Inaki Gandarias

Production of furfural from pentosan-rich biomass: Analysis of process parameters during simultaneous furfural stripping

Among the furan-based compounds, furfural (FUR) shows interesting properties as building-block or industrial solvent. It is produced from pentosan-rich biomass via xylose cyclodehydration. The current FUR production makes use of homogeneous catalysts and excessive amounts of steam. The development of greener furfural production and separation techniques implies the use of heterogeneous catalysts and innovative separation processes. This work deals with the conversion of corncobs as xylose source to be dehydrated to furfural. The results reveal differences between the use of direct corncob hydrolysis and dehydration to furfural and the prehydrolysis and dehydration procedures. Moreover, this work focuses on an economical analysis of the main process parameters during N2-stripping and its economical comparison to the current steam-stripping process. The results show a considerable reduction of the annual utility costs due to use of recyclable nitrogen and the reduction of the furfural purification stages.

One-Pot 2-Methyltetrahydrofuran Production from Levulinic Acid in Green Solvents Using Ni-Cu/Al2 O3 Catalysts.

The one-pot hydrogenation of levulinic acid to 2-methyltetrahydrofuran (MTHF) was performed using a series of Ni-Cu/Al2 O3 catalysts in green solvents, such as water and biomass-derived alcohols. Ni/Al2 O3 provided the highest activity, whereas Cu/Al2 O3 was the most selective, reaching a 75 % MTHF yield at 250 °C after 24 h reaction time. Synergetic effects were observed when bimetallic Ni-Cu/Al2 O3 catalysts were used, reaching a 56 % MTHF yield in 5 h at 250 °C for the optimum Ni/Cu ratio. Remarkably, these high yields were obtained using non-noble metal-based catalysts and 2-propanol as the solvent. The catalytic activity and selectivity results are correlated to temperature programmed reduction (TPR), XRD, and STEM characterization data, identifying the role associated with mixed Ni-Cu particles in addition to monometallic Cu and Ni.

Physicochemical Study of Glycerol Hydrogenolysis Over a Ni–Cu/Al 2 O 3 Catalyst Using Formic Acid as the Hydrogen Source

Glycerol hydrogenolysis to propanediols requires the use of hydrogen as reactant. One interesting option is to directly generate this hydrogen in active sites of the support using hydrogen donors, such as formic acid. The effect that the reacting pressure has on glycerol conversion and product selectivity over a Ni–Cu/Al2O3 catalyst was studied. The negative effect of decreasing the pressure was much more significant when the source of hydrogen was dissolved molecular hydrogen than when it was formic acid. X-ray photoelectron spectroscopy and temperature programmed reduction measurements were performed to understand the effect of Ni–Cu/Al2O3 reduction procedure on the catalytic activity. Semi-batch reactor studies with the Ni–Cu/Al2O3 catalyst were carried out with continuous addition of the hydrogen donor to obtain kinetic data. Langmuir–Hinshelwood type models were developed to describe the direct conversion of glycerol into propanediol, and propanediol further hydrogenolysis to 1-propanol. The model included the competitive adsorption between both glycols. These models were used to obtain valuable data for the optimization of the process.

Unraveling the role of formic acid and the type of solvent in the catalytic conversion of lignin: a holistic approach

The role of formic acid together with the effect of the solvent type and their synergic interactions with a NiMo catalyst were studied for the conversion of lignin into bio-oil in an alcohol/formic acid media. The replacement of formic acid with H2 or isopropanol decreased the oil yield to a considerable degree, increased the solid yield, and altered the nature of the bio-oil. The differences induced by the presence of H2 were comparable to those observed in the isopropanol system, which suggests similar lignin conversion mechanisms for both systems. Additional semi-batch experiments confirmed that formic acid does not act merely as an in situ hydrogen source or hydrogen donor molecule. Actually, is seems to react with lignin through a formylation-elimination-hydrogenolysis mechanism that leads to the depolymerization of the biopolymer. This reaction competes with formic acid decomposition, which gives mainly H2 and CO2 , and forms a complex reaction system. To the best of our knowledge, this is the first time that the distinctive role/mechanism of formic acid has been observed in the conversion of real lignin feedstock. In addition, the solvent, especially ethanol, seems also to play a vital role in the stabilization of the depolymerized monomers and in the elimination/deformylation step.

The Role of the Hydrogen Source on the Selective Production of γ-Valerolactone and 2-Methyltetrahydrofuran from Levulinic Acid

A mechanistic study of the hydrogenation reaction of levulinic acid (LA) to 2-methyltetrahydrofuyran (MTHF) was performed using three different solvents under reactive H2 and inert N2 atmospheres. Under the applied reaction conditions, catalytic transfer hydrogenation and hydrogenation with molecular H2 were effective at producing high yields of γ-valerolactone. However, the conversion of this stable intermediate to MTHF required the combination of both hydrogen sources (the solvent and the H2 atmosphere) to achieve good yields. The reaction system with 2-propanol as solvent and Ni-Cu/Al2 O3 as catalyst allowed full conversion of LA and a MTHF yield of 80 % after 20 h reaction time at 250 °C and 40 bar of H2 (at room temperature). The system showed the same catalytic activity at LA feed concentrations of 5 and up to 30 wt%, and also when high acetone concentration at the beginning of the reaction were added, which confirmed the potential industrial applications of this solvent/catalyst system.

The selective oxidation of n-butanol to butyraldehyde by oxygen using stable Pt-based nanoparticulate catalysts: an efficient route for upgrading aqueous biobutanol

Supported Pt nanoparticles are shown to be active and selective towards butyraldehyde in the base-free oxidation of n-butanol by O2 in an aqueous phase. The formation of butyric acid as a by-product promoted the leaching of Pt and consequently the activity of the catalysts decreased upon reuse. Characterisation showed that the degree to which Pt leached from the catalysts was related to both the metal–support interaction and metal particle size. A catalyst active and stable (<1% metal leaching) in the aqueous reaction medium was obtained when Pt nanoparticles were supported on activated carbon and prepared by a chemical vapour impregnation method. The presence of n-butanol in the aqueous medium is required to inhibit the over oxidation of butyraldehyde to butyric acid. Consequently, high selectivities towards butyraldehyde can only be obtained at intermediate n-butanol conversion.

Influence of the support of bimetallic Pt-WOx catalysts on the 1,3-propanediol formation from glycerol

Three aluminium oxide materials and a HZSM‐5 zeolite were used as supports of bimetallic Pt‐WOx catalysts to establish structure–activity relationships in the glycerol hydrogenolysis reaction. The surface W density and the intimate contact between Pt and WOx were key parameters. Surface W density controls the formation of polytungstates, the only species able to produce the weak Brønsted acidity that is required to produce 1,3‐propanediol selectively. The comparison between the HZSM‐5 and the Al2O3 supports demonstrated that an increment of the medium Brønsted acidity is detrimental for the selective 1,3‐propanediol formation as it promotes reactions that yield 1‐propanol and propane. An increase of the dispersion of Pt on the Pt/WOx/Al2O3 catalysts led to higher glycerol conversions but also promoted the hydrogenolysis routes that lead to 1,2‐ and 1,3‐propanediol similarly. On the contrary, an increase of the Pt metal content favoured the hydrogenolysis route that leads to 1,3‐propanediol significantly. A more intimate contact between Pt and WOx promoted the hydrogenation of the intermediate carbocation, formed and stabilised on a polytungstate active site, into 1,3‐propanediol.

Solvent and catalyst effect in the formic acid aided lignin-to-liquids

The effect of the type of solvent, ethanol or water, and a Ru/C catalyst were studied in the formic acid aided lignin conversion. The best results were obtained in the presence of the Ru/C catalyst and using ethanol as solvent at 300 °C and 10 h (i.e. 75.8 wt% of oil and 23.9 wt% of solids). In comparison to the water system, the ethanol system yields a significantly larger amount of oil and, at 300 °C and 10 h, a smaller amount of solids. The main reasons for this positive effect of the ethanol solvent are i) the formation of ethanol-derived esters, ii) C-alkylations of lignin fragments and iii) the generation of more stable lignin derivatives. The Ru/C exhibits significantly higher lignin conversion activity compared to other Ni-based catalysts, especially at 300 °C, which is related to the enhanced activity of the Ru0 sites towards hydrogenolysis, hydrodeoxygenation and alkylation reactions.