Use of biobased crude glycerol, obtained biocatalytically, to obtain biofuel additives by catalytic acetalization of furfural using SAPO catalysts

Abstract

High-pure crude glycerol, obtained from the transesterification of coconut oil with ethanol using lipase enzyme- type as biocatalyst, has been used for the acetalization of furfural with several SAPO 5 and SAPO 34 catalysts. SAPOs were prepared using microwaves and conventional heating for comparison, and were characterized by X- ray diffraction, nitrogen physisorption, elemental analysis, thermogravimetry of adsorbed cyclohexylamine and scanning electron microscopy techniques. The use of microwaves allowed us the incorporation of slightly higher amounts of silicon into the aluminophosphate structure, and the preparation of the materials in much shorter preparation times, with the subsequent energy saving. Additionally, the SAPOs prepared with microwaves showed lower crystallinity but higher surface area than those prepared by conventional heating. Comparable catalytic results were obtained when these catalysts were tested for the acetalization of furfural with commercial or with the crude glycerol obtained by biocatalytic transesterification of coconut oil, leading to very high selectivity values to the desired mixture dioxane +dioxolane (93–100 %), which can be used as biofuel additives, for conversion values between 60 and 73 %, as determined by gas chromatography. This confirmed the high purity of the glycerol obtained by the biocatalytical process, as previously observed by 1H NMR. SAPO 34 cat-alysts showed higher conversion than SAPO 5 catalysts due to their higher amount of more accessible Brønsted acid sites, related to their structure. Interestingly, catalysts prepared with microwaves resulted in slightly higher conversion values than those prepared by conventional heating. This can be explained by the incorporation of higher amounts of silicon in the framework, probably due to the higher homogeneity of the microwaves heating, which results in a higher amount of protons, as confirmed by TGA of adsorbed cyclohexylamine, responsible for the catalysis. 1. Introduction Valorization strategies of wastes from agri-food processes must necessarily be intertwined with clean technological approaches and eco- industrial management within a sustainable biorefinery concept. Bio- refineries might integrate processes developing cascade approaches, which often require the application of biotechnological and chemical processes in order to obtain high-added value products. Glycerol (1, 2, 3-propanetriol) is obtained in significant amounts as by-product in a great variety of industrial processes, such as trans-esterification of triglycerides to produce fatty acid methyl esters, e.g. biodiesel (about 10% w/w) or through saponification processes [1]. Although glycerol has many applications in cosmetics, pharmaceuticals and food products [2–3], it is necessary to develop new processes to transform this surplus into high-added value products [2,4–8]. For most of these applications, and independently of the origin (synthetic, animal or vegetable fat), crude glycerol should be refined to obtain glycerol with high purity degree [9,10]. Crude glycerol is initially produced in a raw form that contains water and other residues as im-purities depending on the production process. It is usually treated and refined by filtration, adding chemical additives, by fractioned distilla-tion in vacuum or using lower-energy intensive filtration by a series of ion exchanges in resins [11]. Another alternative is to develop cleaner processes to obtain more pure glycerol, for example, by applying enzy-matic technologies.