A perspective on biomass-derived biofuels: From catalyst design principles to fuel properties.

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.

Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol.

The nascent steps in the pyrolysis of the lignin components salicylaldehyde ( o-HOCHCHO) and catechol ( o-HOCHOH) were studied in a set of heated microreactors. The microreactors are small (roughly 1 mm ID × 3 cm long); transit times through the reactors are about 100 μs. Temperatures in the microreactors can be as high as 1600 K, and pressures are typically a few hundred torr.

Understanding Trends in Autoignition of Biofuels: Homologous Series of Oxygenated C5 Molecules.

Oxygenated biofuels provide a renewable, domestic source of energy that can enable adoption of advanced, high-efficiency internal combustion engines, such as those based on homogeneously charged compression ignition (HCCI). Of key importance to such engines is the cetane number (CN) of the fuel, which is determined by the autoignition of the fuel under compression at relatively low temperatures (550-800 K). For the plethora of oxygenated biofuels possible, it is desirable to know the ignition delay times and the CN of these fuels to help guide conversion strategies so as to focus efforts on the most desirable fuels.

Multispectrum analysis of the oxygen A-band.

Retrievals of atmospheric composition from near-infrared measurements require measurements of airmass to better than the desired precision of the composition. The oxygen bands are obvious choices to quantify airmass since the mixing ratio of oxygen is fixed over the full range of atmospheric conditions. The OCO-2 mission is currently retrieving carbon dioxide concentration using the oxygen A-band for airmass normalization.

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical.

Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy.

Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation.

We demonstrate a synthetic route toward the production of propene directly from poly(β-hydroxybutyrate) (PHB), the most common of a wide range of high-molecular-mass microbial polyhydroxyalkanoates. Propene, a major commercial hydrocarbon, was obtained from the depolymerization of PHB and subsequent decarboxylation of the crotonic acid monomer in good yields (up to 75 mol %). The energetics of PHB depolymerization and the gas-phase decarboxylation of crotonic acid were also studied using density functional theory (DFT).

Carbocation Stability in H-ZSM5 at High Temperature.

Zeolites are common catalysts for multiple industrial applications, including alcohol dehydration to produce olefins, and given their commercial importance, reaction mechanisms in zeolites have long been proposed and studied. Some proposed reaction mechanisms for alcohol dehydration exhibit noncyclic carbocation intermediates or transition states that resemble carbocations, and several previous studies suggest that the tert-butyl cation is the only noncyclic cation more stable than the corresponding chemisorbed species with the hydrocarbon bound to the framework oxygen (i.e.

Ethanol dehydration in HZSM-5 studied by density functional theory: evidence for a concerted process.

Dehydration over acidic zeolites is an important reaction class for the upgrading of biomass pyrolysis vapors to hydrocarbon fuels or to precursors for myriad chemical products. Here, we examine the dehydration of ethanol at a Brønsted acid site, T12, found in HZSM-5 using density functional theory (DFT). The geometries of both cluster and mixed quantum mechanics/molecular mechanics (QM:MM) models are prepared from the ZSM-5 crystal structure.

The thermal decomposition of the benzyl radical in a heated micro-reactor. I. Experimental findings.

The pyrolysis of the benzyl radical has been studied in a set of heated micro-reactors. A combination of photoionization mass spectrometry (PIMS) and matrix isolation infrared (IR) spectroscopy has been used to identify the decomposition products. Both benzyl bromide and ethyl benzene have been used as precursors of the parent species, C6H5CH2, as well as a set of isotopically labeled radicals: C6H5CD2, C6D5CH2, and C6H5 (13)CH2.

Pyrolysis of Cyclopentadienone: Mechanistic Insights from a Direct Measurement of Product Branching Ratios.

The thermal decomposition of cyclopentadienone (C5H4═O) has been studied in a flash pyrolysis continuous flow microreactor. Passing dilute samples of o-phenylene sulfite (C6H4O2SO) in He through the microreactor at elevated temperatures yields a relatively clean source of C5H4═O. The pyrolysis of C5H4═O was investigated over the temperature range 1000-2000 K.

Bimolecular decomposition pathways for carboxylic acids of relevance to biofuels.

The bimolecular thermal reactions of carboxylic acids were studied using quantum mechanical molecular modeling. Previous work1 investigated the unimolecular decomposition of a variety of organic acids, including saturated, α,β-unsaturated, and β,γ-unsaturated acids, and showed that the type and position of the unsaturation resulted in unique branching ratios between dehydration and decarboxylation, [H2O]/[CO2]. In this work, the effect of bimolecular chemistry (water-acid and acid-acid) is considered with a representative of each acid class.

Unimolecular thermal decomposition of dimethoxybenzenes.

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.

Polarized matrix infrared spectra of cyclopentadienone: observations, calculations, and assignment for an important intermediate in combustion and biomass pyrolysis.

A detailed vibrational analysis of the infrared spectra of cyclopentadienone (C5H4═O) in rare gas matrices has been carried out. Ab initio coupled-cluster anharmonic force field calculations were used to guide the assignments. Flash pyrolysis of o-phenylene sulfite (C6H4O2SO) was used to provide a molecular beam of C5H4═O entrained in a rare gas carrier.

Comparison of unimolecular decomposition pathways for carboxylic acids of relevance to biofuels.

Quantum mechanical molecular modeling is used [M06-2X/6-311++G(2df,p)] to compare activation energies and rate constants for unimolecular decomposition pathways of saturated and unsaturated carboxylic acids that are important in the production of biofuels and that are models for plant and algae-derived intermediates. Dehydration and decarboxylation reactions are considered. The barrier heights to decarboxylation and dehydration are similar in magnitude for saturated acids (∼71 kcal mol(-1)), with an approximate 1:1 [H2O]/[CO2] branching ratio over the temperature range studied (500-2000 K).

Biomass pyrolysis: thermal decomposition mechanisms of furfural and benzaldehyde.

The thermal decompositions of furfural and benzaldehyde have been studied in a heated microtubular flow reactor. The pyrolysis experiments were carried out by passing a dilute mixture of the aromatic aldehydes (roughly 0.1%-1%) entrained in a stream of buffer gas (either He or Ar) through a pulsed, heated SiC reactor that is 2-3 cm long and 1 mm in diameter.

Unimolecular thermal decomposition of phenol and d5-phenol: direct observation of cyclopentadiene formation via cyclohexadienone.

The pyrolyses of phenol and d(5)-phenol (C(6)H(5)OH and C(6)D(5)OH) have been studied using a high temperature, microtubular (μtubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy.

Thermal decomposition mechanisms of the methoxyphenols: formation of phenol, cyclopentadienone, vinylacetylene, and acetylene.

The pyrolyses of the guaiacols or methoxyphenols (o-, m-, and p-HOC(6)H(4)OCH(3)) have been studied using a heated SiC microtubular (μ-tubular) reactor. The decomposition products are detected by both photoionization time-of-flight mass spectroscopy (PIMS) and matrix isolation infrared spectroscopy (IR). Gas exiting the heated SiC μ-tubular reactor is subject to a free expansion after a residence time of approximately 50-100 μs.

Laser ablation with resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for determining aromatic lignin volatilization products from biomass.

We have designed and developed a laser ablation∕pulsed sample introduction∕mass spectrometry platform that integrates pyrolysis (py) and∕or laser ablation (LA) with resonance-enhanced multiphoton ionization (REMPI) reflectron time-of-flight mass spectrometry (TOFMS). Using this apparatus, we measured lignin volatilization products of untreated biomass materials. Biomass vapors are produced by either a custom-built hot stage pyrolysis reactor or laser ablation using the third harmonic of an Nd:YAG laser (355 nm).

Direct detection of products from the pyrolysis of 2-phenethyl phenyl ether.

The pyrolysis of 2-phenethyl phenyl ether (PPE, C(6)H(5)C(2)H(4)OC(6)H(5)) in a hyperthermal nozzle (300-1350 °C) was studied to determine the importance of concerted and homolytic unimolecular decomposition pathways. Short residence times (<100 μs) and low concentrations in this reactor allowed the direct detection of the initial reaction products from thermolysis. Reactants, radicals, and most products were detected with photoionization (10.

Radical chemistry in the thermal decomposition of anisole and deuterated anisoles: an investigation of aromatic growth.

The pyrolyses of anisole (C(6)H(5)OCH(3)), d(3)-anisole (C(6)H(5)OCD(3)), and d(8)-anisole (C(6)D(5)OCD(3)) have been studied using a hyperthermal tubular reactor and photoionization reflectron time-of-flight mass spectrometer. Gas exiting the reactor is subject to an immediate supersonic expansion after a residence time of approximately 65 mus. This allows the detection of highly reactive radical intermediates.

Current technologies for analysis of biomass thermochemical processing: a review.

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.

Experimental line parameters of the b1 Sigma(g)+ <-- X3 Sigma(g)- band of oxygen isotopologues at 760 nm using frequency-stabilized cavity ring-down spectroscopy.

Positions, intensities, self-broadened widths, and collisional narrowing coefficients of the oxygen isotopologues 16O18O, 16O17O, 17O18O, and 18O18O have been measured for the b1 Sigma(g) + <-- X3 Sigma(g) - (0,0) band using frequency-stabilized cavity ring-down spectroscopy. Line positions of 156 P-branch transitions were referenced against the hyperfine components of the 39K D1 (4s 2S1/2 --> 4p 2P1/2) and D2 (4s 2S1/2 --> 4p 2P3/2) transitions, yielding precisions of approximately 0.00005 cm-1 and absolute accuracies of 0.