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A promising approach for supplementing petroleum-derived fuels to support reductions in green-house gas emissions is to convert abundant biomass feedstocks into renewable carbon-rich oils using pyr...

Catalytic fast pyrolysis (CFP) has been identified as a promising pathway for the production of renewable fuels and co-products. However, continued technology development is needed to increase proc...

Chemical reaction kinetics enable predictive scaling studies and process sensitivity analyses that can substantially accelerate commercial deployment of new catalytic transformation technologies. The absence of suitable kinetic parameters for catalytic fast pyrolysis (CFP) of biomass feedstocks has precluded such de-risking simulation activities. In this work we consider ex situ CFP using a Pt/TiO2 catalyst in a packed bed vapor phase upgrading reactor (VPU) with co-fed H2. We develop a multiscale simulation framework to de-couple apparent kinetics from both intraparticle and reactor-scale transport phenomena. The transport model is integrated with a kinetic scheme that predicts (1) lumped yields of product partially deoxygenated compounds, hydrocarbons, light gases, water, and coke, as well as (2) active site concentration and deactivation of the catalyst. We employ recent advancements in mathematical treatments of cascading reaction systems in the context of an axial-dispersion packed bed reactor model to achieve a rapidly-solving simulation framework that is amenable to iterative regression for kinetic parameter extraction. Results demonstrate accurate predictions of CFP yields within 5% for a variety of conditions, including different reaction times, Pt loadings, and variations in feedstock attributes.

Ex situ catalytic fast pyrolysis (CFP) uses a secondary reactor to upgrade biomass pyrolysis vapors to stabilized CFP oils with reduced oxygen content. In one configuration, the secondary reactor is operated as a packed-bed swing reactor system which allows coke-deactivated beds to be decarbonized in situ while other beds remain online for vapor upgrading. In situ decarbonization must be done carefully to avoid irreversible deactivation and/or physical degradation of catalyst pellets. Given that packed bed reactors are well known to have poor heat transfer characteristics, this is a critical issue impacting scaleability and commercial viability of the technology. To predict thermal excursions during regeneration, finite element computational models have been built to assist in scaling up oxidative decarbonization of a Pt/TiO2 CFP catalyst (0.5 mm spheres) from a bench scale packed bed with 100 g of catalyst to a pilot scale packed bed with 2 kg of catalyst and internal cooling tubes. Based on transient measurements of outlet temperature and effluent CO2 concentration, and using an assumed coke profile and activation energy, this paper demonstrates that specific combinations of effective thermal conductivity and wall heat transfer coefficient can fit bench scale oxidative regeneration data equally well. For the upscaled 2 kg bed, four bench-scale “best fit” parameter pairs give different predictions for location and magnitude of thermal excursions, with the maximum computed bed temperature gradients ranging from 30 °C cm−1 to as high as 3000 °C cm−1. The larger the fraction of heat removal by conduction through the cooling tubes, the greater the differences between the parameter pairs. The modelling results presented in this paper cast doubt on the industrial viability of the proposed combination of catalyst, bed and regeneration process, and point to the need for alternate reactor designs. However, there is considerable uncertainly in some of the key model parameters. The reliability of model predictions can be increased by adding more temperature measurements at key bed locations, testing additional variations in process conditions, performing careful bed dissections to determine the true coke profile, and perhaps most importantly, directly measuring the effective thermal conductivity of the catalyst pellets.

A custom bench-scale continuous-flow catalytic fast-pyrolysis (CFP) reactor system was implemented for the optimization of ex situ CFP and screening of catalysts to gain insight into commercial sca...

Co-processing bio-oils with petroleum-derived feeds in the existing multitrillion dollar refining and distribution infrastructure is an attractive option for introducing renewable energy into the f...

The impact of upgrading temperature and biomass-to-catalyst mass ratio on upgrading pine pyrolysis vapors over HZSM-5 was studied in a dual fluidized bed reactor system. Increasing the upgrading te...

Catalytic fast pyrolysis using the zeolite ZSM-5 is an attractive process for converting lignocellulosic biomass into fuels and chemicals. Ga-modified ZSM-5 has demonstrated improved hydrocarbon yields compared to ZSM-5 due to additional functionality imparted by Ga; however, there is little knowledge of the active Ga species and its role in the catalytic mechanisms. Here, we employ micropyrolyzer – GC-MS experiments and theoretical calculations to demonstrate that a hydrogen-pretreated Ga species (Ga*/ZSM-5) and a reductive environment are critical towards upgrading pine pyrolysis vapors into high yields of alkenes and aromatic hydrocarbons at near atmospheric pressure. The total carbon yield (g C in product per g C in pine) in alkenes and aromatic hydrocarbons under these conditions was 37% compared to 25% for the parent ZSM-5 catalyst. The corresponding carbon yield was only 19% for Ga*/ZSM-5 under inert conditions indicating that both the hydrogen-pretreated Ga* species and reducing atmosphere are required to obtain high hydrocarbon yields. The ratio of carbon in alkenes to carbon in aromatic hydrocarbons increased to 2.5 with Ga*/ZSM-5 under a reductive environment vs. 0.4 for ZSM-5. The carbon yield of alkenes increased with Ga loading; in contrast, increasing catalyst acidity promoted aromatic hydrocarbon production. Experiments conducted with isopropanol demonstrated high selectivity to propene over Ga*/ZSM-5 under reductive environments, indicating enhancement of dehydration reactions. A computational mechanism study was conducted to identify the active Ga species ([GaH2]+, [GaO]+, [Ga(OH)2]+ or [GaH(OH)]+) using the dehydration of isopropanol as a model reaction. Theoretical calculations suggested that [Ga(OH)2]+ and [GaH(OH)]+ are the most likely species responsible for dehydration with 39.7 and 38.8 kcal mol−1 activation energy barriers, respectively, and based on thermodynamic analysis, their ratio in the catalyst is dictated by H2 partial pressure and temperature. The model compound studies and computational results provide mechanistic support for the observed biomass experiments showing increased alkene selectivity.

To mitigate green-house gas (GHG) emissions, governments around the world are enacting legislation to reduce carbon intensity in transportation fuels. Coprocessing biomass and petroleum-derived liquids in existing refineries is a near-term, cost-effective approach for introducing renewable carbon in fuels and enabling refineries to meet regulatory mandates. However, coprocessing biomass-derived liquids in refineries results in variable degrees of biogenic carbon incorporation, necessitating accurate quantification to verify compliance with mandates. Existing refinery control and instrumentation systems lack the means to measure renewable carbon accurately, reliably, and quickly. Thus, accurate measurement of biogenic carbon is key to ensuring refineries meet regulatory mandates. In this Perspective, we present existing methods for measuring biogenic carbon, point out their challenges, and discuss the need for new online analytical capabilities to measure biogenic carbon in fuel intermediates.

Thermochemical conversion of lignocellulosic biomass is a promising route to produce fuels and oxygenated chemicals and could enable circular carbon utilization. In most thermochemical conversion processes, however, some chemical co-products are lost in aqueous waste streams that are both dilute and heterogeneous. Cost-competitive isolation of these chemical co-products is challenging due to the high-purity requirements typically necessary for bulk chemical production. Here, we demonstrate the production and isolation of two biomass-derived monomers, phenol and catechol, from a comprehensively characterized aqueous waste stream generated via catalytic fast pyrolysis. Specifically, we separate phenol and catechol to 97 wt% purity using the industrially relevant processes of liquid–liquid extraction, distillation, and recrystallization. Techno-economic analysis predicts that a mixed phenolics stream can be produced from the waste stream at a minimum selling price of $1.06 kg−1. Overall, this work demonstrates an approach to high-purity oxygenated aromatic compounds that is potentially economically feasible and technically achievable which increases the atom efficiency of thermochemical conversion through waste stream valorization.

The hazards to health and the environment associated with the transportation sector include smog, particulate matter, and greenhouse gas emissions. Conversion of lignocellulosic biomass into biofuels has the potential to provide significant amounts of infrastructure-compatible liquid transportation fuels that reduce those hazardous materials. However, the development of these technologies is inefficient, due to: (i) the lack of a priori fuel property consideration, (ii) poor shared vocabulary between process chemists and fuel engineers, and (iii) modern and future engines operating outside the range of traditional autoignition metrics such as octane or cetane numbers. In this perspective, we describe an approach where we follow a "fuel-property first" design methodology with a sequence of (i) identifying the desirable fuel properties for modern engines, (ii) defining molecules capable of delivering those properties, and (iii) designing catalysts and processes that can produce those molecules from a candidate feedstock in a specific conversion process. Computational techniques need to be leveraged to minimize expenses and experimental efforts on low-promise options. This concept is illustrated with current research information available for biomass conversion to fuels via catalytic fast pyrolysis and hydrotreating; outstanding challenges and research tools necessary for a successful outcome are presented.

This work addresses the effect of the support on the performance of Pd-based catalysts for hydrodeoxygenation of different model molecules (phenol, m-cresol, anisole, guaiacol) in the vapor phase at 573 K. The activity and the selectivity to deoxygenated products strongly depended on the support, regardless the model molecule. For HDO of phenol and m-cresol, benzene and toluene were the dominant products on niobia supported catalysts, whereas cyclohexanone and methylcyclohexanone were the main compounds formed on Pd/SiO2. For HDO of anisole, demethoxylation reaction producing benzene is favored over Pd/Nb2O5 catalyst, while demethylation is the preferred route over Pd/SiO2. Phenol and methanol were the main products observed for HDO of guaiacol over all catalysts but significant formation of benzene was detected over Pd/Nb2O5. The improved deoxygenation performance over the niobia supported catalysts is explained in terms of the oxophilic sites represented by Nb4+/Nb5+ cations. These catalysts were also tested for HDO of pine pyrolysis vapors. All three catalysts were effective for reducing the total yield of oxygenated products. The extent of deoxygenation was highest over the Pd/Nb2O5 and Pd/NbOPO4 catalysts. The effectiveness of Pd/Nb2O5 and Pd/NbOPO4 for deoxygenation of real feeds is in good agreement with the model compound results and suggests that these catalysts are promising materials for the upgrading of pyrolysis vapors to produce hydrocarbon fuels.

Rapid coking and catalyst deactivation are significant problems during catalytic fast pyrolysis of biomass. Cellulose and lignin were found to coke via different mechanisms, resulting in two distinct types of catalyst deactivation. Lignin pyrolysis vapors cause coke formation mainly by external surface coking without limiting access to the active acid sites in the microchannels. Lignin deactivates the surface cracking capability of ZSM-5, resulting in unreacted primary vapors passing through while maintaining aromatization reactions. Cellulose pyrolysis vapors generate coke mainly as an extension of the aromatization reactions on the acid sites, which leads to occlusion of the internal acid sites. This deactivates the upgrading reactions, resulting in decreased aromatics formation, generation of oxygenated intermediates and increased alkylation of 1-ring aromatics and reduced multi-ring aromatics selectivity. The results indicate that the decrease in aromatics formation observed during catalytic pyrolysis...

Opuntia ficus-indica (prickly pear) and Grindelia squarrosa (gumweed) are two exceptionally drought tolerant plant species capable of growing in arid and semiarid environments. Additionally, they have unique cell wall structures. Prickly pear contains pectin and high levels of ash (16.1%) that is predominantly Ca and K. Gumweed has high levels of extractives that contain grindelic acid and monoterpenoids. The objective of this paper was to evaluate how these unique cell wall components alter the pyrolysis performance of prickly pear and gumweed. Using a tandem micropyrolyzer with GC-MS/FID/TCD, a detailed account of the product slate is given for products generated between 450 and 650 °C. Pyrolysis of prickly pear showed that the high levels of ash increase the amount of organics volatilized and shifted product pools, making it possible to generate up to 7.3% carbonyls vs 3.8% for Pinus taeda (loblolly pine) and 10.5% hydrocarbons vs 1.8% for pine depending on reaction conditions. Pyrolysis of gumweed sho...

Catalytic fast pyrolysis (CFP) has emerged as an attractive process for the conversion of lignocellulosic biomass into renewable fuels and products. Considerable research and development has focused on using circulating-bed reactors with zeolite catalysts (e.g., HZSM-5) for CFP because of their propensity to form gasoline-range aromatic hydrocarbons. However, the high selectivity for aromatics comes at the expense of low carbon yield, a key economic driver for this process. In this contribution, we evaluate non-zeolite catalysts in a fixed-bed reactor configuration for an integrated CFP process to produce fuel blendstocks from lignocellulosic biomass. These experimental efforts are coupled with technoeconomic analysis (TEA) to benchmark the process and guide research and development activities to minimize costs. The results indicate that CFP bio-oil can be produced from pine with improved yield by using a bifunctional metal-acid 2 wt% Pt/TiO2 catalyst in a fixed-bed reactor operated with co-fed H2 at near atmospheric pressure, as compared to H-ZSM5 in a circulating-bed reactor. The Pt/TiO2 catalyst exhibited good stability over 13 reaction-regeneration cycles with no evidence of irreversible deactivation. The CFP bio-oil was continuously hydrotreated for 140 h time-on-stream using a single-stage system with 84 wt% of the hydrotreated product having a boiling point in the gasoline and distillate range. This integrated biomass-to-blendstock process was determined to exhibit an energy efficiency of 50% and a carbon efficiency of 38%, based on the experimental results and process modelling. TEA of the integrated process revealed a modelled minimum fuel selling price (MFSP) of $4.34 per gasoline gallon equivalent (GGE), which represents a cost reduction of $0.85 GGE−1 compared to values reported for CFP with a zeolite catalyst. TEA also indicated that catalyst cost was a significant factor influencing the MFSP, which informed additional CFP experiments in which lower-cost Mo2C and high-dispersion 0.5 wt% Pt/TiO2 catalysts were synthesized and evaluated. These materials demonstrated CFP carbon yield and oil oxygen content similar to those of the 2 wt% Pt/TiO2 catalyst, offering proof-of-concept that the lower-cost catalysts can be effective for CFP and providing a route to reduce the modelled MFSP to $3.86–3.91 GGE−1. This report links foundational science and applied engineering to demonstrate the potential of fixed-bed CFP and highlights the impact of coupled TEA to guide research activities towards cost reductions.

Partial deoxygenation of bio-oil by catalytic fast pyrolysis with subsequent coupling and hydrotreating can lead to improved economics and will aid commercial deployment of pyrolytic conversion of biomass technologies. Biomass pyrolysis efficiently depolymerizes and deconstructs solid plant matter into carbonaceous molecules that, upon catalytic upgrading, can be used for fuels and chemicals. Upgrading strategies include catalytic deoxygenation of the vapors before they are condensed (in situ and ex situ catalytic fast pyrolysis), or hydrotreating following condensation of the bio-oil. In general, deoxygenation carbon efficiencies, one of the most important cost drivers, are typically higher for hydrotreating when compared to catalytic fast pyrolysis alone. However, using catalytic fast pyrolysis as the primary conversion step can benefit the entire process chain by: (1) reducing the reactivity of the bio-oil, thereby mitigating issues with aging and transport and eliminating need for multi-stage hydroprocessing configurations; (2) producing a bio-oil that can be fractionated through distillation, which could lead to more efficient use of hydrogen during hydrotreating and facilitate integration in existing petroleum refineries; and (3) allowing for the separation of the aqueous phase. In this perspective, we investigate in detail a combination of these approaches, where some oxygen is removed during catalytic fast pyrolysis and the remainder removed by downstream hydrotreating, accompanied by carbon–carbon coupling reactions in either the vapor or liquid phase to maximize carbon efficiency toward value-driven products (e.g. fuels or chemicals). The economic impact of partial deoxygenation by catalytic fast pyrolysis will be explored in the context of an integrated two-stage process. Finally, improving the overall pyrolysis-based biorefinery economics by inclusion of production of high-value co-products will be examined.

Catalytic fast pyrolysis (CFP) of biomass produces a liquid product consisting of organic and aqueous streams. The organic stream is typically slated for hydrotreating to produce hydrocarbon biofuels, while the aqueous stream is considered a waste stream, resulting in the loss of residual biogenic carbon. Here, we report the detailed characterization and catalytic conversion of a CFP wastewater stream with the ultimate aim to improve overall biomass utilization within a thermochemical biorefinery. An aqueous stream derived from CFP of beech wood was comprehensively characterized, quantifying 53 organic compounds to a total of 17% organics. The most abundant classes of compounds are acids, aldehydes, and alcohols. The most abundant components identified in the aqueous stream were C1-C2 organics, comprising 6.40% acetic acid, 2.16% methanol, and 1.84% formaldehyde on wet basis. The CFP aqueous stream was catalytically upgraded to olefins and aromatic hydrocarbons using a Ga/HZSM-5 catalyst at 500°C. When th...

Biomass particles can experience variable thermal conditions during fast pyrolysis due to differences in their size and morphology, and from local temperature variations within a reactor. These differences lead to increased heterogeneity of the chemical products obtained in the pyrolysis vapors and bio-oil. Here we present a simple, high-throughput method to investigate the thermal history experienced by large ensembles of particles during fast pyrolysis by imaging and quantitative image analysis. We present a correlation between the surface luminance (darkness) of the biochar particle and the highest temperature that it experienced during pyrolysis. Next, we apply this correlation to large, heterogeneous ensembles of char particles produced in a laminar entrained flow reactor (LEFR). The results are used to interpret the actual temperature distributions delivered by the reactor over a range of operating conditions.

The catalytic fast pyrolysis (CFP) of biomass is a promising technology for producing renewable transportation fuels and chemicals. MFI-type catalysts have shown promise for CFP because they produce gasoline range hydrocarbons from oxygenated pyrolysis compounds; however, rapid catalyst deactivation due to coking is one of the major technical barriers inhibiting the commercialization of this technology. Coke deposited on the surface of the catalysts blocks access to active sites in the micropores leading to rapid catalyst deactivation. Our strategy is to minimize rapid catalyst deactivation by adding mesoporosity through formation of MFI nanosheet materials. The synthesized MFI nanosheet catalysts were fully characterized and evaluated for cellulose pyrolysis vapor upgrading to produce olefins and aromatic hydrocarbons. The data obtained from pyrolysis-GCMS (py-GCMS) showed that fresh MFI nanosheets produced similar aromatic hydrocarbon and olefin yields compared to those of conventional HZSM-5. However, ...

Fast pyrolysis and catalytic fast pyrolysis (CFP) of biomass produce a liquid product stream comprised of various classes of organic compounds having different molecule size and polarity. This liquid, either spontaneously in the case of catalytic fast pyrolysis or by water addition for the noncatalytic process separates into a nonpolar organic-rich fraction and a highly polar water-rich fraction. The organic fraction can be used as a blendstock or feedstock for further processing in a refinery while, in the CFP process design, the aqueous phase is currently sent to wastewater treatment, which results in a loss of residual biogenic carbon present in this stream. This work focuses on the catalytic conversion of the biogenic carbon in pyrolysis aqueous phase streams to produce hydrocarbons using a vertical microreactor coupled to a molecular beam mass spectrometer (MBMS). The MBMS provides real-time analysis of products while also tracking catalyst deactivation. The catalyst used in this work was HZSM-5, whi...

Cellulose is the primary biopolymer responsible for maintaining the structural and mechanical integrity of cell walls and, during the fast pyrolysis of biomass, may be restricting cell wall expansion and inhibiting phase transitions that would otherwise facilitate efficient escape of pyrolysis products. Here, we test whether modifications in two physical properties of cellulose, its crystalline allomorph and degree of crystallinity, alter its performance during fast pyrolysis. We show that both crystal allomorph and relative crystallinity of cellulose impact the slate of primary products produced by fast pyrolysis. For both cellulose-I and cellulose-II, changes in crystallinity dramatically impact the fast pyrolysis product portfolio. In both cases, only the most highly crystalline samples produced vapors dominated by levoglucosan. Cellulose-III, on the other hand, produces largely the same slate of products regardless of its relative crystallinity and produced as much or more levoglucosan at all crystall...

The impact of catalyst acidity on the selectivity of upgraded biomass pyrolysis products was studied by passing pine pyrolysis vapors over five ZSM-5 catalysts of varying acidity at 500 °C. The SiO2-to-Al2O3 ratio (SAR) of the ZSM-5 zeolite was varied from 23 to 280 to control the acidity of the catalyst and the composition of upgraded products. The upgraded product stream was analyzed by GCMS. Additionally, catalysts were characterized using temperature programmed desorption, diffuse-reflectance FTIR spectroscopy, N2 physisorption, and X-ray diffraction. The results showed that the biomass pyrolysis vapors were highly deoxygenated to form a slate of aromatic hydrocarbons over all of the tested ZSM-5 catalysts. As the overall acidity of the ZSM-5 increased the selectivity toward alkylated (substituted) aromatics (e.g., xylene, dimethyl-naphthalene, and methyl-anthracene) decreased while the selectivity toward unsubstituted aromatics (e.g., benzene, naphthalene, and anthracene) increased. Additionally, the selectivity toward polycyclic aromatic compounds (2-ring and 3-ring) increased as catalyst acidity increased, corresponding to a decrease in acid site spacing. The increased selectivity toward less substituted polycyclic aromatic compounds with increasing acidity is related to the relative rates of cyclization and alkylation reactions within the zeolite structure. As the acid site concentration increases and sites become closer to each other, the formation of additional cyclization products occurs at a greater rate than alkylated products. The ability to adjust product selectivity within 1-, 2-, and 3-ring aromatic families, as well as the degree of substitution, by varying ZSM-5 acidity could have significant benefits in terms creating a slate of upgraded biomass pyrolysis products to meet specific target market demands.

In this work, Ni/ZSM-5 catalysts with varied nickel loadings were evaluated for their ability to produce aromatic hydrocarbons by upgrading of pine pyrolysis vapors. The effect of catalyst pretreatment by hydrogen reduction was also investigated. Results indicate that the addition of nickel increases the yield of aromatic hydrocarbons while simultaneously increasing the conversion of oxygenates, relative to ZSM-5, and these effects are more pronounced with increasing nickel loading. Additionally, while initial activity differences were observed between the oxidized and reduced forms of nickel on ZSM-5 (i.e., NiO/ZSM-5 versus Ni/ZSM-5), the activity of both catalysts converges with increasing time on stream. These reaction results coupled with characterization of pristine and spent catalysts suggest that the catalysts reach similar active states during catalytic pyrolysis, regardless of pretreatment, as NiO undergoes in situ reduction to Ni by biomass pyrolysis vapors. This reduction of NiO to Ni was confi...

Catalytic fast pyrolysis (CFP) is a conversion process that integrates rapid thermochemical depolymerization of solid feedstocks with catalytic transformation to yield small molecules for fuel and chemical products. This process is well‐suited for the conversion of nonfossil feedstocks such as biomass and waste plastics, and thereby holds great potential for the production of renewable commodities. In spite of many technological developments in various aspects of CFP achieved over decades of research, this technology has yet to attain commercial success for the production of fuels and chemicals from renewable feedstocks. Effective CFP processes require careful coordination of chemical and physical phenomena that span very large length and time scales. A broad spectrum of scientific progress in both pyrolysis and catalytic upgrading has provided the foundation for successful deployment of CFP, although additional progress in process‐scale integration is yet required for commercial realization. Modeling and simulation tools provide an important framework wherein the CFP technologies by be better understood and evaluated from a holistic perspective. Here we provide a detailed description of the multiscale phenomena underlying CFP, describe challenges and associated technical progress, and suggest strategies for an integrated approach to advance this technology toward commercialization. This article is categorized under: Bioenergy > Systems and Infrastructure Bioenergy > Science and Materials

Zeolites are crystalline microporous aluminosilicates that have numerous applications in industry, specifically in catalysis, separation and adsorption. Zeolites catalyze the conversion of biomass-derived pyrolysis vapors into hydrocarbons; however, zeolites frequently suffer from rapid deactivation under pyrolysis conditions. Methanol-to-hydrocarbon processes are closely related to biomass upgrading reactions and several proposed mechanisms are discussed to provide mechanistic insight for biomass upgrading with zeolites. Syntheses of novel zeolites have potential to relieve deactivation factors including mass diffusion limitations of bulky molecules and accumulation of carbonaceous coke on the catalyst surface. Catalytic activity of conventional zeolites is presented to provide insights to evaluate the novel zeolites. Recent advances of the new zeolite structures are also presented in the context of potential future directions for the field.

Catalytic C–C coupling and deoxygenation reactions are essential for upgrading of biomass-derived oxygenates to fuel-range hydrocarbons. Detailed understanding of mechanistic and energetic aspects of these reactions is crucial to enabling and improving the catalytic upgrading of small oxygenates to useful chemicals and fuels. Using periodic density functional theory (DFT) calculations, we have investigated the reactions of furan and acetaldehyde in an HZSM-5 zeolite catalyst, a representative system associated with the catalytic upgrading of pyrolysis vapors. Comprehensive energy profiles were computed for self-reactions (i.e., acetaldehyde coupling and furan coupling) and cross-reactions (i.e., acetaldehyde + furan) of this representative mixture. Major products proposed from the computations are further confirmed using temperature controlled mass spectra measurements. The computational results show that furan interacts with acetaldehyde in HZSM-5 via an alkylation mechanism, which is more favorable than...

Three HZSM-5 catalysts with different binders (alumina, silica, and clay) were evaluated for upgrading of pine pyrolysis vapors. All catalysts were based on the same HZSM-5 with silica to alumina molar ratio of 30. Experiments in micro-scale analytical Py-GCMS/FID showed that fresh catalysts with silica and clay produced predominantly aromatic hydrocarbons at similar carbon yields. The catalyst with alumina gave lower vapor yields and produced both hydrocarbons and partially deoxygenated products, in particular furans. The catalyst with alumina also gave higher coke yields and exhibited faster deactivation than the catalysts with clay and silica binders. The low hydrocarbon yields and coke formation were attributed to the acidic sites provided by alumina and blocking of the zeolite sites. The catalysts with silica and clay as binders were further tested in a 2-inch fluidized bed system for ex situ catalytic pyrolysis of pine. Similar oils were produced over both catalysts with carbon yields of approximately 23 % and oxygen contents of 20–21 %.

Production of value-added furans and phenols from biomass through catalytic fast pyrolysis of pine using molybdenum supported on KIT-5 mesoporous silica was explored. Catalysts containing different loadings of molybdenum were synthesized and characterized by X-ray diffraction, physisorption and chemisorption analysis, various electron microscopic techniques and X-ray photoelectron spectroscopy. Characterization studies indicate that molybdenum is homogeneously distributed over the KIT-5 silica support in a +6 oxidation state. Fast pyrolysis of pine using molecular beam mass spectrometry with fresh Mo catalyst preferentially produced furans and phenols over conventionally observed aromatic hydrocarbons. Detailed investigation of model biopolymers indicates that the furans originated from the carbohydrate portion of the biomass and the phenols emerged predominantly from the lignin portion of biomass. Results obtained from MBMS were complemented using pyrolytic-GCMS.

Catalytic fast pyrolysis of biomass over zeolite catalysts results primarily in aromatic (e.g., benzene, toluene, xylene) and olefin products. However, furans are a higher value intermediate for their ability to be readily transformed into gasoline, diesel, and chemicals. Here we investigate possible mechanisms for the coupling of glycoaldehyde, a common product of cellulose pyrolysis, over HZSM-5 for the formation of furans. Experimental measurements of neat glycoaldehyde over a fixed bed of HZSM-5 confirm furans (e.g., furanone) are products of this reaction at temperatures below 300 °C with several aldol condensation products as coproducts (e.g., benzoquinone). However, under typical catalytic fast pyrolysis conditions (>400 °C), further reactions occur that lead to the usual aromatic product slate. ONIOM calculations were utilized to identify the pathway for glycoaldehyde coupling toward furanone and hydroxyfuranone products with dehydration reactions serving as the rate-determining steps with typical intrinsic reaction barriers of 40 kcal mol-1. The reaction mechanisms for glycoaldehyde will likely be similar to that of other small oxygenates such as acetaldehyde, lactaldehyde, and hydroxyacetone. This study provides a generalizable mechanism of oxygenate coupling and furan formation over zeolite catalysts.

The conversion of biomass primary pyrolysis vapors over several β-zeolites with silica-to-alumina ratios (SAR) varying from 21 to 250 was carried out in a flow microreactor to investigate the effect of number of acid sites on product speciation and deactivation of the catalyst. Experiments were conducted using a horizontal fixed bed semi-batch reactor in which up to 40 discrete 50 mg boats of biomass were pyrolyzed and the vapors upgraded over 0.5 g of the catalyst. Products were measured with a molecular beam mass spectrometer (MBMS). These studies were complemented using a tandem micropyrolyzer connected to a GCMS (py-GCMS) for speciation and quantifying the products. In the py-GCMS experiments, several 0.5 mg loads of pine were pyrolyzed sequentially and the vapors upgraded over 4 mg of catalyst. 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 that: (1) fresh catalyst for β-zeolites with lower SAR (more acid sites) produced primarily aromatic hydrocarbons and olefins with no detectable oxygen-containing species; (2) a suite of oxygenated products was observed from fresh catalysts with high SAR (few acid sites), indicating that 0.5 g of these catalyst materials did not have sufficient acid sites to deoxygenate vapors produced from pyrolysis of 50 mg of pine. This suite of oxygen containing products consisted of furans, phenol and cresols. The amount of coke deposited on each catalyst and the yield of aromatic hydrocarbons increased with the number of acid sites. However, while the catalysts were active, the biomass selectivity towards coke and hydrocarbons remained essentially constant on the catalysts of varying SAR.

Dynamically adjusting the weights in state-averaged multiconfigura- tional self-consistent field (SA-MCSCF) calculations using an energy-dependent functional allows the electronic wave function to smoothly evolve across the potential energy surface (PES) and correctly preserves differing asymptotic electro- nic-state degeneracy patterns. We have developed a generalized dynamic weighting (GDW) method to treat high-lying electronic states. To test the method, a global PES wasconstructedfortheS2(~ B)stateofCHF(CDF),whichliesnearly31000cm -1 above theminimumofthegroundstate.TheGDWmethodwasusedtoproduceSA-MCSCF reference states for subsequent multireference configuration interaction (MRCI) calculations, whose Davidson-corrected energies were extrapolated to the complete basis set limit. Quantum mechanical vibrational energy calculations for CDF were performed using the fitted PES, and the predicted energy levels are in excellent agreement with an extensive set of experimentally determined (optical-optical double resonance) levels, with a mean unsigned error of only 12 cm -1 . SECTION Dynamics, Clusters, Excited States

Pyrolysis and gasification are two of the more promising utilization methods for the conversion of biomass toward a clean fuel source. To truly understand and model these processes requires detailed knowledge ranging from structural information of raw biomass, elemental composition, gas-phase reaction kinetics and mechanisms, and product distributions (both desired and undesired). The various analytical methods of biomass pyrolysis/gasification processing are discussed, including reactor types, analytical tools, and recent examples in the areas of (a) compositional analysis, (b) structural analysis, (c) reaction mechanisms, and (d) kinetic studies on biomass thermochemical processing.

We report studies aimed at unraveling the complicated structure of the CCl 2 A (1)B 1-- X (1)A 1 system. We have remeasured the fluorescence excitation spectrum from approximately 17,500 to 24,000 cm (-1) and report the term energies and A rotational constants of many new bands for both major isotopologues (C (35)Cl 2, C (35)Cl (37)Cl). We fit the observed term energies to a polyad effective Hamiltonian model and demonstrate that a single resonance term accounts for much of the observed mixing, which begins approximately 1300 cm (-1) above the vibrationless level of the A (1)B 1 state. The derived A (1)B 1 vibrational parameters are in excellent agreement with ab initio predictions, and the mixing coefficients deduced from the polyad model fit are in close agreement with those derived from direct fits of single vibronic level (SVL) emission intensities. The approach to linearity and thus the Renner-Teller (RT) intersection is probed through the energy dependence of the A rotational constant and fluorescence lifetime measurements, which indicate a barrier height above the vibrationless level of the X (1)A 1 state of approximately 23,000-23,500 cm (-1), in excellent agreement with ab initio theory.

We report new studies of the B ∼ 1 A ″ ↔ X ∼ 1 A ′ system of CuOH/CuOD, generated in a pulsed discharge source under jet-cooled conditions. Single vibronic level (SVL) emission spectra obtained from the 0 0 0 and 2 0 1 levels of the B ∼ 1 A ″ state reveal new information on the bending and Cu–O stretching frequencies in the ground state. The derived vibrational parameters are in good agreement with recent high level ab initio calculations. Rotationally resolved laser induced fluorescence excitation spectra of the 2 0 1 band were obtained, and a rotational analysis performed for the 63 CuOD isotopomer. Additionally, B ∼ 1 A ″ state fluorescence lifetimes are reported.

In a search for transitions to the low-lying a ˜ 3 A ″ state, we have recorded single vibronic level (SVL) emission spectra of bromochlorocarbene, CBrCl, which probe the vibrational structure of the X ∼ 1 A ′ state up to ∼5500 cm−1 above the vibrationless level. These spectra reveal many previously unassigned levels, and a complete set of vibrational parameters was determined for the X ∼ 1 A ′ state. The derived parameters are compared with recent ab initio predictions.

Building upon our recent observation of the gas-phase electronic spectrum of the iodomethyl cation (CH 2 I + ), we report an extensive study of the electronic spectroscopy of CH 2 I + and its deuterated isotopomers CHDI + and CD 2 I + using a combination of fluorescence excitation and single vibronic level (SVL) emission spectroscopies. The spectra were measured in the gas phase under jet-cooled conditions using a pulsed discharge source. Fluorescence excitation spectra reveal a dominant progression in ν 3 (C-I stretch), the frequency of which is markedly smaller in the upper state. Rotational analysis shows that, while the A constant is similar in the two states, the excited state has significantly smaller B and C constants. These results indicate a lengthening of the C-I bond upon electronic excitation, consistent with calculations which show that this transition is analogous to the well-known π-π* transition in the isoelectronic substituted formaldehydes. SVL emission spectra show progressions involving four of the six vibrational modes; only the C-H(D) stretching modes remain unobserved. The vibrational parameters determined from a Dunham expansion fit of the ground state vibrational term energies are in excellent agreement with the predictions of density functional theory (DFT) calculations. A normal-mode analysis was completed to derive a harmonic force field for the ground state, where resonance delocalization of the positive charge leads to partial double bond character, H 2 C + -I↔ H 2 C=I + , giving rise to a C-I stretching frequency significantly larger than that of the iodomethyl radical.

We report fluorescence excitation and single vibronic level emission spectra of the A ˜ 1 A ″ ↔ X ˜ 1 A ′ system of CDCl in the 500–740 nm region, measured under jet-cooled conditions using a pulsed discharge source. A total of 29 cold bands involving the pure bending levels 2 0 n (n = 2–11), C–D stretching fundamental ( 1 0 1 ), and combination bands 2 0 n 3 0 1 (n = 2–10), 2 0 n 3 0 2 (n = 9), 1 0 1 2 0 n (n = 2–8), and 1 0 1 2 0 n 3 0 1 (n = 7) were observed; most of these are reported here for the first time. Rotational analysis typically yielded band origins and rotational constants for both isotopomers (CD35Cl, CD37Cl). The derived A ˜ 1 A ″ vibrational intervals are combined with previous studies at lower energy to determine excited state barriers to linearity for the 2n, 2n31, and 112n progressions. The A ˜ 1 A ″ state C–D stretching frequency (2229.6 cm−1) is determined here for the first time, in excellent agreement with ab initio theory. Following our observation of new bands in this system, we obtained single vibronic level (SVL) emission spectra which probe the vibrational structure of the X ˜ 1 A ′ state up to ∼8000 cm−1 above the vibrationless level. The total number of X ˜ 1 A ′ and a ˜ 3 A ″ levels observed is more than twice that previously reported, and a complete set of Dunham parameters was determined for the X ˜ 1 A ′ state of CD35Cl and CD37Cl. Comparisons with previous experimental and recent high level ab initio studies are reported. Our results shed new light on the vibrational structure of the X ˜ 1 A ′ , A ˜ 1 A ″ , and a ˜ 3 A ″ states of CDCl, and, more generally, spin–orbit coupling in the monohalocarbenes.

Using an improved discharge recipe for the production of dibromocarbene (CBr 2 ), we recently reassigned the electronic origin of the A ˜ 1 B 1 ← X ˜ 1 A 1 system, based on an extensive data set of isotope shifts for the pure bending transitions [C. Tao, C. Mukarakate, D. Brusse, Y. Mishchenko, S. A. Reid, J. Mol. Spectrosc. 240 (2006) 139–140]. In this study, we report the complete analysis of the fluorescence excitation spectrum of the A ˜ 1 B 1 ← X ˜ 1 A 1 system in the 525–650 nm region, obtained at a rotational temperature of ∼10 K. A total of 32 cold bands involving the pure bending levels 2 0 n with n = 2–19 and combination bands 1 0 1 2 0 n ( n = 1–16) in the A ˜ 1 B 1 ← X ˜ 1 A 1 system were observed; a number of these are reported here for the first time. Rotational analysis typically yielded A rotational constants and band origins for all three bromine isotopomers (C 79 Br 2 , C 79 Br 81 Br, C 81 Br 2 ), and Dunham expansion fits yielded an extensive set of vibrational parameters for each. The isotope shifts are in good agreement with the product rule, and, when plotted vs. bending quantum number, the measured A constants follow a linear trend except for the highest bending levels, where an abrupt increase is observed, indicative of the approach to linearity. This is mirrored in the vibrational intervals, which also change abruptly in this region, and the estimated barrier height of ∼18 800 cm −1 above the vibrationless level of the X ˜ 1 A 1 state is in excellent agreement with the ab initio prediction of Sendt and Bacskay [K. Sendt, G.B. Bacskay, J. Chem. Phys. 112 (2000) 2227–2238]. We also report fluorescence lifetimes as a function of vibrational level and K a ′ ; the lifetimes decrease rapidly with energy, but display no dependence on K a ′ over the measured range. The implications of these results for understanding the excited state structure of this prototypical carbene are emphasized.

The magnitude of the singlet-triplet gap in dichloromethylene (CCl(2)) has been a point of controversy in the recent literature. In this study, we report single vibronic level emission spectra of the A(1)B(1)--X[combining tilde](1)A(1) system of the carbene C(35)Cl(2), which probes the vibrational structure of the X[combining tilde](1)A(1) state up to approximately 10,000 cm(-1) above the vibrationless level. By the careful selection of bands where complete isotope and K(a)' selectivity in excitation was possible, we measured K(a)'-sorted emission spectra in order to test the previously established hypothesis [M.-L. Liu, C.-L. Lee, A. Bezant, G. Tarczay, R. J. Clark, T. A. Miller and B.-C. Chang, Phys. Chem. Chem. Phys., 2003, 5, 1352] that unassigned lines lying above approximately 5,000 cm(-1) belong to levels of the ã(3)B(1) state. The K(a)'-sorting method discriminates between singlet and triplet levels via the (A''-B[combining macron]'') rotational constant, which is significantly larger for pure triplet levels due to the larger equilibrium bond angle. In the region between 3,500 and 9,000 cm(-1) above the vibrationless level of the X[combining tilde](1)A(1) state, we find only a very modest increase in (A''-B[combining macron]''), and approximately 86% of the lines observed between 5,000 and 9,000 cm(-1) can be assigned to X[combining tilde](1)A(1) levels within 3 standard deviations of our Dunham expansion fit, which included more than 140 levels in total. A nearly complete set of Dunham parameters was determined for the C(35)Cl(2) isotopomer, and the X[combining tilde](1)A(1) state term energies up to 4,000 cm(-1) are in excellent agreement with recent variational calculations of Tarczay, et al. [G. Tarczay, T. A. Miller, G, Czakó and A. G. Császár, Phys. Chem. Chem. Phys., 2005, 7, 2881]. Finally, the implication of our results for the singlet-triplet gap in dichloromethylene is discussed.

The unimolecular thermal decomposition mechanisms of o-, m-, and p-dimethoxybenzene (CH3O-C6H4-OCH3) have been studied using a high temperature, microtubular (μtubular) SiC reactor with a residence time of 100 μs. Product detection was carried out using single photon ionization (SPI, 10.487 eV) and resonance enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry and matrix infrared absorption spectroscopy from 400 K to 1600 K. The initial pyrolytic step for each isomer is methoxy bond homolysis to eliminate methyl radical. Subsequent thermolysis is unique for each isomer. In the case of o-CH3O-C6H4-OCH3, intramolecular H-transfer dominates leading to the formation of o-hydroxybenzaldehyde (o-HO-C6H4-CHO) and phenol (C6H5OH). Para-CH3O-C6H4-OCH3 immediately breaks the second methoxy bond to form p-benzoquinone, which decomposes further to cyclopentadienone (C5H4=O). Finally, the m-CH3O-C6H4-OCH3 isomer will predominantly follow a ring-reduction/CO-elimination mechanism to form C5H4=O. Electronic structure calculations and transition state theory are used to confirm mechanisms and comment on kinetics. Implications for lignin pyrolysis are discussed.

The research activities on biofuels and bio-products have been growing steadily regardless the volatility of the crude oil price in the past decade. The major driver is the imperative need of tackling the challenge of climate change. With the low carbon footprints, fuels and chemicals produced from renewable biomass resources, as the replacement of their petroleum counterparts, can contribute significantly on carbon emission reduction.

In this work, we report on the spectroscopy and dynamics of the quasi-linear S(2) state of chlorocarbene, CHCl, and its deuterated isotopologue using optical-optical double resonance (OODR) spectroscopy through selected rovibronic levels of the S(1) state. This study, which represents the first observation of the S(2) state in CHCl, builds upon our recent examination of the corresponding state in CHF, where pronounced mode specificity was observed in the dynamics, with predissociation rates larger for levels containing bending excitation. In the present work, a total of 14 S(2) state vibrational levels with angular momentum l = 1 were observed for CHCl, and 34 levels for CDCl. The range of l in this case was restricted by the pronounced Renner-Teller effect in the low-lying S(1) levels, which severely reduces the fluorescence lifetime for levels with K(a)0. Nonetheless, by exploiting different intermediate S(1) levels, we observed progressions involving all three fundamental vibrations. For levels with long predissociation lifetimes, rotational constants were determined by measuring spectra through different intermediate J levels of the S(1) state. Plots of the predissociation linewidth (lifetime) vs. energy for various S(2) levels show an abrupt onset, which lies near the calculated threshold for elimination to form C((3)P) + HCl on the triplet surface. Our experimental results are compared with a series of high level ab initio calculations, which included the use of a dynamically weighted full-valence CASSCF procedure, focusing maximum weight on the state of interest (the singlet and triplet states were computed separately). This was used as the reference for subsequent Davidson-corrected MRCI(+Q) calculations. These calculations reveal the presence of multiple conical intersections in the singlet manifold.