I. Agirrezabal-Telleria

Furfural production from xylose using sulfonic ion-exchange resins (Amberlyst) and simultaneous stripping with nitrogen

The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.

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.

Aqueous-phase catalytic oxidation of furfural with H2O2: high yield of maleic acid by using titanium silicalite-1

This investigation explores the selective liquid-phase oxidation of furfural to maleic acid (MA) using hydrogen peroxide as an oxidant and titanium silicalite (TS-1) as a catalyst. The effect of temperature and of the concentration of H2O2, furfural and catalyst on the MA yield was studied. The highest yield, 78 mol%, was obtained under the following reaction conditions: 4.6 wt% of furfural, 4.6 wt% of catalyst, a H2O2/furfural mol ratio of 7.5, corresponding to 12.3 wt% of H2O2, 323 K and 24 hours of reaction. To reduce the amount of H2O2 employed, a two-step sequence of reactions was conducted using TS-1 and Amberlyst 70 consecutively as catalysts in the first and second steps, respectively. In this case, a H2O2/furfural mol ratio = 4.4 was required, which is quite close to the stoichiometric ratio (3.0), and a maleic acid yield close to 80% was obtained under 4.6 wt% of furfural, 4.6 wt% of catalyst and 28 h of reaction at 323 K; after 52 h of reaction, the MA yield reached 92%. Fresh and used catalysts were characterised by X-ray diffraction (XRD), Raman spectroscopy, total reflection X-ray fluorescence (TXRF), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption isotherms and thermogravimetric analysis. Ti was largely incorporated within the silicalite framework, but the presence of some TiO2 anatase was also confirmed. Ti leaching was observed, especially during the first run but became much less important in successive cycles. Leaching affects both anatase and Ti species within the silicalite framework. Notwithstanding the leaching, when using pure furfural, TS-1 could be reused for six runs without noticeable deactivation, whereas when using furfural directly derived from biomass, weak but visible deactivation occurred upon reutilisation; this deterioration must be related to the presence of some organic products other than furfural.

Furfural production from xylose + glucose feedings and simultaneous N2-stripping

The current furfural manufacturing process is based on homogeneous catalysts as well as steam as the stripping agent. Novel xylose-dehydration research studies include heterogeneous catalysts with high acidity and tailored selectivity. This work aims to evaluate the effect of additional glucose with the xylose feeding during simultaneous N2-stripping of furfural catalyzed by ion-exchange resins. Given the low batch performance of Amberlyst 70, the N2-stripping data showed high furfural yields and selectivity in the condensate stream. The different continuous feeding configurations showed that xylose/glucose ratios similar to the real pentosan-rich biomass could be fed achieving furfural yields of 75% at 200 °C. Moreover, the proposed study serves as a preliminary study to achieve high xylose conversion and relatively low glucose dehydration rates, showing its potential as a possible future process for the upgrading of carbohydrates to furan-based fuel additives.

Dehydration of xylose and glucose to furan derivatives using bifunctional partially hydroxylated MgF2 catalysts and N2-stripping

The current furfural production yield is low due to the use of non-selective homogeneous catalysts and expensive separation. In this work, partially hydroxylated MgF2 catalysts, synthesized using different water contents, were screened during xylose dehydration in water–toluene at 160 °C. The different Lewis/Bronsted ratios on the MgF2 catalysts showed that under-coordinated Mg can isomerize xylose to xylulose, whilst the surface OH-groups were responsible for the dehydration reactions. The presence of glucose as a co-carbohydrate reduced the furfural selectivity from 86 to 81%, whilst it also led to high 5-hydroxymethylfurfural selectivity. The tests catalyzed by MgF2 in combination with simultaneous N2-stripping showed that a furfural selectivity of 87% could be achieved using low xylose loadings. Moreover, the catalysts regenerated by H2O2 showed high activity during the dehydration tests in water–toluene at 160 °C.

Oxidative steam reforming of methane over nickel catalysts supported on Al2O3–CeO2–La2O3

Nickel catalysts supported on Al2O3, Al2O3–CeO2, Al2O3–La2O3, and Al2O3–CeO2–La2O3 were synthesized via the sol–gel method in acidic solution. The influence of the chemical composition and textural properties of the catalysts on oxidative steam reforming of methane was studied. Methane, oxygen, nitrogen and steam were fed into a fixed bed reactor and tested under atmospheric pressure at 550 °C, with O/C ratio = 0.3, S/C ratio = 1.0, and WHSV = 170.8 h−1. During 6 h of reaction, methane conversion and hydrogen selectivity were determined. Although lanthanide oxides are known to have excellent features, the addition of ceria or lanthana did not improve the catalytic performance of the Ni/Al2O3 system. Nevertheless the addition of both dopants was needed to end up with a stable catalyst. Characterization results revealed a low crystallite size (40 A), a high fraction of accessible Ni0 species (73.6%), migration of nickel and ceria from the bulk to the surface during activity tests, and a very low amount of coke deposited (4.7 mg C per g catalyst) on the Ni/Al2O3–CeO2–La2O3 catalyst that resulted in high catalytic activity.

Regeneration of surface acid sites via mild oxidation on dehydration catalysts

This work reports novel experimental evidence for the use of mild oxidation conditions to remove humin deposits on active xylose dehydration catalysts that showed deactivation. The catalytic regeneration experiments carried out at 70 °C using iron precursors as catalysts and H2O2 as an oxidant show that the catalysts achieve 95% acid site regeneration using the Fenton chemistry.