Rational design of heterogeneous catalysts for biomass conversion - Inputs from computational chemistry

The ever-growing development of biomass-based chemicals calls for a better understanding of the specificities of the corresponding catalytic processes. In this quest, ab initio modeling is a corner-stone that has proven its ability to rationalize the observed trends and then to propose novel catalysts design. Focusing on supported metal catalysts, we show that computational studies started a decade ago with alcohols and small polyols transformation, focusing on activity but also selectivity. Little by little, their scope has been extended to a variety of cellulosic-based chemicals such as levulinic acid or furanic molecules. During the last two years, it has also started to embrace lignin-derived chemicals, such as anisole, guaiacol, etc. Parallel to this scope expansion, the available methodologies have also progressed, triggered by the intrinsic difficulties of modeling biomass valorisation. In particular, improving the inclusion of the water solvent has drawn several groups to propose novel approaches

Understanding Biomass Upgrading Through Hydrogenolysis Reactions: Kinetics and Mechanism

This dissertation involves several hydrogenolysis reactions but is mainly focused on hydrodechlorination (HDC) of chlorobenzene (PhCl) and hydrodeoxygenation (HDO) of 2-furancarboxylic acid (FCA). Hydrodechlorination of PhCl has been the subject of research for some time. Here, we used a Pd/C catalyst to study this reaction though rigorous kinetics and mechanistic analyses in a CSTR reactor. The H2/D2 kinetic isotope effect (KIE) experiment revealed that H2 is not involved in a rate controlling step. The kinetics data are in agreement with similar systems reported before and follow a first-order dependence on chlorobenzene, half order for hydrogen and an inverse first order with respect to HCl. These data suggest a mechanism that involves C-Cl cleavage in the rate controlling step preceded by adsorption of reactant and followed by desorption of products from the surface. The derived rate expression was used in a microkinetic model to predict the observed rates of this reaction. This model successfully captures the experimental trends observed in the kinetic studies. Moreover, motivated by the applications of in situ spectroscopic techniques, the detailed design of an FTIR cell which enables both steady state and transient studies to measure kinetics and investigate the mechanism of reactions at a molecular level, is included. Hydrodeoxygenation of 2-furancarboxylic acid was investigated to produce delta-valerolactone, which represents a series of functionalized lactone molecules that have a potential to be used in prospective polymers. Motivated by excellent HDO activity reported for Ru/TiO2 catalysts, and with the aim of taking advantage of the built-in bifunctionality of this catalyst when introduced to hydrogen, we have used Ru/TiO2 toquantitatively synthesize the functionalized lactone monomer (FDHL). The focus of our work has been to optimize process parameters, including temperature, solvent, catalyst support, metal loading, weight of the catalyst and reaction time, to achieve an acceptable yield for the target product. The yield of 53% to -hexalactone (DHL) for a simple 5-methyl-2-furancarboxylic acid was significantly greater than the previous reports

Fast Pyrolysis Oil Upgrading via HDO with Fe-Promoted Nb₂O₅-Supported Pd-Based Catalysts

ue to the high acid, oxygen and water contents of fast pyrolysis oil, it requires the improvement of its fuel properties by further upgrading, such as catalytic hydrodeoxygenation (HDO). In this study, Nb2O5 was evaluated as a support of Pd-based catalysts for HDO of fast pyrolysis oil. A Pd/SiO2 catalyst was used as a reference. Additionally, the impact of iron as a promoter in two different loadings was investigated. The activity of the synthesized catalysts was evaluated in terms of H2 uptake and composition of the upgraded products (gas phase, upgraded oil and aqueous phase) through elemental analysis, Karl Fischer titration, GC-MS/FID and 1H-NMR. In comparison to SiO2, due to its acid sites, Nb2O5 enhanced the catalyst activity towards hydrogenolysis and hydrogenation, confirmed by the increased water formation during HDO and a higher content of hydrogen and aliphatic protons in the upgraded oil. Consequently, the upgraded oil with Nb2O5 had a lower average molecular weight and was therefore less viscous than the oil obtained with SiO2. When applied as a promoter, Fe enhanced hydrogenation and hydrogenolysis, although it slightly decreased the acidity of the support, owing to its oxophilic nature, leading to the highest deoxygenation degree (42.5 wt.%) and the highest product HHV (28.2 MJ/kg)

Reaction Kinetics Analysis of C-O Hydrogenoloysis in Phenol and 5-Hydroxymethylfurfural

Converting biomass to alternative fuels has attracted significant interest in recent decades. Lignin, a principal component of biomass, is composed of phenolic monomers, which can be depolymerized using fast pyrolysis to yield a “bio-oil”. However, bio-oil is not immediately suitable as a biofuel because of its high oxygen content, and it is necessary to efficiently remove these oxygen atoms by hydrodeoxygenation (HDO). This project is focused on the elucidation of the reaction kinetics associated with carbon-oxygen hydrogenolysis in phenolic molecules, which is a significant reaction for the production of hydrocarbon fuels from biomass pyrolysis oils. The studied molecules are 5-hydroxymethylfurfural (HMF) and phenol, both used as model compounds. For phenol hydrodeoxygenation (HDO) the optimal pathway is direct deoxygenation (DDO), but at relevant temperatures, C-C double bond saturation is a significant side reaction, following the hydrogenation pathway (HYD). The importance of metal-TiO2 sites has been shown for a variety of reactions. Previous research in our group has shown that Ru/TiO2 is highly active for the conversion of phenol to benzene and that water could act as a co-catalyst. In this work, we clarify iv the role of water in C-O hydrogenolysis catalyzed by this material. Here, we designed and carried out a series of reaction kinetics experiments that illustrate the complex effect water has on the DDO mechanism. We measured reaction orders for phenol hydrogenolysis with respect to water and phenol over Ru supported on TiO2 rutile and anatase using a high-pressure liquid phase flow reactor operated in a kinetically-controlled regime. Our most interesting results show that the reaction is positive-order with respect to water for Ru/rutile and negative-order for Ru/anatase. These observations correlate with heats of water adsorption measurements on TiO2 indicating that anatase is more hydrophilic than rutile 1 and suggest that under particular circumstances, water molecules at the interfacial sites could become the most abundant surface intermediate (MASI). Also, the reaction is zero order with respect to phenol in the absence of water for Ru/anatase and it shifts from positive to negative order at higher phenol concentrations for Ru/rutile. Those differences with catalytic support identity suggest that the reaction mechanisms are different for each catalyst. For rutile, we believe that phenol is a MASI at two different sites: the interfacial site and the metal site that leads to the HYD pathway. For anatase, it is expected that phenol is only a MASI at one of those sites. HMF can also undergo hydrodeoxygenation in a series of intermediate reactions until it becomes 2,5-dimethylfuran. We perform a comparison between different Ni and Ru catalysts supported on Co3O4 with respect to literature performance. Our results were consistent with the literature, but we have obtained a different reaction intermediate, product distribution, and site time yields. We believe that those differences are due to difficulties in reproducing the catalysts by the co-precipitation method

Fuel production by hydrocracking of non-olefinic plastics and vacuum gasoil blends

306 p.The catalytic hydrocracking of different blends of non-olefinic polymers (polystyrene, polymethylmethacrylate and polyethylene terephthalate) with vacuum gasoil has been studied to produce fuel streams suitable for inclusion in refinery pools. For this purpose, a catalyst synthesized in the laboratory composed of Pt and Pd supported on a zeolite Y has been used. For all the mixtures, the influence of the operating conditions (time, temperature, pressure) and the effect they have on the yields of the fractions of interest (naphtha and light cycle oil), as well as on their composition, have been tested. In addition, special attention has been paid to the physicochemical phenomena that take place during the reactions in order to analyze the catalyst behaviour and the different causes of its deactivation with a view to its implementation in industrial units. The use of advanced analytical techniques has allowed to establish the compositional framework of all samples regardless of their heavy nature, which has allowed to determine the mechanisms of hydrocracking of plastics, as well as the routes of elimination of different families of compounds. Finally, kinetic modelling of these systems has been carried out for the optimization of the operating conditions by performing simulations aiming at the maximum conversion of the plastics and maximum yield of the target fractions, while minimizing the products of less interest

Lignin Ethanolysis Depolymerization and Product Upgrading with Mesoporous and Palladium Supported Zeolite Catalysts

Lignin is a high-volume farm waste and environmental hazard of paper and pulp industries. To promote the utilization of its rich aromatic units into important chemicals and fuels, efforts were intensively made to breakdown lignin structure with a variety of depolymerization processes involving heating, solvent, and catalysts or their combination. Among those processes, ethanolysis in supercritical conditions shows promising performance for its high lignin conversion and little char formation. To improve the yield and selectivity of aromatics, particularly phenols, we examined the important roles of acidity and pore structure of different zeolite catalyst play in this process. Zeolites with close micropores and acidity defined by their crystal structures including Beta, Y, and ZSM-5 were first examined. Zeolites with the same microporous structure but different acidic strength caused by various H-type sites were further evaluated. Comparisons were further made between HZSM-5 and HY zeolites with unique mesoporous structures and their counterparts with exclusive micropores. Despite the complexity of lignin depolymerization and its greatly diversified products, strong acidity was found effective to cleave both the C-O-C and C-C linkages on lignin structure to receive more phenols while mild acidity works mainly in ether bond breakdown. When the diffusion issues of gigantic lignin intermediate and monomer products are severe (e.g., in microporous zeolites), overall yield and selectivity of lignin depolymerization products fall and the pore size of catalyst becomes dominant between the two key factors. Like in many petrochemical reactions involving bulky molecules, hierarchical pore structure also is important to promote mass transport and increase the exposure and utilization of acidic site inside zeolite catalysts. At the presence of mesopores in zeolites, their pore configuration is less sensitive when comparing with the acidity to decide the yield and selectivity to phenols of C8-C11. These findings provide important guidelines on the selection and design of zeolites with appropriate acidity and pore structure to facilitate lignin depolymerization or other cracking processes. The products of lignin depolymerization are a mixture of various organic compounds including alcohols, ester, phenols, and other large hydrocarbons with high oxygen content (up to 40 wt.%), poor thermal stability, and low heating values (16-19 mJ/kg), insuitable to serve as alternative or replacement to fossil fuel. Hydrotreating step, a classic refinery process to remove oxygen and other unwanted elements in oil by adding hydrogen, is often suggested for the upgrading of bio-oil to increase its C/O ratio, improve its energy density, stability, as well as other required fuel properties. We successfully synthesized new mesoporous zeolites, Meso-ZSM-5, via solid-state crystallization of dry aluminosilicate nanogels. Palladium was further loaded on these zeolites to form a bi-functional catalyst (Pd/Meso-ZSM-5). When used in the hydrodeoxygenation of guaiacol, a major lignin depolymerization compound, Pd/Meso ZSM-5 exhibits superior guaiacol conversion and product distribution when compared with those supported on conventional microporous ZSM-5 counterparts. This is attributed to the improved diffusion and accessibility of active sites inside Meso-ZSM-5 with its unique hierarchically porous structure formed through neighbor nanocrystals connecting at edges. Ring saturated hydrocarbons are largely produced at 200 °C when hydrogenation dominates while alkaylated aromatics become major HDO products as deoxygenation becomes favorable at 250 °C. Unlike the disappointing conversion and severe coking issue over many HDO catalysts, this catalyst shows excellent anti-coking performance at various temperature conditions. These encouraging results demonstrated the great potential of Pd/Meso-ZSM-5 catalyst in bio-oil upgrading processes and may ignite the wide use in emerging renewable energy fields as well as many other reactions in traditional fossil fuel industrials

Hydrocracking of Cerbera manghas Oil with Co-Ni/HZSM-5 as Double Promoted Catalyst

The effect of various reaction temperature on the hydrocracking of Cerbera manghas oil to produce a paraffin-rich mixture of hydrocarbons with Co-Ni/HZSM-5 as doubled promoted catalyst were studied. The Co-Ni/HZSM-5 catalyst with various metal loading and metal ratio was prepared by incipient wetness impregnation. The catalysts were characterized by XRD, AAS, and N2 adsorption-desorption. Surface area, pore diameter, and pore volume of catalysts decreased with the increasing of metals loading. The hydrocracking process was conducted under hydrogen initial pressure in batch reactor equipped with a mechanical stirrer. The reaction was carried out at a temperature of 300-375 oC for 2 h.  Depending on the experimental condition, the reaction pressure changed between 10 bar and 15 bar.   Several parameters were used to evaluate biofuel produced, including oxygen removal, hydrocarbon composition and gasoline/kerosene/diesel yields. Biofuel was analyzed by Fourier Transform Infrared Spectroscopic (FTIR) and gas chromatography-mass spectrometry (GC-MS). The composition of hydrocarbon compounds in liquid products was similar to the compounds in the gasoil sold in unit of Pertamina Gas Stations, namely pentadecane, hexadecane, heptadecane, octadecane, and nonadecane with different amounts for each biofuel produced at different reaction temperatures. However, isoparaffin compounds were not formed at all operating conditions. Pentadecane (n-C15) and heptadecane (n-C17) were the most abundant composition in gasoil when Co-Ni/HZSM-5 catalyst was used. Cerbera Manghas oil can be recommended as the source of non-edible vegetable oil to produce gasoil as an environmentally friendly transportation fuel. Copyright © 2017 BCREC Group. All rights reservedReceived: 20th May 2016; Revised: 30th January 2017; Accepted: 10th February 2017How to Cite: Marlinda, L., Al-Muttaqii, M., Gunardi, I., Roesyadi, A., Prajitno, D.H. (2017). Hydrocracking of Cerbera manghas Oil with Co-Ni/HZSM-5 as Double Promoted Catalyst. Bulletin of Chemical Reaction Engineering & Catalysis, 12 (2): 167-184 (doi:10.9767/bcrec.12.2.496.167-184)Permalink/DOI: http://dx.doi.org/10.9767/bcrec.12.2.496.167-18