Nanda Kishore

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.

CFD simulations on the effect of catalysts on the hydrodeoxygenation of bio-oil

Bio-oil derived from lignocellulose biomass is an emerging alternative resource to conventional fossil fuel. However, the as-obtained unprocessed bio oil is oxy-rich, has low pH and contains high moisture, which suppresses the heating value; thus, its mixing with conventional fuel is not compatible. Therefore, studies on the upgradation of bio oil using catalytic hydrodeoxygenation (HDO) have become prominent in recent years. This study presents computational fluid dynamics (CFD) based simulation results on the effect of catalysts (Pt/Al2O3, Ni–Mo/Al2O3, Co–Mo/Al2O3) on the upgradation of bio oil using a hydrodeoxygenation process in an ebullated bed reactor. These numerical simulations are performed using an Eulerian multiphase flow module that is available in a commercial CFD based solver, ANSYS Fluent 14.5. Prior to obtaining the new results, the present numerical solution methodology is validated by reproducing some of the experimental results on the upgradation of bio oil available in the literature. Furthermore, the influence of weight hourly space velocities (WHSVs), operating temperature, and pressure inside the reactor for the different catalysts on the performance of HDO for bio oil upgradation in an ebullated bed reactor are delineated. It is observed that the gaseous stream products are higher in the presence of Pt/Al2O3 catalyst; phenols are higher when Ni–Mo/Al2O3 is used, and higher aromatics are obtained with the Co–Mo/Al2O3 catalyst. Finally, a comparison among the mass fraction of the individual species of three phases with respect to different catalysts for various combinations of WHSV, temperature and pressure values are presented.

Momentum and Heat Transfer Phenomena for Power–Law Liquids in Assemblages of Solid Spheres of Moderate to Large Void Fractions

This work extends our previously reported results for the flow of and heat transfer from expanded beds of solid spheres to power–law fluids by using a modified and more accurate numerical solution procedure. Extensive results have been obtained to elucidate the effects of the Reynolds number (Re), the Prandtl number (Pr), the power–law index (n), and the bed voidage (ϵ) on the flow and heat transfer behavior of assemblages of solid spheres in the range of parameters: 1 ≤ Re ≤ 200, 1 ≤ Pr ≤ 1000, 0.6 ≤n ≤ 1.6, and 0.7 ≤ϵ ≤ 0.999999. The large values of bed voidage are included here to examine the behavior in the limit of an isolated sphere. As compared to Newtonian fluids, for fixed values of the Reynolds number and the voidage, the total drag coefficient decreases and the average Nusselt number increases for shear thinning fluids (n < 1); whereas, for shear thickening fluids (n > 1), the opposite behavior is observed. The drag results corresponding to bed voidage, ϵ = 0.99999, are very close to that of a single sphere; whereas, the heat transfer results approach this limit at ϵ = 0.999. Based on the present numerical results, simple correlations for drag coefficient and average Nusselt number are proposed which can be used to calculate the pressure drop for the flow of a power–law fluid through a bed of particles, or rate of sedimentation in hindered settling and the rate of heat transfer in assemblages of solid spheres in a new application. Broadly speaking, all else being equal, shear-thinning behavior promotes heat transfer, whereas shear-thickening behavior impedes it.

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.

CFD simulations of catalytic hydrodeoxygenation of bio-oil using Pt/Al2O3 in a fixed bed reactor

The upgradation of pyrolysis bio-oil by a hydrodeoxygenation (HDO) process using a Pt/Al2O3 catalyst is numerically investigated using a computational fluid dynamics (CFD) based commercial solver, ANSYS Fluent 14.5. In the simulations, a fixed bed reactor with concurrent upflow of unprocessed bio-oil and H2 gas is introduced. The dimensions of the reactor and the thermo-physical properties of all three phases are adopted from experimental data available in the literature. The size of the catalyst particles is 10 μm and a loading of 60 g is used in the present simulations. The main aim of this work is to numerically investigate the effects of weight hourly space velocity (WHSV), temperature (T) and pressure (P) on the upgradation of bio-oil using catalytic hydrodeoxygenation and to delineate the effects of pertinent parameters on the distribution of the various products of the upgraded biofuel. For this purpose, the following ranges of parameters are considered in this work: weight hourly space velocity, WHSV = 2–4 h−1, temperature, T = 623–673 K, and pressure, P = 6996–10443 kPa. Briefly, the results indicate that a lower WHSV and higher pressure are favourable for the yield of aromatics and the conversion of high non-volatile components, however the effect of temperature is negligible. Finally, a comparison is made between the conversion of high non-volatiles and phenols and the yield of alkanes and aromatics obtained in fixed bed and fluidized reactors for identical values of WHSV, temperature and pressure. It is found that the performance of the HDO of bio-oil using a Pt/Al2O3 catalyst in a fixed bed reactor is superior in all aspects in comparison to fluid bed reactors in the present range of pertinent parameters.

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.

A numerical study on flow and drag phenomena of spheroid bubbles in Newtonian and shear-thinning power-law fluids

Abstract Effects of the Reynolds number, aspect ratio of spheroid bubbles, and power-law behavior index of shear-thinning liquids on the flow and drag behavior of spheroid bubbles are elucidated using a computational fluid dynamics-based numerical solver, ANSYS Fluent 14. The solution methodology is extensively benchmarked via detailed domain and grid independence study and by comparing present results of spherical bubbles in Newtonian and shear-thinning power-law fluids with their literature counterparts. Further extensive new results are reported over a wide range of pertinent conditions as follows: Reynolds number, Re: 1 – 200; aspect ratio of spheroid bubbles, e: 0.5 – 2.5, and power-law behavior index, n: 0.2 – 1. The size of the recirculation wake decreases with decreasing power-law index, and/or with decreasing bubble aspect ratio, and/or with decreasing Reynolds number. For bubbles of aspect ratio e > 1, a crossover Reynolds number is observed with respect to the power-law index, i.e. below the crossover Reynolds number, the drag coefficient of bubble increases with decreasing power-law index; whereas, above the crossover Reynolds number, a reverse trend is observed. Finally, based on the present numerical results, a simple predictive correlation is proposed for the total drag coefficients of spheroid bubbles rising in Newtonian and power law liquids, which can be used in new applications.

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.