Continuous Catalytic Esterification and Hydrogenation of a

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Continuous Catalytic Esterification and Hydrogenation of a Levoglucosan/Acetic Acid Mixture for Production of Ethyl Levulinate/Acetate and Valeric Biofuels Roger N. Hilten, Justin Weber, and James R Kastner Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01896 • Publication Date (Web): 10 Oct 2016 Downloaded from http://pubs.acs.org on October 13, 2016

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Continuous Catalytic Esterification and Hydrogenation of a Levoglucosan/Acetic Acid Mixture for Production of Ethyl Levulinate/Acetate and Valeric Biofuels Roger Hilten, Justin Weber, James R. Kastner* Biochemical Engineering, College of Engineering The University of Georgia, Athens GA 30602, USA *Corresponding author phone: 706-583-0155; fax: 706-542-8806 e-mail: [email protected]

ABSTRACT

A mixture of levoglucosan (LG) and acetic acid (AA), representing water extracted fast pyrolysis oil, were continuously converted to ethyl levulinate (EL) and ethyl acetate (EA) using H-ZSM5 [120-230°C, 600 psig, 80% ethanol (v/v)]. Fractional conversion of both reactants was 65% or greater at temperatures above 120°C and space time yields (STY) approached 140 and 15 g/Lcat/h for EA and EL respectively, at 180°C (LHSV=4.9 h-1). Two potential pathways for EL formation from levoglucosan were apparent, one with glucose and ethyl α-d-glucopyranoside as intermediates, and the other with furfural. Adding metal functionality (Ru/H-ZSM5) resulted in the production of valerate biofuels (esters of carboxylic acids C3 or greater; e.g., pentanoic and hexanoic acid ethyl esters) and EA from the mixture in the presence of hydrogen. Conversions for LG and AA using Ru/H-ZSM5 were similar to H-ZSM5, but ethyl levulinate space time yield declined (∼5 g/L-cat/h) as valerate biofuel STY increased (∼10 g/L-cat/h) at an optimum temperature of 180°C. Our results indicate that valerate biofuels can be produced from levoglucosan (and possibly other sugars) in a continuous single stage, integrated process. However, due to low yields and coke formation, it is clear that ethanol/water ratios, pore size, and acid site type and density, must be optimized when coupled with metal functionality for industrial application.

Index Words: Continuous, Zeolite, Esterification, Hydrogenation, Levoglucosan, Ethyl Levulinate, Ethyl Valerate 1 ACS Paragon Plus Environment

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INTRODUCTION Fast pyrolysis of lignocellulosics is a rapid thermal process that generates an energy dense, oxygenated liquid hydrocarbon stream, also known as fast pyrolysis oil (FPO), in high yields (60-75%). In theory, FPO can be catalytically converted to drop-in biofuels (stream’s that can be blended with current fuels in a range of proportions without modifying current infrastructure).1,2 However, due to the presence of water (30-40%), reactive acids (e.g., 30-100 g/L acetic acid), aldehydes (furfural), and anhydrosugars such as levoglucosan (50-150 g/L), FPO is acidic (corrosive), unstable (polymerization reactions increase viscosity), and difficult to catalytically upgrade to a drop-in biofuel.3,4 The carboxylic acids and anhydrosugars are difficult to remove or transform to fuel intermediates, cross reactions occur causing polymerization, and tars and other compounds cause coking.5 Much effort has focused on stabilizing the oil for storage and shipment to bio/refineries by alcohol addition (esterification and acetalization without catalyst), mild catalytic hydrodeoxygenation, and acid-catalyzed cracking.2-4, 6, 8, 9 Esterification without catalysts typically leads to incomplete conversion of acids, and other key compounds (e.g., acetol and levoglucosan) in the oil are not converted to upgradable intermediates9 or the pathways for conversion of these compounds is rarely studied. Catalytic decarboxylation (CO2 loss) and decarbonylation (CO loss) of the acids and aldehydes have been proposed to deoxygenate and stabilize the oil for further treatment. However, these processes produce lower molecular weight products, lower fuel yield, and waste a carbon source, since there are very high concentrations of oxygenated compounds in bio-oil. Catalytic upgrading of pyrolysis oils using current acid catalysts (e.g., zeolites, such as HZSM-5) and FCC catalysts is difficult due to coke formation and catalyst deactivation.7-8 Catalytic hydrodeoxygenation typically requires precious metal catalysts and hydrogen, and results in limited conversion of the acids.5 Given the high levels of acetic acid and levoglucosan, as well as aldehydes and ketones, in fast pyrolysis oil, simultaneous conversion (e.g., simultaneous esterification, ketonization, and deoxygenation) of these compounds to chemicals and fuels appears to be a viable alternative to catalytic hydrodeoxygentation using precious metal catalysts. Recent reports suggest that levoglucosan and acids in the oil can be separately esterified to form alkyl levulinates using solid acid catalysts,10-11 yet little information is available on the transformation of the mixture although these two components represent the largest fraction in FPO. Ethyl levulinate is a gasoline, diesel, 2 ACS Paragon Plus Environment

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or biodiesel fuel blending agent and potential platform chemical.12 Another reaction pathway which has rarely been considered is conversion of levoglucosan (LG) to valeric biofuels. This pathway would require a bi-functional (acid-metal) catalyst to generate alkyl levulinates from LG with subsequent hydrogenation to valerate esters. Valerate esters are fully compatible with transportation fuels.13,14 Most research on this pathway has focused on catalytic hydrogenation of homogeneous acid derived levulinic acid,13,14 with no reports in the literature on direct conversion of LG to valerate esters. Use of solid acid-metal catalysts represent a significant advantage over homogeneous liquid phase acids, since they eliminate corrosion problems and can potentially be reused. Hu et al. 2012 indicate that levoglucosan can be converted to either methyl or ethyl levulinate (alkyl levulinates) when alcohol/water mass ratios exceed 5-10% alcohol via direct esterification of the sugar and subsequent rearrangement to the alkyl levulinate using acidic resins [Amberlyst 70].10 Lange et al., 2010 used bi-functional catalysts (e.g., Pt/H-ZSM5) to continuously convert levulinic acid to valerate esters in a multi-step process, yet direct conversion of sugars to valerate esters has not been investigated. The Hu et al., 2012 work was limited to the use of sulfonated polystyrene resins as catalysts in batch systems (3 h). These acidic resins have low surface area and thermal stability, potentially limiting their space time yields (STY’s, g product/L-catalyst/h) and the ability to be used in continuous reaction systems at higher temperatures. Batch reactors are inherently non-steady state thus leading to difficulties in accurately measuring reaction rates, product yields, selectivity, and space time yields. The development of continuous routes, especially if operational at lower residence times, would be of great interest. To date, there has been little research investigating continuous catalytic esterification/hydrogenation of key compounds in the fast pyrolysis oil using solid acid-metal catalysts. Such studies would enable accurate measurement of reaction rates, space time yields, selectivity, and catalyst longevity. Alternative to acidic resins, acidic zeolites and metal functionalized zeolites may provide a better alternative, since their acidity and hydrogenation activity can be manipulated to alter reaction pathways, they typically have higher surface areas, they are thermally stable, and zeolites can be used to convert the recovered oxygenates to gasoline (e.g., methanol or ethanol to gasoline processes, MTG or ETG).15,16 The goal of this work was to determine the feasibility of continuously generating ethyl levulinate and valerate

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esters directly from levoglucosan in fast pyrolysis oil using solid acid/metal catalysts and to gain a better understanding of the reaction pathways.

EXPERIMENTAL SECTION Catalysts. Five catalysts were used in this study, a granular activated carbon (Darco 4-12 mesh, Sigma-Aldrich), H-ZSM5 (Zeolyst International, CBV 5524 G), Ru/H-ZSM5 (5 wt.% Ru, by wet impregnation), Ru/C (5 wt.% Ru, by wet impregnation on the Darco activated carbon), and a commercially available sulfonated styrene–divinylbenzene macroreticular resin – Amberlyst 70 (Dow).

Catalyst Preparation. NH4-ZSM5 catalyst (Zeolyst International, CBV 5524 G) was received from the manufacturer as a fine powder with published values of 425 m2/g, 5 µm, and 50 for surface area, particle size and SiO2/Al2O3 ratio, respectively. The acidic form, H-ZSM5, was used as the solid acid catalyst and as a support for the generation of the bi-functional catalyst Ru/H-ZSM5 (5 wt.% Ru). H-ZSM5 was produced by calcining NH4-ZSM5 (Zeolyst International, CBV 5524 G) at 550 °C for 4 h in air to remove NH3 and produce the hydrogen form, H-ZSM5, resulting in stronger acid pore sites. The pH was measured by mixing catalyst in water at a 1:1 ratio, then measuring the pH of the water using a standard pH probe. After calcining, the pH declined from 4.98 to 3.06. To minimize the pressure drop across the catalyst bed, the catalyst was granulated by thoroughly mixing with water in a beaker, drying at 100 °C, physical crumbling/crushing, and sieving to the desired size, ∼2−4 mm. Preparation of Ru/H-ZSM5 (5 wt.% Ru) catalyst used the incipient wetness impregnation technique and the following method. An aqueous solution of water and ethanol (9:1 v/v) and the Ru salt (RuCl3H2O - Sigma) was first prepared. The pH of the solution was adjusted to solubilize the salt, if needed, with 2 mL of HNO3 (68%). Approximately 108 g of granulated H-ZSM5 was contacted with a volume of the salt solution equal to the pore volume of H-ZSM5 (0.185 mL/g based on BET analysis). After contact the solution was covered with parafilm and stored in the dark at room temp for 12 h. Subsequently, the material was dried at 105°C for 12 h in air and stored in a sealed container. Next the material was calcined in air at 500°C for 5 h. Prior to runs the catalyst was activated catalyst by placing 10 g in the tubular reactor (Parr) under a flow of 100 mL/min of 5 % H2 / 95 % N2 and heated at 10 °C/min to 500°C and held for 2 h. The 4 ACS Paragon Plus Environment

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expected metal loading was 5%. Catalytic esterification activity was also tested using a commercially available sulfonated styrene–divinylbenzene macroreticular resin – Amberlyst 70 (Dow). Amberlyst 70 resin has a reported particle size of 0.50 mm, thermal stability limit of 190 °C, and surface area of 36 m2/g. Amberlyst 70 was purchased as a dry brown spherical bead and used as received. Preparation of Ru/C (5 wt.% Ru) catalyst used the incipient wetness impregnation technique and the following method. A granular activated carbon (GAC) was used as the support for this material (Darco 4-12 mesh, Sigma-Aldrich), with a measured surface area and pore volume of 506 m2/g and 0.55 ml/g, respectively. An aqueous solution of water and ethanol (9:1 v/v) and the Ru salt (RuCl3H2O - Sigma) was first prepared. The pH of the solution was adjusted to solubilize the salt, if needed, with 2 mL of HNO3 (68%). Approximately 91 g of GAC was contacted with a volume of the salt solution equal to the pore volume of the GAC (0.55 mL/g based on BET analysis). After contact the solution was covered with parafilm and stored in the dark at room temp for 12 h. Subsequently, the material was dried at 105°C for 12 h in air and stored in a sealed container. Next the material was calcined in air at 500°C for 5 h. Prior to runs the catalyst was activated catalyst by placing 10 g in the tubular reactor (Parr) under a flow of 100 mL/min of 5 % H2 / 95 % N2 and heated at 10 °C/min to 500°C and held for 2 h. The expected metal loading was 5%.

Catalyst Characterization. Surface areas of the solid acid catalysts were measured using a 7point BET analysis equation (Quantachrome AUTOSORB-1C; Boynton Beach, FL). Pore size distribution, average pore radius, and total pore volume were estimated from N2 desorption curves using BJH analysis. H-ZSM5 and Ru/H-ZSM5 were analyzed by NH3 TPD as reported in the supplemental information to determine acid site concentration. Recovered catalysts were washed with an equal volume mixture of toluene, acetone, and methanol to remove tar, dried at 105 °C for 1 hour, cooled to room temperature, and weighed to determine the mass of tar removed. Catalyst coke formation was determined by heating the washed catalyst in a thermogravimetric analyzer (TGA) at 10 °C/min to 650 °C under air flow (50 ml/min). The change in the mass of catalyst was assumed to be due to the complete combustion of coke.


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Analytical. Conversion and product yields for esterification of the acetic acid/levoglucosan mixture was determined using GC/FID, GC/MS, and HPLC. Ethyl levulinate, ethyl acetate, acetic acid (confirmation with HPLC), cyclopentanone, and furfural were quantified via 5-point standard curves using a GC/FID. Acetic acid, levoglucosan, glucose, fructose, furfural (confirmation with GC/FID), and 5-hydroxymethylfurfural were quantified using HPLC and 5point standard curves. Longer chain methyl esters (C3-C8), acetals, and cyclic ketone concentrations were estimated using quantitative GC/MS methods outlined in the supplemental information. GC/FID analysis was performed on an HP 5890 with an HP Innowax capillary column. Chemical composition of the reacted samples was also determined by GC-MS analysis (HP6890, mass spectrometer HP-5973) using an HP-5 MS column. Details for both methods ared provided in the supplemental information. The water soluble components in the oil were analyzed by a high performance liquid chromatography (LC-20 AT, Shimadzu Corp., USA) equipped with a RID-10A refractive index detector and a 7.8×300 mm Coregel 64-H transgenomic analytical column for sugars (e.g., levoglucosan) and carboxylic acids (e.g., acetate). Acetic acid, levoglucosan, glucose, fructose, furfural, and 5-hydroxymethylfurfural in the liquid samples were identified by comparing retention times with standards and quantified using a 5-point standard curve. Catalytic Esterification and Hydrogenation. A mixture of levoglucosan (86.3 g L-1) and acetic acid (43.2 g L-1) in DI water and ethanol (80% ethanol, vol%) was continuously pumped downward using an HPLC pump across a packed bed reactor or PBR (Parr Moline, IL) maintained at 120, 150, 180, or 230 °C in a tube furnace (Thermocraft Lab-Temp 1760-watt tube furnace) at 600 psig. The PBR consisted of a 2.4 cm inner diameter reactor with a 38 cm length. A 15 cm preheater section was incorporated into the reactor to ensure that bio-oil was in vapor phase prior to crossing the catalyst bed (2 g Amberlyst 70, 5 g zeolites, for a packing height of 0.6 cm for Amberlyst 70 and 2.7 cm for the zeolites, given a bulk density of 0.77 and 0.41 g/cm3, respectively) that was held in place by stainless-steel screens and quartz wool above and below the bed. Liquid feed was typically 1.0 cm3 min−1, corresponding to a catalyst mass to feed ratio (W/F) of 0.11 h (g cat/g feed -1 h-1) for H-ZSM5 and Ru/H-ZSM5 catalystst. Note, the feed rate was calculated including ethanol. When using Amberlyst 70 (2 g) the liquid feed was typically 6 ACS Paragon Plus Environment

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0.5 cm3 min−1, corresponding to a catalyst mass to feed ratio (W/F) of 0.09 h (g cat/g feed -1 h-1). The liquid feed was mixed with an inert gas (N2) or H2 (100% H2) which had a flow rate of 100 cm3 min−1 (controlled using mass flow controllers - Brooks Delta II Smart). Weight hourly space velocity (WHSV) was calculated as the mass flow rate (g h−1) of liquid feed, divided by the catalyst mass (g) and ranged from 9-11 g feed g cat-1 h-1. These reaction conditions corresponded to a liquid hourly space velocity at inlet conditions [LHSV = reactant liquid flow rate (cm3 h−1)/catalyst packing volume (cm3)] ranging from 4.92 h−1 for the zeolites to 11.55 h-1 for Amberlyst 70. The outlet gas passed through a custom designed condenser vessel (Parr) and was chilled using a Brookfield TC-602 water bath. Yield (Y) was defined as the moles of product (ethyl levulinate or ethyl acetate) formed per mole of reactant (levoglucosan or acetate) fed and selectivity (S) as the moles of product formed per mole of reactant converted. Definitions for conversion (X) and space time yield or conversion (STY or STC) are provided in the supplemental information.

RESULTS AND DISCUSSION Catalyst Characterization. Except for Amberlyst 70, all of the prepared catalysts had high surface areas ranging from 260-400 m2/g for the zeolites (Table 1). The incorporation of metal (Ru) into HZSM-5 had little effect on surface area and pore size (Table 1). The Amberlyst 70 reportedly has a significantly larger average pore size than the other catalysts (Table 1). N2 adsorption isotherms for the zeolite catalysts were of Type I with hysteresis occurring between the adsorption and desorption paths (again, there were no significant differences upon metal incorporation into the zeolites, Figs. 1S, 2S). NH3-TPD analysis of the catalysts clearly noted differences between Type 1 (100-270°C) and 2 (270-500°C) sites upon metal incorporation (Fig. 1). Ruthenium incorporation into H-ZSM5 apparently created more Type 2 sites and increased the strength of Type 1 sites (raised the NH3 desorption temperature – Fig. 1 and Table 1), which as will be discussed later, apparently altered the pathway for ethyl levulinate synthesis. The peaks noted at 133°C and 173°C are considered weak sites and thought to be due to NH3 physisorption, and were not included in the acid site density calculations. In general five types of solid acid catalysts have been investigated in the catalytic esterification of sugars – acidic zeolites, sulfonated metal oxides (TiO2, ZrO2), heteropoly acids (Fe-H3PW12O40), sulfonated polystyrene resins (e.g., Amberlyst 70), and sulfonated carbon 7 ACS Paragon Plus Environment

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nanotubes.12 In the presence of alcohols two potential pathways for glucose and fructose transformation have been reported and appear to be influenced by acid density and Type 1 to 2 ratios.12 Larger pore sized zeolites (6-8 °A pore diameter, such as faujasites and H beta) with relative equal densities of Type 1 and 2 acid sites (based on NH3-TPD, Type 1: 100-270°C, Type 2: 270-500°C, 1:2 ratio of 1:0.36 to 1:0.81) and Si/Al ratios from 6-20 reportedly give the highest ethyl levulinate (EL) yield from glucose in batch reactors (41% at 160°C, 20h).17-18 Using the large pore size zeolites, EL yields of 11% were achieved from xylose, although the pathway to EL is unclear.17 It should be noted that the results using faujasites and H beta zeolites were not conducted in the presence of water, which can alter the reaction pathways and yields. A large pore sized zeolite, USY, was shown to generate a 10% EL yield from glucose at 180°C in 2.5 h in the presence of 20% water, again in batch reactors.19 These results from recently published papers and patents suggest that a balanced ratio of Type 1 and 2 acid sites improves ethyl levulinate yields from both glucose and xylose. Our results for H-ZSM5 are similar to Saravanamurugan et al., 2013 who reported a Type 1:2 ratio of 1:1.14, and Type 1 and 2 acid site densities of 211 and 240 µmoles/g, respectively.18 Luo et al., 2013 report higher type 2 acid site density for Ru/H-ZSM5 relative to H-beta Ru impregnated zeolite, which increased activity for hydrogenation of levulinic acid and γ-valerolactone to pentatonic acid and pentanoic acid ethyl ester.14 As discussed later, we believe the higher density of type 2 sites in Ru/H-ZSM5 increased the rate of levoglucosan hydrolysis to glucose and glucose esterification, while also providing hydrogenation activity.

Catalytic Esterification Using Acid Catalysts. In our initial work we tested activated carbon (GAC) and Ru on GAC as a catalyst. The granular activated carbon (GAC) material did not produce ethyl levulinate at any temperature (120, 180, 230 °C), but did produce ethyl acetate, furfural, and 5-methyl-2-furancarboxaldehyde (data not shown). We view this material as a control, since activated carbon typically has very weak acid sites on the surface (e.g., -COOH) and little to no metal functionality. The formation of ethyl acetate indicates autocatalysis of ethanol and acetic acid and thus we can’t claim that H-ZSM5 or the other catalysts were solely responsible for acetic acid esterification. Since ethyl levulinate was not formed using GAC we did not quantify these results. Ru/C did produce ethyl levulinate, but yield and STY was lower than H-ZSM5 and Ru/H-ZSM5 (Fig. 6S). When H2 was added to Ru/C, ethyl levulinate (EL) 8 ACS Paragon Plus Environment

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yield and STY was significantly reduced, and ≥ C3 ethyl esters and pentanoic acid ethyl esters (valeric esters) were not formed. Taken together, as discussed later, it is clear that Ru (a metal site), the strong acid sites in H-ZSM5, and H2 were required for promotion of EL (acid sites) and valeric ester formation (acid and metal sites, and H2). Next, using the acid zeolites, a series of experiments were performed in which mixtures of levoglucosan or LG (86 g L-1) and acetic acid or AA (44 g L-1) in an ethanol-water mixture (80% EtOH:20% water, v/v) were catalytically transformed over a range of temperatures (120, 180, 230°C) at 600 psig (typically 0.5-1h runs). In a typical experiment a batch (50-100 ml) of the LG/AA mixture in the ethanol/water solution was pumped across the packed bed reactor at 1 ml/min in a N2 or H2 carrier gas (100 ml/min). In most runs, 5 grams of catalyst was used in the 2.54 cm ID by 30.5 cm long reactor (typically 2.5-5.0 cm in catalyst packing height). The feed and condensed liquid products were analyzed via GC/MS, GC/FID, and HPLC. The acid zeolite H-ZSM5 (SiO2/Al2O3 ratio = 50, 0.5–1 mm particle size) clearly transformed levoglucosan and acetic acid to ethyl levulinate (EL) and ethyl acetate (EA) respectively (Fig. 2). Yields and selectivity for ethyl acetate were high (85%, 120°C), yet low (4.0%, 180°C) for ethyl levulinate (Fig. 3). Increasing reaction temperature reduced EA yield and space time yield (STY), but increased EL yield and STY up to 180°C. Although EL yields were low, conversions of levoglucosan and acetic acid were > 60% at 180°C and furfural formed at the higher temperatures (Fig. 2 and 3). The liquid stream generated at 180°C using H-ZSM5 contained 5 g/L of EL (and 45 g/L of EA) at a space time yield of 17 g EL/Lcat/h (total STY of 167 g esters/Lcat/h). Space time yields and EL yield at 180°C were marginally lower for the Ru modified H-ZSM5 (14 g/L/h, 3.2% - Figs. 3S). Interestingly, the Amberlyst 70 catalyst did not form ethyl levulinate under any of the conditions tested (Fig. 4S), although levoglucosan conversion was ∼100%, yet did form ethyl acetate at higher STY’s and yields compared to HZSM5 (compare Figs. 3 and 4S at 180°C). Analysis of the product liquid via GC/MS did not reveal the presence of any other compounds besides ethyl acetate and acetic acid. As previously noted, Saravanamurugan et al., 2014, 2013 reported ethyl levulinate (EL) yields of 41% from glucose in batch reactors at 160°C for 20 h using larger pore sized zeolites with roughly equal ratio of Type 1 to 2 acid sites (H-USY), compared to 2% EL using H-ZSM5 (1:1.14), without the initial presence of water.17-18 When using water these authors observed a 9 ACS Paragon Plus Environment

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decrease in EL yield to 11% under identical conditions. Xu et al., 2013 used USY zeolite to generate a 10% EL yield from glucose at 180°C in 2.5 h in the presence of 20% water, again in batch reactors.19 Assuming our reaction occurred in a liquid phase, the residence time approached 0.2 h (based on LHSV) using H-ZSM5 and Ru/H-ZSM5. Our EL yield of 4% (Fig. 3) using H-ZSM5 is comparable to that of Saravanamurugan et al., 2013, yet was achieved in a significantly shorter residence time in a continuous process.

Levoglucosan and acetic acid conversions greater than 60% yet low yields (or decreasing yields for EA) indicated either the formation of intermediates or products other than ethyl levulinate or EL (Fig. 3). Analysis of the liquid phase using GC/MS and HPLC revealed the formation of diethoxyethane (presumably from ethanol), toluene, ethyl benzene, xylene, methylated benzenes and naphthalenes, and glucose (Fig. 2). As the temperature increased, the primary difference in intermediate/product formation was the formation of furfural (MF 954, Prob 78.5) and trace levels of γ-valerolactone (MF 941, Prob 77.9), pentanonic acid ethyl ester (MF 761, Prob 45.7), and cyclic ketones (cyclopentanone, 3-methyl-2-cyclopenten-1-one, 2,3dimethyl-2-cyclopenten-1-one [MF 887, Prob 64]; Fig. 2). The formation of glucose indicates acid hydrolysis of levoglucosan and possible conversion to ethyl levulinate via fructose or ethyl glucoside.12,17-18 We observed trace levels of EGP (ethyl α-d-glucopyranoside, MF 925, Prob 95.9) using HZSM-5, but only at 120°C (Fig. 2), suggesting the possibility of this pathway for formation of EL. The formation of diethoxyethane and aromatic hydrocarbons indicate an ethanol to gasoline pathway (Fig. 2) is operational under these conditions using H-ZSM5.16 We also can’t rule out the possible formation of ethylene and unreacted ethanol vapor, since we did not analyze the gas phase. Finally, it’s possible that acetate contributed to the formation of hydrocarbons. Recent research indicates that feeding compounds with effective H/C ratios of 2 (eq. 1) or greater significantly reduces coking when transforming oxygenates using acid zeolites.20 ு ஼

=

(ுିଶ଴) ஼

Eq. 1,

where H,C, and O are the number of hydrogen, carbon and O atoms in the compound Mentzel and Holm (2011) show that when co-feeding methanol and acetic acid, a significant portion of acetate carbon forms C5+ aliphatics and C6-10 aromatics, potentially through acetone (via ketonization) or methyl acetate formation, and increases catalyst longevity.20 We believe a 10 ACS Paragon Plus Environment

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similar mechanism may be occurring when co-feeding ethanol and acetic acid (especially since the Eff. H/C ratio for ethanol is 2), but only to a minor level since our temperatures were lower than typical reaction temperatures for ETG processes (350-450°C).

Catalytic Esterification Using Metal/Acid Catalysts. Although the Ru/H-ZSM5 did not generate higher EL yields, selectivity or space time yields compared to H-ZSM5 (Fig. 3S), there were interesting differences in intermediate and product formation that provide insight into reaction pathways. The ruthenium exchanged/calcined H-ZSM5 clearly indicated the formation of glucose (Fig. 7S), ethyl α-d-glucopyranoside (EGP, more so than H-ZSM5), and 5hydroxymethyl furfural or 5-HMF (MF 882, Prob 74.1) at 120°C and subsequent reduction of EGP (qualitative analysis based on reduction in peak area ratio – Fig. 8S) and formation of ethyl levulinate at 180°C, indicating that two possible pathways (one via EGP and the other via 5HMF) for the formation of EL was potentially active with this catalyst (Fig. 11S). The formation of EGP at lower temperatures using Ru/H-ZSM5 may have been due to the increased acid site strength relative to HZSM-5 (Fig. 1 and Table 1). Given the formation of glucose from levoglucosan (LG) using these solid acid catalysts, we next wanted to confirm glucose as an intermediate in the formation of EL. Thus, catalytic esterification reactions using pure glucose were performed. Fructose formation was observed (0.45-3.4 g L-1, 180°C) using both H-ZSM5 and Ru/H-ZSM5, suggesting these zeolites isomerized glucose and that fructose is a potential intermediate in the formation of EL. Additionally, both furfural and 5-hydroxymethyl furfural (5HMF) were formed and the production of ethyl levulinate was confirmed (Fig. 9S). The formation of furfural and 5HMF from LG reportedly occurs via acid hydrolysis to form glucose and subsequent dehydration using solid acid catalysts.21 Ethyl levulinate yields and STY were similar to the results for levoglucosan (~5% from glucose versus results in Table 2). Analysis of the GC/MS chromatograms also indicated the formation of γ-valerolactone (GVL) at trace levels from both catalytic esterification of glucose (180°C, Fig. 9S), as well as levoglucosan (only at 230°C for HZSM5, and at 180 and 230°C for Ru/H-ZSM5). GVL can form from furfural or EL hydrogenation,22-23 suggesting in our case that GVL was possibly produced via transfer hydrogenation using ethanol as the hydrogen donor. Such a mechanism may also explain the low 11 ACS Paragon Plus Environment

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levels of pentanoic acid ethyl ester using H-ZSM5 and Ru/H-ZSM5 without H2 (Fig. 2, 230°C and Fig. 8S). A speculative reaction pathway based on these results is presented in Figure 11S.

Catalytic Esterification/Hydrogenation. Given the trace levels of GVL formed, we next wanted to explore if adding metal functionality to the zeolite would produce higher levels of GVL and valeric biofuels in the presence of hydrogen. Ruthenium was selected due to its reported superior activity in aqueous phase hydrogenations on both carbon and oxide supports, the extensive work in catalytic hydrodeoxygenation of fast pyrolysis oil using Ru, its reported high selectivity for GVL, and its ability to form pentanoic acid from levulinic acid.12,14, 24-27 Subsequently a series of experiments were performed with added H2 at the same conditions tested previously. Upon hydrogen addition, the ethyl levulinate yield and STY decreased significantly (Table 2) and the optimum temperature for EL formation also shifted to a higher temperature (220°C, compare Fig. 4 with 3S). Similarly, when comparing results at 180°C, ethyl acetate yield and STY were reduced for both H-ZSM5 and Ru/H-ZSM5 in the presence of H2 (compare Figs. 3 with 5S and 4 with 3S). Analysis of the collected liquid from these reactions did not indicate evidence of increased GVL formation. However, the formation of longer chain ethyl esters, such as pentanoic (ethyl valerate) and hexanoic (caproic acid) acid ethyl esters, were observed (Fig. 5). Significant levels of such products were not observed for H-ZSM5 in the presence of hydrogen (data not shown). These results suggest that GVL is formed from levoglucosan and rapidly esterified and hydrogenated forming ethyl valerate.13-14,19,27 The formation of valeric and caproic esters peaked at 180°C, similar to EL formation without the presence of H2 (Fig. 5). The presence of hydrogen also reduced coke formation when using both H-ZSM5 and Ru/H-ZSM5, yet only at the reaction temperature (180°C), which resulted in the highest EL yield and STY (Fig. 12S and 13S). The possible pathway for valeric ester formation is shown in Figure 11S. Although the ≥ C3 ethyl ester levels (propanoic acid to hexanoic acid ethyl esters) were low (~3%), we do believe these results represent one of the first reports for direct catalytic conversion of levoglucosan to valerate esters. The increased level of valerate esters in the presence of H2 and reduction in EL yield, indicate the need for metal/acid functionality in the catalyst and suggest 5-HMF, furfural, and EL are intermediates in the formation of the longer chain ethyl esters (Fig. 5 and 11S). We could not find reports in the literature on direct 12 ACS Paragon Plus Environment

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conversion of levoglucosan (or other sugars) to pentanoic acid ethyl esters (valeric esters), but Lanzafame et al., 2011 has reported synthesis of ethyl levulinate from 5HMF using mesoporous solid acid catalysts (5 h, 140°C).28 Strong Bronsted acid sites favored EL formation at yields of 47% without the presence of water. These authors also proposed single-stage production of valerate esters via this pathway if the catalyst had hydrogenation functionality.28 Recently, Li et al., 2016 demonstrated catalytic transfer hydrogenation using ethanol to form GVL and ethyl levulinate (35-40% GVL, 18-20% ester) from glucose and cellobiose using NiZr oxides (200°C, 5h), yet there was no evidence of ethyl valerate formation.29 Transformation of the sugars required the additional presence of an acid catalyst (zeolite HY6).29

Spent Catalyst Characterization. After the reactions, catalysts were collected, washed with solvent to determine tar levels, and then coke levels were estimated. Tar levels were higher at lower reactions temperatures and decreased with increasing reaction temperatures; the exception being Ru/H-ZSM5 in the presence of H2 (Table 1S). For H-ZSM5 (w/o H2) and Ru/H-ZSM5 (with H2), as reaction temperature increased, coke formation increased (Table 1S, Fig. 12S). The presence of hydrogen reduced coke formation when using both H-ZSM5 and Ru/H-ZSM5, yet only at the reaction temperature (180°C), which was most apparent in the TGA analysis. Hydrogen addition reduced the high temperature coke (i.e., the peak evolved from 400-600°C in TGA analysis) using H-ZSM5 and eliminated this peak using Ru/H-ZSM5 in the TGA analysis (Fig. 13S). Relative to fresh catalyst, the spent catalyst had significantly lower surface areas and pore volumes (Table 1 vs. Table 1S). Surface area inversely correlated with an increase in reaction temperature; i.e., in general, surface area declined with increasing reaction temperature. The notable exception was when H2 was added; in this case, surface area increased with increasing temperature for spent catalyst (Table 1S). Coke formation has been reported for catalytic hydrogenation studies of levulinic acid to GVL and pentanoic acid, and valerate esters in solvents other than water (γ-valerolactone, dioxane and ethanol), when using metal (Ru, Ni)/acid (H-ZSM5) catalysts.13,14, 30 The surface area of Ru/H-ZSM5 and Ru/H-β decreased significantly (55% and 27%) and coke content increased to 5.5 and 10.7 wt.% respectively.14 There was no measurable reduction in surface area


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and only 1.3-1.8 wt.% coke when using Ru/TiO2, yet this catalyst produced low levels of pentanoic acid and its ester due its weak acid sites and the inability to perform ring opening of GVL.14 Our much larger reduction in surface area and higher coke levels (Ru/H-HZSM5, 180°C, +H2) could be attributable to the presence of water and the use of levoglucosan or LG (i.e., the furan intermediates derived from LG) as the substrate. Strong acid sites, as in Ru/H-ZSM5, are known to form humins from furfural in the presence of water (more so than in other solvents, such as ethanol) and polycyclic aromatics from furans.10, 31 Our spent catalyst characterization results do suggest that prolonged time on stream (> 1-2 h in our work) would lead to deactivation. Interestingly, valeric acid/ester yields could be maintained at 90% for 22 h using Ru/H-ZSM5 if levulinic acid in ethanol was the reactant (240°C, 3 MPa H2), and could be maintained at these yields for 500 h if a Ni/H-ZSM5 doped with potassium was used and periodic regeneration via calcination and H2 reduction was imposed. Potassium doping reduced acid site strength in Ni/H-ZSM5, reducing coke formation and acid site leaching, yet not to a level preventing formation of pentanoic acid and its esterification. Taken together these results suggest continuous conversion of LG (and glucose) to valeric esters can be improved by reducing the water content and acid site strength in the catalyst. CONCLUSIONS Our results indicate that single-stage, continuous esterification with ethanol and hydrogenation of levoglucosan using a bi-functional zeolite (metal-acid sites) produces ethyl levulinate and a range of ethyl esters with carbon numbers greater than three, but primarily pentanoic acid ethyl ester or EV (valerate biofuels). The strong acid functionality is required for hydrolysis of levoglucosan and subsequent esterification, dehydration and ring opening steps, mostly evidenced by the formation of glucose, ethyl α-d-glucopyranoside, furfural, 5HMF, GVL, and ethyl levulinate from levoglucosan. The metal functionality is required for hydrogenation activity and is indicated by the formation of valeric biofuels (yield increase) and reduction in EL yield using Ru/H-ZSM5 and hydrogen. A reaction temperature of 180°C was optimum for both EL and EV formation with increasing temperature leading to a reduction in yields. Although direct evidence has not been presented, we speculate that the low EL and EV yields are partly due to coke formation and the imbalance between the kinetic diameter of the substrates (levoglucosan, 6.7 Å; glucose, 8.6 Å) and intermediates relative to H-ZSM5 pore size (6.3 Å).31 14 ACS Paragon Plus Environment

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ACKNOWLEDGEMENTS The authors graciously thank Joby Miller, Richard Spier, and Andrew Smola for their invaluable contributions of time and effort in GC/MS, HPLC, GC/FID analysis and catalyst characterization. Support for this research was provided in part by a grant from the Southeastern Sun Grant Center with funds provided by the U.S. Department of Transportation Research and Innovative Technology Administration (DTOS59-07-G-00050) and by DOE (DEFG3608GO8814: Biorefining and Carbon Cycling Program).

SUPPORTING INFORMATION: Includes additional, materials and methods, catalyst characterization results, space time yield plots, equations for yield, selectivity, space time conversion and yield, product concentration plots, GC/MS chromatograms, potential reaction pathway, and catalyst coke analysis

REFERENCES 1. Huber, G.W. (Chair). Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels: Next Generation Hydrocarbon Biorefineries. Based on the June 25-26, 2007 Workshop, Washington, D.C., Sponsored by NSF, DOE, and ACS. p.1-179. 2. Vispute, T.P.; Zhang, H.; Sanna, A.; Xiao, R.; Huber. G.W. Science 2010, 330, 1222-1227. 3. Diebold, J. P. A Review of the chemical and physical mechanisms of the storage stability of fast pyrolysis bio-oils; Subcontractor Report for the National Renewable Energy Laboratory NREL/SR570-27613; National Renewable Energy Laboratory: Golden, CO, 2000. 4. Diebold, James P. (Natl Renewable Energy Lab, Golden, United States); Czernik, Stefan. Energy and Fuels, v 11, n 5, p 1081-1091, Sep-Oct 1997. 5. Zacher, A.H.; Olarte, M.V.; Santosa, D.M.; Elliott, D.C.; Jones, S.B. Green Chem., 2014, 16, 491. 6. Mahfud, F.; Melián-Cabrera, I.; Manurung, R.; Heeres, H. Process Safety & Environmental Protection: Transactions of the Institution of Chemical Engineers Part B 2007, 85(5), 466-472. 7. Gayubo, A.G.; Aguayo, A.T.; Atutxa, A.; Atutxa, A.; Bilbao, J. J Chem Technol Biotechnol, 2005, 80, 1244–1251. 8. Gayubo, A.G.; Aguayo, A.T.: Atutxa, A.; Prieto, R.; Bilbao, J. Energy and Fuels, 2004, 18, 16401647. 9. Hilten, R.; Bibens, B.; Kastner, J.R.; Das, KC. Energy and Fuels, 2010, 24, 673–682. 10. Hu, X.; Wu, L.; Wang, Y.; Mourant, D.; Lievens, C.; Gunawan, R.; Li, C-Z. Green Chem., 2012, 14, 3087. 15 ACS Paragon Plus Environment

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

11. Ciddor, L.; Bennett, J.A.; Hunns, J.A.; Wilson, K.; Lee, A.F. J Chem Technol Biotechnol 2015; 90: 780–795. 12. Démolis, A.; Essayem, N.; Rataboul, F. ACS Sustainable Chem. Eng. 2014, 2, 1338−1352. 13. Lange, J-P.; Price, R.; Ayoub, P.M.; Louis, J.; Petrus, L.; Clarke, L.; Gosselink, H. Angew. Chem. Int. Ed. 2010, 49, 4479 –4483. 14. Luo, W.; Deka, U.; Beale, A.M.; van Eck, E.R.H.; Bruijnincx, P.C.A.; Weckhuysen, B.M. Journal of Catalysis. 301 (2013) 175–186. 15. Whitcraft, D.R.; Veryklos, X.E.; Yutharasan, R. Ind. Eng. Chem. Process Des. Dev. 1983, 22, 452457. 16. Sun J., Wang Y. ACS Catal. 2014, 4, 1078−1090. 17. Saravanamurugan, S.; Riisager, A. Conversion of Carbohydrates to Levulinic Acid Esters, International Patent No., WO 2014/020153 A1. 2014. 18. Saravanamurugan, S.; Riisager, A. ChemCatChem. 2013, 5, 1754-1757. 19. Xu, G-Z.; Chang, C.; Zhu, W-N.; Li, B.; Ma, X-J.; Du, F-G. Chemical Papers 67 (11) 1355–1363 (2013). 20. Mentzel, U.V.; Holm, M.S. Applied Catalysis A: General 396, 39-67 (2011). 21. Kaldstrom, M.; Kumar, N.; Heikkila, T.; Tiitta, M.; Salmi, T.; Murzin. D.Y. ChemCatChem 2010, 2, 539 – 546. 22. Antunes, M.M.; Lima, S.; Neves, P.; Magalhães, A.L.; Fazio, E.; Fernandes, A.; Neri, F.; Silva, C.M.; Rocha, S.M.; Ribeiro, M.F.; Pillinger, M.; Urakawa, A.; Valente, A.A. Journal of Catalysis 329 (2015) 522–537. 23. Li, H.; Fang, Z.; Yang, S. ACS Sustainable Chem. Eng. 2016, 4, 236−246 24. Wildschut, J.; Melián-Cabrera, I.; Heeres, H.J. Applied Catalysis B: Environmental 99 (2010) 298– 306. 25. Michel, C.; Gallezot, P. ACS Catal. 2015, 5, 4130−4132. 26. Wang,H.; Lee, S-J.; Olarte, M.V.; Zacher, A.H. ACS Sustainable Chem. Eng. In Press. 2016. 27. Pan, T.; Deng, J.; Xu, Q.; Xu, Y.; Guo, Q-Y.; Fu, Y.Green Chem., 2013, 15, 2967. 28. Lanzafame, P.; Temi, D.M.; Perathoner, S.; Centi, G.; Macario, A.; Aloise, A.; Giordano, G. Catalysis Today 175 (2011) 435– 441. 29. Li, H.; Fang, Z.; Yang, S. ChemPlusChem 2016, 81,135 –142.


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30. Sun, P.; Gao, G.; Zhao, Z.; Xia, C.; Li, F. App Cat B: Env. 189 (2016) 19-25. 31. Jae, J.; Tompsett, G.A.; Foster, A.J.; Hammond, K.D.; Auerbach, S.M.; Lobo, R.F.; Huber, G.W. Journal of Catalysis. 279 (2011) 257–268.


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Table 1: Physical properties of zeolites, metal impregnated zeolites, and sulfonated acidic resin. H-ZSM5

Ru/H-ZSM5

Amberlyst 70a

Activated Carbon

Ru/C

Surface Area (m2/g)

316

313

31-36

506

721

Pore Volume (cm3/g)

0.17

0.17

0.015-0.33

0.55

0.41

11

11

195-220

NP

11.4

0.41

0.41

0.77

0.34-0.54 b

0.34-0.54 b

200-300°C, µmoles NH3/g (Type 1)

231

170

NP

NP

NP

300-500°C, µmoles NH3/g (Type 2)

293

360

NP

NP

NP

Total Acid Sites, µmoles NH3/g

524

530

NP

NP

NP

1:1.27

1:2.2

NP

NP

NP

Catalyst Properties

Average Pore Size (radius Å) Bulk Density, g/cm3 Acid Sites (NH3-TPD)

Type 1: Type 2 Ratio a

Rohm and Haas Amberlyst 70 product data sheet; Rohm and Haas, Philadelphia, PA, USA, 2005

b

, Darco granular activated carbon, product data sheet, Sigma-Alrich

NP: Not performed


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Table 2: Summary of catalytic esterification results for ethyl levulinate formation from levoglucosan in the presence of acetic acid. Catalyst

H-ZSM5

Ru/H-ZSM5

Amberlyst 70

Reaction Conditions

T,°°C

Yield

Selectivity

(mol/mol fed)

(mol/mol converted)

% Coke

% Carbon Recovered

w/o H2

120 180 230

0.01 0.04 0.03

+H2

120 180 230

w/o H2

0.03 0.05 0.03

4.0 20.1 13.0

100 86.3 63.0

0.00 0.012 0.018

0.00 0.015 0.019

21.0 15.4 16.7

100.0 77.6 72.1

0.00 5.36 7.75

DEE DEE DEE

120 180 230

0.00 0.03 0.02

0.00 0.03 0.02

14.9 20.7 11.8

100 82.3 96.7

0.00 11.95 7.83

DEE DEE DEE

+H2

120 180 230

0.010 0.009 0.013

0.001 0.010 0.013

8.3 13.0 15.3

80.0 69.0 59.7

4.48 3.88 5.53

-

-

-

w/o H2

120 150 180

0.0 0.0 0.0

0.0 0.0 0.0

NP NP NP

NP NP NP

0.0 0.0 0.0

DEE DEE DEE

-

-

a DEE-1,1-diethoxyethane b Little methylated benzenes formed compared to HZSM-5 w/o H2 c Ethyl alpha-d-glucopyranoside d heptanoic/pentanoic acid ethyl esters, reduction in BTEX


Space Time Yield (g/Lcat/h) 6.26 DEEa DEE 17.07 12.40 DEE

Intermediates/End Products

Glucose Glucose Glucose

-

Furfural Furfural

-

-

Furfural Furfural BTEXb

Glucose EGPc Furfural Glucose EGPc Furfural Glucose Furfural

BTEX BTEX

BTEX

Furfural BTEX BTEXd Furfural BTEXd -

-

Energy & Fuels

10

NH3 TPD Analysis

9

HZSM5

133°°C 173°C

8

Ru-HZSM5

7 TCD Signal, mV

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

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250°C 223°C

6

430°C

5 4 3 2

410°C

1 0 0.00

100.00

200.00

300.00

400.00

500.00

600.00

Temperature, °C

Figure 1: Ammonia TPD analysis of freshly prepared H-ZSM5 and Ru/HZSM5 with the baseline subtracted.


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Energy & Fuels 30000000

HZSM5-120C

1

25000000

TIC Abundance

4 7

20000000

2

5

IS

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6 10000000 5000000

3 9

0 0

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HZSM5-180C

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20000000

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5000000 0 0

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HZSM5-230C

1

25000000

TIC Abundance

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20000000

6

IS 15000000

3 2

10000000 5000000

11 12

13

8

7

0 0

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10

Time, min

15

20

25

Figure 2: GC/MS analysis of liquid products formed via catalytic reaction of ethanol, levoglucosan, and acetic acid using H-ZSM5. (1) ethyl acetate, (2) acetic acid, (3) furfural, (IS) hexanol, (4) 1-ethyl-3methyl-benzene, (5) 1-ethyl-4-methyl-benzene, (6) ethyl levulinate, (7) 1,4-diethyl-2-methyl benzene, (8) levoglucosan, (9) ethyl α-d-glucopyranoside, (10) 1,1-diethoxy-ethane, (11) pentanoic acid, ethyl ester, 12) γ-valerolactone, (13) 2,3-dimethyl 2-cyclopenten-1-one. Note, glucose formation was observed via HPLC and is not shown. 21 ACS Paragon Plus Environment

Energy & Fuels

0.80

300

0.60

200

0.40

100

0.20

0

0.00 120

140

160

180

200

220

Fractional Conversion

400

100

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1.00

240

Temperature, °C STC-LG

Acetic-X

LG-X

200

16

180

14

160

12

140 120

10

100

8

80

6

60

4

40

Ethyl Acetate

Ethyl Levulinate

20

2

0

0 100

120

140

160

180

200

220

Ethyl Levulinate - Space Time Yield (g/L-cat/h)

Ethyl Acetatie, Space Time Yield (g/L-cat/h)

STC-AA

240

0.90

0.050

0.80

0.045

0.70

0.040 0.035

0.60

0.030

0.50

0.025 0.40

0.020

0.30

0.015

0.20

Ethyl Acetate-Y

Ethyl Acetate-S

0.010

0.10

Ethyl Lev-Y

Ethyl Lev-S

0.005

0.00

0.000 100

120

140

160

180

200

220

Ethyl Levulinate Yield and Selectivity

Temperature, °C

Ethyl Acetate-Yield and Selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Space Time Conversion, g/Lcat/h

500

240

Temperature, °C

Figure 3: Space time conversion (STC) and yields (STY, Y), and selectivity (S) for catalytic esterification of acetic acid and levoglucosan using H-ZSM5 (W/F = 0.11 h). LG is levoglucosan and X is conversion. 22 ACS Paragon Plus Environment

1.00

400

0.80

300

0.60

200

0.40

100

0.20

0

0.00 120

140

160

180

200

220

Fractional Conversion

500

100

240

Temperature, °C Acetic

LG

Ethyl Acetate STY, L-cat/h

160

12

140

10

120 8

100 80

6

60

4

40 2

20 0

0 100

120

140

160

Ethyl Acetate

180

Temperature, °C Ethyl Levulinate

200

220

240

≥C3 Ethyl Esters

0.90

0.035

0.80

0.030

0.70 0.025

0.60 0.50

0.020

0.40

0.015

0.30

0.010

0.20 0.005

0.10 0.00

0.000 100

120

140

160

180

Ethyl Levulinate and Valerate STY, g/L-cat/h

STC-LG

200

220

240

Ethyl Levulinate and C3 Ester Selectivity

STC-AA

Ethyl Acetate Selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels Space Time Conversion, g/Lcat/h

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Temperature, °C Ethyl Acetate-S

Ethyl Lev-S

≥C3 Ethyl Esters

Figure 4: Space time conversion (STC) and yields (STY), and selectivity (S) for catalytic esterification of acetic acid and levoglucosan using Ru/H-ZSM5 in the presence of H2. STY is space time yield. 23 ACS Paragon Plus Environment

35000000

Energy & Fuels

TIC Abundance

30000000

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25000000 20000000

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15000000

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IS

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5

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8 6

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0 0

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B, Ru-HZSM5-H2-180°°C

35000000

1

TIC Abundance

30000000 25000000 20000000

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15000000

IS 17

10000000

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5000000

11 14 13 15 16 12 3

184

19 6 7 8

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0 0 30000000

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1

C-Ru-HZSM5-H2-230°°C

25000000

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IS

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3

21 20 22

5000000

6 17 18

19

7

23

0 0

5

10

15

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25

Time, min Figure 5: Effect of H2 on liquid products formed via catalytic reaction of ethanol, levoglucosan, and acetic acid using Ru/H-ZSM5. (1) ethyl acetate, (2) acetic, (3) furfural, (IS) hexanol, (4) benzene, 1-ethyl-3-methyl, (5) benzene, 1-ethyl-4-methyl-, (6) pentanoic acid, 4-oxo-, ethyl ester, (7) benzene, 1,4-diethyl-2-methyl-, (8) β-D-glucopyranose, 1,6-anhydro-, (9) ethyl α-d-glucopyranoside, (10) furan, tetrahydro-, (11) ethane, 1,1-diethoxy-, (12) 2H-pyran, tetrahydro-3-methyl-, (13) 3-hexanone, (14) pentane, 1-ethoxy-, (15) cyclopentanone, 3-methyl-, (16) hexane, 1-ethoxy-, (17) pentanoic acid, ethyl ester, (18) pentanoic acid, 2-methyl-, ethyl ester, (19) hexanoic acid, ethyl ester, (20) ethane, 1-ethoxy-1-methoxy-, (21) propanoic acid, ethyl ester, (22) cyclopentanone, (23) pentanoic acid, 2-methyl-4-oxo-, ethyl ester. Note: glucose formation was observed via HPLC and is not shown.


Continuous Catalytic Esterification and Hydrogenation of a

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