Use of Acidic Ion-Exchange Resins in the Transformation of Biomass into Biofuels

Introduction Lignocellulose (65-85% of biomass) is an inexpensive non edible biomass that can be an excellent source of for biofuels and chemicals. These new fuels are called second generation biofuels or advanced biofuels.... [ view full abstract ]

Introduction

Lignocellulose (65-85% of biomass) is an inexpensive non edible biomass that can be an excellent source of for biofuels and chemicals. These new fuels are called second generation biofuels or advanced biofuels. Fig. 1 shows the main routes to produce biofuels from lignocellulose. In this reaction pathway, the formation of several platform (building block) chemicals such as furfural, 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA) is highlighted. However, the release of sugar from lignocellulose and its transformation into biofuels is uneconomic compared with to first generation biofuels obtained from edible sources, since platform molecules are highly oxygenated compounds and their conversion into liquid fuels requires a partial oxygen removal. The present work shows the potential of acidic ion-exchange resins as a promising low-cost catalyst to be used in many reactions from biomass to biofuels with the same catalytic activity than other acid solids but under milder conditions (<190 ºC).

Method

Experiments have been carried out in a batch stirred reactor at 50-150ºC and under pressure using several gel type and macroreticular acidic ion-exchange resins. Liquid samples were taken hourly and analyzed by means of GC and HPLC.

Results and conclusions

Table 1 lists some of our works on certain reactions shown in Fig. 1. Using ion exchange resins is a good option to produce 5-HMF, levulinic acid, levulinic esters and C₁₂⁺ oxygenated intermediate molecules under mild conditions. Work on optimization of the reaction conditions using ion-exchange resins as catalysts has recently started. Results are promising. For example, the esterification reaction of levulinic acid with 1-butanol proceeds with practically total conversion and selectivity to the corresponding ester on Dowex 50Wx2 at temperatures as low as 80ºC. Working at low temperatures avoids the formation of undesired byproducts like humins.

To tailor the best resin, the study between the resin morphological/structural properties and the catalytic activity relation is required. Furthermore, tests on catalyst reusability are of utmost importance for process economics.