Catalytic upgrading of fast pyrolysis bio-oils applying nickel-based catalysts

Motivated by the population growth, climate change and limited fossil fuel resources, renewable alternatives for fuels and chemicals production are becoming more and more important. Biomass, especially residual lignocellulosic biomass shows a significant potential as feedstock for bioenergy, due to its high carbon content and short-term availability. Among the thermochemical conversion technologies, fast pyrolysis for biomass liquefaction can be considered already well stablished, as several commercial plants are spread worldwide. However, fast pyrolysis bio-oil, the main product of fast pyrolysis, currently shows limited bioenergy application as boiler fuel for heat production. It can be explained by its chemical composition and properties, as fast pyrolysis bio-oil is an acidic multi-component product, with low energetic density due to its high content of water and oxygenated compounds. Moreover, wood is the only feedstock currently used commercially. In order to expand the feedstock range and application viability, an additional upgrading treatment may be required in order to improve the fast pyrolysis properties, meeting existing fuel standards. In order to do so, catalytic hydrotreatment is considered a promising upgrading treatment, as it is a well-known technology currently applied in petroleum refineries for heteroatoms removal from crude oil. However, due to the differences in chemical composition, the hydrotreatment conditions applied to crude oil cannot be simply applied to fast pyrolysis bio oil. Although research in this field has been carried out for a few decades, there are still open questions to enable hydrotreatment to produce fuel oils from residual biomass in stable processes. By developing a robust fast pyrolysis bio-oil hydrotreatment process, small biorefineries units could be installed near to feedstock sourcing or even be installed in biorefinery units already stablished, such as a sugarcane biorefinery, in which high volumes of residual biomass are generated. Also, co-processing of crude oil and fast pyrolysis bio-oil in petroleum refineries may be a feasible option. In view of the importance of the hydrotreatment for expansion of the range of chemicals obtained by thermochemical conversion of residual biomass, the presented work investigated the hydrotreatment of fast pyrolysis bio-oil applying nickel-based catalysts. In a systematic evaluation nickel-based catalysts with different metal loading, supports and promoters have been studied. Overall, six nickel-based catalyst were screened and compared to ruthenium supported in activated carbon. The hydrotreatment conditions in terms of reaction time, temperature and pressure were optimized and fast pyrolysis bio-oils derived from beech wood and residual biomass (sugarcane bagasse) were hydrotreated. Additionally, the heavy phase separated from beech wood bio-oil, characterized by its high content of lignin-derived compounds, was hydrotreated. The effect of deactivation by sulphur on the hydrotreatment was investigated by use of model substances in a continuously operated trickle bed reactor, since with this reactor the deactivation can be observed depending on time (in contrast to batch experiments). Finally, a 2 step upgrading approach of a previously upgraded fast pyrolysis bio-oil was proposed and verified. Initially two high loaded nickel-based catalysts (monometallic nickel and nickel chromium) were evaluated in comparison to Ru/C by batch hydrotreatment of beech wood bio-oil at 80 bar, 4 h, 175 °C and 225 °C. Both nickel-based catalysts revealed similar hydrodeoxygenation activities for the conditions applied and the nickel catalysts showed the higher hydrogenation activity compared to Ru/C. The nickel-chromium catalyst demonstrated the highest activity for conversion of organic acids, ketones and sugars, attributed to the strength of the acid sites promoted by chromium oxide. When applied in a second hydrotreatment step of a previously upgraded oil, the oxygen content of the oil was reduced by 64.8 % in comparison to the original feedstock while the water concentration was reduced by 90 %. Nearly 96 % of the organic acids were converted and the higher heating value was increased by 90.1 %. Despite nickel-chromium demonstrated the best activity in the one step hydrotreatment reactions and contributed significantly in the 2-step upgrading, the oxygen content of 25.3 wt.% dry basis in the upgraded oil was still considered high. Thus, the upgrading conditions were further optimized, aiming to achieve higher hydrodeoxygenation performance. The conditions of batch hydrotreatment were optimized with nickel-chromium catalyst considering two pressures (80 and 100 bar), four temperatures (175 °C, 225 °C, 275 °C and 325 °C), for both the complete beech wood fast pyrolysis bio-oil, as well as for the heavy phase after spontaneous separation induced by intentional ageing of the bio-oil. At higher temperatures, increased hydrodeoxygenation levels were reached, while at higher pressure larger hydrogen consumption was observed with no significant influence on hydrodeoxygenation. The best conditions among all tested was obtained by hydrotreating the beech wood bio-oil at 325 °C and 80 bar; in this case, 43 % of hydrodeoxygenation was reached. Although improved hydrodeoxygenation activity observed with nickel-chromium at optimized conditions, the results motivated the synthesis and evaluation of new nickel-based catalysts, targeting higher deoxygenation levels. In the next part of this study, four nickel-based catalyst were synthesized by wet impregnation and evaluated for the hydrotreatment of beech wood fast pyrolysis bio-oil. The catalysts were supported in silica and zirconia and the influence of copper as promoter was studied. Among them, nickel-silica was the most active for hydrodeoxygenation, reducing the oxygen content of the upgraded beech wood fast pyrolysis bio-oil by more than 50 %. The highest degree of water removal as well as low gas and char production were also considered good properties attributed to this catalyst. The investigation on repeated cycles of hydrotreatment with the same catalyst showed a remaining activity even after the fourth reuse, in which 43 % of oxygen was removed. Thus, based on the results obtained with Ni/SiO2, this catalyst was selected together with nickel-chromium catalyst to be used for hydrotreatment of fast pyrolysis bio-oil from residual biomass, as until this point the study had considered only wood-based fast pyrolysis bio oil. Based on the studies so far, the integration of hydrotreatment into a thermochemical conversion route of residues in a sugarcane refinery was proposed. For that, the study encompassed sugarcane bagasse characterization, fast pyrolysis and hydrotreatment of the so derived bio-oils with nickel-chromium and nickel-silica catalyst. The detailed investigation of the bagasse and the fast pyrolysis bio-oil compositions allowed the correlation of the biomass building blocks with the monomers obtained. The hydrotreatment showed that nickel-chromium showed highest activity for organic acids conversion, as previously observed with beech wood bio-oil, whereas nickel-silica revealed more active for conversion of aromatics. Hydrodeoxygenation of 43.3 % was obtained with nickel-silica. Although both catalysts demonstrated to be active at the conditions evaluated, the high viscosities of the upgraded oils in comparison to those obtained from fast pyrolysis showed that polymerization took place and must be further investigated in detail, as it is one of the limiting factors for further application of fast pyrolysis bio-oil hydrotreatment. Overall, this studied showed to be very promising and future studies are planned. In the final part of the thesis, both high loaded nickel-based catalysts studied in the first chapters were selected for a detailed investigation in a continuous operated tricked bed hydrotreatment reactor, due to the similar nickel concentration, nickel particle size and support. The selection of both catalysts aimed to investigate the influence of sulfur on long term catalyst deactivation and the role of chromium in catalyst deactivation. Both catalysts were active for conversion of model substances over more than 48 h of reaction time. By the presence of sulfur, the selectivity of both catalysts changed, mainly towards alkene formation, while the activity remained in the same range. Formation of Ni3S2 was observed for both catalysts, but the highest intensity in the diffraction peak of metallic nickel in the nickel-chromium catalyst might be an indication of higher resistance to sulfur poisoning in comparison to Ni catalyst. In general, the catalysts were active for the conditions tested, although the hydrogenation activity was compromised by sulfur poisoning. Overall, all the catalysts tested in this study were active for hydrotreatment of fast pyrolysis bio-oils. If only stabilization of reactive compounds such as aldehydes and furfurals is required, all of them could be considered suitable candidates. In terms of hydrodeoxygenation activity, Ni/SiO2 showed the highest performance, while nickel-chromium showed to be the most active for conversion of organic acids and superior hydrogenation capacity than Ni/SiO2

Adsorção de compostos sulfurados e nitrogenados do óleo diesel em coluna de carvão ativado

Resumo: A poluição gerada pela queima de combustíveis fósseis dos veículos automotivos vem despertando preocupações nos últimos anos. Legislações mais restritivas, que visam à minimização do enxofre dos combustíveis, têm incentivado à comunidade científica na busca de processos complementares aos processos atuais, que permitam a adequação às novas exigências e minimizem o teor de enxofre nos combustíveis. Neste estudo, buscou-se avaliar a dessulfurização e a desnitrogenação do diesel por meio da adsorção, avaliando sua utilização como um processo complementar aos processos atualmente utilizados nas refinarias. Dois carvões ativados comerciais de coco de babaçu foram avaliados quanto à capacidade de adsorção frente aos compostos sulfurados e nitrogenados do diesel comercial e carga sintética. Ambos foram avaliados na sua forma original e impregnados com solução aquosa de CuCl220. As características texturais dos carvões originais e impregnados também foram avaliadas, na qual observou-se que a impregnação reduz a área específica dos carvões, assim como a área e volume de microporo, porém promove o aumento da remoção de enxofre e nitrogênio do diesel. A partir do teste preliminar de adsorção em batelada, o carvão denominado CAC3 foi selecionado para estudo em leito fixo, na sua forma original e impregnado com CuCl, com o objetivo de avaliar a capacidade adsortiva em um sistema dinâmico, além da porosidade, densidade de empacotamento e tempo de saturação, utilizando diesel comercial e carga sintética. Utilizando um leito de 55 cm do CAC3 na sua forma original, foi possível reduzir em aproximadamente 73% a concentração de enxofre e 84% do nitrogênio do diesel comercial nos primeiros pontos amostrais do diesel efluente da coluna. Já com o carvão impregnado nos primeiros pontos, a redução da concentração de enxofre obtida foi de 93,4%. Após 16 h de corrida, a concentração de nitrogênio encontrava-se em 60 ppm (C/C= 0,25), evidenciando a elevada capacidade adsortiva do carvão impregnado pelos nitrogenados. O carvão CAC3 impregnado e não impregnado apresentou zonas de transferência de massa alongadas e tempos de saturação superiores a 10 h, o que pode ser atribuído a adsorções competitivas entre os diferentes compostos presentes no diesel. A capacidade adsortiva para os nitrogenados foi superior aos sulfurados com diesel comercial e carga sintética, sendo que com a carga sintética a capacidade dos nitrogenados foi aproximadamente cinco vezes superior à dos sulfurados. Testes de regeneração foram preliminarmente realizados em batelada, utilizando solventes distintos. O tolueno foi selecionado para os testes em leito fixo, pois foi o solvente que proporcionou a maior recuperação da capacidade adsortiva. A temperatura de dessorção foi otimizada em 40 ºC e então cinco adsorções consecutivas foram realizadas. A redução mais acentuada no reuso em ciclos foi obtida entre a primeira e a segunda adsorção, porém com o aumento do número de adsorções, a redução foi sendo minimizada. Após a quinta adsorção ainda foi possível remover 28% do enxofre presente no diesel com o carvão original e 70% do nitrogênio utilizando o carvão impregnado. Além disso, com a dessorção em leito fixo foi possível remover praticamente todo o enxofre e o nitrogênio dos carvões com um tempo inferior a duzentos minutos de regeneração

Two Steps Upgrading of Beech Wood Fast Pyrolysis Bio-oil with Nickel-based Catalysts

Upgrading of fast pyrolysis bio-oil through catalyst hydrotreatment has been suggested as a complementary step to produce oil with improved properties. The upgrading reduces the oxygen and water concentration at the same time that allows the carbon recovery in the bio-oil. Reactive compounds are stabilized and organic acids are mostly concentrated in the aqueous phase formed after the reaction. Due to the high activity and low cost, nickel-based catalysts are promising for production of upgraded oils. Although almost half of the oxygen is removed with a single step upgrading, deeper hydrodeoxygenation is required in order to obtain organic liquids miscible with petroleum-derived products. It can be achieved by sequential hydrotreatment with specific catalysts in each of the steps. Hence, in the present work a beech wood fast pyrolysis bio-oil was upgraded in two steps applying two nickel-based catalysts. A catalyst with higher hydrodeoxygenation activity (Ni/SiO2, 7.9 wt.%) was used in the first step, whereas a catalyst with higher hydrogenation activity (Ni-Cr/SiO2, 30 wt.% metallic nickel, 26 wt.% NiO, 15 wt.% of Cr2O3 and 1.5 wt.% of graphite in diatomaceous earth support 27 wt.%) was employed in the second step. The reactions were conducted in a batch autoclave at 325 ºC and 80 bar of H2. The bio-oil initially hydrotreated with a Ni/SiO2 catalyst prepared by wet impregnation showed a reduction of 44.85 % of the oxygen content and 77.8 % less water in comparison to the initial bio-oil. Carbon, on the other hand increased from 59.9 wt.%, dry basis to 72.9 wt.%, dry basis, respectively. After the second upgrading reaction with Ni-Cr/SiO2, the oxygen concentration was further reduced to 11.6 wt.%, reducing 64.8 % of the original oxygen concentration, and reducing around 90 % of the water content. Additionally, most of the organic compounds were concentrated in the upgraded oil, as the aqueous phase after the second upgrading step was composed by 97 % of water. Such improvement was reflected in the high carbon concentration in the upgraded oil ([C] = 78.6 wt.%), in the HHV (36.9 MJ/Kg), 90.1 % higher in comparison to the original beech wood fast-pyrolysis bio-oil and in the hydrocarbons identified in the two-steps upgraded oil. Hence, the two steps hydrotreatment with adequate catalyst seems to be a promising upgrading process in order to obtain fast pyrolysis oil with improved properties. Please click Additional Files below to see the full abstract

Selective Detection of Aromatic Compounds with a Re-Designed Surface Acoustic Wave Sensor System Using a Short Packed Column

A self-developed and newly re-designed chemical SAW sensor system composed of four polymer-coated and four differently modified nano-diamond-coated SAW sensors was applied to measure aromatic compounds in gasoline in a low-cost, fast, and easy way. An additional short packed column at the system inlet improve the selectivity for various possible fuel applications. The column allows the direct sampling of liquid fuels and pre-separates the different components in groups (aromatic and aliphatic compounds) from a fuel sample. Since the sensors employed show linearity towards concentration, an easy quantification of single fuel components was possible even within the group of aromatic compounds

Hydrotreatment of Fast Pyrolysis Bio-oil Fractions Over Nickel-Based Catalyst

Residual biomass shows potential to be used as a feedstock for fast pyrolysis bio-oil production for energetic and chemical use. Although environmentally advantageous, further catalytic upgrading is required in order to increase the bio-oil stability, by reducing reactive compounds, functional oxygen-containing groups and water content. However, bio-oils may separate in fractions either spontaneously after ageing or by fractionated condensation. Therefore the effects of upgrading on different fast pyrolysis bio-oil (FPBO) fractions obtained from a commercially available FPBO were studied by elemental analysis, GC-MS and 1H-NMR. Not only the FPBO was upgraded by catalytic hydrotreatment, but also the heavy phase fraction formed after intentional aging and phase separation. The reactions were conducted between 175 and 325 °C and 80–100 bar by using a nickel–chromium catalyst in batch experiments. The influence of the hydrotreatment conditions correlated with the composition of the upgraded products. Higher oxygen removal was obtained at higher temperatures, whereas higher pressures resulted in higher hydrogen consumption with no significant influence on deoxygenation. At 325 °C and 80 bar 42% of the oxygen content was removed from the FPBO. Compounds attributed to pyrolysis oil instability, such as ketones and furfural were completely converted while the number of alcohols detected in the upgraded products increased. Coke formation was observed after all reactions, especially for the reaction with the fraction rich in lignin derivatives, likely formed by polymerization of phenolic compounds mainly concentrated in this phase. Independently of the feedstock used, the upgraded bio-oils were very similar in composition, with reduced oxygen and water content, higher energy density and higher carbon content

Fast Pyrolysis Oil Upgrading via HDO with Fe-Promoted Nb₂O₅-Supported Pd-Based Catalysts

ue to the high acid, oxygen and water contents of fast pyrolysis oil, it requires the improvement of its fuel properties by further upgrading, such as catalytic hydrodeoxygenation (HDO). In this study, Nb2O5 was evaluated as a support of Pd-based catalysts for HDO of fast pyrolysis oil. A Pd/SiO2 catalyst was used as a reference. Additionally, the impact of iron as a promoter in two different loadings was investigated. The activity of the synthesized catalysts was evaluated in terms of H2 uptake and composition of the upgraded products (gas phase, upgraded oil and aqueous phase) through elemental analysis, Karl Fischer titration, GC-MS/FID and 1H-NMR. In comparison to SiO2, due to its acid sites, Nb2O5 enhanced the catalyst activity towards hydrogenolysis and hydrogenation, confirmed by the increased water formation during HDO and a higher content of hydrogen and aliphatic protons in the upgraded oil. Consequently, the upgraded oil with Nb2O5 had a lower average molecular weight and was therefore less viscous than the oil obtained with SiO2. When applied as a promoter, Fe enhanced hydrogenation and hydrogenolysis, although it slightly decreased the acidity of the support, owing to its oxophilic nature, leading to the highest deoxygenation degree (42.5 wt.%) and the highest product HHV (28.2 MJ/kg)

Evaluation of High-Loaded Ni-Based Catalysts for Upgrading Fast Pyrolysis Bio-Oil

The catalytic activity of high-loaded Ni-based catalysts for beech wood fast-pyrolysis bio-oil hydrotreatment is compared to Ru/C. The influence of promoter, temperature, reaction time, and consecutive upgrading is investigated. The catalytic activity is addressed in terms of elemental composition, pH value, H₂ consumption, and water content, while the selectivity is based on the GC-MS/FID results. The catalysts showed similar deoxygenation activity, while the highest hydrogenation activity and the highest upgraded oil yields were obtained with Ni-based catalysts. The elemental composition of upgraded oils was comparable for 2 and 4 h of reaction, and the temperature showed a positive effect for reactions with Ni–Cr and Ru/C. Ni–Cr showed superior activity for the conversion of organic acids, sugars and ketones, being selected for the 2-step upgrading reaction. The highest activity correlates to the strength of the acid sites promoted by Cr₂O₃. Consecutive upgrading reduced the content of oxygen by 64.8% and the water content by 90%, whereas the higher heating value increased by 90.1%. While more than 96% of the organic acid content was converted, the discrepancy of aromatic compounds quantified by ¹H-NMR and GC-MS/FID may indicate polymerization of aromatics taking place during the second upgrading step

Synthesis and Regeneration of Nickel-Based Catalysts for Hydrodeoxygenation of Beech Wood Fast Pyrolysis Bio-Oil

Four nickel-based catalysts are synthesized by wet impregnation and evaluated for the hydrotreatment/hydrodeoxygenation of beech wood fast-pyrolysis bio-oil. Parameters such as elemental analysis, pH value, and water content, as well as the heating value of the upgraded bio-oils are considered for the evaluation of the catalysts’ activity and catalyst reuse in cycles of hydrodeoxygenation after regeneration. The reduction temperature, selectivity and hydrogen consumption are distinct among them, although all catalysts tested produce upgraded bio-oils with reduced oxygen concentration, lower water content and higher energy density. Ni/SiO2, in particular, can remove more than 50% of the oxygen content and reduce the water content by more than 80%, with low coke and gas formation. The evaluation over four consecutive hydrotreatment reactions and catalyst regeneration shows a slightly reduced hydrodeoxygenation activity of Ni/SiO2, mainly due to deactivation caused by sintering and adsorption of poisoning substances, such as sulfur. Following the fourth catalyst reuse, the upgraded bio-oil shows 43% less oxygen in comparison to the feedstock and properties comparable to the upgraded bio-oil obtained with the fresh catalyst. Hence, nickel-based catalysts are promising for improving hardwood fast-pyrolysis bio-oil properties, especially monometallic nickel catalysts supported on silica

Thermal Conversion of Sugarcane Bagasse Coupled with Vapor Phase Hydrotreatment over Nickel-Based Catalysts: A Comprehensive Characterization of Upgraded Products

In the present work, we compared the chemical profile of the organic compounds produced in non-catalytic pyrolysis of sugarcane bagasse at 500 °C with those obtained by the in-line catalytic upgrading of the vapor phase at 350 °C. The influence over the chemical profile was evaluated by testing two Ni-based catalysts employing an inert atmosphere (N2) and a reactive atmosphere (H2) under atmospheric pressure with yields of the liquid phase varying from 55 to 62%. Major changes in the chemical profile were evidenced in the process under the H2 atmosphere, wherein a higher degree of deoxygenation was identified due to the effect of synergistic action between the catalyst and H2. The organic fraction of the liquid phase, called bio-oil, showed an increase in the relative content of alcohols and phenolic compounds in the GC/MS fingerprint after the upgrading process, corroborating with the action of the catalytic process upon the compounds derived from sugar and carboxylic acids. Thus, the thermal conversion of sugarcane bagasse, in a process under an H2 atmosphere and the presence of Ni-based catalysts, promoted higher deoxygenation performance of the pyrolytic vapors, acting mainly through sugar dehydration reactions. Therefore, the adoption of this process can potentialize the use of this waste biomass to produce a bio-oil with higher content of phenolic species, which have a wide range of applications in the energy and industrial sectors