Recent trends and developments in pyrolysis-gas chromatography: review

Pyrolysis-gas chromatography (Py-GC) has become well established as a simple, quick and reliable analytical technique for a range of applications including the analysis of polymeric materials. Recent developments in Py-GC technology and instrumentation include laser pyrolysis and non-discriminating pyrolysis. Progress has also been made in the detection of low level polymer additives with the use of novel Py-GC devices. Furthermore, it has been predicted that future advances in separation technology such as the use of comprehensive two-dimensional gas chromatography will further enhance the analytical scope of Py-GC

Understanding the thermochemical conversion of biomass to overcome biomass recalcitrance

Thermochemical conversion technologies are promising pathways for producing environmentally benign, sustainable biofuels and value-added chemicals from biomass. However, reaction pathways and chemistry behind these technologies such as pyrolysis and solvolysis of biomass are very complex. Contributing to the complexity are the many factors that could affect the reaction mechanisms. This research focuses on an external effect on thermal decomposition and internal reaction chemistry to provide an insight into the biomass decomposition for better performance. First, the effect of low concentration of oxygen in sweep gas during biomass pyrolysis in fluidized bed was investigated for practical purpose. It was found that the partial oxidative pyrolysis can increase the yield of pyrolytic sugars. A continuation of the study was performed to produce sugar-rich bio-oil from the biomass passivation of alkali and alkaline earth metals. Partial oxidative pyrolysis of passivated biomass produced approximately 21 wt% hydrolyzable sugars in bio-oil. Additionally, partial oxidative pyrolysis also prevented clogging within the reactor by reducing char agglomerations ensuring continuous operation. Second, solvolytic conversion of lignin was studied using a micro reactor in the presence of a hydrogen donor solvent. The results showed that hydrogen donor solvents were effective in converting lignin into alkylphenols. It was found that a hydrogen donor solvent could suppress repolymerization reactions by stabilizing the primary products to alkyl-substituted phenols. Pyrolysis mechanisms of lignin were further studied using methoxy substituted α-O-4 dimeric model compounds. Pyrolysis of aryl-ether linkage primarily involved homolytic cleavage. It was discovered that methoxy group substitution on the aromatic ring increases the reactivity toward C - O homolysis. Additionally, free radicals in the condensed phase of the pyrolysis products were detected by electron paramagnetic resonance spectroscopy, providing information on the presence of oxygen-centered phenoxy and carbon-centered benzyl radicals. Furthermore, methoxy group substitution was revealed to promote oligomerization reactions to form large molecular weight compounds. Lastly, a quantitative investigation of free radicals in bio-oil and their potential role in condensed-phase polymerization was conducted. It was confirmed that both lignin and cellulose pyrolysis involve homolytic cleavage generating free radicals. Lignin bio-oil fractions contained a significant amount of radicals, which were found to be stable species due to highly delocalized in a pi system

Production of renewable chemicals and energy from waste biomass

With the rapid growth of world population and developing industries, the production of wastes has dramatically increased in the past decades. Due to environmental concerns and limited landfill space, the disposal of wastes has been subjected to strict regulations. Beneficial uses of wastes such as recycling/reuse, land applications, energy production, and resource recovery have been advocated greatly. This thesis presents the utilization of two types of solid waste: lignin and waste paper/plastic. Through thermochemical conversion, wastes can be converted to chemicals and energy. This aims at reducing the energy dependence on fossil fuels while achieving effective waste management. Lignin is the main byproduct from pulping and paper industry and is usually combusted to provide the heat for the pulping process. However, its poly-methoxylated phenylpropane structure makes lignin a potential natural source for phenolic and aromatic chemicals. Obtaining high yield of chemicals from lignin is a challenge due to its complex structure and unreactive nature. In this thesis, the pyrolysis of lignin extracted from maple wood and a β-O-4 oligomeric lignin model compound is presented. Advanced analytical techniques were utilized to obtain a comprehensive characterization of pyrolysis products. The results show that carbon concentrated solid char is the major pyrolysis product for both extracted lignin and β-O-4 oligomeric lignin model compound. Reaction chemistry is proposed based on a free radical reaction mechanism. Additionally, a new coal combustion technology utilizing Re-Engineered FeedstockTM (ReEF), was evaluated for pulverized coal combustion emission control. The ReEF consists of non-recyclable fibers/plastics and commercialized flue gas desulfurization (FGD) sorbent. This novel feedstock is combusted to produce energy while capturing the sulfur dioxide generated during coal combustion. It is demonstrated that up to 85% of sulfur dioxide reduction was achieved when co-firing coal with ReEF in a lab scale fluidized bed combustor. Through the kinetics study, combustion of waste fibers/plastics accelerates the sorbent sintering in ReEF which leads to a lower total sulfur uptake compared with pure FGD sorbent. However, the time of maximum reaction rate of sorbent sulfation is delayed in ReEF which indicates the ReEF can prevent the sorbent from early time sulfation. The application of ReEF will have positive impacts on the environment and society by supplementing coal combustion, reducing greenhouse gas emissions, and minimizing wastes that will go to landfill

Essential scientific mapping of the value chain of thermochemical converted second-generation bio-fuels

A profound and comprehensive comparison of thermochemical techniques for second-generation biofuel production from technical, economic, commercial, and environmental perspectives.</p

Where does the Oxygen go? – Pathways and Partitioning in Autothermal Pyrolysis

Autothermal fast pyrolysis (AFP), a variation of fast pyrolysis (FP) admitting a small amount of oxygen to provide process heat, has notable merit as a biomass-to-biofuels conversion process. As a result of heat transfer and product collection advantages over standard non-oxidative FP, it has the potential to generate a higher quality product in a more economically competitive manner. Initial investigation and process development efforts, first led by Kwang Ho Kim, and Joseph Polin, respectively, at the Bioeconomy Institute, generated many further questions about the process. One notable question was “where does the energy come from to support autothermal pyrolysis” – to which the obvious answer is exothermic reactions, but beyond that is not well understood. This work explored the chemistry underlying autothermal (partial oxidative) pyrolysis, as distinguished from standard non-oxidative pyrolysis of whole biomass. A critical literature review was carried out to develop a theoretical mechanistic framework which was then applied to a process base case, and experimentally tested. Key findings of the literature review included reaction mechanisms for the oxidation of: lignin interunit linkages, lignin monomers (and their functionalities), cellulose dimers and monomers, and hemicellulose units and functionalities. As discussed in the cellulose oxidation section, oxidation could occur by means of assisting glycosidic bond hydrolysis (either at a chain end (unzipping) or mid-chain (cracking)), effectively increasing levoglucosan yield, or by oxidation of ring functionalities. If cellulose’s substituents were to measurably react with Reactive Oxygen Species (ROS), the C6 primary alcohol would be the likely candidate, oxidizing to a C6 aldehyde or carboxylic acid, yet theoretically possible for ring-hydroxyls to oxidize. Similarly to celluloses, hemicellulose might be oxidized by four means; polymer-end-wise chain scission initiation (primary peeling), mid-chain scission, end-chain unit degradation (secondary peeling), or side-chain oxidation. Because of its branched and heterogeneous nature, and tendencies for decomposition of monomeric units following complete depolymerization during non-oxidative pyrolysis, fewer hemicellulose hexoses and pentoses would likely be recovered during oxidative pyrolysis. Lignin, also structurally diverse, has many possible routes for oxidation. From linkage studies, it is apparent that oxidation of the β- or γ-hydroxyl (in the case of a β-O-4’ linkage), or the α-hydroxyl (for α-O-4’ linkages) greatly weakens ether linkages, making susceptible to cleavage. Lignin’s phenolic substituents are prone to oxidation to aldehydes, carboxylic acids and ketones. Those side chains with reactive double bonds could be oxidatively cleaved or encourage a concerted decomposition reaction. Because products of oxidation can be further oxidized themselves, care must be taken in extrapolating out composition trends to scaled-operation. Even considering these routes which would effect a change in product composition, the most significant effects might come simply due to improved reaction conditions (heat transfer, heating rate, and ventilation (due to greater gas production)). Experimental work identified reactor limitations, and explored partial oxidation of a number of model compounds, representative of cellulose, hemicellulose, as well as lignin monomers and linkages. It is important to note that the findings of the micropyrolyzer studies are not directly applicable to continuous reactor chemistry due to the fundamentally different hydrodynamics and heat transfer. Additionally, biopolymer characteristics and interaction effects are not accounted for in the monomer and dimer model compound studies, as would be seen with whole biomass

Origin of compositional differences in organic matter abundance and oil potential of cherty and clayey Cenomanian black levels in the Umbria-Marche basin (Italy).

International audienceRock-Eval pyrolysis of a large set of Cenomanian samples, collected from the black levels (clayey, cherty and mixed) in three sections of the Umbria-Marche basin, showed large differences in organic matter (OM) quantity and quality. The chert samples systematically exhibit much lower TOC contents, markedly lower HI and higher OI. This reflects the extensive oxidative destruction of the initial kerogen that occurred upon the chertification of some clayey sediments. A comparative study, by a combination of microscopic, spectroscopic and pyrolytic methods, was performed on kerogens of the chert and clay layers of a representative mixed level. The various fractions of the initial kerogen underwent differential destruction or alteration during chertification, resulting in (i) relative enrichments of microfossils and woody debris although lignin was altered by demethoxylation and (ii) extensive destruction of the amorphous fraction while it remained predominant. The amorphous fraction retained in the chert kerogen showed large changes in composition related to oxygen incorporation and probably escaped complete destruction owing to oxidative reticulation. The above features account for the pronounced systematic differences in OM abundance and oil potential between the chert and clay layers in the black levels

Hydrogenolysis of lignin in ZnCl₂ and KCl as an inorganic molten salt medium

Lignin can be converted into monomeric products with the aid of molten salt media. Molten zinc chloride (ZnCl₂)/potassium chloride (KCl) mixtures are suitable for this purpose. The application of an eutectic mixture with low melting points leads to similar main products as are obtained by pyrolysis. The hydrogenolysis of an organosolv lignin in molten salts of ZnCl₂/KCl was investigated as a function of reaction temperature, residence time, and lignin concentration, and the composition of liquid products and monophenols was analyzed by gas chromatography-mass spectrometry (GC-MS). The yields can be optimized by the proper selection of the reaction temperature. A longer residence time and higher lignin concentrations lead to increased formation of solid residues and gaseous products. The liquid products mainly consist of substituted phenols derived from lignins. Polymeric products are the result of condensation reactions (i.e., the formation of new C-C linkages in the course of secondary reactions)

Effect of microwave and thermal co-pyrolysis of low rank coal and pine wood on product distributions and char structure

peer-reviewedDirect conversion of a low-rank coal into valuable chemicals or improving its char’s coking value became very demanding goals in coal utilization strategies. In this work, the co-pyrolysis of a low-rank lignite coal and pine wood sawdust biomass blended at a 3:1 coal-to-biomass ratio was investigated along with original coal and biomass samples by microwave assisted and conventional thermal methods at 550℃ under nitrogen and ambient pressure. The carbon structure and its reactivity in generated chars and the product distributions were greatly affected by the applied heating mechanism and the presence of biomass during coal pyrolysis. High gas and low tar yields were observed for all microwave chars in comparison to thermal chars, regardless of composition. The addition of biomass to coal increased the tar yield under both methods and to a higher extent under the microwave. This agrees with the high gas yield and high aromatic-to-aliphatic fraction observed under the microwave and the presence of biomass. The high O/C ratio and low fixed carbon content in a biomass structure relative to coal affect the product distribution during microwave pyrolysis. This could selectively heat the biomass in the sample, remove its polar groups, and convert it into an efficient microwave absorber biochar that can decompose coal efficiently during co-pyrolysis. The aromatic carbon stacking and its ordering in the generated chars were investigated by powder X-ray diffraction, Raman spectroscopy, dielectric property measurements, and electron spin resonance techniques. A synergistic effect was observed upon biomass addition during microwave coal pyrolysis. Electron spin resonance spectroscopy revealed that the microwave coal/biomass char is the most stable char with the lowest free radical concentration. This agrees with the highest IG/Iall band area ratio calculated from Raman analysis revealing a more graphitic nature for carbon in this char. Similarly, the dielectric properties confirmed that the addition of biomass to coal under the microwave has the highest loss tangent, indicating a high graphitic nature compared to pure biochar or coal char