Marta Paniagua

Efficient Isomerization of Glucose to Fructose over Zeolites in Consecutive Reactions in Alcohol and Aqueous Media

Isomerization reactions of glucose were catalyzed by different types of commercial zeolites in methanol and water in two reaction steps. The most active catalyst was zeolite Y, which was found to be more active than the zeolites beta, ZSM-5, and mordenite. The novel reaction pathway involves glucose isomerization to fructose and subsequent reaction with methanol to form methyl fructoside (step 1), followed by hydrolysis to re-form fructose after water addition (step 2). NMR analysis with (13)C-labeled sugars confirmed this reaction pathway. Conversion of glucose for 1 h at 120 °C with H-USY (Si/Al = 6) gave a remarkable 55% yield of fructose after the second reaction step. A main advantage of applying alcohol media and a catalyst that combines Brønsted and Lewis acid sites is that glucose is isomerized to fructose at low temperatures, while direct conversion to industrially important chemicals like alkyl levulinates is viable at higher temperatures.

Acetalisation of bio-glycerol with acetone to produce solketal over sulfonic mesostructured silicas

Sulfonic acid-functionalized mesostructured silicas have demonstrated excellent catalytic behaviour in the acetalisation of glycerol with acetone to yield 2,2-dimethyl-1,3-dioxolane-4-methanol, also known as solketal. This molecule constitutes an excellent compound for the formulation of gasoline, diesel and biodiesel fuels. The activity achieved with arenesulfonic acid-functionalized silica is comparable to that displayed by Amberlyst-15. Optimal production of solketal over arenesulfonic acid mesostructured silica has been established for a reaction system consisting of three consecutive 2-step batches (30 min under reflux and an evaporation step under vacuum), and using a 6/1 acetone/glycerol molar ratio. The use of lower grades of glycerol, such as technical (purity of 91.6 wt%) and crude (85.8 wt%) glycerol, has also provided high conversions of glycerol over sulfonic acid-modified heterogeneous catalysts (84% and 81%, respectively). For refined and technical glycerol the catalysts have been reused, without any regeneration treatment, up to three times, keeping the high initial activity. However, the high sodium content in crude glycerol deactivates the sulfonic acid sites by cation exchange. This deactivation is readily reversed by simple acidification of the catalyst after reaction.

Etherification of biodiesel-derived glycerol with ethanol for fuel formulation over sulfonic modified catalysts.

The present study is focused on the etherification of biodiesel-derived glycerol with anhydrous ethanol over arenesulfonic acid-functionalized mesostructured silicas to produce ethyl ethers of glycerol that can be used as gasoline or diesel fuel biocomponents. Within the studied range, the best conditions to maximize glycerol conversion and yield towards ethyl-glycerols are: T=200 °C, ethanol/glycerol molar ratio=15/1, and catalyst loading=19 wt%. Under these reaction conditions, 74% glycerol conversion and 42% yield to ethyl ethers have been achieved after 4 h of reaction but with a significant presence of glycerol by-products. In contrast, lower reaction temperatures (T=160 °C) and moderate catalyst loading (14 wt%) in presence of a high ethanol concentration (ethanol/glycerol molar ratio=15/1) are necessary to avoid the formation of glycerol by-products and maximize ethyl-glycerols selectivity. Interestingly, a close catalytic performance to that achieved using high purity glycerol has been obtained with low-grade water-containing glycerol.

Xylose Isomerization with Zeolites in a Two-Step Alcohol–Water Process

Isomerization of xylose to xylulose was efficiently catalyzed by large-pore zeolites in a two-step methanol-water process that enhanced the product yield significantly. The reaction pathway involves xylose isomerization to xylulose, which, in part, subsequently reacts with methanol to form methyl xyluloside (step 1) followed by hydrolysis after water addition to form additional xylulose (step 2). NMR spectroscopy studies performed with (13) C-labeled xylose confirmed the proposed reaction pathway. The most active catalyst examined was zeolite Y, which proved more active than zeolite beta, ZSM-5, and mordenite. The yield of xylulose obtained over H-USY (Si/Al=6) after 1 h of reaction at 100 °C was 39%. After water hydrolysis in the second reaction step, the yield increased to 47%. Results obtained from pyridine adsorption studies confirm that H-USY (6) is a catalyst that combines Brønsted and Lewis acid sites, and isomerizes xylose in alcohol media to form xylulose at low temperature. The applied zeolites are commercially available; do not contain any auxiliary tetravalent metals, for example, tin, titanium, or zirconium; isomerize xylose efficiently; are easy to regenerate; and are prone to recycling.

One-pot cascade transformation of xylose into γ-valerolactone (GVL) over bifunctional Brønsted–Lewis Zr–Al-beta zeolite

The one-pot conversion of xylose into GVL in 2-propanol has been achieved over bifunctional Zr- and Al-containing beta zeolite catalysts, prepared via a post-synthetic route, possessing both Bronsted and Lewis functionalities. A GVL yield of 35 mol% was obtained at 190 °C after 48 h.

Dehydration of Xylose to Furfural in Alcohol Media in the Presence of Solid Acid Catalysts

Different solid acid catalysts, which include several zeolites, zirconium oxide based catalysts, and materials that contain sulfonic acids, have been evaluated in the dehydration of xylose to furfural in alcohol media. Alcohol media were selected to reduce side reactions, many of which occur in aqueous media. Among the tested alcohols, 2‐propanol provided better results and yielded a higher furfural production than ethanol and methanol. Catalyst screening evidenced that small‐pore‐size zeolites (H‐ZSM5) or catalysts that show weak acidity (tungstated zirconia) were unable to promote the desired transformation. Kinetic studies performed for the different types of materials revealed that the nature of the acid sites influenced the catalytic performance of the different solid acids to the extent of conditioning the main reaction pathway for the transformation of xylose into furfural. Thus, whereas Lewis acids seem to promote furfural production by the direct dehydration of xylose, Brønsted‐type catalysts lead to alkyl xylosides as intermediates in the overall transformation. Although both types of catalysts provide high furfural yields in short reaction times, especially at high temperatures, commercially available β‐zeolite with an adequate combination of Brønsted and Lewis acids sites seems to contain the right physicochemical properties to maximize furfural production.

Sulfonic acid heterogeneous catalysts for dehydration of C6-monosaccharides to 5-hydroxymethylfurfural in dimethyl sulfoxide

Abstract Sulfonic acid-functionalized heterogeneous catalysts have been evaluated in the catalytic dehydration of C 6 monosaccharides into 5-hydroxymethylfurfural (HMF) using dimethyl sulfoxide (DMSO) as solvent. Sulfonic commercial resin Amberlyst-70 was the most active catalyst, which was ascribed to its higher concentration of sulfonic acid sites as compared with the other catalysts, and it gave 93 mol% yield of HMF from fructose in 1 h. With glucose as the starting material, which is a much more difficult reaction, the reaction conditions (time, temperature, and catalyst loading) were optimized for Amberlyst-70 by a response surface methodology, which gave a maximum HMF yield of 33 mol% at 147 °C with 23 wt% catalyst loading based on glucose and 24 h reaction time. DMSO promotes the dehydration of glucose into anhydroglucose, which acts as a reservoir of the substrate to facilitate the production of HMF by reducing side reactions. Catalyst reuse without a regeneration treatment showed a gradual but not very significant decay in catalytic activity.

Efficient one-pot production of γ-valerolactone from xylose over Zr-Al-Beta zeolite: rational optimization of catalyst synthesis and reaction conditions

The one-pot conversion of xylose into γ-gammavalerolactone in 2-propanol over bifunctional Zr-Al-Beta zeolites, prepared via a post-synthetic route, was optimized in terms of both catalyst synthesis and reaction conditions. In the catalyst preparation, the use of Zr(NO3)4 as zirconium source as well as the tuning of the amount of water used during the impregnation had a strong impact on the activity of the Zr species due to an improved dispersion of Zr species. As for the aluminium to zirconium exchange, an optimal Al/Zr ratio of 0.20 was identified to provide a catalyst with better activity. The modelization of the catalytic system through experimental design methodology allowed to identify the optimal values of the most influential reaction conditions: temperature 190 °C, catalyst loading 15 g L−1, and starting xylose concentration 30.5 g L−1. Under these optimized reaction conditions, Zr-Al-Beta catalyst provides a GVL yield from xylose (ca. 34%) after only 10 h. The catalysts are stable and reusable after thermal regeneration at 550 °C.

Chemical routes for the conversion of cellulosic platform molecules into high-energy-density biofuels

Abstract In this chapter, we will highlight different chemical routes to convert highly functionalized sugars (glucose and xylose) coming from the hydrolysis of nonedible lignocellulosic biomass into high-energy-density biofuels with reduced oxygen content and improved H/C ratio. Firstly, this chapter will be focused on the chemical catalytic upgrading of lignocellulosic-based platform molecules (5-HMF, levulinic acid, and furfural) to oxygenated second-generation biofuels and the effect of the blending with conventional fuels. Then, the latest developments in the effective transformation of oxygenated platform molecules into liquid hydrocarbon fuels will also be discussed. This valorization strategy is based on the combination of oxygen removal processes and C C coupling reactions to increase the molecular weight with the aim of yielding a mixture of liquid hydrocarbons with a carbon number in the range of conventional fuels. Both type of advanced biofuels are shown as a good alternative to conventional biofuels (biodiesel and bioethanol).

ZrO2-SBA-15 catalysts for the one-pot cascade synthesis of GVL from furfural

Controlling the thickness of zirconia monolayers coated over SBA-15 offers an effective way to tune catalytic performance for the acid-mediated and hydrogen transfer (Meerwein Ponndorf Verley, MPV) cascade transformation of furfural to γ-valerolactone. Complementary mechanistic and kinetic modelling establishes the existence of the two distinct zirconium active species (weak and strong acid sites), whose balancing enables optimisation of the cascade and hence maximal γ-valerolactone (GVL) production.