Brent H. Shanks

Influence of inorganic salts on the primary pyrolysis products of cellulose

Processing bio-oil with the help of currently existing petroleum refinery infrastructure has been considered as a promising alternative to produce sustainable fuels in the future. The feasibility of bio-oil production and upgrading processes depend upon its chemical composition which in turn depends on the biomass composition and the process conditions of the fast pyrolysis reactions. The primary goal of this paper was to investigate the effect of mineral salts including mixtures of salts in the form of switchgrass ash on the chemical speciation resulting from primary pyrolysis reactions of cellulose and to gain an insight of the underlying mechanisms. Various concentrations of inorganic salts (NaCl, KCl, MgCl(2), CaCl(2), Ca(OH)(2), Ca(NO(3))(2), CaCO(3) and CaHPO(4)) and switchgrass ash were impregnated on pure cellulose. These samples were pyrolyzed in a micro-pyrolyzer connected to a GC-MS/FID system. Effects of minerals on the formation of (a) low molecular weight species - formic acid, glycolaldehyde and acetol, (b) furan ring derivatives - 2-furaldehyde and 5-hydroxy methyl furfural and (c) anhydro sugar - levoglucosan are reported exclusively. Further, the effect of reaction temperature ranging from 350 to 600 degrees C on the pyrolysis speciation of pure and ash-doped cellulose is also reported. The pyrolysis speciation revealed the competitive nature of the primary reactions. Mineral salts and higher temperatures accelerated the reactions that led to the formation of low molecular weight species from cellulose as compared to those leading to anhydro sugars.

Organosulfonic acid-functionalized mesoporous silicas for the esterification of fatty acid

Abstract Organosulfonic acid-functionalized mesoporous silicas were synthesized in a one-step approach of co-condensing inorganic–organic reagents in the presence of different surfactant templates with in situ oxidation of the thiol groups to the sulfonic acid groups. The resulting materials were tested for their catalytic performance in the esterification of fatty acid with methanol to produce methyl esters. The performance of the functionalized mesoporous materials demonstrated a strong dependence on the median pore diameter of the catalyst as well as the acidic strength of the organosulfonic acid group. The activity of the organosulfonic acid-functionalized silicas in the esterification was compared to that of standard acidic resins. The results indicate the potential of rational catalysis design using organic–inorganic mesoporous materials.

Understanding the Fast Pyrolysis of Lignin

In the present study, pyrolysis of corn stover lignin was investigated by using a micro-pyrolyzer coupled with a GC-MS/FID (FID=flame ionization detector). The system has pyrolysis-vapor residence times of 15-20 ms, thus providing a regime of minimal secondary reactions. The primary pyrolysis product distribution obtained from lignin is reported. Over 84 % mass balance and almost complete closure on carbon balance is achieved. In another set of experiments, the pyrolysis vapors emerging from the micro-pyrolyzer are condensed to obtain lignin-derived bio-oil. The chemical composition of the bio-oil is analyzed by using GC-MS and gel permeation chromatography techniques. The comparison between results of two sets of experiments indicates that monomeric compounds are the primary pyrolysis products of lignin, which recombine after primary pyrolysis to produce oligomeric compounds. Further, the effect of minerals (NaCl, KCl, MgCl(2), and CaCl(2)) and temperature on the primary pyrolysis product distribution is investigated. The study provides insights into the fundamental mechanisms of lignin pyrolysis and a basis for developing more descriptive models of biomass pyrolysis.

Product Distribution from the Fast Pyrolysis of Hemicellulose

Hemicellulose is one of the major constituents of biomass. Surprisingly, only very limited information regarding its product distribution under fast pyrolysis conditions is available in the literature. In the present study, a combination of several analytical techniques, including micro-pyrolyzer-GC-MS/FID, gas analysis, and capillary electrophoresis, were used to study the primary pyrolysis product distribution of hemicelluloses extracted and purified from switchgrass. A total of 16 products were identified and quantified, which accounted for 85% of the overall mass balance. The pyrolysis behavior of hemicellulose was found to be considerably different than cellulose and was explained on the basis of a proposed mechanism for glycosidic bond cleavage. Further, the effect of minerals and temperature was investigated. The study provides insight into the fast pyrolysis behavior of hemicellulose and provides a basis for developing models that can predict bio-oil composition resulting from overall biomass fast pyrolysis.

Platform biochemicals for a biorenewable chemical industry

The chemical industry is currently reliant on a historically inexpensive, petroleum-based carbon feedstock that generates a small collection of platform chemicals from which highly efficient chemical conversions lead to the manufacture of a large variety of chemical products. Recently, a number of factors have coalesced to provide the impetus to explore alternative renewable sources of carbon. Here we discuss the potential impact on the chemical industry of shifting from non-renewable carbon sources to renewable carbon sources. This change to the manufacture of chemicals from biological carbon sources will provide an opportunity for the biological research community to contribute fundamental knowledge concerning carbon metabolism and its regulation. We discuss whether fundamental biological research into metabolic processes at a holistic level, made possible by completed genome sequences and integrated with detailed structural understanding of biocatalysts, can change the chemical industry from being dependent on fossil-carbon feedstocks to using biorenewable feedstocks. We illustrate this potential by discussing the prospect of building a platform technology based upon a concept of combinatorial biosynthesis, which would explore the enzymological flexibilities of polyketide biosynthesis.

Distinguishing primary and secondary reactions of cellulose pyrolysis

The objective of this study was to elucidate primary and secondary reactions of cellulose pyrolysis, which was accomplished by comparing results from a micro-pyrolyzer coupled to a GC-MS/FID system and a 100 g/hr bench scale fluidized bed reactor system. The residence time of vapors in the micro-pyrolyzer was only 15-20 ms, which precluded significant secondary reactions. The fluidized bed reactor had a vapor residence time of 1-2 s, which is similar to full-scale pyrolysis systems and is long enough for secondary reactions to occur. Products from the fluidized bed pyrolyzer reactor were analyzed using a combination of micro-GC, GC-MS/FID, LC-MS and IC techniques. Comparison between the products from the two reactor systems revealed that the oligomerization of leglucosan and decomposition of primary products such as 5-hydroxymethyl furfural, anhydro xylopyranose and 2-furaldehyde were the major secondary reactions occurring in the fluidized bed reactor. This study can be used to build more descriptive pyrolysis models that can predict yield of specific compounds.

Characterization of mesoporous alumina molecular sieves synthesized by nonionic templating

Mesoporous aluminas were produced by nonionic supramolecular templating and characterized to determine the stability of their physical structure during extended calcination at elevated temperatures. The effect of synthesis temperature on the physical structure of these materials and the resulting thermal evolution from synthesized aluminum hydroxide to transitional alumina was studied using thermogravimetric analysis. A high resolution multiple quantum magic angle spinning NMR spectroscopy method was used to determine quantitatively the evolution of the aluminum coordination during the thermal processing. The mesoporous alumina exhibited high stability upon prolonged heating, which is essential for their future applications in catalytic chemistry.

Synthesis of hierarchically structured aluminas under controlled hydrodynamic conditions

Aluminas having hierarchical bimodal pore structures with regular arrayed macropores interconnected with mesopores were synthesized in a cone/plate apparatus that provided well-defined hydrodynamic conditions. A parametric synthesis study was performed to better understand the synthesis conditions required to form the hierarchical structures. The synthesis experiments demonstrated that the hierarchnical structure could only be formed under limited mixing conditions. The mesoporous structure, which was created by interstitial porosity between boehmite nanoparticles, was formed independently of the macropores and was not significantly impacted by the use of a surfactant, whereas the formation of the macropores required the presence of an alkoxide droplet within the synthesis mixture and the surfactant played no role other than to influence the hydrodynamic conditions during synthesis.

Catalytic conversion of carbohydrate-derived oxygenates over HZSM-5 in a tandem micro-reactor system†

In this study, carbohydrate-derived pyrolysis oxygenates were used as model compounds to investigate the effect of functional group and molecular size on the product formation from their catalytic conversion over HZSM-5. Functional groups in oxygenates were found to strongly affect the oxygen removal pathway, leading to variations in hydrocarbon formation. This study also found that oxygenates of smaller molecular size tended to form more hydrocarbons and less coke. Coking on the external surface of catalysts was greatest for the largest oxygenates. Isotopic labeling experiments demonstrated that the aldehyde group of HMF was cleaved before the furanic ring diffused into the HZSM-5 catalyst. Product distribution from catalytic pyrolysis of glucose was the same as the weighted sum of products obtained by the catalytic pyrolysis of individual oxygenates known to arise from non-catalytic pyrolysis of glucose. This suggests that oxygenates released during pyrolysis of carbohydrate have no significant interaction during their catalytic conversion over HZSM-5.

Pyrolysis reaction networks for lignin model compounds: unraveling thermal deconstruction of β-O-4 and α-O-4 compounds

Although lignin is one of the main components of biomass, its pyrolysis chemistry is not well understood due to complex heterogeneity. To gain insights into this chemistry, the pyrolysis of seven lignin model compounds (five β-O-4 and two α-O-4 linked molecules) was investigated in a micropyrolyzer connected to GC-MS/FID. According to quantitative product mole balance for the reaction networks, concerted retro–ene fragmentation and homolytic dissociation were strongly suggested as the initial reaction step for β-O-4 compounds and α-O-4 compounds, respectively. The difference in reaction pathway between compounds with different linkages was believed to result from thermodynamics of the radical initiation. The rate constants for the different reaction pathways were predicted from ab initio density functional theory calculations and pre-exponential literature values. The computational findings were consistent with the experiment results, further supporting the different pyrolysis mechanisms for the β-ether linked and α-ether linked compounds. A combination of the two pathways from the dimeric model compounds was able to describe qualitatively the pyrolysis of a trimeric lignin model compound containing both β-O-4 and α-O-4 linkages.