Hydrodeoxygenation Step Research Articles

Sustainable Aviation Fuel Molecules from (Hemi)Cellulose: Computational Insights into Synthesis Routes, Fuel Properties, and Process Chemistry Metrics.

Production of sustainable aviation fuels (SAFs) can significantly reduce the aviation industry's carbon footprint. Current pathways that produce SAFs in significant volumes from ethanol and fatty acids can be costly, have a relatively high carbon intensity (CI), and impose sustainability challenges. There is a need for a diversified approach to reduce costs and utilize more sustainable feedstocks effectively. Here, we map out catalytic synthesis routes to convert furanics derived from the (hemi)cellulosic biomass to alkanes and cycloalkanes using automated network generation with RING and semiempirical thermochemistry calculations. We find >100 energy-dense C8-C16 alkane and cycloalkane SAF candidates over 300 synthesis routes; the top three are 2-methyl heptane, ethyl cyclohexane, and propyl cyclohexane, although these are relatively short. The shortest, least endothermic process chemistry involves C-C coupling, oxygen removal, and hydrogen addition, with dehydracyclization of the heterocyclic oxygens in the furan ring being the most endothermic step. The global warming potential due to hydrogen use and byproduct CO2 is typically 0.7-1 kg CO2/kg SAF product; the least CO2 emitting routes entail making larger molecules with fewer ketonization, hydrogenation, and hydrodeoxygenation steps. The large number of SAF candidates highlights the rich potential of furanics as a source of SAF molecules. However, the structural dissimilarity between reactants and target products precludes pathways with fewer than six synthetic steps, thus necessitating intensified processes, integrating multiple reaction steps in multifunctional catalytic reactors.

Highly selective hydrodeoxygenation catalyst for sustainable aviation fuel production from used cooking oil

The production of Sustainable Aviation Fuel (SAF) utilizing used cooking oil (UCO) as a renewable bio-waste resource holds immense potential for promoting sustainability in the aviation sector. In this study, SAF synthesis via hydrodeoxygenation of pretreated UCO over Ni-Mo/alumina-silica catalysts followed up hydroisomerization of deoxygenated oil has been investigated in a fixed-bed reactor. The effect of Al2O3/SiO2 ratio on the physico-chemical properties of Al2O3-SiO2 support and on the overall hydrodeoxygenation performance of the Ni-Mo catalyst supported on Al2O3-SiO2 has been investigated. NiMo catalyst supported on Al2O3-SiO2 in a 70:30 ratio achieved 86.69 % UCO conversion during the hydrodeoxygenation step and exhibited 74.79 % jet range hydrocarbon fuel selectivity under mild conditions (350°C, 1.1 h⁻¹ WHSV, 6 MPa, H2/oil (v/v): 400). The catalyst activity remained stable for >100 hours highlighting its good stability under the experimental conditions investigated. This work demonstrates the potential of tailor-made supported catalysts for highly selective single-step conversion of UCO into jet-range hydrocarbons, offering a significant step towards the production of sustainable aviation fuels.

Selective hydrodeoxygenation of α, β-unsaturated carbonyl compounds to alkenes

Achieving selective hydrodeoxygenation of α, β-unsaturated carbonyl groups to alkenes poses a substantial challenge due to the presence of multiple functional groups. In this study, we develop a ZnNC-X catalyst (X represents the calcination temperature) that incorporates both Lewis acidic-basic sites and Zn-Nx sites to address this challenge. Among the catalyst variants, ZnNC-900 catalyst exhibits impressive selectivity for alkenes in the hydrodeoxygenation of α, β-unsaturated carbonyl compounds, achieving up to 94.8% selectivity. Through comprehensive mechanism investigations and catalyst characterization, we identify the Lewis acidic-basic sites as responsible for the selective hydrogenation of C=O bonds, while the Zn-Nx sites facilitate the subsequent selective hydrodeoxygenation step. Furthermore, ZnNC-900 catalyst displays broad applicability across a diverse range of unsaturated carbonyl compounds. These findings not only offer valuable insights into the design of effective catalysts for controlling alkene selectivity but also extend the scope of sustainable transformations in synthetic chemistry.

Hybrid Gasoline Production from Black Liquor through Coprocessing

A new route is presented as a stepwise upgrading process from black liquor issued from the kraft process to hybrid gasoline: (i) hydrothermal liquefaction (HTL) to produce biocrude, (ii) removal of alkaline metal salts, (iii) hydrodeoxygenation (HDO) for oxygen removal and decrease of molar weight, and finally (iv) coprocessing with vacuum gas oil (VGO) by catalytic cracking to produce gasoline as a second-generation transportation biofuel. A high degree of deoxygenation was found to be quite beneficial to the further cracking of the refined crude oil into gasoline fractions. Thus, for this coprocessing step, it was found that, by limiting the percentage of added pretreated biocrude to about 10 wt %, high naphtha yields (45% compared to 48% for pure VGO cracking) were maintained, and without a significant change in the coke yield. This result is promising since naphtha, the gasoline-rich fraction, is the main target product in FCC. More research is needed in the detailed characterization of the coprocessing products and in checking the quality and compatibility of the hybrid fuel with gasoline standards. Further optimization in the HTL and HDO steps can likely be achieved, possibly allowing coprocessing of larger quantities of HDO biocrude than 10 wt %.

Electrolysis Can Be Used to Resolve Hydrogenation Pathways at Palladium Surfaces in a Membrane Reactor.

For common hydrogenation chemistries that occur at high temperatures (where H2 is adsorbed and activated at the same surface which the substrate must also adsorb for reaction), there is often little consensus on how the reactions (e.g., hydro(deoxy)genation) actually occur. We demonstrate here that an electrocatalytic palladium membrane reactor (ePMR) can be used to study hydrogenation reaction mechanisms at ambient temperatures, where the catalyst does not necessarily undergo structural reorganization. The ePMR uses electrolysis and a hydrogen-selective palladium membrane to deliver reactive hydrogen to a catalyst surface in an adjacent compartment for reaction with an organic substrate. This process forms the requisite metal-hydride surface for hydrogenation chemistry, but at ambient temperature and pressure, and without a H2 source. We demonstrate the utility of this analytical tool by studying the hydrogenation of benzaldehyde at palladium nanocubes with dimensions of 13–24 nm. This experimental design enabled us to resolve that the alcohol product forms at the facial sites, whereas the hydrodeoxygenation step occurs at edge sites. These observations enabled us to develop the first site-specific definition of how a carbonyl species undergoes hydro(deoxy)genation.

Hydrothermal liquefaction versus catalytic hydrodeoxygenation of a bioethanol production stillage residue to platform chemicals: A comparative study

Biobased chemicals like phenols and aromatics are preferably produced from cheap biomass waste streams. In this work, we have explored the potential of a eucalyptus-derived second generation bioethanol production stillage (BPS) residue for this purpose. A comparative study between a hydrothermal liquefaction (HTL) and a catalytic hydrodeoxygenation (HDO) step, as well as a 2-step HTL-HDO approach is reported, targeting at value-added low molecular weight platform chemicals (mainly alkylphenols and aromatics). HDO was observed to be a more suitable strategy than HTL for the production of organic oils enriched in valuable monomers. The direct HDO of the BPS using a commercial Ru/C catalyst at 450 °C and 100 bar H2 pressure led to an organic product oil (30.7 wt%) with a total monomer yield of 25.2 wt% (13.2 wt% of alkylphenolic+aromatics), compared to a 53.2 wt% of a product oil with 10.0 wt% monomers for the HTL step (305 °C). A 2-step HTL-HDO strategy was compared with the direct HDO approach. Comparable alkylphenolic+aromatic yields were obtained through this approach based on initial BPS intake (13.2 wt% vs 12.3 wt% for the direct HDO and HTL-HDO approach, respectively). Lower HTL temperatures (305 °C) for the first step are preferred to prevent over hydrogenation in the subsequent HDO step. As such, HTL appears a suitable pre-treatment for BPS and can (i) solve the issues related to the feeding of solids in pressurized continuous reactors for HDO and (ii) prevent coke formation during the HDO step, thus improving catalyst stability and durability.

The conversion of coconut oil into hydrocarbons within the chain length range of jet fuel

The present work concerns the conversion of coconut oil into hydrocarbons within the chain length range of jet biofuel through the pathway called hydroprocessing of esters and fatty acids (HEFA). The aim is to employ the resulting mixture as an alternative biofuel in the aviation sector. The process involved two steps: (i) hydrodeoxygenation (HDO) over a sulfided NiMo/Al2O3 catalyst, followed by (ii) hydroisomerization (HIS) over a Pt/SAPO-11 catalyst. Preliminary tests were carried out with model compounds: lauric acid and n-dodecane for HDO and HIS, respectively. In both steps, middle processing temperatures (~ 340–350 °C) were low enough to prevent excessive cracking but high enough to provide acceptable reaction rates and to prevent coke formation. The HDO step rendered a mixture constituted basically by n-alkanes. The subsequent HIS permitted to increase the content of branched chains. The final HEFA-SPK (where SPK is the abbreviation for synthetic paraffinic kerosene) had an acidic index zero and a relatively high content of monomethylalkanes. Furthermore, due to the fatty chain composition of the starting oil, the chain length distribution of the resulting biofuel matched well with that of conventional jet fuels, so that subsequent steps of cracking and fractionation, which increase costs and reduce the process yield, were not required. The obtained results are encouraging in terms of using coconut oil-based HEFA-SPK in the formulation of sustainable alternative jet fuels at competitive costs and with relevant environmental and social benefits.

Limited life cycle and cost assessment for the bioconversion of lignin-derived aromatics into adipic acid.

Lignin is an abundant and heterogeneous waste byproduct of the cellulosic industry, which has the potential of being transformed into valuable biochemicals via microbial fermentation. In this study, we applied a fast-pyrolysis process using softwood lignin resulting in a two-phase bio-oil containing monomeric and oligomeric aromatics without syringol. We demonstrated that an additional hydrodeoxygenation step within the process leads to an enhanced thermochemical conversion of guaiacol into catechol and phenol. After steam bath distillation, Pseudomonas putida KT2440-BN6 achieved a percent yield of cis, cis-muconic acid of up to 95 mol% from catechol derived from the aqueous phase. We next established a downstream process for purifying cis, cis-muconic acid (39.9 g/L) produced in a 42.5 L fermenter using glucose and benzoate as carbon substrates. On the basis of the obtained values for each unit operation of the empirical processes, we next performed a limited life cycle and cost analysis of an integrated biotechnological and chemical process for producing adipic acid and then compared it with the conventional petrochemical route. The simulated scenarios estimate that by attaining a mixture of catechol, phenol, cresol, and guaiacol (1:0.34:0.18:0, mol ratio), a titer of 62.5 (g/L) cis, cis-muconic acid in the bioreactor, and a controlled cooling of pyrolysis gases to concentrate monomeric aromatics in the aqueous phase, the bio-based route results in a reduction of CO2 -eq emission by 58% and energy demand by 23% with a contribution margin for the aqueous phase of up to 88.05 euro/ton. We conclude that the bio-based production of adipic acid from softwood lignins brings environmental benefits over the petrochemical procedure and is cost-effective at an industrial scale. Further research is essential to achieve the proposed cis, cis-muconic acid yield from true lignin-derived aromatics using whole-cell biocatalysts.

Catalytic hydropyrolysis of lignin: Suppression of coke formation in mild hydrodeoxygenation of lignin-derived phenolics

Lignin, with its polyaromatic structure and as a main component of lignocellulosic biomass, is considered as an important renewable source of aromatics which are currently obtained from fossil fuels. Lignin pyrolysis gives a liquid product with a high content of phenolic compounds which can be further upgraded to aromatic hydrocarbons through catalytic approaches. In this work, in-situ catalytic hydropyrolysis combined with a subsequent ex-situ catalytic hydrodeoxygenation step was implemented to achieve an enhanced conversion of kraft lignin into aromatic hydrocarbons. The main point is that the ex-situ catalytic upgrading was conducted at mild conditions (temperature: 350 °C; pressure: 1 atm). HY was used as in-situ catalyst for enhanced decomposition of lignin. Fe/HBeta, FeReOx/MCM-41, Fe/ZrO2 and FeReOx/ZrO2 were used as ex-situ catalyst, among which the oxophilic, mesoporous and mild-acidic catalyst of FeReOx/ZrO2 revealed the highest HDO efficiency. Importantly, FeReOx/MCM-41, Fe/ZrO2 and FeReOx/ZrO2 led to significantly lower yield of coke compared to a zeolite-supported catalyst like Fe/HBeta. This suppression of coke formation is a result of reduced phenolic trapping inside catalyst mainly due to the mesoporosity and moderate acid strength of catalyst.

Zn-loaded HY zeolite as active catalyst for iso-propylation of biomass-derived phenolic compounds: A comparative study on the effect of acidity and porosity of zeolites

Liquid bio-oil formed from pyrolysis of lignocellulosic biomass needs further upgradation by CC bond formation reaction between the phenolic compounds and small oxygenates to retain the maximum amount of carbon in the fuel range (C10C13), prior to hydrodeoxygenation step. In this contribution, we have explored the gas-phase alkylation of m-cresol with iso-propanol over zeolites like HZSM5, HBEA, HMCM22, HY, and ZnY solid acid catalysts. The fresh and spent catalysts were characterized by XRD, N2 sorption, ICP-MS, Py-FTIR, NH3-TPD, SEM, and TEM techniques. The time-on-stream and temperature studies were carried out over these catalysts at a WHSV value of 2.8h−1 to analyze the role of different active acidic sites as well as their pore dimensions on the catalytic activity and product distribution. Among all the catalysts, formation of thymol by C-alkylation was highly dominant over ZnY which has strong Lewis acid sites. Coke analysis revealed that HBEA was found to rapidly deactivate by coking (16.4% coke) and pore blocking. Time-on-stream study at 250°C showed that maximum conversion of m-cresol (92%) was obtained on fresh ZnY catalyst having strong Lewis acidity and moderate Bronsted acidity, confirming the fact that strong Lewis acidity in combination with Bronsted acidity improved the stability of iso-propyl cation and consequently, enhanced the conversion of m-cresol. Moreover, the presence of Zn2+ content in FAU zeolite framework was found to alter its acid site distribution and pore volume as compared to HY zeolite and resulted in predominant mono-alkylated product formation, especially thymol.

Dual‐bed catalyst system for the direct synthesis of high density aviation fuel with cyclopentanone from lignocellulose

In this article, we demonstrated an integrated process for the direct production of tri(cyclopentane) with cyclopentanone which can be obtained from lignocellulose. The reaction was carried out in a dual‐bed continuous flow reactor. In the first bed, cyclopentanone was selectively converted to 2,5‐dicyclopentylcyclopentanol over the Pd‐MgAl‐HT (hydrotalcite) catalyst. Under solvent‐free and mild conditions (443 K, 0.1 MPa H2), high carbon yield (81.2%) of 2,5‐dicyclopentylcyclopentanol was achieved. Subsequently, the 2,5‐dicyclopentylcyclopentanol was further hydrodeoxygenated to tri(cyclopentane) in the second bed. Among the investigated catalysts, the Ni‐Hβ‐DP prepared by deposition‐precipitation (DP) method exhibited the highest activity for the hydrodeoxygenation step. By using Pd‐MgAl‐HT as the first bed catalyst and Ni‐Hβ‐DP as the second bed catalyst, tri(cyclopentane) was directly produced at high carbon yield (80.0%) with cyclopentanone as feedstock. This polycycloalkane has high density (0.91 kg/L) and can be used as additive to improve the density and volumetric heating value of bio‐jet fuel. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2754–2761, 2016

Kinetics, thermodynamics and mechanisms for hydroprocessing of renewable oils

Intrinsic kinetics, diffusivity, energy calculations and reaction mechanism studies for the conversion of plant-oil triglycerides over Ni-W/SiO2-Al2O3 hydrocracking catalyst is reported. Specific insights into reaction mechanisms, are established using kinetic modeling and validated with experimental results. Diffusion studies and effectiveness factor calculations established diffusion–free intrinsic kinetics, with an activation energy of 115kJ/mole required for triglycerides conversion. Thermodynamic calculations further established that the heat released during propane removal step (1.15MJ/kg) was 8-times higher than that for hydrodeoxygenation step (0.14MJ/kg) and lowest for hydrocracking reactions (0.08MJ/kg). Such high exothermicity resulted in high temperature gradient across the catalyst bed (370°C above the reaction temperature).

One-pot aqueous phase catalytic conversion of sorbitol to gasoline over nickel catalyst

The carbon chain extension and hydrodeoxygenation steps play critical roles in the high-energy-density hydrocarbons production. In this paper, a systematic study had been carried out to investigate one-pot aqueous phase catalytic conversion of sorbitol to gasoline (STG) over bifunctional Ni-based catalysts. Characterization technologies of N2 physisorption, X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and NH3 temperature-programmed desorption (NH3-TPD) were used to study the textural properties, phase compositions, acid behavior and morphologies of the catalysts. The catalytic performances were tested in a fixed bed reactor. It was found that the physically mixed Ni/HZSM-5 and Ni/silica-gel (mesoporous SG) catalyst realized the carbon chain extension and exhibited excellent performances on hydrodeoxygenation (HDO) reaction (46.9% of gasoline (C5–C12) yield and 45.5% of C7–C12 hydrocarbons in the gasoline products). Especially, the temperature of STG (553–593K) was lower obviously than that of the traditional methanol to gasoline (MTG) process (623–773K). It provided a novel transformation of sorbitol to long-chain alkanes by one-pot process over the bifunctional catalyst (Ni@HZSM-5/SG), wherein hydrodeoxygenation, ketonization and aldol condensation steps were integrated.

Kinetic and FTIR studies of 2-methyltetrahydrofuran hydrodeoxygenation on Ni2P/SiO2

The hydrodeoxygenation of 2-methyltetrahydrofuran (2-MTHF) at a medium pressure of 0.5MPa is studied over a Ni2P/SiO2 catalyst. Contact time studies show the formation of n-pentanal, 1-pentanol, 2-pentanone, 2-pentanol, and 2-pentene, as reaction intermediates and the production of pentane and butane as major products. The results are consistent with adsorption of 2-MTHF followed by rate-determining ring-opening to form either 1-pentoxide or 2-pentoxide alkoxide intermediates. Subsequent hydrogen-transfer steps produce the various intermediates, a decarbonylation step of the pentanal forms n-butane and CO, and further hydrodeoxygenation steps result in n-pentane. Fitting of the results using a rake mechanism that considers adsorbed intermediates gives excellent agreement with experimental data, and agrees with a simulation with a simpler first-order model. The more detailed rake analysis indicates that the surface species from the 1-pentoxide intermediate are ten-fold more plentiful than those produced from the 2-pentoxide intermediate. In situ infrared measurements support this reaction mechanism.

Kinetics and mechanism of m-cresol hydrodeoxygenation on a Pt/SiO2 catalyst

The Langmuir–Hinshelwood kinetic model was employed to investigate the hydrodeoxygenation (HDO) of m-cresol in the vapor phase over Pt/SiO2, at 300°C. The model takes into account the competitive adsorption and secondary reactions of all possible reactants and products. Therefore, independent measurements of the conversion of the reaction intermediates 3-methyl-cyclohexanone and 3-methyl-cyclohexanol were done at various levels of conversion and incorporated in the kinetic fitting of the model. The kinetic analysis of these reactions over the Pt/SiO2 catalyst confirms that hydrogenation and dehydrogenation reactions occur at faster rates than the hydrodeoxygenation steps. The hydrogenation/dehydration followed by dehydrogenation (HYD route) was shown to be a minor deoxygenation pathway. The actual hydrodeoxygenation path is proposed to proceed via a tautomerization route that starts with a fast and reversible tautomerization of m-cresol to an unstable ketone intermediate (3-methyl-3,5-cyclohexadienone) over the catalyst surface. In the case of the Pt/SiO2 catalyst, the CC bonds of the unstable ketone intermediate are fully hydrogenated to the saturated ketone (3-methyl-cyclohexanone). Sequential hydrogenation of this ketone produces a saturated alcohol (3-methyl-cyclohexanol). In the absence of surface acidity, this path only leads to the two ring-saturated products. When the support is acidic enough, dehydration of the alcohol to 3-methyl-1-cyclohexene followed by dehydrogenation leads to toluene. The kinetic analysis conducted here shows that this path is very limited over Pt/SiO2. By contrast, the toluene selectivity can be dramatically enhanced when using TiO2 and ZrO2 as the catalyst supports. This enhancement is not through the hydrogenation/dehydration/dehydrogenation path, but rather through the direct dehydroxylation mentioned above, which is favored by the incorporation of oxophilic sites in the catalysts. The oxophilic sites increase the rate of chemoselective hydrogenation of the carbonyl group of the m-cresol tautomer (3-methyl-3,5-cyclohexadienone) to a very reactive unsaturated alcohol (3-methyl-3,5-cyclohexadienol), which can be easily dehydrated to toluene, even in the absence of any significant catalyst acidity.

Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels

Two-step catalytic hydrodeoxygenation (HDO) of fast pyrolysis oil was investigated for translating pyrolysis oil to transportation grade hydrocarbon liquid fuels. At the first mild HDO step, various organic solvents were employed to promote HDO of bio-oil to overcome coke formation using noble catalyst (Ru/C) under mild conditions (300°C, 10MPa). At the second deep HDO step, conventional hydrogenation setup and catalyst (NiMo/Al2O3) were used under severe conditions (400°C, 13MPa) for obtaining hydrocarbon fuel. Results show that the phenomenon of coke formation is effectively eliminated, and the properties of products have been significantly improved, such as oxygen content decreases from 48 to 0.5wt% and high heating value increases from 17 to 46MJkg−1. GC–MS analysis indicates that the final products include C11C27 aliphatic hydrocarbons and aromatic hydrocarbons. In short, the fast pyrolysis oils were successfully translated to hydrocarbon liquid fuels using a two-step catalytic HDO process.

Second-generation biofuels by co-processing catalytic pyrolysis oil in FCC units

Previous research showed that hydrodeoxygenated (HDO) pyrolysis-oils could successfully be co-processed with vacuum gasoil (VGO) in a labscale fluid catalytic cracking (FCC) unit to bio-fuels. Typically the hydrodeoxygenation step takes place at ∼300°C under 200–300bar of hydrogen. Eliminating or replacing this step by a less energy demanding upgrading step would largely benefit the FCC co-processing of pyrolysis oils to bio-fuels. In this paper a bio-oil that has been produced by catalytic pyrolysis (catalytic pyrolysis oil or CPO) is used directly, without further upgrading, in catalytic cracking co-processing mode with VGO. The results are compared to the co-processing of upgraded (via HDO) thermal pyrolysis oil. Though small but significant differences in the product distribution and quality have been observed between the co-processing of either HDO or CPO, they could be corrected by further catalyst development (pyrolysis and/or FCC), which would eliminate the need for an up-stream hydrodeoxygenation step. Moreover, the organic yield of the catalytic pyrolysis route is estimated at approximately 30wt.% compared to an overall yield for the thermal pyrolysis followed by a hydrodeoxygenation step of 24wt.%.

Production of high quality diesel from cellulose and hemicellulose by the Sylvan process: catalysts and process variables

The Sylvan (2-methylfuran) diesel process involves the conversion of pentose biopolymers into premium diesel via furfural, by means of hydroxyalkylation/alkylation and hydrodeoxygenation reactions. In the hydroxyalkylation/alkylation step two Sylvan molecules are reacted with an aldehyde or a ketone to yield C12+ oxygenated intermediate molecules. Thus, the manuscript describes first the performance of the hydroxyalkylation/alkylation step with different soluble and solid catalysts, and among solids delaminated zeolites were identified as promising catalysts. The scope of the process has also been studied by reacting Sylvan with different aldehyde and ketone molecules. It has been found that for the one-step trimerization of Sylvan, sulfuric acid appears the most adequate catalyst and can be reused. The final hydrodeoxygenation step is studied in detail starting with C14 intermediates generated from two Sylvan and one butanal molecules as well as with the product generated by direct trimerization of Sylvan to yield the final corresponding mono-branched paraffinic diesel product. The Sylvan diesel process is an environmentally friendly process able to produce a high yield (87%) of a premium diesel with a cetane number of >70 and upper pour point of −75 °C from non-food biomass.