Browsing by Author "Louw, Anke"

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    Adsorption of 3,7-dimethyl-1-octanol in single and binary mixtures using Selexsorb CD®
    (Stellenbosch : Stellenbosch University, 2023-03) Louw, Anke; Schwarz, Cara Elsbeth; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering.
    ENGLISH ABSTRACT: The petrochemical industry is considered to be one of the large contributors to the global economy. The hydrocarbons produced by it are readily used as fuels. The product streams engendered by hydrocarbon production can contain low concentrations of by-products such as alcohols, which have inherent industrial value. Adsorption is a favoured method of separating 1-alcohols from an n-decane stream, as it is the most versatile, economic, and environmentally friendly among separation methods. It is a three-step process consisting of an external mass transfer, an internal mass transfer and adsorption onto active sites. The process typically occurs by means of physisorption or chemisorption. The aim of this study is to expand the limited 1-alcohol adsorption database by investigating the adsorption of 3,7-dimethyl-1-octanol (3,7- DMO), 1-octanol&3,7-DMO and 1-decanol&3,7-DMO from n-decane while using Selexsorb CD® (SCD). The project scope includes the investigation of these systems at different temperatures and initial concentrations and adsorbate ratios for the binary component systems through experimental work and kinetic and equilibrium Modelling. The experimental work was conducted using a bench-scale water bath batch-adsorption system. Mesh baskets were filled with 10 g adsorbent and fully submerged in beakers containing a solution of 0.5-3.3 alcohol and the remainder n-decane. Kinetic and equilibrium studies were conducted along with displacement tests for the two binary systems. Kinetic and equilibrium isotherm models were fitted to the datasets by using nonlinear regression. Certain project shortcomings were identified when it was consistently seen that the kinetic data generated for 3,7-DMO, 1-decanol&3,7-DMO and 1-octanol&3,7-DMO adsorption onto SCD was accompanied by a drop in adsorbate loading from 7 h to 24 h. The major project shortcoming was the primary batch experimental setup which had beakers open to atmosphere that facilitated evaporation of the water in the water bath and subsequent condensation of said water vapour dripping into the solution. Additionally, solution evaporation also took place which meant that the assumption of constant volume of solution throughout the 24 h experiment was incorrect. A secondary batch experimental setup, where the feed stock was submerged in a sealed Schott bottle, minimised the potential of evaporation or condensate droplets forming in the solution and the kinetic profiles generated at 45 °C approached equilibrium with no drop in adsorbate loading between 7 to 24 h. For the adsorption of 3,7-dimethyl-1-octanol, it was found that an increase in initial concentration increased the equilibrium adsorbent loading achieved but that it plateaued beyond 1.5 mass%. An increase in temperature increased the adsorbent loading achievable for the first 7 h. The maximum adsorbate loading achievable for 3,7-DMO onto SCD was found to be approximately 114 mg.g-1. The pseudo-second-order model (R2 = 0.98) was the best fitting kinetic model and the Langmuir and Redlich-Peterson equilibrium isotherm models (R2 = 0.9) fitted the single equilibrium data best. Stellenbosch University https://scholar.sun.ac.za iv In the case of the two binary component systems, it was found that temperature had no discernible effect on the adsorbent loading. An increase in overall initial concentration increased the adsorbent loading for the first 7 h, but the equilibrium adsorbent loading appeared to fluctuate with no discernible trend. The binary component systems both indicated that the Elovich model fitted the data well at 25 Σ and the pseudo-second-order model fitted best at 45 Σ . The rate constant and maximum loading were higher at 45 Σ as compared to 25 Σ . The binary component isotherm models that fit the two binary component systems best were the extended Freundlich and modified competitive Langmuir model indicating that both systems were heterogeneous in nature and interaction does occur between adsorbate molecules. could not predict the binary component adsorbate loadings as accurately as the single component models. Displacement tests showed that linear, smaller molecules are preferentially adsorbed when compared to branched, larger molecules. The displacement potential ranked from largest to smallest was 1-octanol, 1-decanol and 3,7-DMO. Recommendations for future studies include quantifying through experimental work some thermodynamic properties such Gibbs free energy and entropy of adsorption. All future batch adsorption tests are recommended to be performed on experimental setups that seal the adsorption system and prevents water ingress or solution evaporation. Lastly, semi-continuous experiments can be performed to obtain 3,7-DMO adsorption data when the solution is allowed to flow through a packed bed rather than stirred.