucose and 5-hydroxumethylfurfural (5-HMF) were the major products. The initial reaction rate could be tuned by the density of acid sites on the surface of solid. At a low density of acid sites (0.1–0.3 µmol·m−2), the initial reaction rate had a pronounced inverse correlation. Increasing the LAS/BAS from 0.3 to 2.5 slightly stimulated the formation of the target products. The catalytic properties of NbZr catalysts prepared by microwave treatment were studied in cellulose transformation in a flow set-up. Glucose was found to be the major product. The maximum yield of glucose was observed in the presence of the sample of 17%Nb/ZrO2. Increasing Nb content resulted in the formation of Nb-associated acid centers and, in turn, increasing catalyst acidity and activity.

Phosphorus-modified mesoporous niobium pentoxide catalyst for fast pyrolysis of cellulose to selective production of levoglucosenone

Catalytic fast pyrolysis of biomass/cellulose is a promising way for the production of levoglucosenone (LGO) and other value-added anhydrosugars. Herein, ammonium dihydrogen phosphate (NH4H2PO4) modified mesoporous niobium pentoxide (P-Nb2O5) was first applied to selectively produce LGO. The catalyst had a stable amorphous mesoporous structure with abundant activity species (Nb-O-Nb, Nb-O-P, P-OH, and PO43-), which affected the dehydration and depolymerization reactions of cellulose to alter the competing relationship between levoglucosan (LG) and LGO. Micro-scale pyrolysis experiments demonstrated that the yield of LGO reached 19.6 wt% under the optimized condition (P loading of 50 wt%, pyrolysis temperature of 400 °C, and catalyst-to-cellulose mass ratio of 7). In lab-scale experiments, the highest yield of LGO attained 16.5 wt%, and the catalytic activity could maintain over 80% after five recycles. Overall, the P-Nb2O5 has been proven to be a promising catalyst to produce LGO from cellulose.

Direct Conversion of Cellulose into 5-HMF by Transition-Metal Doped Montmorillonite Catalyst in Water

AbstractCatalysts are very important in the use of cellulose, the main component of biomass, as a raw material for the large-scale production of liquid fuels and chemicals. 5-Hydroxymethylfurfural (HMF) is an extremely important intermediate in the fine chemical industry. HMF can be synthesized by acid-catalyzed dehydration of fructose, glucose, cellulose, or sucrose. The conversion of cellulose to HMF is challenging due to its chemical structure. The objective of the present study was to devise a more facile synthesis method using transition metal-doped montmorillonite catalysts (10Cr-Mnt, 10Cu-Mnt, 10Fe-Mnt, and 10Zn-Mnt) by wet impregnation. Samples were characterized by X-ray powder diffraction, specific surface area, and NH3-TPD analyses. The synthesized catalysts were used for the conversion of cellulose to 5-HMF in an aqueous medium. Among the metals studied, Cr showed the greatest catalytic activity. With the use of this catalyst, efficient conversion of cellulose to 5-HMF was achieved, affording a conversion yield of 93.47% and 5-HMF yield of 9.07% within 6 h at 200°C. The study described here could be useful for the efficient conversion of cellulose into 5-HMF, as well as into other biomass-derived chemicals.

Multifunctional Superamphiphobic Cotton Fabrics with Highly Efficient Flame Retardancy, Self-Cleaning, and Electromagnetic Interference Shielding

Here, a facile method is reported to prepare multifunctional cotton fabrics with high flame retardancy, high electrical conductivity, superamphiphobicity, and high electromagnetic shielding. The cotton fabric surface was first modified with phytic acid (PA), which promoted dehydration and carbonization of cellulose to increase flame retardancy in the process of pyrolysis. Tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) coating with nanospheres as interlayers created hierarchical roughness that facilitated the construction of superamphiphobic surfaces and provided adhesion sites for silver nanoparticles. In addition, the TA-APTES coating improved flame retardancy because the APTES-containing silicon could form silicon carbon layers to isolate heat and oxygen. Subsequently, the surface energy of the composite cotton fabric was reduced by fluorine-containing molecules. The prepared composite cotton fabric exhibited excellent superamphiphobicity with contact angles of 160.3 and 152° for water and olive oil, respectively. The conductivity and EMI shielding efficiency of the prepared composite cotton fabric reached 629.93 S/cm and 76 dB, respectively. Importantly, the composite cotton fabric maintained a relatively stable EMI shielding efficiency even after cyclic bending and abrasion tests. Moreover, the composite cotton fabric possessed a high limiting oxygen index (LOI) of 45.3% and self-extinguishing properties with the peak heat release rate (PHHR) and total heat release (THR) reduced by 73 and 67%, respectively, than the pure cotton fabric, indicating the outstanding flame retardancy.

Effect of H3PO4 and NaOH additives on the Co-carbonization of cellulose and N-containing compounds to produce N-doped chars

N-doped carbons have significant applications in electronics, materials, and as tools for environmental services. However, few studies focus on N-containing compounds’ carbonization strategies to increase char N retention. For this purpose, H3PO4 and NaOH were used as additives during the co-carbonization of cellulose and four N-containing compounds (lysine, melamine, chitosan, and dicyandiamide (DCD)). Thermogravimetric and Py-GC/MS studies showed significant interactions between the N-containing compounds and cellulose with acid and basic additives. In all cases, an increase in char yield was observed. Acid-base treated samples were carbonized in a spoon reactor at 500 °C, and the resulting chars were thoroughly characterized. The maximum char yields were obtained in the presence of H3PO4 due to the impact of this additive on cellulose dehydration. N’s content in the char product varied from 2 to 12 wt. % depending on the N source. N conversion efficiency increases in the presence of H3PO4. In the case of chitosan, we obtained N conversion efficiencies as high as 77 % in acidic conditions. The deconvoluted XPS N 1s spectra showed that each acid-treated char contained a dominant pyrrolic N form, likely due to the acid’s effect on forming furanic compounds. NaOH-treated chars were richer in pyridinic structures. The first step in N-integration to biochar is the Maillard reaction. Carbonyls and amines react to form glycosylamine and the Amadori product. These intermediates form a Schiff’s base of hydroxymethyl furfural in acidic conditions. In basic conditions, reductones are produced. These are important mediators of melanoidins. The melanoidins are subjected to aromatization and polycondensation reactions to form N-containing polyaromatic ring systems at high temperatures.

High-efficiency and durable glycerol-based reactive flame retardants for cotton fabric

A novel efficient and durable glycerol-based reactive flame retardant, ammonium triphosphoric acid glycerol ester, was successfully synthesized. Ammonium triphosphoric acid glycerol ester was grafted onto cotton fabrics through dip-pad-dry-cure technology, and cotton fabrics with excellent and durable flame retardancy were prepared. The limiting oxygen index value of the cotton fabric treated with 20% ammonium triphosphoric acid glycerol ester reached 37.3%, which was maintained at 26.5% after 50 laundry cycles. The treated cotton fabrics were not ignited in the vertical burning tests, much char formed, and still kept their fiber shapes after combustion. The results of X-ray diffraction patterns and Fourier transform infrared spectroscopy showed that the treatment had little detrimental effect on the original structure of the cotton fabrics. Ammonium triphosphoric acid glycerol ester can effectively promote cellulose dehydration into char, and play a flame retardant role in both condensed phase and gas phase. Mechanical property testing shows that the mechanical properties of cotton fabrics treated with 20% ammonium triphosphoric acid glycerol ester are maintained well, and can serve as clothing fabrics and decorative supplies.

Micro-pyrolysis of various lignocellulosic biomasses in molten chloride salts

In fast pyrolysis, the use of molten salts (i.e. eutectic mixtures) has shown potential for improving the heating rates of biomass, which is essential when targeting high bio-liquid yields. Techniques that allow faster screening of suitable eutectic salt mixtures for biomass pyrolysis before scaling up, are thus necessary. To validate a technique for rapid molten salt pyrolysis, micro-scale pyrolysis (py-GC-MS) has been carried out at 350 °C. Different chloride salt compositions (melting point of ∼ 200 °C) were tested in micro-pyrolysis of cellulose, pinewood, wheat straw, and softwood/hardwood Kraft lignin, at biomass to salt ratios from 1 to 20 (wt% biomass/wt% salts). Chloride molten salts pyrolysis highly promoted the depolymerization and dehydration of cellulose resulting mainly in the production of furfural and acetic acid, which are of interest when targeting the production of value-added chemicals. However, some of the eutectic mixtures used were not stable because they hydrolyzed (HCl detection) and volatilized during pyrolysis. Hydrolysis of salts was counteracted partially by adding ZnO, and fully by using less ZnCl2 in the eutectic mixture. On the other hand, the volatilization of salts inside the micro-reactor was suppressed by limiting the time at which the salts were kept at reaction temperatures. It was observed that the salts had a major catalytic effect on the pyrolysis volatiles when compared to those from pure lignocellulosic biomass. Molten salts pyrolysis of Lignoboost Kraft lignin selectively produced guaiacol and syringol, whereas pinewood and wheat straw, like cellulose, resulted mostly in the production of furfural and acetic acid. Overall, the yield of volatiles from all lignocellulosic feedstock was less in the presence of chloride molten salts, which indicated that the salts favored the production of char and/or non-condensable gases, instead of volatiles.

Perspective on the disposal of PVC artificial leather via pyrolysis: Thermodynamics, kinetics, synergistic effects and reaction mechanism

With the massive production and discard of PVC artificial leather, it is urgently needed to find an efficient and environment-friendly method to dispose of this material made from PVC and blended cloth (BC). As a widely accepted way to dispose of municipal solid waste, pyrolysis was chosen for this study. The pyrolysis experiments of PVC, BC, and their mixture were conducted to characterize PVC artificial leather’s pyrolysis behavior and product characteristics. TG-FTIR and kinetics analysis showed the strong synergistic effect between PVC and cellulose in BC occurred at 240 °C – 314 °C, resulting in cellulose dehydration and aromatization. An exceptionally high tar yield of 54.96 wt% was obtained by fast pyrolysis of the mixture at 500 °C. GC–MS analysis of tar proved BC consisted of cellulose, PET, and PA. The high tar yield of co-pyrolysis came from the synergistic effects of PVC on cellulose and PET, both of which formed terephthalic acid, di(2-chloroethyl) ester (TADE). At 500 °C, the tar of the mixture mainly contained TADE (18.72 wt%), terephthalic acid (18.56 wt%), and aromatics (19.04 wt%). The co-pyrolysis interaction mechanism at 500 °C was deduced. Our study could provide theoretical guidance for recycling PVC artificial leather waste.

Toward Economical and Sustainable Production of Renewable Plastic: Integrative System-Level Analyses.

2,5-Furandicarboxylic acid (FDCA) is one of the promising renewable plastic monomers enabling to address several environmental issues, instead of petroleum-based terephthalic acid (TPA). In this study, an integrative process for the co-production of FDCA and furfural as well as activated carbon was developed, and the economic feasibility and environmental sustainability for the proposed process were evaluated. In the proposed process, there were major four catalytic conversion reactions: (1) hydrolysis of biomass to its derivatives (cellulose, hemicellulose, and lignin), (2) dehydration of hemicellulose to furfural, (3) dehydration of cellulose to 5-hydroxymethylfurfural (HMF), and (4) successive oxidation of HMF to FDCA. Particularly, a heat exchanger network coupled with a heat pump was established to minimize the utility consumption, thereby reducing 72 % of the heating requirement. Techno-economic analysis revealed that the minimum selling price of FDCA was $1380 ton-1 , which is comparable to that of petroleum-based TPA ($1445 ton-1 ). Uncertainty analysis using the Monte Carlo simulation method was employed to quantify the risk associated with the unforeseen market condition. From the life-cycle assessment, we observed that the proposed process is more environmentally sustainable than conventional TPA production in terms of climate change and fossil depletion metrics.

Energy Densification of Biomass-Derived Furfurals to Furanic Biofuels by Catalytic Hydrogenation and Hydrodeoxygenation Reactions

The concomitant hydrolysis and dehydration of biomass-derived cellulose and hemicellulose to furfural (FUR) and 5-(hydroxymethyl)furfural (HMF) under acid catalysis allows a dramatic reduction in the oxygen content of the parent sugar molecules with a 100% carbon economy. However, most applications of FUR or HMF necessitate synthetic modifications. Catalytic hydrogenation and hydrogenolysis have been recognized as efficient strategies for the selective deoxygenation and energy densification of biomass-derived furfurals generating water as the sole byproduct. Efficient and eco-friendly catalysts have been developed for the selective hydrogenation of furfurals affording renewable furanic compounds such as 2-methylfuran, 2,5-dimethylfuran and 2-methyltetrahydrofuran with potential applications as biofuel, solvent and chemical feedstock. Hydrogen gas or hydrogen donor molecules, required for the above processes, can also be renewably obtained from biomass using catalytic processes, enabling a circular economy. In this review, the recent developments in the energy densification of furfurals to furanic compounds of commercial significance are elaborated, emphasizing the role of catalyst and the reaction parameters employed. Critical discussion on sourcing hydrogen gas required for the processes, using hydrogen donor solvents, catalyst design and the potential markets of furanic intermediates have been made. Critical evaluations of the accomplishments and challenges in this field are also provided.

Evolution of carbon nanostructure during pyrolysis of homogeneous chitosan-cellulose composite fibers

Chitosan-cellulose composite fibers spun using a Lyocell technology are characterized by a homogeneous distribution and a close packing of the two biopolymers inside the fibrous matrix. Due to the intimate contact of cellulose and chitosan, synergistic effects can be observed during the pyrolysis of the composite fibers. In this study, the catalytic role of chitosan in altering the cellulose pyrolysis pathway in the composite fibers at moderate treatment temperatures up to 900 °C is confirmed. Analyses of the evolved gases during pyrolysis revealed that chitosan promoted cellulose dehydration and substantially decreased the formation of levoglucosan, explaining the higher char yield. The enhanced dehydration reaction is associated with the formation of intermolecular crosslinks due to the incorporation of nitrogen from chitosan in the resulting carbon structures. Nitrogen could also contribute to the in-plane disorder in the aromatic clusters when the pyrolysis is carried out at 500–700 °C, although the in-plane disorder is less noticeable from 700 to 900 °C. Nevertheless, the size of the aromatic cluster continues to grow when the composite fibers are pyrolyzed in a temperature range of 500–900 °C.

Kinetic Study of Paper Waste Thermal Degradation

Paper waste generation has been rising in the past decades, with a large amount being landfilled. These paper wastes can be great energy sources after thermal treatment since they are considered carbon neutral. These wastes contain mainly cellulose, hemicellulose, lignin, and some minerals. The thermal decomposition of cellulose, hemicellulose, and lignin have been extensively studied, however, the knowledge of thermal degradation of paper wastes at lower temperatures, which are more practical for industrial applications are still lacking. In this study, paper wastes have been characterized and thermogravimetric analyses were performed from 200°C to 400°C and the char produced were analyzed by nuclear magnetic resonance (NMR) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. Two kinetic approaches were taken while developing the kinetic model of paper waste thermal degradation: (i) reconstructing the TGA results of paper waste thermal degradation by an additive law of the degradation of cellulose, hemicellulose and lignin; (ii) considering paper waste as one material and develop a multi-step consecutive reaction mechanism that focuses on solid products at different temperatures. It was observed that there are potential interactions between cellulose, hemicellulose and lignin during paper waste degradation. Therefore, the second approach was concluded to be more plausible, and one set of kinetic parameters were determined according to the experimental results at different temperatures. These results provided insights into the degradation kinetic mechanism and solid product distribution of the paper waste. It was found that the first reaction was due to dehydration of cellulose and the 6th and 7th reaction can be attributed to the thermal degradation of lignin. The NMR and FTIR results also validated that the cellulose started degrading at lower temperatures, and lignin degradation became more pronounced at higher temperatures.

Direct catalytic conversion of bagasse fibers to furan building blocks in organic and ionic solvents

The applications of lignocellulosic wastes to produce a wide variety of products, including biochemicals, biomaterials, and biofuels, can be an effective solution for utilizing these valuable waste materials. In this study, the production of furan building blocks from bagasse fibers was investigated by treating unbleached fibers with NMMO, [Bmim]Cl, and TMAH at different temperatures using AlCl3 and CrCl2 as the catalysts. The resulted liquors were extracted with CH2Cl2 to obtain furan rich fraction. Analysis of extracted fractions with GC/MS indicates the production of various furanic compounds due to catalytic solvolysis with different solvents at elevated temperatures. 2(3H)-Furanone and 2-methyl-THF were the main products of catalytic treatment of bagasse fibers with NMMO. Treatment by [Bmim]Cl resulted in 2,5-dihydro furanone as the dominant product at elevated temperatures. Furan carboxylic acid methyl ester and 2,5-furan dicarboxylic acid dimethyl ester were the main TMAH reaction products with unbleached fibers. The results indicate that the type of solvent affects the solvolysis rate and dehydration of cellulose to furanic compounds. Moreover, increasing the temperature led to an increase in the formation of the furanic compounds.Graphical abstract

A new index for hydrochar based on fixed carbon content to predict its structural properties and thermal behavior

Biomass is an important source for the preparation of nanocarbon materials. And hydrothermal carbonization is also used to prepare carbon materials with rich functional groups. In this paper, the correlation between the degree of hydrothermal carbonization and the structure of hydrochar obtained from camellia shell, rice husk and tobacco stem were studied by establishing a mathematical relationship between the fixed carbon index (FCI) and the fiber content, functional group strength, specific surface area, average particle size and initial pyrolysis temperature of hydrochar, respectively. The results showed that the lignin content was linearly increased with the FCI. The decomposition order of biomass was followed by dehydration of cellulose and hemicellulose, demethylation cracking, lignin oxidation, polycondensation of cellulose and hemicellulose products, and lignin cleavage reaction with the increase of FCI. The specific surface area of hydrochar increased linearly from 0.28 m2/g to 25.09 m2/g, while the particle size of hydrogenated carbon decreased more slowly. The initial pyrolysis temperature of hydrochar had the lowest value (125°C–147 °C) when the FCI was around 0.5. Hydrothermal carbonization can reduce the activation energy of hemicellulose and cellulose.

Eco-friendly, efficient and durable fireproof cotton fabric prepared by a feasible phytic acid grafting route

Eco-friendly, efficient fireproof cotton fabrics were prepared by a feasible chemical grafting of phytic acid (PA). The treated cotton fabrics (COTP) exhibited excellent thermal stability and flame resistance with limiting oxygen index (LOI) of 42.5%. Compared with other fireproof cotton fabrics, COTP displayed outstanding washing durability, the LOI maintained at 28.3% after 50 laundering cycles. Vertical burning test and cone calorimetry demonstrated self-extinguishing behavior and significantly improved flame retardancy of COTP. The peak heat release rate and the total heat release of COTP3-90 was notably declined by 65.5 and 71.4%, respectively. Moreover, lower smoke production and release were found with reduction in total smoke production of 12.5% and total smoke rate of 18.8% compared with untreated cotton fabric. The improved flame retardancy of COTP was speculated that PA catalyzed cellulose dehydration and carbonization to facilitate the formation of residual char, reduce the release of flammable gases and heat/mass transfer.

Hydrolysis–dehydration of cellulose to glucose and 5-hydroxymethylfurfural over Sibunit solid acid carbon catalysts under semi-flow conditions

Glucose is a widely used chemical, food and feedstock. 5-Hydroxymethylfurfural (5-HMF) is one of the platform molecules, which could be applied in chemical and fuel industries. This work presents the possibility of glucose and 5-HMF production from inedible cellulose, which is the main component of renewable plant (wood) biomass via one-pot hydrolysis–dehydration over solid acid catalysts based on Sibunit carbon material. The catalysts prepared via oxidation with wet air mixture, HNO3, sulfonation by fuming H2SO4 at 80–200 °C or combination of the techniques demonstrated high activity under hydrothermal semi-flow conditions. Dependences of both glucose and 5-HMF formation on catalyst acidity and the nature and amount of surface acid groups are revealed. The total surface acidity but not the chemical nature of the groups is responsible for effective cellulose hydrolysis to glucose. On the other hand, sulfo groups demonstrate noticeable activity in 5-HMF formation from glucose. Glucose and 5-HMF can be derived from the polysaccharide with yields up to 75 and 10%, respectively.

Dehydration of saccharides to anhydro-sugars in dioxane: effect of reactants, acidic strength and water removal in situ

The dehydration of cellulose in polar aprotic solvents produces high-value anhydro-sugars, opening up a new avenue for the utilization of cellulose. However, there are still some problems that need to be solved. Herein, we selected some carbohydrates (e.g. cellulose, starch, cellobiose, maltose, methyl-β-D-glucopyranoside and methyl-α-D-glucopyranoside) to examine the influence of different glycosidic bonds and substituents on the preparation of levoglucosan (LGA). The results of LGA yields, reaction rate constants and activation energies from different saccharides show that β-glycosidic bond is more vulnerable to break, forming LGA more easily. The activation energies of the latter 4 carbohydrates are 89.9, 104.2, 93.3, 113.6 kJ/mol, respectively. The strength of acid affects the dehydration process of cellulose greatly. These acids whose pKa values are between − 3 and − 2, including p-toluenesulfonic acid, methanesulfonic acid, and sulfuric acid, can achieve the best yields of LGA and levoglucosenone (LGO). Accordingly, those acids with higher pKa value have no catalytic activity, whereas the rate of cellulose degradation using lower pKa valued acids as catalyst is too fast to be efficiently monitored and carbonization is severe. The side reaction of cellulose hydrolysis and the formation of byproducts including 5-hydroxymethylfurfural (HMF) and furfural (FF) could be suppressed effectively through the addition of phosphorus pentoxide as water absorbent into the reaction system. The molar concentration ratio of LGO and (HMF + FF + Glucose) reached 12.04, which is 105% higher than those without water absorbent. This ratio can reach 21.38 in LGA dehydration into LGO process when phosphorus pentoxide was added.

Investigation on the Catalytic Behavior of Alkali Metals and Alkaline Earth Metals on the Biomass Pyrolysis Assisted with Real-Time Monitoring

In this study, the catalytic behavior of alkali metals and alkaline earth metals (AAEMs) on the pyrolysis of lignocellulosic biomass was investigated, assisted with the online monitoring of synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Rice husk was pretreated by acid washing and AAEMs (Na+, K+, Ca2+, Mg2+) infusion before pyrolysis. Py–GC/MS and Py–SVUV-PIMS analysis were conducted at 550 °C. The effects of AAEMs on the distribution and the time-evolution of pyrolysis products were comprehensively discussed. With the catalysis of alkali metals, the reaction process was promoted while the duration of the whole pyrolysis process was shortened. The fragmentation followed by ring-fission of sugar units was enhanced, resulting in an increase of aldehyde, ketones, and acids. The ether bond fracture in lignin and the secondary thermal cracking of big molecule phenolics were enhanced, resulting in an increase of phenolics. Phenol and m-cresol were found partly formed by the secondary decomposition of bigger phenolic molecules or oligomers in the late pyrolysis stage. Compared with alkali metals, alkali earth metals have stronger Lewis acidity, which are more conducive to the dehydration of cellulose to form anhydrosugars as well as the secondary dehydration conversion of anhydrosugars to form other dehydrated products. Under the catalysis of alkali earth metals, most of the furfural is generated by the decomposition of hemicellulose in the early pyrolysis stage and a small part came from the secondary conversion of anhydrosugars in the late pyrolysis stage. The dehydration capacity of alkali earth metals induced the repolymerization between phenolic products, resulting in a decrease of the yield of phenolics products.