Robert J. Evans

Direct mass-spectrometric studies of the pyrolysis of carbonaceous fuels. III: Primary pyrolysis of lignin

Abstract The primary pyrolysis of lignins derived from different types of biomass and by the major separation methods has been investigated by molecular-beam sampling mass spectrometry. The lignins separated by the steam-explosion and kraft processes have altered pyrolysis characteristics while ball-milled lignins yield nearly the same product slate as observed in native biomass samples. The predominant and first-formed products, as determined by mass spectrometry, appear to be the precursor monomers, coniferyl and sinapyl alcohol. There is a distinct lack of higher-molecular-weight oligomers as is commonly observed in the pyrolysis of other types of natural and synthetic polymers. A group of peaks, with the most predominant being m/z 272, appear at masses greater than the monomer masses, but are significantly below the dimer mass range. A third group of predominant peaks are present at masses lighter than the monomers and consist of methoxyphenols that have double bonds and carbonyl groups in the alkyl side chains that are in conjugation with the aromatic ring, enhancing thermal stability. The results indicate that the thermolysis of the alkyl-aryl ether linkage, which is the major bonding unit in lignin, and the limited availability of transferable hydrogen, are the major factors that lead to the predominance of these products. The observed product distributions are indicative of specific, sterically favored rearrangement reactions, which allow devolatilization from the hydrogen deficient, solid matrix and favor double bond formation in the alkyl side chain of the products. A discussion of possible mechanisms of formation is given based on these results and the results of other workers in lignin pyrolysis.

Catalytic conversion of microalgae and vegetable oils to premium gasoline, with shape-selective zeolites

Abstract A seminal paper by Mobil researchers in 1979 demonstrated that a remarkable range of materials were convertible to a similar, high-octane, aromatic, gasoline product slate when passed over HZSM-5, a medium-pore, shape-selective, acid catalyst. These materials ranged from low molecular weight oxygenates, such as methanol, to high molecular weight latexes and vegetable oils. In this paper, we briefly review the thermochemical conversion options for algal and vegetable lipids, present the potential advantages of the zeolite approach and consider the possibility of converting either the whole algae or vegetable oil seed, or crudely extracted lipids, to a product virtually indepedent of fatty acid composition of the lipid. Experimental data on pyrolysis, and on product slates and yields over H-ZSM5, are shown for rapeseed oil, tripalmitin and algal lipids. The pyrolyzer-catalytic reactor, and the ambient pressure, molecular beam, mass spectrometric analytical sampling system, are shown and briefly described.

Kinetic analysis of the gas-phase pyrolysis of carbohydrates

Cellulose-derived pyrolysis products and selected primary products, 5-hydroxymethyl furfural (5-HMF), levoglucosan and hydroxyacetaldehyde (HAA) were used as starting materials for kinetic studies of gas-phase pyrolysis by using flow tube reactors and product detection with molecular beam mass spectrometry (MBMS). Multivariate data analysis was used to identify major product classes for lumped product kinetic analysis. The methodology employed in this work was verified using ethyl allyl ether (EAE) pyrolysis. Two-step sequential models based on lumped primary, secondary and tertiary products were developed for levoglucosan, 5-HMF and cellulose derived pyrolysis products. A one-step model was developed for HAA. Reaction rates and Arrhenius parameters are presented based on these empirical models.

Hydrogen from biomass: state of the art and research challenges

The report was prepared for the International Energy Agency (IEA) Agreement on the Production and Utilization of Hydrogen, Task 16, Hydrogen from Carbon-Containing Materials. Hydrogens share in the energy market is increasing with the implementation of fuel cell systems and the growing demand for zero-emission fuels. Hydrogen production will need to keep pace with this growing market. In the near term, increased production will likely be met by conventional technologies, such as natural gas reforming. In these processes, the carbon is converted to CO2 and released to the atmosphere. However, with the growing concern about global climate change, alternatives to the atmospheric release of CO2 are being investigated. Sequestration of the CO2 is an option that could provide a viable near-term solution. Reducing the demand on fossil resources remains a significant concern for many nations. Renewable-based processes like solar- or wind-driven electrolysis and photobiological water splitting hold great promise for clean hydrogen production; however, advances must still be made before these technologies can be economically competitive. For the near-and mid-term, generating hydrogen from biomass may be the more practical and viable, renewable and potentially carbon-neutral (or even carbon-negative in conjunction with sequestration) option. Recently, the IEA Hydrogen Agreement launched a new task to bring together international experts to investigate some of these near- and mid-term options for producing hydrogen with reduced environmental impacts. This review of the state of the art of hydrogen production from biomass was prepared to facilitate in the planning of work that should be done to achieve the goal of near-term hydrogen energy systems. The relevant technologies that convert biomass to hydrogen, with emphasis on thermochemical routes are described. In evaluating the viability of the conversion routes, each must be put in the context of the availability of appropriate feedstocks and deployment scenarios that match hydrogen to the local markets. Co-production opportunities are of particular interest for near-term deployment since multiple products improve the economics; however, co-product development is not covered in this report. Biomass has the potential to accelerate the realization of hydrogen as a major fuel of the future. Since biomass is renewable and consumes atmospheric CO2 during growth, it can have a small net CO2 impact compared to fossil fuels. However, hydrogen from biomass has major challenges. There are no completed technology demonstrations. The yield of hydrogen is low from biomass since the hydrogen content in biomass is low to being with (approximately 6% versus 25% for methane) and the energy content is low due to the 40% oxygen content of biomass. Since over half of the hydrogen from biomass comes from splitting water in the steam reforming reaction, the energy content of the feedstock is an inherent limitation of the process . The low yield of hydrogen on a weight basis is misleading since the energy conversion efficiency is high. However, the cost for growing, harvesting, and transporting biomass is high. Thus even with reasonable energy efficiencies, it is not presently economically competitive with natural gas steam reforming for stand-alone hydrogen without the advantage of high-value co-products. Additionally, as with all sources of hydrogen, production from biomass will require appropriate hydrogen storage and utilization systems to be developed and deployed. The report also looked at promising areas for further research and development. The major areas for R,D and D are: feedstock preparation and feeding; gasification gas conditioning; system integration; modular systems development; valuable co-product integration; and larger-scale demonstrations. These are in addition to the challenges for any hydrogen process in storage and utilization technologies.

Two High-Throughput Techniques for Determining Wood Properties as Part of a Molecular Genetics Analysis of Hybrid Poplar and Loblolly Pine

Two new high-through put techniques, computer tomography X-ray densitometry (CT scan) and pyrolysis molecular beam mass spectrometry (pyMBMS), coupled with quantitative trait loci (QTL) analysis, were tested as a means to overcome the time and cost associated with conventional characterization of biomass feedstock components. Applications of these two techniques were evaluated using hybrid poplar for the CT scan and loblolly pine for the pyMBMS. Segregating progeny from hybrid poplar varied in specific gravity, with individual mean estimates ranging from 0.21–0.41. Progeny from loblolly pine varied in lignin, α cellulose, and mannan contents, with individual mean estimates of lignin content ranging from 28.7–33.1%, α cellulose content from 28.8–43.5% and mannan content from 4.2–10.1%. QTL analysis of the loblolly pine data suggested that eleven QTLs were associated with individual feedstock characteristics and that two QTLs for several feedstock components were linked to the same position on the loblolly pine genetic map. Each QTL individually accounted for 7–13% of the total phenotypic variation in associated loblolly pine feedstock components.

The pyrolysis of anisole (C6H5OCH3) using a hyperthermal nozzle

Abstract We have investigated the pyrolysis of anisole (C6H5OCH3), a model compound for methoxy functional groups in lignin. An understanding of the pyrolysis of this simple compound can provide valuable insight into the mechanisms for the thermal decomposition of biomass. Our emphasis in this study is the formation of polynuclear aromatic hydrocarbons (PAHs) and in particular we investigate the formation of naphthalene. The route to the formation of naphthalene from anisole follows the simple unimolecular decomposition of anisole, which leads to the phenoxy radical and then cyclopentadienyl radical. This chemical pathway has been demonstrated before, but the subsequent reaction of two cyclopentadienyl radicals to give naphthalene has only been the subject of theoretical investigations. We have used matrix isolation FTIR spectroscopy together with photoionization time-of-flight (TOF) mass spectrometry to identify intermediates in this reaction mechanism. Using this technique, we have trapped phenoxy and cyclopentadienyl radicals and measured their IR spectra. The formation of these species is confirmed in our TOF mass spectrometer. We have also identified the formation of 9,10-dihydrofulvalene, the adduct from the reaction of two cyclopentadienyl radicals. Finally, we have used molecular beam mass spectrometry (MBMS) and factor analysis to demonstrate the formation of naphthalene from the pyrolysis of anisole.

Chemistry of Tar Formation and Maturation in the Thermochemical Conversion of Biomass

An understanding of the molecular details of tar formation and maturation in thermochemical processes is fundamental to the development of gasification and gas cleaning systems for high efficiency applications, such as in internal combustion engines or in gas turbines. Tars are functionally defined as the condensible organic fraction from gasifier effluents, and hence, are generally considered to be aromatic in nature. This definition does not allow a distinction between classes of compounds which originate under different reaction regimes, such as the primary pyrolysis products, which may be in the gasifier effluent because of low temperature operation or due to process upsets, and high molecular weight polynuclear aromatic hydrocarbons, which are produced under higher reaction severity and are the precursors of particulate matter formation. This paper describes the effect of time, temperature, and oxygen on product composition and the maturation of tars through distinct classes of products. The effect of oxygen at temperatures of 600 °C to 700° C is shown to accelerate the destruction of primary pyrolysis products but has no significant effect on benzene.

Molecular-beam mass-spectrometric analysis of lignocellulosic materials: I. Herbaceous biomass

Abstract A rapid analytical technique has been developed to qualitatively screen and quantitatively analyze biomass feedstocks for conversion into hydrocarbon fuels and chemicals. In this rapid analytical pyrolysis approach, herbaceous biomass feedstocks stored in the open without cover for 6 to 9 months were characterized using the molecular-beam mass spectrometer (MBMS). The biomass materials were pyrolyzed at 600°C and the volatile pyrolysis products were analyzed in real time by the MBMS. The mass spectral data were further analyzed by multivariate statistical techniques (Factor Analysis). The contents of nitrogen compounds, pentosans and hexosans estimated from the pyrolysis mass-spectrometric/multivariate analysis techniques correlated well with the results obtained by conventional wet chemical methods. However, lignin correlation was very weak because of the presence of microbial degradation products of biomass (humic material) that interfered with the Klason lignin analysis. This rapid analytical technique was used to analyze various fractions of the stored biomass feedstocks. A comparison of exposed surface biomass materials and the unexposed materials showed that the exposed fraction lost 30% (wt) of the carbohydrate component of the biomass relative to the fresh material.

Real-time monitoring of the deactivation of HZSM-5 during upgrading of pine pyrolysis vapors.

The conversion of pine pyrolysis vapors over fixed beds of HZSM-5 catalyst was studied as a function of deactivation of the catalyst, presumably by coking. Small laboratory reactors were used in this study in which the products were identified using a molecular beam mass spectrometer (MBMS) and gas chromatography mass spectrometry (GCMS). In all of these experiments, real-time measurements of the products formed were conducted as the catalyst aged and deactivated during upgrading. The results from these experiments showed the following: (1) Fresh catalyst produces primarily aromatic hydrocarbons and olefins with no detectable oxygen-containing species. (2) After pyrolysis of roughly the same weight of biomass as weight of catalyst, oxygenated products begin to appear in the product stream. This suite of oxygen containing products appears different from the products formed when the catalyst is fresh and when the catalyst is completely deactivated. In particular, phenol and cresols are measured while upgrading pine, cellulose and lignin pyrolysis vapors, suggesting that these products are intermediates or side products formed during upgrading. (3) After the addition of more pyrolysis vapors, the product stream consists of primary vapors from pine pyrolysis. Catalyst samples collected at various points during deactivation were analyzed using a variety of tools. The results show that carbon build-up is correlated with catalyst deactivation, suggesting that deactivation is due to coking. Further, studies of nitrogen adsorption on the used catalyst suggest that coking initially occurs on the outside of the catalyst, leaving the micropores largely intact. From a practical point of view, it appears that based upon this study and others in the literature, the amount of oxygen in the upgraded products can be related to the level of deactivation of the HZSM-5 catalyst, which can be determined by how much pyrolysis vapor is run over the catalyst.

A study of the mechanisms of vanillin pyrolysis by mass spectrometry and multivariate analysis

The pyrolysis of vanillin (3-methoxy-4-hydroxy-benzaldehyde) was studied to determine the reaction pathways that lead to the formation of aromatics and to establish an empirical kinetic model. Molecular beam mass spectrometry and multivariate data analysis were used to follow the complicated pyrolysis chemistry and to determine quantitative kinetic parameters of aromatic hydrocarbon formation. The pyrolysis of vanillin is modeled as a lumped, two-step, sequential process. Possible identification of reaction intermediates is discussed utilizing known reaction mechanisms and thermochemistry for anisole (C 6 H 5 OCH 3 ), phenol (C 6 H 5 OH), and benzaldehyde (C 6 H 5 CHO).