Structured Polyvinyl Alcohol/Zeolite/Carbon Composites Prepared Using Supercritical Fluid Extraction Techniques as Adsorbent for Bioethanol Dehydration

Abstract

Introduction. Adsorption is a purification process with a more efficient energy level than others. Adsorption performance is strongly influenced by the ability of the adsorbent to be used; therefore, the modification of the adsorbent becomes a very important key for the purification process that occurs. Methods. In this study, the preparation of composite adsorbents was carried out by combining polyvinyl alcohol (PVA), zeolite (Zeo), and activated carbon (AC) as precursors. The crosslinking process was fulfilled by adding glutaraldehyde to the precursor mixtures followed by a supercritical fluid CO2 extraction (SFE) technique to create conditions for the crosslinking process. The composites were analyzed using Braunner–Emmet–Teller (BET) surface area analysis, Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy with energy dispersive X-ray (SEM/EDX-mapping), while individual and composite adsorbents were evaluated for their ability in bioethanol dehydration at various initial concentrations of ethanol and temperature. Results. The BET characterization shows that composite preparation under supercritical CO2 conditions provides reasonable surface areas, which are proportional to the content of activated carbon. The crosslinking process has been described by FTIR data interpretation, showing that PVA and glutaraldehyde were properly distributed on Zeo and AC precursors. The DSC characterization results give information that PVA successfully forms hydrophilic composites within Zeo and AC. The SEM micrograph analysis shows the formation of pores on the surface and cross section in structured adsorbents. The experimental adsorption shows that an increasing amount of AC in the composites increases the capacity of water adsorption (i.e., 0.80 gram of water/gram of adsorbent for PVA/Zeo/AC = 1 : 1 : 1 at 22°C). However, the effect is not significant when the ratio of AC is less than 0.5. As expected, the lower temperature increases the adsorption capacity. Further, by using approximately 4.5 gram adsorbents composite in 30 ml of water-ethanol mixtures, high concentration of bioethanol (>99%) can be achieved at various temperatures from 22°C to 40°C and bioethanol initial concentration from 88% to 96%. Conclusion. The SFE technique provides distinguished adsorbents composite properties. Further, the new composites provide about four times better adsorption capacity than that showed in the individual adsorbents test. The addition of AC influences on increasing the capacity and adsorption kinetics value.

The Influence of Activated Carbon as Adsorbent in Adsorptive – Distillation of Ethanol–Water Mixture

“…The results of the adsorptive-distillation process for the ethanol-water mixture under the second variable, which is the initial ethanol concentration (90% v/v and 95% v/v, are shown in Figure 3. Based on Figure 3 above, it can be observed that the initial ethanol concentration of 95% v/v yields a better curve compared to the initial ethanol concentration, resulting in a larger number of ethanol molecules undergoing adsorption (Laksmono et al, 2019). However, increasing the initial ethanol concentration introduces complexities, and it results in a higher loading rate, indicating more ethanol molecules adsorbed per unit of time.…”

“…This surplus enhances the adsorption process, allowing for a more efficient and extensive interaction between the activated carbon and the water molecules. As a result, a larger quantity of water is selectively removed from the mixture, reducing its concentration within the liquid phase (Laksmono et al, 2019). Consequently, the remaining liquid phase contains a higher proportion of ethanol.…”

The influence of crosslinking temperature on the spectroscopic, thermal, andmechanical properties of poly(vinyl alcohol)/zeolite composites

“…As shown in Figure 1b, changes in the intensity and position of this peak for samples 4-6 were representative of the interactions between the PVA and CL after treatment at different crosslinking temperatures [29,30]. After modification of zeolite with PVA at 140°C, the OH stretching frequency of the PVA shifted from 3309 to 3250 cm −1 , which indicates the formation of crosslinking between PVA, TA, and CL to form a solid compound through the hydrogen bonding mechanism [31][32][33][34]. The specific peaks at 2922 cm −1 and 1319 cm −1 were related to the presence of the C-H stretching and bending of PVA chains, respectively.…”

The Production of Bioethanol from Lignocellulosic Biomass: Pretreatment Methods, Fermentation, and Downstream Processing

“…Adsorption is a cost-effective and environmentally friendly alternative to extractive and azeotrope distillation and is used on a large scale to purify ethanol. Many traditional porous adsorbents have been applied to capture either water or ethanol from distillates and culture broths, such as zeolites [152][153][154][155], silicate [156], activated carbons [157], composite adsorbents (e.g., polyvinyl alcohol/zeolite/carbon composites, and composite silica-divinylbenzene) [158][159][160], polymeric resins, activated carbons metal−organic frame-works [160,161], etc. Biomass has also been investigated as an alternative adsorbent since it is an abundant, eco-friendly, inexpensive, and easily regenerated material.…”