Improving the Bio-Oil Quality of Residual Biomass Pyrolysis by Chemical Activation: Effect of Alkalis and Acid Pre-Treatment

Abstract

In this study, we investigated the acid (HCl) and alkali (KOH) chemical activation of açaí seeds (Euterpe Oleraceae, Mart.) pre-treatment before pyrolysis at temperatures of 350–450 °C in order to assess how reactions proceed when affected by temperature. Chemical composition of bio-oil and aqueous phase were determined by GC-MS and FT-IR. The bio-char is characterized by XRD. For the activation with KOH, the XRD analysis identified the presence of Kalicinite (KHCO3), the dominant crystalline phase in bio-char, while an amorphous phase was identified in bio-chars for the activation with HCl. The experiments have shown that bio-oil yield increases with temperature for the KOH activated biomass and decreases for the acid activated one. The KOH bio-oil is primarily composed of alcohols and ketones, showing the lowest acid values when compared with the HCl one, which is composed mainly of carboxylic acids and phenols. An increase in alcohol content and a decrease in ketones in the KOH bio-oil with temperature suggests conversion reactions between these two functions. For HCl bio-oil, carboxylic acid concentration increases with temperature while phenols decrease. For production of hydrocarbons, KOH activated biomass pyrolysis is better than acid-activated one, since no hydrocarbons were produced for HCl bio-oil.

Improving the Antioxidant Activity, Yield and Hydrocarbon Content of Bio-Oil from Açaí Seeds Pyrolysis by Chemical Activa-Tion: Effect of Temperature and Molarity

“…These findings are consistent with the bio-oil yields reported by Serrão et al [30], who conducted a study on the pyrolysis of Açaí seeds in a natural setting, and with the yields reported by Castro et al [11], who investigated the pyrolysis of Açaí seeds in pilot, bench, and laboratory scales. The bio-char yields obtained in this study are also in agreement with similar data reported in the literature for the pyrolysis of Açaí seeds, whether in their natural state [17][18][19] or chemically activated [8,[20][21][22][23][24][25][26][27][28][29][30][31]. It is important to note that the observed increase in bio-oil yield with increasing temperature is attributed to the temperature range being within the range of maximum decomposition, where the original material is primarily decomposed into its initial products.…”

“…The impregnation process was conducted at room temperature. The formed suspension was then transferred to a paper filter, washed with 120 mL of distilled water, and left to rest for 24 hours, following a previously described method [31]. Subsequently, it was dried at 100 °C ± 5 °C for 24 hours.…”

“…The effect of temperature on the average antioxidant capacity of pyrolysis bio-oil are shown in Table 3. As previously described, pyrolysis is a complex process involving the thermal degradation of biomass, and reaction conditions, particularly temperature, plays a critical role in determining the chemical composition of the bio-oil [31]. At different pyrolysis temperatures, various intermediate reactions occur, leading to the formation of different chemical compounds within the bio-oil, but also production of a gaseous and a solid phase with different composition and characteristics [9,[30][31][32].…”

“…Although research has been conducted on the pyrolysis of residual Açaí seeds [8,11,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], most of these studies have focused on producing activated carbon/bio-adsorbents [8,[17][18][19][20][21][22][23][24][25][26][27][28][29]. These studies have used residual Açaí seeds in their natural state [17][18][19] or activated residual Açaí seeds [8,[20][21][22][23][24][25][26][27][28][29][30][31] and have involved chemical activation with NaOH [8,21,…”

“…In addition, temperature is one of the key factors influencing the thermochemical decomposition of biomass compounds during the production of bio-oil by pyrolysis. The bio-oil obtained by pyrolysis of Açaí seeds contains hydrocarbons and a oxygenate fraction rich in phenols [31][32], which are of great interest due to their potential applications as sources of antioxidants, nutraceuticals, and preservatives in the food industry [34]. In the food industry, phenolic compounds are recognized for their natural antioxidant properties.…”