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Furfural Production

The major fraction of xylans from olive endocarp (about 20% w/w) can be used for furfural production by acid hydrolysis. According to Montane et al. (2002) 95 kg furfural could be obtained from one ton of dry olive stones working with 0.25 M sulfuric acid at high temperatures (240°C) and short reaction times (150 s) [18].

Xilooligosaccharide Production

Partial hydrolysis of hemicellulose from olive stones allows to obtain xylooligosaccharides, which are carbohydrates with low degree of polymerization (DP between 2 and 7) generated by the binding of molecules of D-xylose by P-1,4-glycosidic bonds. These compounds have a high economic potential due to their interesting applications, among which may be mentioned the production of monosaccharides [35], the production of biodegradable thermoplastics [36] and hydrogels [37], and synthesis of antileukemic drugs [38]. However, the most interesting alternative for xylooligosaccharide manufacture is in the formulation of prebiotics to enable selective growth of bifidobacteria in the human colon [39]. To this end it is necessary to develop strategies to ensure not only a correct separation of products, which can be achieved by solvent extraction, adsorption, gel filtration [40], ultrafiltration [41] or nanofiltration [42], but also achieve optimum profile molecular weights using, for example, enzyme membrane reactors [43]. Cuevas et al., (2013) studied the effect of the hydrothermal treatment on olive stones (temperature ranging from 195°C to 225°C) for the production of oligosaccharides [23]. The highest yield (16.9 kg product / 100 kg of raw material, equivalent to 60% of the original hemicellulose) was obtained at 210°C. These oligosaccharides were mainly composed of D-xylose (89% w/w). Furthermore, Nabarlatz et al. (2007) investigated the composition of oligosaccharides obtained hydrothermally (179°C- 23 min) from the same raw material, and reported that its contents in D-xylose and acetyl groups were 86.5 and 13.5%, respectively [22].

Manufacture of Plastic Materials

A suitable fractionation of olive stones would allow to recovery most of the lignin. Thus in literature it is described a procedure consisting in a steam explosion treatment (227°C, 4 min) followed by extraction of the resulting solid with NaOH (2%, w/w, at room temperature) and subsequent precipitation with sulfuric acid (pH 2-3), which resulted in an alkali-extracted lignin.

The low carbohydrate content and the properties of this extracted lignin make it an excellent prepolymer for the manufacture of plastics or resins [6]. Olive endocarps could also be subjected to liquefaction in the presence of phenol to generate monomers useful in the production of phenol-formaldehyde resins [44], or be subjected to oxypropylation to produce biopolyols [45]. Moreover, olive stones have been assayed as plastic filled [46, 47, 48, 49].

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