Pyrolysis and Combustion of Cellulosic Materials

Saccharides as Particulate Matter Tracers of Biomass Burning: A Review

The adverse effects of atmospheric particulate matter (PM) on health and ecosystems, as well as on meteorology and climate change, are well known to the scientific community. It is therefore undeniable that a good understanding of the sources of PM is crucial for effective control of emissions and to protect public health. One of the major contributions to atmospheric PM is biomass burning, a practice used both in agriculture and home heating, which can be traced and identified by analyzing sugars emitted from the combustion of cellulose and hemicellulose that make up biomass. In this review comparing almost 200 selected articles, we highlight the most recent studies that broaden such category of tracers, covering research publications on residential wood combustions, open-fire or combustion chamber burnings and ambient PM in different regions of Asia, America and Europe. The purpose of the present work is to collect data in the literature that indicate a direct correspondence between biomass burning and saccharides emitted into the atmosphere with regard to distinguishing common sugars attributed to biomass burning from those that have co-causes of issue. In this paper, we provide a list of 24 compounds, including those most commonly recognized as biomass burning tracers (i.e., levoglucosan, mannosan and galactosan), from which it emerges that monosaccharide anhydrides, sugar alcohols and primary sugars have been widely reported as organic tracers for biomass combustion, although it has also been shown that emissions of these compounds depend not only on combustion characteristics and equipment but also on fuel type, combustion quality and weather conditions. Although it appears that it is currently not possible to define a single compound as a universal indicator of biomass combustion, this review provides a valuable tool for the collection of information in the literature and identifies analytes that can lead to the determination of patterns for the distribution between PM generated by biomass combustion.

Combination of Pre- and Post-Mercerization Processes for Cotton Fabric

The dyeing process commonly deteriorates the luster of pre-mercerized cotton fabric, so post-mercerization processes are regularly applied to compensate for this. Herein, the influence of combining pre-mercerization with CS (caustic solution) or LA (liquid ammonia) and post-mercerization with CS or LA on the morphological structure, dyeing performance, tensile strength, and stiffness of woven cotton fabric was investigated. The crystallinity index values greatly decreased from 73.12 to 51.25, 58.73, 38.42, and 40.90% after the combined mercerization processes of LA–LA, CS–CS, LA–CS, and CS–LA, respectively. Additionally, the CS–LA- and LA–CS-treated samples exhibited a mixture of cellulose II and cellulose III allomorphs. The combined mercerization processing of cotton fabric resulted in slightly worse thermal stability. The LA and CS pre-mercerization processes increased the dye exhaustion, although the former decreased the dye fixation rate while the latter increased it by 4% for both dyes. The color strength of the dyed cotton fabric increased after both post-mercerization processes. Moreover, the fabric stiffness and mechanical properties showed an increasing trend due to the combined mercerization efforts.

Influence of Sequential Liquid Ammonia and Caustic Mercerization Pre-Treatment on Dyeing Performance of Knit Cotton Fabric

A two-stage sequential pretreatment including caustic mercerization (CM) and liquid ammonia (LA) treatment was applied to investigate the influence on dyeing performance and handle of knit cotton fabric, and the relationship between dye size and dyeing properties. Various techniques were applied to characterize all the treated fabrics. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses of the treated fabrics confirmed that both sequential treatments decreased the crystallinity of cotton fabric more than only the CM or LA treatment. The pattern of cellulose I was transferred to a mixed configuration of cellulose II and cellulose III after the CM/LA or LA/CM treatment. Thermal performances measured by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) techniques showed that the thermal stability of the treated cotton only marginally decreased. The wicking height increased after the sequential CM/LA treatment, indicating that the hydrophilicity of the fabric increased. The dye absorption and color uniformity were better for the reactive dye with a smaller molecular weight (Reactive Red 2) compared with the one with a larger molecular weight (Reactive Red 195). The total dye fixation efficiency (T%) increased to 72.93% and 73.24% for Reactive Red 2 dyeings of CM/LA- and LA/CM-cotton fabric from 46.75% of the untreated fabric, respectively; the T% increased to 65.33% and 72.27% for Reactive Red 195 dyeings of CM/LA- and LA/CM-cotton fabric from 35.17% of the untreated fabric, respectively. The colorfastness and dye exhaustion and fixation percentages of the samples were enhanced after the treatments. Furthermore, compared to the single CM or LA treatment, the softness handle properties were further improved after the fabrics were sequentially treated by CM/LA. The developed pre-treatment of CM/LA can be used in the textile industry to promote the dyeability, handle, and mechanical properties of knit cotton fabrics.

A Review on Natural Fiber-Reinforced Geopolymer and Cement-Based Composites

The use of ecological materials for building and industrial applications contributes to minimizing the environmental impact of new technologies. In this context, the cement and geopolymer sectors are considering natural fibers as sustainable reinforcement for developing composites. Natural fibers are renewable, biodegradable, and non-toxic, and they exhibit attractive mechanical properties in comparison with their synthetic fiber counterparts. However, their hydrophilic character makes them vulnerable to high volumes of moisture absorption, thus conferring poor wetting with the matrix and weakening the fiber–matrix interface. Therefore, modification and functionalization strategies for natural fibers to tailor interface properties and to improve the durability and mechanical behavior of cement and geopolymer-based composites become highly important. This paper presents a review of the physical, chemical and biological pre-treatments that have been performed on natural fibers, their results and effects on the fiber–matrix interface of cement and geopolymer composites. In addition, the degradation mechanisms of natural fibers used in such composites are discussed. This review finalizes with concluding remarks and recommendations to be addressed through further in-depth studies in the field.

Thermal Biomass Conversion: A Review

In this paper, the most important methods of thermal conversion of biomass, such as: hydrothermal carbonization (180–250 °C), torrefaction (200–300 °C), slow pyrolysis (carbonization) (300–450 °C), fast pyrolysis (500–800 °C), gasification (800–1000 °C), supercritical steam gasification, high temperature steam gasification (>1000 °C) and combustion, were gathered, compared and ranked according to increasing temperature. A comprehensive model of thermal conversion as a function of temperature, pressure and heating rate of biomass has been provided. For the most important, basic process, which is pyrolysis, five mechanisms of thermal decomposition kinetics of its components (lignin, cellulose, hemicellulose) were presented. The most important apparatuses and implementing devices have been provided for all biomass conversion methods excluding combustion. The process of combustion, which is energy recycling, was omitted in this review of biomass thermal conversion methods for two reasons. Firstly, the range of knowledge on combustion is too extensive and there is not enough space in this study to fully discuss it. Secondly, the authors believe that combustion is not an environmentally-friendly method of waste biomass utilization, and, in the case of valuable biomass, it is downright harmful. Chemical compounds contained in biomass, such as biochar, oils and gases, should be recovered and reused instead of being simply burnt—this way, non-renewable fuel consumption can be reduced.

Acid-Catalysed Conversion of Carbohydrates into Furan-Type Molecules in Zinc Chloride Hydrate

Acid-catalysed conversion of biomass, specifically cellulose, holds promise to create value-added, renewable replacements for many petrochemical products. We investigated an unusual acid-catalysed transformation of cellulose and cellobiose in the biphasic solvent system zinc chloride hydrate (ionic liquid)/anisole. Here, furyl hydroxymethyl ketone and furfural are obtained as major products, which are valuable but less commonly formed in high yields in transformations of cellulosic substrates. We explored this chemistry in small-scale model reactions and applied the optimised methods to the conversion of cellulose in bench-scale processes. The optimum reaction system and preferred reaction conditions are defined to select for highly desirable furanoid products in the highest known yields (up to 46 %) directly from cellulose or cellobiose. The method avoids the use of added catalysts: the ionic solvent zinc chloride hydrate possesses the intrinsic acidity required for the hydrolysis and chemical transformation steps. The process involves inexpensive media for the catalytic conversion of cellulose into high-value products under mild processing conditions.

Pyrolysis Kinetic Modelling of Wheat Straw from the Pannonian Region

The pyrolysis/devolatilization is a basic step of thermochemical processes and requires fundamental characterization. In this paper, the kinetic model of pyrolysis is specified as a one-step global reaction. This type of reaction is used to describe the thermal degradation of wheat straw samples by measuring rates of mass loss of solid matter at a linear increase in temperature. The mentioned experiments were carried out using a derivatograph in an open-air environment. The influence of different factors was investigated, such as particle size, humidity levels, and the heating rate in the kinetics of devolatilization. As the measured values of mass loss and temperature functions transform in Arrhenius coordinates, the results are shown in the form of saddle curves. Such characteristics cannot be approximated with one equation in the form of Arrhenius law. For use in numerical applications, transformed functions can be approximated by linear regression for three separate intervals. Analysis of measurement resulting in granulation and moisture content variations shows that these factors have no significant influence. Tests of heating rate variations confirm the significance of this impact, especially in warmer regions. The influence of this factor should be more precisely investigated as a general variable, which should be the topic of further experiments.

Kinetic analysis of cellulose pyrolysis: a short review

Since the 1950s, cellulose pyrolysis has been the subject of intense study, with kinetic analyses forming a major part of these studies. They represent useful tools for a better understanding of the physicochemical process and for the proper design of industrial pyrolysis units. Until recently, the methods most frequently used in these analyses were based on model-fitting, i.e. the fitting of the experimental data to a number of mathematical models. Nowadays, other methods, so-called “model-free” methods, are considered to be more suited. These are based on the principle that, at constant conversion, the reaction rate depends only on temperature. In its first part, this short review presents the particularities and drawbacks of the traditional model-fitting models. Subsequently, several main contributions in this field are listed and discussed. Finally, the more suited “model-free” (isoconversional) methods are explained and several main studies presented, as well as a comparison of this method with the model-fitting ones.

Levoglucosan formation from crystalline cellulose: importance of a hydrogen bonding network in the reaction

Levoglucosan (1,6-anhydro-β-D-glucopyranose) formation by the thermal degradation of native cellulose was investigated by MP4(SDQ)//DFT(B3LYP) and DFT(M06-2X)//DFT(B3LYP) level computations. The computational results of dimer models lead to the conclusion that the degradation occurs by a concerted mechanism similar to the degradation of methyl β-D-glucoside reported in our previous study. One-chain models of glucose hexamer, in which the interchain hydrogen bonds of real cellulose crystals are absent, do not exhibit the correct reaction behavior of levoglucosan formation; for instance, the activation enthalpy (Ea =≈38 kcal mol(-1) ) is considerably underestimated compared to the experimental value (48-60 kcal mol(-1) ). This problem is solved with the use of two-chain models that contain interchain hydrogen bonds. The theoretical study of this model clearly shows that the degradation of the internal glucosyl residue leads to the formation of a levoglucosan precursor at the chain end and levoglucosan is selectively formed from this levoglucosan end. The calculated Ea (56-62 kcal mol(-1) ) agrees well with the experimental value. The computational results of three-chain models indicate that this degradation occurs selectively on the crystalline surface. All these computational results provide a comprehensive understanding of several experimental facts, the mechanisms of which have not yet been elucidated.

Optimization of microwave-assisted extraction of carbohydrates from industrial waste of corn starch production using response surface methodology

Microwave-assisted extraction (MAE) was applied for production of carbohydrates mainly consisting of arabinoxylan from corn pericarp which is an industrial waste of corn starch production by using hot compressed water as a solvent. The solubilization rate increased with increase in heating temperature and reached 75.2% at 220 °C. The main extracted materials were carbohydrates consist of glucose, xylose and arabinose indicating solubilization of starch and hemicellulose, while residues were composed of cellulose. Four independent variables (heating temperature, come-up time, heating time and solid to liquid ratio) were optimized for maximizing the carbohydrates yield using the response surface methodology including fractional factorial design, the path of steepest ascent and central composite design. The optimized condition was as follows; heating temperature 176.5 °C, come-up time 2 min, heating time 16 min and solid to liquid ratio 1/20 (g/mL), respectively. The maximal yield attained 70.8% of carbohydrates with predominant production of xylo-oligosaccharides.

Structural and physico-chemical characterization of hemicelluloses from ultrasound-assisted extractions of partially delignified fast-growing poplar wood through organic solvent and alkaline solutions

One organic and three alkaline hemicellulosic fractions were isolated by an ultrasound-assisted extraction which partially delignified the fast-growing poplar wood. Successive treatments were conducted with dimethyl sulfoxide under ultrasonic irradiation at 570W, 25 degrees C for 30min, 70% ethanol containing 1% NaOH, 3% NaOH and 6% NaOH at 75 degrees C for 3h, respectively. The four hemicellulosic fractions obtained were comparatively studied by sugar analysis, alkaline nitrobenzene oxidation of bound lignin, GPC, FT-IR, 1D and 2D NMR spectroscopy as well as TGA and DTA. The results showed that the ultrasonic treatment and sequential extractions with three different concentrations of NaOH led to a release of 75.5% of the original hemicelluloses and 96.2% of the lignin. All four purified hemicellulose fractions contained relatively low amounts of associated lignin, ranging between 0.96 and 3.10%. In addition, the hemicellulosic fraction H(4) isolated with 6% NaOH is formed by a linear backbone of four (beta-1-->4)-xylopyranosyl residues and at least one of the xylose residues is monosubstituted at C-2 by a 4-O-methylglucuronic acid, giving a typical ratio of 4-O-methyl glucuronic acid to Xyl of 1 to 4.

Lignocellulosic materials in building elements. Part III. Recycled newsprint waste paper in manufacturing light‐weight agro‐gypsum panels

Describes the novel utilization of waste newsprint paper as inexpensive agro‐fibers for production of lightweight building panels. Thermal gravimetric analysis of treated news paper fibers was studied as a method for testing fire retardancy of agro‐fibers in light building panels. The activation energy of degradation stages was evaluated by applying the Coats and Redfern method of analysis. Results showed that the treatment of newsprint waste with 6 per cent sodium silicate also improved fire retardancy in addition to improving the compressive strength of the produced panels, with the reduction in the bulk density to ∼28.6 per cent compared with gypsum panel. Such treatment gives the produced panels a relatively low water absorption property compared with those produced by other treatments.

Gas chromatography/mass spectrometric characterisation of pyrolysis/silylation products of glucose and cellulose

The mass spectra of trimethylsilyl (TMS) derivatives of possible hydroxylated pyrolysis products of glucose and cellulose were recorded by gas chromatography/mass spectrometry (GC/MS) analyses of TMS derivatives of 2-hydroxymethylfuran, 2-hydroxy-1-methyl-1-cyclopenten-3-one, 5-(hydroxymethyl)-2-furaldehyde, 5-methyl-2-furoic acid, 4-hydroxy-6-methyl-(2H)-pyran-2-one, 2-methyl-3-hydroxy-(4H)-pyran-4-one (maltol) and 1,6-anhydro-beta-D-glucopyranose (levoglucosan, LG). Also, 2-O-TMS-1,6-anhydro-beta-D-glucopyranose, 4-O-TMS-1,6-anhydro-beta-D-glucopyranose and 2,4-bis-O-TMS-1,6-anhydro-beta-D-glucopyranose were identified from the interpretation of electron impact and chemical ionisation mass spectra of products obtained from partially silylated levoglucosan solutions, together with information from the known relative reactivities of OH groups of anhydrosugars. A peak at m/z 116 was found to be characteristic of the mass spectra of partially silylated anhydrosugars, and is absent from the mass spectra of the persilylated species. Pyrolysis/GC/MS of cellulose in the presence of hexamethyldisilazane afforded principally the 2- and 4-TMS ethers and the 2,4-bis-TMS ether of LG, whereas the 5-TMS-oxymethyl-2-furaldehyde was a prominent pyrolysis/silylation product of glucose. The mass spectra of other relevant pyrolysis/silylation products are presented.