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Abstract: Pistachio and walnut shells accumulate in large quantities as waste during food processing and represent a promising lignocellulosic biomass for the extraction of valuable components. Subcritical water technology was used as an environmentally friendly technique to study the extraction of active ingredients and other valuable degradation products from walnut and pistachio waste. Subcritical water extraction (SWE) was carried out under different process conditions (temperature (150–300 ◦C) and short reaction times (15–60 min)) and compared with conventional extraction using different organic solvents (acetone, 50% acetone and ethanol). The extracts obtained from pistachio and walnut shell waste are rich in various bioactive and valuable components. The highest contents of total phenols (127.08 mg GA/g extract at 300 ◦C for 15 min, from walnut shells), total flavonoids (10.18 mg QU/g extract at 200 ◦C for 60 min, from pistachio shells), total carbohydrates (602.14 mg TCH/g extract at 200 ◦C for 60 min, from walnut shells) and antioxidant activity (91% at 300 ◦C, for 60 min, from pistachio shells) were determined when the extracts were obtained via subcritical water. High contents of total phenols (up to 86.17 mg GA/g extract) were also determined in the conventional extracts obtained with ethanol. Using the HPLC method, sugars and their valuable derivatives were determined in the extracts, with glucose, fructose, furfurals (5-hydroxymethylfurfural (5-HMF) and furfural) and levulinic acid being the most abundant in the extracts obtained by subcritical water. The results show that subcritical water technology enables better exploitation of biowaste materials than conventional extraction methods with organic solvents, as it provides a higher yields of bioactive components such as phenolic compounds and thus extracts with high antioxidant activity, while at the same time producing degradation products that are valuable secondary raw materials.
Keywords: pistachio shells, walnut shells, subcritical water extraction, conventional extraction, waste biomass, valuable compounds, sugars, furfurals
Published in DKUM: 01.07.2025; Views: 0; Downloads: 7
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Abstract: Corncobs are a widespread and renewable by-product of corn cultivation that are typically considered waste or low-value material. Corncobs contain hemicellulose, cellulose, and lignin, which can be converted into valuable products using suitable techniques. Subcritical water is increasingly used as a green medium for the extraction of valuable components from biomass, as it has many advantageous properties (high yield, pure extracts, shorter times) compared to other organic solvents. For this reason, subcritical water was used in this study to extract valuable components from corncobs at different temperatures (150–250 °C) and reaction times (10–60 min). During the decomposition of corncobs, numerous valuable products are formed in the aqueous phase depending on the temperature and reaction time. In addition to sugars and their derivatives, phenolic compounds were also formed, which are of great importance in numerous applications. It was found that at low temperatures (150–170 °C) the hemicellulose in the corncobs begins to decompose and, in particular, the sugars (glucose, xylose, arabinose, and galactose) are initially formed in the aqueous phase. Higher temperatures (200 and 250 °C) are more favorable for the decomposition of corncobs into valuable components. The yield of sugars increases with temperature due to the degradation of the cellulose content of the lignocellulosic biomass. At the same time, several new valuable products (furfural, 5-hydroxymethylfurfural (5-HMF), 1,3-dihydroxyacetone, levulinic acid, and formic acid as well as phenolic components) are formed through the degradation of lignin and the further degradation of sugars. The most important products are certainly the furfurals, which are central platform compounds. The highest furfural content was reached at 200 °C and 60 min and accounted for almost half of all components in the aqueous phase (472.01 ± 5.64 mg/g dry extract). These biomass-derived sugars and derivatives can be used in the production of fuels, pharmaceuticals, biodegradable polymers, and surfactants.
Keywords: corncobs, subcritical water, biomass, valuable compounds, sugar derivates
Published in DKUM: 07.02.2025; Views: 0; Downloads: 10
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Abstract: Plastics are widely used due to their versatile properties and numerous applications. However, the proper management of plastic waste is a major challenge, even though it is recyclable. The process of repeated recycling can cause the quality of the material to decrease as unwanted contaminants and pollutants increase. This can affect the chemical recycling of plastics at the end of their life and the recovery of secondary products that can be used in other applications. In this study, the chemical degradation of virgin polypropylene (vPP) and recycled polypropylene (rPP) was investigated in supercritical water at a temperature of 450 °C and a reaction time of 15 to 240 min. The oil phase was the primary decomposition product and was obtained in high yield, which reached a maximum after 30 min of reaction time and was 96.9 % for vPP and 94.5 % for rPP. The results of our study show that there are some differences in the product composition depending on which material (vPP or rPP) is chemically recycled.
Keywords: virgin polypropylene, plastics, chemical degradation, chemical recycled
Published in DKUM: 18.04.2024; Views: 235; Downloads: 19
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Abstract: Onesnaževanje z odpadnimi vodami predstavlja velik delež onesnaževanja narave. V teh odpadnih vodah se pogosto nahajajo tudi težke kovine, ki jih moramo zaradi ogrožanja okolja, živali in ljudi iz vode odstraniti. Kot poceni metoda za odstranjevanje težkih kovin iz vode, se je uveljavila adsorpcija. V iskanju učinkovitih ter poceni adsorbentov, se je dobro izkazala tudi žlindra, ki je stranski produkt pri proizvodnji jekla. V diplomskem delu predstavljamo rezultate raziskave adsorpcijskih lastnosti bele žlindre. Žlindri smo najprej določili specifično površino BET, volumen por, premer por, velikost delcev in zeta potencial. Nadalje smo preučevali vpliv pH in koncentracije na adsorpcijo železovih, bakrovih in svinčevih ionov. Hkrati smo preučili še medsebojni vpliv izbranih ionov na adsorpcijo. Preučevali smo učinkovitost in kapaciteto adsorpcije in iz rezultatov ugotovili, da pH minimalno vpliva na adsorpcijo bakra in železa, svinec pa ima adsorpcijski maksimum pri pH 7. Pri preiskovanju vpliva koncentracije smo ugotovili, da učinkovitost adsorpcije s koncentracijo narašča za svinec, na baker in železo pa skoraj ne vpliva, saj je bila učinkovitost v območju koncentracij od 1 mM do 13 mM 100 %. Medsebojni vpliv ionov daje pozitivne rezultate na učinek adsorpcije.
Keywords: adsorpcija, žlindra, težke kovine, zeta potencial, BET
Published in DKUM: 17.09.2019; Views: 1646; Downloads: 116
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