Characterization of hydroprocessed fast pyrolysis oil fractions

Production of renewable fuel from biomass has both environmental and national security implications. Considering that liquid transportation fuels massively affects the way we live, technology to produce fuels need to be both technologically-appropriate and economical. Fast pyrolysis remains as one of the most promising thermochemical processing technologies for converting solid biomass into a liquid that can be further upgraded into hydrocarbon fuels. The presence of various types of oxygen-containing functional groups confer pyrolysis oils with unwanted fuel properties such as acidity and low heating value. In order to remove these oxygen functionalities, catalytic hydrodeoxygenation or hydroprocessed is needed. This process involves the catalytic treatment of pyrolysis oils at high temperature and high pressure hydrogen, similar to that employed in the petroleum industry to remove sulfur from crude oil. However, hydroprocessed fast pyrolysis oil is complicated by both the thermal and chemical instability of the pyrolysis oil itself and the presence of water, giving importance to proper catalysts design considerations. Hydroprocessing further produces water and COx gas species as a means to expel the oxygen. The aqueous phase typically contains very low to negligible amount of carbon while the organic phase will contain a mixture of hydrocarbons. If the degree of deoxygenation is lower, larger amounts of carbon are present in the aqueous phase while recalcitrant oxygen species, like phenols and carboxylic acids appear in the organic phase. This in turn can affect the composition of the different fractions generated after distillation of the organic phase product. This presentation aims to discuss both the characterization of the various hydrotreated fast pyrolysis oil fractions, including elemental, 13C NMR and autoignition properties. It will also describe the hydrotreating processes used to obtain the different degrees of deoxygenation. References: Olarte MV, Padmaperuma AB, Ferrell JR III, Christensen, ED, Hallen RT, Lucke RB, Burton SD, Lemmon TL, Swita MS, Chupka G, Elliott DC, Drennan C. 2017. “Characterization of upgraded fast pyrolysis oak oil distillate fractions from sulfided and non-sulfided catalytic hydrotreating”. Fuel. 202: 620 – 630. Olarte MV, Albrecht KA, Bays, TJ, Polikarpov E, Maddi B, Linehan JC, O’Hagan MJ, Gaspar DJ. 2019. “Autoignition and select properties of low sample volume thermochemical mixtures from renewable sources”. Fuel. 238: 493 – 506

Co-hydrotreatment of bio-oil and yellow greases using NiMo catalyst

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Trickle bed co-processing of yellow greases and pyrolytic lignin

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Bio-oil Stabilization by Hydrogenation over Reduced Metal Catalysts at Low Temperatures

The thermal and chemical instability of biomass fast pyrolysis oil (bio-oil) presents significant problems when it is being converted to hydrocarbon transportation fuels. Development of effective approaches for stabilizing bio-oils is critical to the success of the biomass fast pyrolysis and bio-oil upgrading technology. Catalytic hydrogenation to remove reactive species in bio-oil has been considered as one of the most efficient ways to stabilize bio-oil. This paper provides a fundamental understanding of hydrogenation of actual bio-oils over a Ru/TiO₂ catalyst under conditions relevant to practical bio-oil hydrotreating processes. The results indicated hydrogenation of various components of the bio-oil, including sugars, aldehydes, ketones, alkenes, aromatics, and carboxylic acids, over the Ru/TiO₂ catalyst and 120 to 160 °C. Hydrogenation of these species significantly changed the chemical and physical properties of the bio-oil and overall improved its thermal stability, especially by reducing the carbonyl content, which represented the content of the most reactive species (i.e., sugar, aldehydes, and ketones). The change of content of each component in response to increasing hydrogen additions suggests the following bio-oil hydrogenation reaction sequence: sugar conversion to sugar alcohols, followed by ketone and aldehyde conversion to alcohols, followed by alkene and aromatic hydrogenation, and then followed by carboxylic acid hydrogenation to alcohols. Sulfur poisoning of the reduced Ru metal catalysts was significant during hydrogenation; however, the inorganics at low concentrations had minimal impact at short times on stream, indicating that sulfur poisoning was the primary deactivation mode for the bio-oil hydrogenation catalyst. The knowledge gained during this work will allow rational design of more effective catalysts and processes for stabilizing and upgrading bio-oils

Evolution of Functional Groups during Pyrolysis Oil Upgrading

In this work, we examine the evolution of functional groups (carbonyl, carboxyl, phenol, and hydroxyl) during hydrotreatment at 100–200 °C of two typical wood derived pyrolysis oils from BTG and Amaron in a batch reactor over Ru/C catalyst for reaction time of 4 h. An aqueous and an oily phase were obtained. The contents of the functional groups in both phases were analyzed by GC/MS, ³¹P NMR, ¹H NMR, CHN, KF titration, UV fluorescence, carbonyl groups by Faix and phenols by Folin−Ciocalteu method. The consumption of hydrogen was between 0.007 and 0.016 g/(g of oil), and 0.001–0.020 g of CH₄/(g of oil), 0.005–0.016 g of CO₂/(g of oil), and 0.03–0.10 g of H₂O/(g of oil) were formed. The contents of carbonyl, hydroxyl, and carboxyl groups in the volatile GC-MS detectable fraction decreased (80, 65, and ∼70%, respectively), while their behavior in the total oil and hence in the nonvolatile fraction was more complex. The carbonyl groups initially decreased having a minimum at ∼125–150 °C and then increased, while the hydroxyl groups had a reversed trend. This might be explained by the initial hydrogenation of the carbonyl groups to form hydroxyls, followed by continued dehydration reactions at higher temperatures that may have increased their content. The ³¹P NMR analysis was on the limit of its sensitivity for the carboxylic groups to precisely detect changes in the upgraded nonvolatile fraction; however, the more precise titration method showed that the concentration of carboxylic groups in the nonvolatile fraction remains constant with increased hydrotreatment temperature. The UV fluorescence results show that repolymerization increases with temperature, starting as low as 125 °C. ATR-FTIR method coupled with deconvolution of the region between 1490 and 1850 cm^–1 was shown to be a good tool for following the changes in carbonyl groups and phenols of the stabilized pyrolysis oils. The deconvolution of the IR bands around 1050 and 1260 cm^–1 correlated very well with the changes in the ³¹P NMR silent O groups (likely ethers). Most of the H₂O formation could be explained from the significant reduction of these silent O groups (from 12% in the fresh oils, to 6 to 2% in the stabilized oils) most probably belonging to ethers

Characterization of the Water-Soluble Fraction of Woody Biomass Pyrolysis Oils

This paper reports a study of the chemical composition of the water-soluble (WS) fraction obtained by cold water precipitation of two commercial wood pyrolysis oils (BTG and Amaron). The fraction studied accounts for between 50.3 and 51.3 wt % of the oils. With the most common analytical techniques used today for the characterization of this fraction (KF titration, GC–MS, hydrolyzable sugars, and total carbohydrates), it is possible to quantify only between 45 and 50 wt % of the fraction. Our results confirm that most of the total carbohydrates (hydrolyzable sugars and nonhydrolyzable) are soluble in water. The ion chromatography hydrolysis method showed that between 11.6 and 17.3 wt % of these oils were hydrolyzable sugars. A small quantity of phenols detectable by GC–MS (between 2.5 and 3.9 wt %) were identified. It is postulated that the unknown high molecular weight fraction (30–55 wt %) is formed by highly dehydrated sugars rich in carbonyl groups and WS phenols. The overall content of carbonyl, carboxyl, hydroxyl, and phenolic compounds in the WS fraction was quantified by titration, the Folin–Ciocalteu method, ³¹P NMR, and ¹H NMR. The WS fraction contains between 5.5 and 6.2 mmol/g carbonyl groups, between 0.4 and 1.0 mmol/g carboxylic acid groups, between 1.2 and 1.8 mmol/g phenolic −OH, and between 6.0 and 7.9 mmol/g of aliphatic alcohol groups. Translation into weight fractions of the WS was done by supposing surrogate structures for the water-soluble phenols, carbonyl groups, and carboxyl groups, and we estimated the content of WS phenols (21–27 wt %), carbonyls (5–14 wt %), and carboxyls (0–4 wt %). Together with the total carbohydrates (23–27 wt %), this approach leads to >90 wt % of the WS material in the bio-oils being quantified. We speculate the larger portion of the difference between the total carbohydrates and hydrolyzable sugars is the missing furanic fraction. Further refinement of the suggested methods and development of separation schemes to obtain and quantify subfractions with homogeneous composition (e.g., carbohydrates, high molecular weight WS phenols, furans, and dehydrated sugars) warrant further investigation

Effect of Carboxylic Acids on Corrosion of Type 410 Stainless Steel in Pyrolysis Bio-Oil

Biomass-derived oils are renewable fuel sources and commodity products and are proposed to partially or entirely replace fossil fuels in sectors generally considered difficult to decarbonize such as aviation and maritime propulsion. Bio-oils contain a range of organic compounds with varying functional groups which can lead to polarity-driven phase separation and corrosion of containment materials during processing and storage. Polar compounds, such as organic acids and other oxygenates, are abundant in bio-oils and are considered corrosive to structural alloys, particularly to those with a low-Cr content. To study the corrosion effects of small carboxylic acids present in pyrolysis bio-oils, type 410 stainless steel (SS410) specimens were exposed in bio-oils with varying formic, acetic, propionic and hexanoic acid contents at 50 °C during 48 h exposures. The specific mass change data show a linear increase in mass loss with increasing formic acid concentration. Interestingly, a mild corrosion inhibition effect on the corrosion of SS410 specimens was observed with the addition of acetic, propionic and hexanoic acids in the bio-oil

Hydronium-Ion-Catalyzed Elimination Pathways of Substituted Cyclohexanols in Zeolite H‑ZSM5

Hydronium ions in the pores of zeolite H-ZSM5 show high catalytic activity in the elimination of water from cyclohexanol in aqueous phase. Substitution induces subtle changes in rates and reaction pathways, which are concluded to be related to steric effects. Exploring the reaction pathways of 2-, 3-, and 4-methylcyclohexanol (2-McyOH, 3-McyOH, and 4-McyOH), 2<i>-</i> and 4<i>-</i>ethylcyclohexanol (2-EcyOH and 4-EcyOH), 2-<i>n</i>-propylcyclohexanol (2-PcyOH), and cyclohexanol (CyOH) it is shown that the E2 character increases with closer positioning of the alkyl and hydroxyl groups. Thus, 4-McyOH dehydration proceeds via an E1-type elimination, while <i>cis</i>-2-McyOH preferentially reacts via an E2 pathway. The entropy of activation decreased with increasing alkyl chain length (ca. 20 J mol^–1 K^–1 per CH₂ unit) for 2-substituted alcohols, which is concluded to result from constraints influencing the configurational entropy of the transition states