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.
Bioprivileged molecules: creating value from biomass Shanks, Brent H; Keeling, Peter L
Green chemistry : an international journal and green chemistry resource : GC,
2017, Letnik:
19, Številka:
14
Journal Article
Recenzirano
The petrochemical industry is built on C
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-C
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alkenes and aromatics as intermediate molecules, which are converted to a range of products. This industry is highly developed with little opportunity ...for new chemical products. In comparison biological-derived intermediates from biomass have the potential to introduce a new set of intermediate molecules, which can be converted to molecules that directly replace petrochemicals. Even more promising is the potential to convert biological-derived intermediates to novel chemical species that impart enhanced performance properties in their end use. Here the concept of bioprivileged molecules is introduced as a useful new paradigm for developing biobased chemicals. Included are muconic acid, 5-hydroxymethylfurfural and triacetic acid lactone as example bioprivileged molecules. Also, discussed is the research needed to move this concept forward.
Bioprivileged molecules generated from biomass can be converted to both novel molecules and drop-in replacements.
Catalyst stability is one of the greatest challenges faced for the utilization of heterogeneous catalysts in the development of biomass conversion to chemicals and fuels. As many biomass ...transformations are performed in water, hydrothermal stability of supported metal catalysts is especially critical. This Review aims to increase attention on the hydrothermal stability of supported metal catalysts by looking at the stability of common catalyst supports, deactivation modes, and strategies to improve their durability. While common oxides such as silica, alumina, zeolite, and zirconia are not stable to hydrolytic attack, carbon, and titania show promising resistance. In addition to catalyst support leaching, amorphization, and collapse caused by hydrothermal conditions, supported metal catalysts can deactivate by sintering, leaching, poisoning, carbon deposition, and restructuring of the active metal sites. Several strategies are discussed to improve stability of supported metal catalysts: coating on the oxide, overcoating on the supported metal catalyst, metal–support interaction, embedding metal particles, bimetallic catalysts, reactor design and process optimization, and other methods. A fundamental understanding of liquid–solid interactions and deactivation mechanisms, as well as strategies to improve the catalyst durability will help to develop robust catalytic materials for the scale-up and further application of aqueous-phase biomass conversion processes.
Interest in utilizing biorenewable feedstocks to produce fuels and chemicals has risen greatly in the past decade due to the economic, political and environmental concerns associated with diminishing ...petroleum reserves. A fundamental challenge lying ahead in the development of efficient processes to utilize biomass feedstock is that, unlike their petroleum counterparts, biomass contains an excess amount of oxygen. Therefore, catalytic strategies such as dehydration and hydrogenolysis amongst others have been extensively studied as platform technologies for deoxygenation. In this review, we primarily discuss the catalytic dehydration of C
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carbohydrates to 5-hydroxymethylfurfural, which has attracted much attention due to the versatility of using furanic compounds as an important platform intermediate to synthesize various chemicals. The emphasis is on the fundamental mechanistic chemistry so as to provide insights for further catalyst/catalytic system design. After separately discussing fructose and glucose dehydration, this review summarizes recent progress with bi-functional catalyst systems for tandem glucose/fructose isomerization and subsequent fructose dehydration, thereby realizing highly selective HMF production directly from the more abundant and cheaper C
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sugar feedstock, glucose.
Interest in utilizing biorenewable feedstocks to produce fuels and chemicals has risen greatly in the past decade due to the economic, political and environmental concerns associated with diminishing petroleum reserves.
Understanding the Fast Pyrolysis of Lignin Patwardhan, Pushkaraj R.; Brown, Robert C.; Shanks, Brent H.
ChemSusChem,
November 18, 2011, Letnik:
4, Številka:
11
Journal Article
Recenzirano
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, MgCl2, and CaCl2) 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.
Gone in a flash: Renewable alternatives for crude oil can be obtained from fast pyrolysis of lignin—a major component of biomass. However, many oligomeric compounds in the form of aerosols are produced during this process, which limit its utilization. This study reports the primary pyrolysis product distribution data of lignin and provides significant insights on the mechanism of oligomer formation.
Nitrogen and sulfur were simultaneously doped into the framework of mesoporous CMK-3 as metal-free catalysts for direct biorenewable alcohol fuel cells. Glucose, NH3, and thiophene were used as ...carbon, nitrogen and sulfur precursors, respectively, to prepare mesoporous N-S-CMK-3 with uniform mesopores and extra macropores, resulting in good O2 diffusion both in half cell and alcohol fuel cell investigations. Among all investigated CMK-3 based catalysts, N-S-CMK-3 prepared at 800 degree C exhibited the highest ORR activity with the onset potential of 0.92 V vs. RHE, Tafel slope of 68 mV dec-1, and 3.96 electron transfer number per oxygen molecule in 0.1 M KOH. The alkaline membrane-based direct alcohol fuel cell (DAFC) with N-S-CMK-3 cathode displayed 88.2 mW cm-2 peak power density without obvious O2 diffusion issue, reaching 84% initial performance of that with a Pt/C cathode. The high catalyst durability and fuel-crossover tolerance led to stable performance of the N-S-CMK-3 cathode DAFC with 90.6 mW cm-2 peak power density after 2 h operation, while the Pt/C cathode-based DAFC lost 36.9% of its peak power density. The high ORR activity of N-S-CMK-3 can be attributed to the synergistic effect between graphitic-N and S (C-S-C structure), suggesting great potential to use N-S-CMK-3 as an alternative to noble metal catalysts in the fuel cell cathode.
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.
Biomass pyrolysis is an attractive technique to produce bio‐oil that can be upgraded to renewable fuels. However, systematic understanding of the pyrolysis pathways and resulting composition of the liquid product has remained limited. The primary pyrolysis product distribution of hemicelluloses—one of the major components of biomass—and the effect of process parameters is reported, providing a better understanding of biomass pyrolysis and helping to build descriptive pyrolysis models.
Deoxygenating biomass pyrolysis vapors prior to condensation would ideally yield chemically stable and petroleum-miscible streams comprised primarily of hydrocarbons that could be integrated into the ...existing refinery infrastructure. Both in-situ and ex-situ catalytic fast pyrolysis have shown promising results in terms of product quality, i.e., lower acidity, higher heating values, and product stability. However, these improvements come at the expense of carbon loss as CO, CO2, and coke, as well as cracking of larger molecules (potentially more valuable) into smaller molecules. It is thus of utmost importance to track the carbon, both product distribution and carbon yields, in order to obtain the full picture of deoxygenation efficacy. Despite potentially interesting results reported in the literature, it is unfortunately difficult to compare the true ability of various catalyst systems for deoxygenating biomass pyrolysis vapors primarily due to insufficient product characterization and data reporting. In this review paper, it is argued that results ultimately need to be reported in terms of carbon yields of individual products. This would enable an accurate accounting of where the carbon ultimately resides after processing, which is required for a more conclusive comparison between various systems. This information would enable the identification of effective catalytic systems for pyrolysis vapor deoxygenation and accelerate the advancement of catalyst design. Additionally, hydrodeoxygenation is discussed as a promising process in terms of carbon recovery. This article aims to propose a set of standard criteria for future reports on deoxygenation of biomass pyrolysis vapors by scrutinizing the existing literature.
•Pyrolysis vapor deoxygenation holds promise for bio-oil integration in refineries.•Deoxygenation efficacy depends on product quality, quantity, and speciation.•Measuring the quantity of product species requires individual carbon yields.•Carbon should be tracked from feed into all products (i.e. gas, liquid, solid).•The field's progress relies on a standard reporting method accounting for carbon.
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, MgCl2, CaCl2, Ca(OH)2, Ca(NO3)2, CaCO3 and CaHPO4) 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°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.
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