Anand Mohan Verma

DFT study on gas-phase hydrodeoxygenation of guaiacol by various reaction schemes

Abstract Guaiacol is an important phenolic component present in pyrolytic bio-oils; and in this work its hydrodeoxygenation (HDO) by various reaction schemes has been considered within the framework of density functional theory. In this computational study, primarily three reaction schemes for the HDO of guaiacol are considered. In the first reaction scheme (RS 1), guaiacol undergoes hydrogenolysis at O–CH3 bond site of methoxy group to produce catechol and methane followed by HDO of catechol forming phenol and water, followed by HDO of phenol producing benzene and water and finally benzene leading to cyclohexane formation. In the second reaction scheme (RS 2), guaiacol undergoes hydrogenolysis at Caromatic–O bond of methoxy group producing phenol and methanol followed by hydrotreatment of phenol to form cyclohexane along with same intermediates as in the first reaction scheme. In the third reaction scheme (RS 3), HDO of guaiacol compound at Caromatic–OH sigma bond produces anisole and water; and then anisole follows two secondary pathways to produce cyclohexane. In this computational study, the transition state optimisations, vibrational frequency and IRC calculations are carried out by B3LYP functional with 6-311+g(d,p) basis set using Gaussian 09 and Gauss View 5 software package.

Gas phase conversion of eugenol into various hydrocarbons and platform chemicals

The unprocessed bio-oil derived from pyrolysis of lignocellulosic biomass is a mixture of hundreds of oxy-compounds which vitiate the quality of bio-oil. Eugenol is one of the most promising model compounds of the phenolic fraction of unprocessed bio-oil and it comprises two oxy-functionals, namely, hydroxyl and methoxy functionals. In this study, eight reaction pathways are carried out, using eugenol as the model compound, producing many important products viz. toluene, propylbenzene, guaiacol, allylbenzene, 4-propylphenol, isoeugenol, etc. in a gas phase environment by using the B3LYP/6-311+g(d,p) level of theory under the density functional theory (DFT) framework. The thermochemical study of these reactions is also carried out in a wide range of temperatures between 298–898 K with an interval temperature of 100 K and fixed pressure of 1 atm. The direct cleavage of the functional groups of eugenol followed by an atomic hydrogenation reaction to produce lower fraction products is found to be not favourable; however, an atomic hydrogenation reaction prior to the removal of functional groups of eugenol makes these reactions more favourable. The activation energy for the production of guaiacol from eugenol under reaction scheme 2 is reported to be 10.53 kcal mol−1 only, which is the lowest activation energy required amongst all reaction schemes. The reaction scheme 5, i.e., the production of propylcyclohexane from eugenol, is reported to be the most exothermic and spontaneous reaction at all temperature conditions; however, ΔG values increase with increasing temperature and ΔH values decrease with increasing temperature.

Molecular modelling approach to elucidate the thermal decomposition routes of vanillin

The presence of very high amounts of oxy-components in unprocessed bio-oil after thermochemical conversion of lignocellulosic biomass is an undesirable property of bio-oil. This results in severe drawbacks for raw bio-oil which are considered to be undesirable characteristics of any fuel, e.g., low heating value, corrosiveness, high viscosity, and low stability. Therefore, it is necessary to eliminate oxygen atoms from the components of bio-oil. On the other hand, the very high number of oxy-components in unprocessed bio-oil offers an excellent platform to acquire various specialty chemicals. Therefore, in this work, vanillin (4-hydroxy-3-methoxy-benzaldehyde) is considered as a model compound of lignin-derived bio-oil, and various chemical conversions are conducted to achieve lower molecular weight hydrocarbon fractions and several important intermediates, e.g., benzene, guaiacol, o-cresol, p-hydroxybenzaldehyde, m-methoxybenzaldehyde, phenol and o-quinonemethide. Bond dissociation energy studies were carried out to observe the potential chemical breakage sites of vanillin. Chemical reaction mechanisms are proposed according to the various bond dissociation possibilities, and potential energy surfaces are reported for each reaction scheme. The production of guaiacol from vanillin using atomic hydrogenation at the aromatic carbon of the Caromatic–CHO bond of vanillin followed by formyl group removal was found to be the pathway requiring the lowest activation energy (only 10.13 kcal mol−1). The present results are in accordance with their experimental counterparts wherever applicable. The thermochemical phenomena of these reactions were studied in a wide temperature range, i.e., 598 to 898 K for the gas phase and 298 to 498 K for the aqueous phase, at a fixed pressure of 1 atm. The aqueous phase environment was created by a SMD model using water as the solvent. All reaction schemes in both phases were favourable under all temperature conditions except for the formation of phenol from vanillin via the formation of 5-formylsalicylaldehyde, as reported in reaction schemes 7a and 7a1.

Thermochemistry analyses for transformation of C6 glucose compound into C9, C12 and C15 alkanes using density functional theory

ABSTRACT The hydrolysis of cellulose fraction of biomass yields C6 glucose which further can be transformed into long-chain hydrocarbons by C–C coupling. In this study, C6 glucose is transformed into three chain alkanes, namely, C9, C12 and C15 using C–C coupling reactions under the gas and aqueous phase milieus. The geometry optimisation and vibrational frequency calculations are carried out at well-known hybrid-GGA functional, B3LYP with the basis set of 6-31+g(d,p) under the density functional theory framework. The single point energetics are calculated at M05-2X/6-311+g(3df,2p) level of theory. All thermochemical properties are calculated over a wide range of temperature between 300 and 900 K at an interval of 100 K. The thermochemistry suggested that the aqueous phase behaviour is suitable for the hydrolysis of sugar into long-chain alkanes compared to gas-phase environment. The hydrodeoxygenation reactions under each reaction pathway are found as most favourable reactions in both phases; however, aqueous phase dominates over gas phase in all discussed thermodynamic parameters.

Platinum catalyzed hydrodeoxygenation of guaiacol in illumination of cresol production: a density functional theory study

The unprocessed bio-oil obtained by the pyrolysis of lignocellulosic biomass comprises hundreds of oxy-components which vitiate its quality in terms of low heating value, low stability, low pH, etc. Therefore, it has to be upgraded prior to its use as transportation fuel. In this work, guaiacol, a promising compound of the phenolic fraction of unprocessed bio-oil, is considered as a model component for studying its hydrodeoxygenation over a Pt3 catalyst cluster. The production of catechol, 3-methylcatechol, m-cresol and o-cresol from guaiacol over a Pt3 cluster is numerically investigated using density functional theory. Further, the kinetic parameters are obtained over a wide range of temperature, i.e. 473–673 K at an interval of 50 K. Briefly, results indicate that O─H and C─H bond scissions determine the reaction rates of ‘guaiacol to catechol’ and ‘catechol to 3-methylcatechol’ reactions with activation energies of 30.32 and 41.3 kcal mol−1, respectively. On the other hand, C─O bond scissions determine the rates of 3-methylcatechol to m- and o-cresol production reactions, respectively. The kinetics of all reactions indicate that ln k versus 1/T plots are linear over the entire range of temperature considered herein.

Quantum chemical study on gas phase decomposition of ferulic acid

ABSTRACT Ferulic acid, representing phenolic fraction of bio-oil, is considered to be a model compound in this study for its decomposition into various end products such as ethylbenzene, eugenol, cis-isoeugenol, vanillin, 4-ethylguaiacol, guaiacol, and acetovanillone using density functional theory approach. Results of bond dissociation energies indicate that cleavage of methyl group from ferulic acid is the lowest energy-demanding bond scission amongst all 14 bond cleavages. Primary end product by decomposition of ferulic acid is found to be ethylbenzene and its production occurs through the formation of intermediate products such as 4-hydroxycinnamic acid, cinnamic acid and styrene. Demethoxylation of ferulic acid gives rise to the production of 4-hydroxycinnamic acid which further undergoes the formation of cinnamic acid by dehydroxylation reaction route. The formation of cinnamic acid in this study is carried out using three reaction schemes 1–3 and its further reduction to ethylbenzene is performed using two reaction possibilities. Finally, favourable pathway is found to be decarboxylation of cinnamic acid to produce vinylbenzene followed by the production of ethylbenzene using hydrogenation of C=C chain double bond. Furthermore, thermochemistry of each reaction scheme is performed at atmospheric pressure and at a wide range of temperature of 598–898 K.

Kinetics of Decomposition Reactions of Acetic Acid Using DFT Approach

Excessive amount of oxygen content in unprocessed bio-oil deteriorates the quality of bio-oil which cannot be used in transportation vehicles without upgrading. Acetic acid (CH3COOH) is a vital component of ‘acids’ catalogue of unprocessed bio-oil produced from thermochemical conversions of most of biomass feedstocks such as switchgrass, alfalfa, etc. In this study, the decomposition reactions of acetic acid are carried out by two reaction pathways, i.e., decarboxylation and dehydration reactions. In addition, the reaction rates of decomposition are analysed in a wide range of temperatures, i.e., 298-900 K and at atmospheric pressure.

A Succinct Review on Upgrading of Lignin-Derived Bio-oil Model Components

Increasing energy demand and depleting non-renewable energy resources have centred the researcher’s cognition to develop a sustainable technology that can exploit renewable energies. Renewable energies include solar energy, wind energy, tidal energy, hydropower, biomass but leaving a snag there that only biomass, as the renewable energy resource, could be the sustainable alternative for transportation fuels because it delivers sustainable carbon. Biomass comprises of three main units, i.e. cellulose, hemicellulose, and lignin. In the recent past, cellulose and hemicellulose have acquired much attention but, on the other hand, lignin scuffled to get proper consideration. However, earlier it has been used to produce a less effective heat and electricity by combustion. Currently, lignin is magnanimous amongst researchers because of its higher energy density, great source for phenolic fine chemicals, etc. Bio-oils derived from fast pyrolysis of lignocellulosic biomass comprise of more than 300 oxy-compounds which vitiate its quality in the form of low pH value, less stable, highly viscous, and low heating value for the application as transportation fuel. Therefore, it needs the proper upgradation technology to make it exploitable for transportation fuels. Here in this chapter, a succinct review is carried out for the lignin-derived bio-oil model compounds such as phenol, guaiacol, anisole, vanillin, and eugenol. Guaiacol component is one of the key components in phenolic fraction of bio-oil because its presence in bio-oil is often higher and, in addition, other higher molecular weight phenolic model compounds such as vanillin and eugenol reduce to guaiacol majorly. Furthermore, guaiacol component can successfully represent a higher fraction of lignin structure because of attachment of hydroxyl and methoxy groups in its molecular structure.

Current Advances in Bio-Oil Upgrading: A Brief Discussion

Conventional fuels being on their verge of depletion and regularly increasing air pollution demand a robust need of a promising energy resource to meet the present energy demand and diminish the pollution concerns. The renewable energy resources, for instance, wind energy, tidal energy, solar energy, geothermal energy, biomass are presently being employed widely across the globe. However, out of all renewable energy resources, only biomass ensures the sustainability of carbon element for existing transportation vehicles. There have been enormous amount of research regarding the biomass and its conversion into bio-oil, but the suitable and economical bio-oil upgradation technology is still challenging. The raw bio-oil derived from the thermochemical conversion of lignocellulosic biomass comprises of a huge number of oxy-compounds which vitiate its quality as biofuel; therefore, the research regarding the upgradation of raw bio-oil is emerging as one of the fastest and exciting research field amongst researchers across the globe. In this chapter, a comprehensive review of types of biomass, available methods of conversion, bio-oil chemistry, and the bio-oil upgradation is carried out. In addition, single component-wise upgradation of raw bio-oil components, e.g. glucose, fructose, acetic acid, furfural, glycerol, over various catalysts is reviewed. Along with the experimental works, this article also aims for the review of several contemporary theoretical works which are carried out for the investigations of the reaction mechanisms behind the conversion of various bio-oil components. Currently, the density functional theory (DFT) is widely applied as a computational tool for the accurate investigation of reaction mechanisms of various bio-oil components; therefore, numerous studies based on the DFT methods are also included.