With increased availability and decreased cost, ethanol is potentially a promising platform molecule for the production of a variety of value-added chemicals. In this review, we provide a detailed summary of recent advances in catalytic conversion of ethanol to a wide range of chemicals and fuels. We particularly focus on catalyst advances and fundamental understanding of reaction mechanisms involved in ethanol steam reforming (ESR) to produce hydrogen, ethanol conversion to hydrocarbons ranging from light olefins to longer chain alkenes/alkanes and aromatics, and ethanol conversion to other oxygenates including 1-butanol, acetaldehyde, acetone, diethyl ether, and ethyl acetate.

Recent Advances in Catalytic Conversion of Ethanol to Chemicals

Alcohol coupling, also known as the Guerbet reaction, is a potentially important process to increase the value of short chain alcohols. Metal oxides, metal phosphates, and supported transition metals, such as copper, are important components of heterogeneous catalysts for the reaction. However, the wide variety of catalyst compositions, reaction conditions, and reactor configurations used to study the reaction complicate a direct comparison of various catalysts. In this review, rates over different catalysts will be compared, the influences of the acid and base properties of the catalyst on product selectivity will be presented, and possible reaction paths to accomplish alcohol coupling will be discussed.

Heterogeneous Catalysts for the Guerbet Coupling of Alcohols

https://biblio.ugent.be/publication/6928710/file/6928721.pdf

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

Ethanol is presently the most common liquid fuel derived from biomass. One way of meeting the growing demand for heavier middle-distillate fuels — diesel and jet fuels comprising hydrocarbons of typically 8–22 carbon atoms — is to derive these from ethanol. This Review describes the chemistries and processes involved in the conversion of ethanol into diesel and jet fuel drop-in replacements and blendstocks. This conversion of ethanol relies on reactions including dehydration (to olefins), dehydrogenation (to aldehydes), hydrogenation (of C=C and C=O bonds), acid-catalysed olefin oligomerization, metal-catalysed olefin oligomerization, aldolization and ketonization. We discuss the thermodynamics, kinetics, process integration and catalyst development of different approaches. Some routes, particularly those based on olefin oligomerization, have been realized on the pilot scale. Other routes are currently in laboratory stages. This Review provides a framework for understanding how to convert ethanol into distillate-range molecules and the key research problems to be addressed. Ethanol has emerged as a potential alternative feedstock for the synthesis of middle-distillate transportation fuels. This Review describes the chemistry of ethanol-to-distillate processes and challenges associated with improving current technologies and implementing new ones.

Chemistries and processes for the conversion of ethanol into middle-distillate fuels

Vapor-phase synthesis of 3-pentanone from 1-propanol over CeO2–Fe2O3 catalysts was investigated, and the reaction pathway was discussed in comparison with the reactions of propanal and n-propyl propionate over the CeO2–Fe2O3. 1-Propanol was preferentially converted into 3-pentanone over the CeO2–Fe2O3 catalysts at 450 °C, and propanal, 3-hydroxy-2-methylpentanal, and n-propyl propionate were observed as by-products. The addition of Fe2O3 to CeO2 enhances the ability of CeO2 for the catalytic dehydrogenation of 1-propanol to propanal without losing the ability for the dimerization of propanal. The turnover frequency (TOF) based on a basic site varies with Fe content. Both the selectivity–conversion curves and similarity in the TOF between the reactants of 1-propanol at 450 °C and propanal at 400 °C suggest that propanal is an initial intermediate converting into the final product, 3-pentanone. The formation of 3-pentanone from 1-propanol over the CeO2–Fe2O3 proceeds via aldol addition of propanal into 3-hydroxy-2-methylpentanal, followed by the decomposition into 3-pentanone, while n-propyl propionate is formed as a mere by-product.

Synthesis of 3-pentanone from 1-propanol over CeO2–Fe2O3 catalysts

Gas phase conversion of ethanol–water mixtures on copper-based catalysts leads to a significant yield of acetone. Copper catalysts containing lanthanum oxide stabilized with zirconia, in the form of the so-called La2Zr2O7 pyrochlore compound, exhibit the best performance for the selective conversion of ethanol into acetone with yields of 96% of the stoichiometric amount at 400°C. Acid–base properties of the pyrochlore in addition to its higher specific surface area and copper dispersion can explain the better catalytic behavior in comparison to the other tested copper catalysts. The most plausible reaction mechanism involves ethanol dehydrogenation to acetaldehyde followed by oxidation to acetic acid and further ketonisation to yield acetone.

S. Parodi

Papers

Catalytic transformation of ethanol into acetone using copper–pyrochlore catalysts