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This study presents the effect of thermal treatment (450, 500, 600, 750, and 800 °C) on a Romanian clinoptilolite-rich natural zeolite, along with the interaction of raw and thermally treated zeolites with simulated gastric fluid (SGF, pH = 1.20) at different zeolite to SGF ratios and exposure times. The zeolites were characterized using gravimetric analysis, X-ray fluorescence, powder X-ray diffraction (pXRD), and Fourier transform infrared (FT-IR) spectroscopy. The chemical composition of the zeolite subjected to thermal treatment did not change significantly with the increase of temperature. Structural changes were not detectable by pXRD and FT-IR analyses in the zeolites thermally treated up to 500 °C, while above 600 °C a gradual structural breakdown of zeolite was noticed. At high temperatures, the broad, low-intensity peaks in pXRD patterns indicated the partial amorphization of the crystalline structure. The pXRD and FT-IR analyses showed that the crystalline structure of zeolites remains unaffected after their exposure to SGF. The results revealed that the amounts of Fe, Na, Mg, K, Ca, Al, and Si released depends mainly on the zeolite to SGF ratio, and to a lower extent on the thermal treatment temperature, while the exposure time of 1 to 7 days does not have a significant impact on the elements released in SGF.

In this paper, the production of a second-generation bioethanol from lignocellulosic vineyard cutting wastes was investigated in order to define the optimal operating conditions of the autohydrolysis pretreatment, chlorite delignification and simultaneous saccharification and fermentation (SSF). The autohydrolysis of vine-shoot wastes resulted in liquors containing mainly a mixture of monosaccharides, degradation products and spent solids (rich in cellulose and lignin), with potential utility in obtaining valuable chemicals and bioethanol. The autohydrolysis of the vine-shoot wastes was carried out at 165 and 180 °C for 10 min residence time, and the resulted solid and liquid phases composition were analysed. The resulted liquid fraction contained hemicellulosic sugars as a mixture of alpha (α) and beta (β) sugar anomers, and secondary by-products. The solid fraction was delignified using the sodium chlorite method for the separation of lignin and easier access of enzymes to the cellulosic sugars, and then, converted to ethanol by the SSF process. The maximum bioethanol production (6%) was obtained by autohydrolysis (165 °C), chlorite delignification and SSF process at 37 °C, 10% solid loading, 72 h. The principal component analysis was used to identify the main parameters that influence the chemical compositions of vine-shoot waste for different varieties.

Vineyards waste has a great importance as biomass, a renewable source of energy. In this paper eight vine shoot varieties were used for the production of pellets by densification of feedstock materials with four ranges of moisture contents (6–8%, 8–10%, 10–12% and 12–15%). A moisture content of 10% gave durability higher than 97.5% and a calorific value greater than 17 MJ kg−1 and the small durability was obtained for 6–8% moisture. The study shows the significant influence of water during densification. The physicochemical and energetic properties of pellets were evaluated in accordance with ISO 17225-6 (2014). The obtained pellets were also structurally characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). SEM analysis showed the formation of carbon microsphere after pelletization, due to the increase of bulk density and durability of pellets. Also, XRD analysis revealed the crystallinity of cellulose, while TGA analysis showed a total decomposition of pellets. The obtained pellets were burned in a domestic boiler and the flue gases were measured. The preliminary results showed that the vineyard residues had higher emissions, but below the admitted limits, with the exception of carbon monoxide content. The obtained results suggested that the biomass wastes can be used for the production of pellets, aiming to enhance the research for the manufacturing of these sustainable biofuels with some remarks regarding risk of corrosion and slag formation during prolonged use.

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