Hydrotreatment of lignin and its bio-oils over transition metal sulfide-based supported and unsupported catalysts

The scarcity of fossil feedstocks and the deterioration of the current global climate condition have prompted the search for reliable alternatives for fossil fuel replacement. Biomass feedstocks such as lignin can be used to produce renewable bio-oils that can fill the gap left by fossil-derived oils. Such bio-oils require an upgrading process, such as catalytic hydrodeoxygenation (HDO), to improve their quality for use as advanced biofuels and chemicals. Transition metal sulfides (TMS) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. This thesis focuses on the hydrotreatment of a model bio-oil compound, propylguaiacol (PG), and an actual bio-feedstock, Kraft lignin (KL), over TMS-based supported and unsupported catalysts.\ua0 In the first study, catalysts based on MoS2 supported on γ-Al2O3 and promoted by transition metals, such as Nickel (Ni), Copper (Cu), Zinc (Zn), and Iron (Fe) were evaluated for the HDO of PG in a batch reactor setup. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a 94% yield of deoxygenated cycloalkanes, however, 42% of the phenolics remained in the reaction medium after 5 h for the sulfided Cu-promoted catalyst. It was also found that the sulfided Zn- and Fe-promoted catalysts gave a final yield of 19% and 16% at full PG conversion, respectively, for deoxygenated aromatics. A pseudo-first kinetic model that took into consideration the main side reactions was developed to elucidate the deoxygenation routes for the HDO of PG using sulfided catalysts. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. This work also demonstrated that the activity of the transition metal promoters for the HDO of PG correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin.The main focus of the second study was on the effect of the annealing treatment of a hydrothermally synthesized unsupported MoS2 catalyst. The prepared unsupported catalysts were studied and evaluated for the HDO of PG. The annealing treatment of the as-synthesized catalyst under N2 flow at 400 \ub0C for 2 h was found to enhance the HDO activity of PG. The effect on catalysts activity of hydrothermal synthesis time and acid addition combined with the annealing treatment was also studied for the same model reaction. The annealed MoS2 with a synthesis time of 12 h in an acidic environment was found to have improved crystallinity and to exhibit the highest degree of deoxygenation of all the studied catalysts, moreover, giving a full PG conversion after 4 h and a final 4-propylbenzene selectivity of 23.4 %. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2 micelles, resulting in smaller particles that affected HDO activity. The annealed unsupported MoS2 that gave the best performance for HDO of PG was further evaluated for the hydrotreatment of KL. The annealed unsupported MoS2 demonstrated a high capacity for deoxygenation with a selectivity of 78.6% and 20.1% for cycloalkanes and aromatics from KL, respectively. The results also indicate that a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield

Slurry Hydrotreatment of Biomass Materials over Metal Sulfide-based Supported and Unsupported Catalysts

The scarcity of fossil feedstocks and the deterioration of the current global climate condition have prompted the search for reliable alternatives for fossil fuel replacement. Biomass feedstocks are abundant, carbon-rich, and renewable bioresources that can be used to produce renewable bio-oils that can fill the gap left by fossil-derived oils. Such bio-oils require an upgrading process, such as catalytic hydrodeoxygenation (HDO), to improve their quality for use as advanced biofuels and chemicals. Transition metal sulfides (TMS) are typically used in the traditional petroleum refining industry. In this thesis, we have explored the use of unsupported and supported metal sulfides in the hydrotreatment of Propylguaiacol (PG), a bio-oil model compound, Kraft lignin (KL), and pyrolysis bio-oil. In the recent work, the co-processing of the Kraft lignin and pyrolysis oil over the unsupported NiMoS was also performed.Firstly, MoS2 supported on γ-Al2O3 catalysts and promoted by transition metals, such as Nickel (Ni), Copper (Cu), Zinc (Zn), and Iron (Fe) were evaluated for the HDO of PG in a batch reactor setup. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a 94% yield of deoxygenated cycloalkanes, however, 42% of the phenolics remained in the reaction medium after 5 h for the sulfided Cu-promoted catalyst A pseudo-first kinetic model that took into consideration the main side reactions was developed to elucidate the deoxygenation routes for the HDO of PG using sulfided catalysts. It was demonstrated that the activity of the transition metal promoters for the HDO of PG correlated to the yield of deoxygenated products from the hydrotreatment of KL. Further, the effect of the annealing treatment of a hydrothermally synthesized unsupported MoS2 dispersed catalyst was studied and evaluated for the HDO of PG. The annealing treatment of the as-synthesized catalyst under N2 flow at 400 \ub0C for 2 h was found to enhance the HDO activity of PG. The annealed unsupported MoS2 demonstrated a high capacity for deoxygenation with a selectivity of 78.6% and 20.1% for cycloalkanes and aromatics from KL hydrotreatment, respectively. The results also indicate that a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield.The main hurdle during Kraft lignin liquefaction was the occurrence of repolymerization reactions during depolymerization that lead to the production of undesired solid char residues and subsequently cause low bio-oil yield. In this regard, the combination of NiMo sulfides with various ultra-stable Y zeolites (USY) for the KL hydrotreatment was studied. The use of the physical mixture of the unsupported NiMoS and the USY support was also studied to better understand the role of the catalyst components, and their interactions during lignin depolymerization, HDO, and also repolymerization of the reactive lignin intermediates. Further work was then extended to the co-hydrotreatment of KL and pyrolysis oil over the unsupported NiMo Sulfides. The synergistic effect between the complex feedstocks (KL and pyrolysis oil) was further explored by investigating the effect of supplementing various bio-oil monomers during KL liquefaction. It was found that the strategy of co-feeding bio-derived monomers and pyrolysis oil in the KL hydrotreatment presented an insight for co-processing and also the role of second co-feed was able to facilitate efficient lignin depolymerization increasing the desired bio-liquid yield and limiting lignin condensation. Further, a two-stage fast pyrolysis bio-oils (FPBO) processing concept that involves first a stabilization step in the slurry hydrocracker over an unsupported NiMoS and then followed by downstream fixed-bed hydrotreating producing renewable hydrocarbon was studied. The liquid products were thoroughly analyzed to understand their chemical and physical properties

Slurry Hydroconversion of Solid Kraft Lignin to Liquid Products Using Molybdenum- and Iron-Based Catalysts

Kraft lignin is an abundantly available and largely underutilized renewable material with potential for production of biobased fuels and chemicals. This study reports the results of a series of slurry hydroprocessing experiments with the aim of converting solid Kraft lignin to liquid products suitable for downstream refining in more conventional reactors. Experiments reported in this study were conducted by feeding a lignin slurry to an already hot, liquid-filled reactor to provide momentaneous heating of the lignin to the reaction temperature. This modified batch procedure provided superior results compared to the regular batch experiments, likely since unwanted repolymerization and condensation reactions of the lignin during the heating phase was avoided, and was therefore used for most of the experiments reported. Experiments were performed using both an unsupported Mo-sulfide catalyst and Fe-based catalysts (bauxite and hematite) at varied reaction temperatures, pressures, and catalyst loadings. The use of Mo-sulfide (0.1% Mo of the entire feed mass) at 425 \ub0C and 50 bar resulted in complete conversion of the Kraft lignin to nonsolid products. Very high conversions (>95%) could also be achieved with both sulfided bauxite or hematite at the same temperature and pressure, but this required much higher catalyst loadings (6.25% bauxite or 4.3% hematite of the total feed mass), and around 99% conversion could be achieved at higher temperatures but at the expense of much higher gas yields. Although requiring much higher loadings, the results in this study suggest that comparatively nonexpensive Fe-based catalysts may be an attractive alternative for a slurry-based process aimed at the hydroconversion of solid lignin to liquid products. Possible implementation strategies for a slurry-based hydroconversion process are proposed and discussed

The promotor and poison effects of the inorganic elements of kraft lignin during hydrotreatment over nimos catalyst

One-pot deoxygenation of kraft lignin to aromatics and hydrocarbons of fuel-range quality is a promising way to improve its added value. Since most of the commercially resourced kraft lignins are impure (Na, S, K, Ca, etc., present as impurities), the effect of these impurities on the deoxygenation activity of a catalyst is critical and was scrutinized in this study using a NiMoS/Al2O3 catalyst. The removal of impurities from the lignin indicated that they obstructed the depolymerization. In addition, they deposited on the catalyst during depolymerization, of which the major element was the alkali metal Na which existed in kraft lignin as Na2S and single-site ionic Na+. Conditional experiments have shown that at lower loadings of impurities on the catalyst, their promotor effect was prevalent, and at their higher loadings, a poisoning effect. The number of moles of impurities, their strength, and the synergism among the impurity elements on the catalyst were the major critical factors responsible for the catalyst’s deactivation. The promotor effects of deposited impurities on the catalyst, however, could counteract the negative effects of impurities on the depolymerization

Hydrotreatment of lignin dimers over NiMoS-USY: effect of silica/alumina ratio

Sulfides of NiMo over a series of commercial ultra-stable Y zeolites were studied in an autoclave reactor to elucidate the effect of silica/alumina ratio (SAR = 12, 30, and 80) on the cleavage of etheric C-O (beta-O-4) and C-C (both sp(3)-sp(2) and sp(2)-sp(2)) linkages present in native/technical lignin and lignin derived bio-oils. 2-Phenethyl phenyl ether (PPE), 4,4-dihydroxydiphenylmethane (DHDPM), and 2-phenylphenol, (2PP) were examined as model dimers at 345 degrees C and 50 bar of total pressure using dodecane as the solvent. The etheric C-O hydrogenolysis activity was found to be in the order NiMoY30 > NiMoY12 > NiMoY80, despite a high initial rate of C-O cleavage over NiMoY12 owing to its high acid density. A high degree of hydrodeoxygenation (HDO) and hydrocracking reactions were observed with NiMoY30 yielding >80% of deoxygenated products of which similar to 58% are benzene, toluene, and ethylbenzenes. A similar experiment with DHDPM showed the rapid cleavage of the methylene-linked C-C dimer (sp(3)-sp(2)) to phenols and cresols even with the low acid density (high SAR) catalyst, NiMoY80. Direct hydrocracking of the recalcitrant 5-5 \u27 linkage in 2PP is very slow, however, it cleaved via a cascade of HDO, ring-hydrogenation, and hydrocracking reactions. A high degree of hydrogenolysis and hydrocracking occurs over NiMoY30 due to suitable balance between acidity and pore accessibility, enhanced proximity between acidic and deoxygenation sites leading to a slightly higher dispersion of Ni promoted MoS2 crystallites. Overall, the product spectrum consisted of a high yield of deoxygenated products. The carbon content on the recovered catalyst was in the range of 3-7 wt%. These results pave the way for effective catalysts to break recalcitrant linkages present in lignin to obtain a hydrocarbon-rich liquid transportation fuel. An experiment with Kraft lignin over NiMoY30 shows good selectivity for deoxygenated aromatics and cycloalkanes in the liquid phase

Thermal annealing effects on hydrothermally synthesized unsupported MoS2 for enhanced deoxygenation of propylguaiacol and kraft lignin

Catalytic hydrodeoxygenation (HDO) is an important hydrotreating process that is used to improve the quality of bio-oils to produce biomass-derived fuel components and chemicals. Molybdenum disulfide (MoS2) has been widely used as a catalyst in hydrodesulfurization (HDS) applications for several decades, which can be further improved for effective unsupported catalyst synthesis. Herein, we studied a universally applicable post-annealing treatment to a hydrothermally synthesized MoS2\ua0catalyst towards developing efficient unsupported catalysts for deoxygenation. The effect of the annealing treatment on the catalyst was studied and evaluated for HDO of 4-propylguaiacol (PG) at 300 \ub0C with 50 bar H2\ua0pressure. The annealing of the as-synthesized catalyst under nitrogen flow at 400 \ub0C for 2 h was found to enhance the HDO activity. This enhancement is largely induced by the changes in the microstructure of MoS2\ua0after the annealing in terms of slab length, stacking degree, defect-rich sites and the MoS2\ua0edge-to-corner site ratio. Besides, the effect of hydrothermal synthesis time and acid addition combined with the annealing treatment on the MoS2\ua0catalytic activity was also studied for the same model reaction. The annealed MoS2\ua0with a synthesis time of 12 h under an acidic environment was found to have improved crystallinity and exhibit the highest deoxygenation degree among all the studied catalysts. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2\ua0micelles, resulting in smaller particles that affected the HDO activity. The annealed unsupported MoS2\ua0with the best performance for PG hydrodeoxygenation was further evaluated for the hydrotreatment of kraft lignin and demonstrated a high deoxygenation ability. The results also indicate a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield. This research uncovers the importance of a facile pretreatment on unsupported MoS2\ua0for achieving highly active HDO catalysts

Upgrading of triglycerides, pyrolysis oil, and lignin over metal sulfide catalysts: A review on the reaction mechanism, kinetics, and catalyst deactivation

Human activities such as burning fossil fuels for energy production have contributed to the rising global atmospheric CO2 concentration. The search for alternative renewable and sustainable energy sources to replace fossil fuels is crucial to meet the global energy demand. Bio-feedstocks are abundant, carbon-rich, and renewable bioresources that can be transformed into value-added chemicals, biofuels, and biomaterials. The conversion of solid biomass into liquid fuel and their further hydroprocessing over solid catalysts has gained vast interest in industry and academic research in the last few decades. Metal sulfide catalysts, a common type of catalyst being used in the hydroprocessing of fossil feedstocks, have gained great interest due to their low cost, industrial relevance, and easy implementation into the current refining infrastructures. In this review, we aim to provide a comprehensive overview that covers the hydrotreating of various bio-feedstocks like fatty acids, phenolic compounds, pyrolysis oil, and lignin feed using sulfided catalysts. The main objectives are to highlight the reaction mechanism/networks, types of sulfided catalysts, catalyst deactivation, and reaction kinetics involved in the hydrotreating of various viable renewable feedstocks to biofuels. The computational approaches to understand the application of metal sulfides in deoxygenation are also presented. The challenges and needs for future research related to the valorization of different bio-feedstocks into liquid fuels, employing sulfided catalysts, are also discussed in the current work

Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression

Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation

Elucidating the role of NiMoS-USY during the hydrotreatment of Kraft lignin

Major hurdles in Kraft lignin valorization require selective cleavage of etheric and C–C linkages and subsequent stabilization of the fragments to suppress repolymerization reactions to yield higher monomeric fractions. In this regard, we report the development of efficient NiMo sulfides and ultra-stable Y zeolites for the reductive liquefaction and hydrodeoxygenation of Kraft lignin in a Parr autoclave reactor at 400 \ub0C and 35 bar of H2 (@25 \ub0C). Comparing the activity test without/with catalyst, it is revealed that NiMo sulfides over ultra-stable Y zeolites (silica/alumina = 30) achieved a significant reduction (∼50 %) of the re-polymerized solid residue fraction leading to a detectable liquid product yield of 30.5 wt% with a notable monocyclic and alkylbenzenes selectivity (∼61 wt%). A physical mixture counterpart, consisting of hydrothermally synthesized unsupported NiMoS and Y30, on the other hand, shows lower selectivity for such fractions but higher stabilization of the lignin fragments due to enhanced access to the active sites. Moreover, an extended reaction time with higher catalyst loading of the impregnated NiMoY30 facilitated a remarkable alkylbenzene (72 wt%) selectivity with an increased liquid yield of 38.9 wt% and a reduced solid residue of 16.4 wt%. The reason for the high yield and selectivity over NiMoY30, according to the catalyst characterization (H2-TPR, XPS, TEM) can be ascribed to enhanced stabilization of depolymerized fragments via H2-activation at a lower temperature and high hydrodeoxygenation ability. In addition, the better proximity of the acidic and deoxygenation sites in NiMoY30 was beneficial for suppressing the formation of polycyclic aromatics