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

Abstract

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 H 2 O 2 , 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 H 2 O 2 /furfural mol ratio of 7.5, corresponding to 12.3 wt% of H 2 O 2 , 323 K and 24 hours of reaction. To reduce the amount of H 2 O 2 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 H 2 O 2 / furfural mol ratio ¼ 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), N 2 adsorption-desorption isotherms and thermogravimetric analysis.Ti was largely incorporated within the silicalite framework, but the presence of some TiO 2 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.

Production of furfural from xylose and corn stover catalyzed by a novel porous carbon solid acid in γ-valerolactone

“…7 Furfural is a versatile chemical derived from pentosane-rich agricultural and forestry residues such as corn cobs, corn stover, saw dust, and straw. Despite the reported concerns in regards to the production of potential biofuels and fuel additives, such as 2-methylfuran, 8,9 g-valerolactone [10][11][12] and long chain hydrocarbons, 13 using furfural as a feedstock, conversion of furfural into valuable chemicals, such as dicarboxylic acid, [14][15][16] furfuryl alcohol 17 and tetrahydrofurfuryl alcohol 18 -which has broad uses in polymer, rubber, and pharmaceutical applicationsattracted the interest of many researchers. Ultimately, it is agreed that the production and utilization of furfural would be benecial for mitigating the energy and environment crisis and increasing protability of a biorenery economical prots.…”

Oxidation of furfural in aqueous H2O2 catalysed by titanium silicalite: Deactivation processes and role of extraframework Ti oxides

“…Modest yields have been accomplished by using O2 as oxidant [7,8,10]; the latter presents also the drawback of requiring high O2 pressure (1-2 MPa). To the best of our knowledge, the highest yield of MAc (close to 80 %) has been obtained using hydrogen peroxide as oxidant and titanium silicalite (TS-1) as catalyst [9]. Other catalysts have also been tested in the oxidation with hydrogen peroxide, possessing strong Brønsted acid sites like sulfonic groups [11,12].…”

“…The reason for the high MAc yield found with TS-1 seems to be related to the different mechanism through which the reaction proceeds. A route involving hydroxy-furan-2(5H)-one (HFONE) as an intermediate is selectively preferred in the case of TS-1 (see Scheme 1 for the mechanism proposed elsewhere [9]), whereas in the case of catalysts having sulfonic groups two different routes are possible, one affording succinic acid and the other one yielding MAc and its derived acids [9,11,12].…”

“…It has been proposed that TS-1 is selective for this reaction because of the presence of isolated tetrahedral sites incorporated to the silicalite framework [9,20,21]. The first step of the reaction has been proposed to be the epoxidation of one of the double bonds of the furan ring and the substitutional Ti atoms are well known to be active in the epoxidation of double bonds (the first step of the proposed mechanism) [22].…”

“…Recently there has been research directed at developing new renewable routes to produce some of these two commodities by oxidation of biomass-derived platforms like butanol [3], levulinic acid [4], hydroxymethylfurfural [5] and furfural [6][7][8][9][10][11][12][13]. MA and MAc can be interconverted into each other, and therefore the production of one of them implies the availability of the other.…”