Hydrogen via steam reforming of liquid biofeedstock

This review examines the use of steam reforming to convert bioliquids, such as ethanol, glycerol, butanol, vegetable oil, bio-oils and biodiesel, into hydrogen gas. The focus of the research was to investigate the research being undertaken in terms of catalyst developments for the steam reforming of the aforementioned feedstock, and to determine the perspective opportunities in this area. Hydrogen production by steam reforming of bio-oil, ethanol and pure glycerol has been widely investigated; several thermodynamic and catalytic investigations are available restricting new investigations. In contrast, hydrogen production from waste streams, vegetable oil, biodiesel and butanol is very recent and has room for further developments

Thermodynamic evaluation of dry reforming of vegetable oils for production of synthesis gas

The dry reforming (DR) is a promising technology for utilization of greenhouse gas, carbon dioxide, to produce synthesis gas for downstream synthesis of valuable chemicals and fuels. In this study, equilibrium of DR and autothermal dry reforming (ATDR) of vegetable oils was investigated by Gibbs free energy minimization method. The effects of various process variables of DR and ATDR of vegetable oils such as temperature (673–1273 K), carbon dioxide-to-carbon mole ratio (CCMR) (0.5–3.0), and oxygen-to-carbon mole ratio (OCMR) (0–1.0) were studied to obtain equilibrium products composition, thermodynamically promising operating conditions, and thermoneutral conditions of the process. The study revealed that insignificant amount of coke and compounds containing two or more carbon atoms were formed for both DR and ATDR of vegetable oils. The hydrogen yield was found to increase with increase in temperatures for DR of vegetable oil. At temperature 983 K and above, the hydrogen yield was found to increase with CCMR, reach maxima, and then decrease with further increase in CCMR. The carbon dioxide conversion and yield of CO and water were increased and yield of methane was decreased with increase in temperature. The yield of CO and water were increased and the conversion of carbon dioxide and yield of methane were decreased with increase of CCMR. For ATDR of vegetable oils, the reduced yield of CO and methane and enhanced yield of water and hydrogen (up to temperature of maximum hydrogen yield) were observed compared to that of DR. From critical analysis of the results of DR and ATDR of vegetable oil, the optimum conditions for maximum yield of hydrogen with very low yield of methane were determined as 1000–1050 K, CCMR of about 1, and oxygen-to-carbon mole ratio of 0.6–0.7. It was observed that about 80% hydrogen yield with 78–83 moles of CO and 0.2–0.6 moles of methane per mole of vegetable oil could be obtained under the optimum conditions

Hydrodeoxygenation of Triglyceride and Karanja oil for the Production of Green Diesel over Supported Metal and Metals-support Composite Catalysts

Transportation fuels play an extremely vital role in the daily life of today’s modern civilization. At present, the transportation fuels are predominantly derived from finite fossil fuels. It is one of the leading energy-consuming sectors with the stake of about 28% of the energy consumption in the world. The bio-fuels are the attractive alternatives to fossil fuels derived transportation fuels. The biodiesel has thus been attracted huge attention globally as a potential substitute of petro-diesel. The lower calorific value and unfavorable cold flow properties, however, limit the application of biodiesel as blending with petro-diesel to the extent of 20 wt% only for direct use in an unmodified combustion engine. Therefore, the methods of production of hydrocarbon analogous liquid transportation fuels from biomass are highly essential for shifting dependency away from limited fossil fuels. Triglycerides are the promising feedstock for the production of hydrocarbon transportation fuels due to their simplicity in chemical structure and lower content of oxygen compared to cellulosic biomass. Moreover, the triglycerides are composed of C8-C24 fatty acids with the majority being C16 and C18 fatty acids. Therefore, the removal of oxygen heteroatoms from triglycerides will lead to diesel range hydrocarbons commonly known as green diesel. Hydrodeoxygenation (HDO) in the presence of high hydrogen pressure is a promising approach for the production of green diesel in high yield from triglycerides. India has estimated annual production potential of 20 million tons of inedible oil seeds (e.g. karanja, neem, mahua etc) with only a few percentage of utilization with the share of karanja oil seeds being 0.2 million tons alone. In the present work, the HDO of pure triglyceride and karanja oil was investigated using supported nickel catalyst and ordered mesoporous Ni-alumina and NiMo-alumina composite catalysts. The objectives of the present work are (i) HDO of pure triglyceride over alumina supported nickel catalyst to delineate a comprehensive reaction mechanism and develop a mechanistic kinetic model over a wide range of process conditions, (ii) HDO of neat karanja oil over supported (γ-Al2O3, SiO2, and HZSM-5) nickel catalyst to articulate the roles of acidity of the catalysts, nickel loading on γ-Al2O3, and temperature on conversion of oxygenates and product distribution and to demonstrate the suitability of the green diesel for direct application as transportation fuel, (iii) HDO of karanja oil using ordered mesoporous nickel-alumina composite catalyst to demonstrate its superior catalytic activity compared to γ-Al2O3 and mesoporous alumina supported nickel catalyst in relation to their structural properties, and (iv) HDO of karanja oil using NiMo-alumina composite catalyst to demonstrate its superior catalytic activity compared to mesoporous alumina supported NiMo catalyst in relation to their structural properties. The supported nickel catalysts were prepared by incipient wetness impregnation method. The ordered mesoporous Ni-alumina and NiMo-alumina composite catalysts were prepared by one-pot evaporation-induced self-assembly method. The catalysts were characterized by BET, temperature programmed reduction (TPR), temperature programmed desorption of NH3 (NH3-TPD), pulse chemisorption, UVvis-NIR, Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and 27Al solid state NMR. The spent catalysts were further characterized using Fourier transform infrared (FTIR) spectroscopy and thermo gravimetric analysis (TGA). The physicochemical properties of karanja oil such as acid value, iodine value, FAME composition, density, viscosity, and elemental composition (CHNS-O) were measured using standard methods. Similarly, green diesel was characterized to measure density, viscosity, pour point, flash and fire point, elemental composition, lower calorific value, and chemical composition. HDO studies were performed in a 300 ml stainless steel high-pressure batch reactor in batch and semi-batch mode. The products of the liquid samples were identified with a gas chromatography (GC) equipped with a mass spectrometer detector and quantified by GC equipped with a flame ionization detector. The gas samples were analyzed by online GC equipped with a thermal conductivity detector and flame ionization detector. A wide range of linear alkanes (C12-C22) was observed as hydrocarbon products during HDO of karanja oil. Palmitic acid, stearic acid, hexadecanol, octadecanol, octadecanal, mono-palmitate, mono-stearate, and fatty esters were observed as oxygenated intermediates depending upon the nature of the catalyst. The gas phase analysis further revealed the formation of CO, CO2, and C1- C5 hydrocarbons. During HDO of triglyceride (1:2 molar mixtures of tripalmitin and tristearin), it was observed that triglyceride instantaneously converted to respective fatty acids through di-glyceride and mono-glyceride intermediates with propane as a coproduct. The fatty acids then undergo reduction under hydrogen atmosphere over the metallic site of the catalyst to form the fatty aldehyde. The fatty aldehyde further converted to alkane mainly through two different reaction pathways (RP-I and RP-II). Following RP-I, the fatty aldehydes subsequently converted to the corresponding alkane through decarbonylation reaction with the release of one mole of CO. The HDO of triglycerides was found follow RP – I predominately over supported nickel catalyst. In RP – II, the fatty aldehydes further reduced to corresponding fatty alcohols. The fatty alcohols then undergo dehydration to corresponding olefins followed by its hydrogenation to the alkane. The RP – II was dominating one over NiMo-alumina composite catalyst. The formation of fatty esters (RP – III) was observed over NiMo-alumina composite catalysts. The cracking reaction (RP – IV) was observed only at elevated reaction temperatures. The rate constants of the kinetic model were estimated based on the experimental results at the different temperatures for HDO of triglyceride. The rate constant corresponding to RP-I was significantly higher than that of RP-II. The activation energy for the reduction of fatty acids to fatty aldehydes, reduction of fatty aldehydes to fatty alcohols, decarbonylation of fatty aldehydes to n-alkane were 80 kJ/mol, 85 kJ/mol and 90 kJ/mol respectively. The rate constants were further correlated with catalyst loading by a linear correlation with zero intercept. The product distribution profiles obtained for estimated kinetic parameters were agreed well with the experiments. The developed kinetic model was, further, validated using experimental data at various hydrogen-to-nitrogen mole ratios in the gas phase. HDO of neat karanja oil was investigated in a semi-batch reactor over supported (γ-Al2O3, SiO2, and HZSM-5) nickel catalyst, The catalysts were associated with both dispersed and bulk nickel/nickel oxide depending on the extent of nickel loading and nature of support. Virgin karanja oil was composed of 76 wt% C18 fatty acids with 15 wt% oxygen. Nickel exhibited stronger interaction with γ-Al2O3 than SiO2 and HZSM-5. γ-Al2O3 supported nickel catalyst thus demonstrated superior HDO activity with least tendency towards cracking. On the other hand, catalytic cracking become significant over strongly acidic HZSM-5 and 5.7 mmol Ni/HZSM-5 leading to the formation of the larger extent of lighter alkanes. γ-Al2O3 supported nickel catalyst with low nickel loading (≤3.0 mmol) led to a large extent of cracking with high wt% of lighter alkanes. With ≥4.3 mmol nickel loading on γ-Al2O3, the reaction, however, proceeded largely through HDO pathway. The thermal cracking became prominent above 653 K. The optimal process conditions for maximizing HDO pathway were 653 K and 5.7 mmol nickel loading on γ-Al2O3 at 35 bars H2. ∼80 wt% of KO converted to the liquid product with 65 wt% C15-C18 hydrocarbons and H/C atomic ratio of 1.97. Physicochemical properties of the liquid product were matched reasonably well with the specification of light diesel oil. Mesoporous nickel-alumina composite catalysts are mainly associated with dispersed tetrahedral (or octahedral) coordinated nickel aluminate with strong metal-support interaction and a negligible amount of extra-framework nickel. Mesoporous nickel-alumina composite catalysts thus demonstrated superior catalytic activity over γ-Al2O3 and mesoporous alumina supported nickel catalysts. The NiMo-alumina composite catalysts demonstrated superior catalytic activity for HDO of karanja oil over mesoporous alumina supported nickel catalyst. It was mainly due to (i) stronger metal-support interaction with a lesser extent of bulk nickel oxide, (ii) the presence of larger extent of nickel-molybdenum alloy and lesser extent of Al2(MoO4)3, (iii) slightly higher surface area than mesoporous alumina supported NiMo. The RP-II was the dominating reaction route over NiMo-alumina composite catalyst with octadecane as the dominating product. The selectivity towards octadecane was increased with increasing molybdenum content in NiMoalumina composite catalyst

Reforming of vegetable oil for production of hydrogen: A thermodynamic analysis

The vegetable oils are one of the promising renewable feedstock for production of hydrogen suitable for application in hydrogen based fuel cells for electrical power generation. In the present work, a thermodynamic equilibrium analysis of steam reforming (SR) and autothermal steam reforming (ATSR) of vegetable oils to synthesis gas was investigated by Gibbs free energy minimization method. The thermodynamic equilibrium analysis was performed considering the vegetable oils as a mixture of triglycerides containing three same fatty acid groups in the structure. The property method used for equilibrium analysis was first regressed using available physical and chemical properties of the considered triglycerides. The regressed property method was then used to calculate the equilibrium products composition. The effects of various parameters of SR of vegetable oils, temperature and steam-to-carbon ratio (SCR), on hydrogen yield and selectivity of CO and methane was studied in a broad range of temperature (573-1273 K) and SCRs (1-6). The optimum conditions for SR of vegetable oils were then determined for maximum hydrogen yield with very low selectivity of methane. The thermodynamic equilibrium analysis of ATSR of vegetable oils was then performed at different oxygen-to-carbon ratios and thermoneutral conditions were then determined for various operating conditions

Reaction mechanism and kinetic modeling for the hydrodeoxygenation of triglycerides over alumina supported nickel catalyst

The present work provides a systematic study to delineate the reaction mechanism and develop a mechanistic kinetic model for the hydrodeoxygenation (HDO) of triglycerides (TG) over alumina supported nickel catalyst. The HDO of 1:2 molar mixtures of tripalmitin and tristearin was studied in a batch reactor over a wide range of process conditions. The results showed that TG instantaneously converted to respective fatty acids. The fatty acids further converted to the fatty aldehydes. The fatty aldehydes, then, rapidly converted to alkanes by two parallel reaction pathways. The decarbonylation of fatty aldehyde (RP-I) was the dominating route compared to the reduction of the fatty aldehyde to fatty alcohol followed by its dehydration and hydrogenation (RP-II). A mechanistic kinetic model was developed based on the observed reaction pathway to correlate the experimental results. The rate constants for the conversion of palmitic acid and stearic acid to alkanes were matched closely with each other thereby demonstrating that HDO is independent of fatty acid chain length. The developed kinetic model was further validated using experimental data at various hydrogen-to-nitrogen mole ratios in the gas phase. Furthermore, the rate constants obtained for various catalyst loadings were correlated by a linear equation with zero intercept

Reaction mechanism and kinetic modeling for the hydrodeoxygenation of triglycerides over alumina supported nickel catalyst

The present work provides a systematic study to delineate the reaction mechanism and develop a mechanistic kinetic model for the hydrodeoxygenation (HDO) of triglycerides (TG) over alumina supported nickel catalyst. The HDO of 1:2 molar mixtures of tripalmitin and tristearin was studied in a batch reactor over a wide range of process conditions. The results showed that TG instantaneously converted to respective fatty acids. The fatty acids further converted to the fatty aldehydes. The fatty aldehydes, then, rapidly converted to alkanes by two parallel reaction pathways. The decarbonylation of fatty aldehyde (RP-I) was the dominating route compared to the reduction of the fatty aldehyde to fatty alcohol followed by its dehydration and hydrogenation (RP-II). A mechanistic kinetic model was developed based on the observed reaction pathway to correlate the experimental results. The rate constants for the conversion of palmitic acid and stearic acid to alkanes were matched closely with each other thereby demonstrating that HDO is independent of fatty acid chain length. The developed kinetic model was further validated using experimental data at various hydrogen-to-nitrogen mole ratios in the gas phase. Furthermore, the rate constants obtained for various catalyst loadings were correlated by a linear equation with zero intercept

Hydrodeoxygenation of karanja oil over supported nickel catalysts: influence of support and nickel loading

Production of hydrocarbon transportation fuels from triglycerides is extremely important to reduce dependency on limited fossil fuels. The present article provides a systematic examination of hydrodeoxygenation (HDO) of karanja oil (KO) in a semi-batch reactor over supported (γ-Al2O3, SiO2, and HZSM-5) nickel catalysts. The catalysts were associated with both dispersed and bulk nickel/nickel oxide depending on the extent of nickel loading and nature of the support. Virgin KO is composed of ~76 wt% C18 fatty acids with ~15 wt% oxygen. HDO of KO resulted in a wide range of alkanes (C10–C22) with n-heptadecane being the major one. Transformation of KO into alkanes proceeds through three distinct routes: HDO, catalytic cracking, thermal cracking, or their combination. Highly acidic catalysts (HZSM-5 and Ni/HZSM-5) promote catalytic cracking leading to formation of a large amount of lighter alkanes. The cracking reaction becomes significant over the γ-Al2O3 supported nickel catalyst with ≤15 wt% nickel loading at elevated temperatures. A strong metal–support interaction favored the HDO pathway over the γ-Al2O3 supported nickel catalyst with ≥20 wt% nickel loading. About 80 wt% of KO was converted to the liquid product with physicochemical properties comparable with light diesel oil

Kinetics of hydrodeoxygenation of stearic acid using supported nickel catalysts: Effects of supports

The hydrodeoxygenation of fatty acids derived from vegetable and microalgal oils is a novel process for production of liquid hydrocarbon fuels well-suited with existing internal combustion engines. The hydrodeoxygenation of stearic acid was investigated in a high pressure batch reactor using n-dodecane as solvent over nickel metal catalysts supported on SiO2, γ-Al2O3, and HZSM-5 in the temperature range of 533-563 K. Several supported nickel oxide catalysts with nickel loading up to 25 wt.% were prepared by incipient wetness impregnation method and reduced using hydrogen. The catalysts were then characterized by BET, TPR, H2 pulse chemisorption, TPD, XRD, and ICP-AES. Characterization studies revealed that only dispersed nickel oxide was present up to 15 wt.% nickel loading on γ-Al2O3. The acidity of the supports depends on nickel loading of oxidized catalysts and increases with increasing nickel loading up to 15 wt.%. n-Pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and l-octadecanol were identified as products of hydrodeoxygenation of stearic acid with n-heptadecane being primary product. The catalytic activity and selectivity to products for hydrodeoxygenation of stearic acid depends strongly on acidity of the supports. The maximum selectivity to n-heptadecane was observed with nickel supported γ-Al2O3 catalyst. A suitable reaction mechanism of hydrodeoxygenation of stearic acid was delineated based on products distribution. The conversion of stearic acid was increased with increasing reaction time, nickel loading on γ-Al2O 3, temperature, and catalyst loading. Complete conversion of stearic acid was accomplished with more than 80% selectivity to n-heptadecane at reasonable reaction temperature of 563 K after 240 min of reaction using 15 wt.% Ni/γ-Al2O3 catalyst. An empirical kinetic model was also developed to correlate the experimental data

Hydrodeoxygenation of karanja oil using ordered mesoporous nickel-alumina composite catalysts

This study presents a systematic investigation of hydrodeoxygenation (HDO) of karanja oil over ordered mesoporous nickel-alumina composite catalysts. These catalysts were prepared by the evaporation-induced self-assembly method. The catalysts showed the ordered mesoporous structure up to 15 wt% nickel content in the catalyst. The mesoporous structure, however, became disorder beyond this nickel content. The catalysts were associated with catalytically active dispersed tetrahedral (or octahedral) coordinated nickel aluminate with strong interaction with alumina and a negligible amount of catalytically poor extra-framework nickel. The mesoporous nickel-alumina composite catalysts thus demonstrated superior catalytic activity compared to mesoporous alumina and γ-Al2O3 supported nickel catalysts. Wide ranges of linear paraffins (C14-C22) were formed in the reaction with C17 alkane as the main product. The conversion of oxygenates was enhanced with the rise in initial hydrogen pressure and nickel content in the catalyst without affecting product distribution much. The cracking of heavy hydrocarbons was, however, significant at elevated reaction temperatures, resulting in high selectivity to C17 alkane. For the optimum nickel loading of 20 wt%, the conversion of oxygenates was almost 100% with about 70 wt% C17 alkane and 15 wt% each lower and higher than C17 alkanes at 633 K and 2 h reaction time