Single and binary component adsorption of 1-alcohols from an alkane using various activated alumina adsorbents

Bosman, Catharine Elizabeth (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: During surfactant production, an alcohol-alkane stream is produced which requires separation. Adsorption has been shown to be a technically viable process for the removal of single 1-alcohol contaminants from an alkane stream; however, little knowledge exists on the binary 1-alcohol adsorption. The aim of this study was to gain knowledge on the single and binary component adsorption of 1-alcohol contaminants from a n-alkane solvent using activated alumina adsorbents. The objectives of the study included: (i) the measurement and investigation of single and binary component adsorption data; (ii) the modelling of the equilibrium adsorption isotherms; and, (iii) the modelling of the adsorption kinetics of these systems. Investigation of the experimental data included comparing the adsorption abilities of three activated alumina adsorbents (Activated Alumina F220, Selexsorb CDx® and Selexsorb CD®); investigating the effect of temperature, initial adsorbate concentration and alcohol carbon chain length on the adsorption of 1-alcohols (1-hexanol, 1-octanol and 1-decanol) from n-decane; a comparison of single and binary 1-alcoholadsorption; and, an investigation of interaction in the binary 1-alcohol systems. Adsorption data was measured using a bench-scale batch adsorption system. The experimental procedure entailed immersing beakers containing alcohol-alkane solutions (1-alcohol concentration < 3.3 mass%) and adsorbent in a water bath, maintained at a specified temperature (25oC or 45oC), and measuring the alcohol concentration over time. When comparing the adsorbents, Selexsorb CDx® and Selexsorb CD® were found to exhibit slightly greater adsorbent loadings than Activated Alumina F220 for most systems, with overall equilibrium adsorbent loadings of approximately 110 to 130 mg/g for the single component systems and slightly more, 128 to 150 mg/g, for the binary component systems. Overall, increased temperature exhibited a corresponding increase in adsorbent loading. Adsorbent loading was found to increase with increasing initial alcohol concentration up to a concentration of approximately 1 to 1.2 mass% after which the equilibrium adsorbent loadings remained relatively constant. The alcohol carbon chain length had minimal effect on adsorption, with some cases exhibiting an increased rate of adsorption for the shorter chain alcohols. When comparing the adsorption of a 1-alcohol in a single and binary component system (with the specific 1-alcohol having an equal initial concentration in both systems), the adsorbent loading of the 1-alcohol in thebinary component system was notably poorer than in the corresponding single component system. Consequently, antagonistic/competitive behaviour was found to be predominant in the initial adsorbate concentration range of 1 to 1.5 mass%. For the single and binary component systems, the Redlich-Peterson (R2 > 0.96) and Extended Freundlich models (R2 > 0.85 for most systems) were found to provide the best correlation of the equilibrium data, respectively. The binary component isotherm models, however, provided poor correlation of the data. The single and binary component adsorption kinetics were found to be very similar with the pseudo-second-order model providing a good correlation of the kinetic data (R2 > 0.96 for most systems). The Intra-particle diffusion model was almost equally well suited to the data. Ultimately, the adsorption of single and binary 1-alcohols from n-decane using activated alumina adsorbents was found to be a technically viable process, with adsorption proposed to be dominated by weak chemisorption, and competitive adsorption slightly favouring shorter carbon chain alcohols.

AFRIKAANSE OPSOMMING: Tydens surfaktantproduksie word ʼn alkohol-alkaanstroom geproduseer wat skeiding benodig. Adsorpsie is gewys om ʼn tegniese uitvoerbare proses te wees vir die verwydering van enkel 1-alkohol kontaminante uit ʼn alkaanstroom, maar daar bestaan min kennis oor die adsorpsie van binêre 1-alkohole. Die doel van hierdie studie was om kennis te verkry oor die enkel- en binêre komponent adsorpsie van 1-alkohol kontaminante uit ʼn n-alkaan oplosmiddel deur geaktiveerde alumina adsorbeermiddels te gebruik. Die doelwitte van die studie het ingesluit: (i) die opmeting en ondersoek van enkel- en binêre komponent adsorpsiedata; (ii) die modellering van die ekwilibrium adsorpsie isoterme; en, (iii) die modellering van die adsorpsiekinetika van hierdie sisteme. Ondersoek van die eksperimentele data het vergelyking van drie geaktiveerde alumina adsorbeermiddels (Geaktiveerde Alumina F220, Selexsorb CDx® en Selexsorb CD®) ingesluit; die ondersoek van die effek van temperatuur, aanvanklike adsorbeermiddelkonsentrasie en alkoholkoolstofkettinglengtes op die adsorpsie van 1-alkohole (1-heksanol, 1-oktanol en 1-dekanol) van n-dekaan; ʼn vergelyking van enkel- en binêre 1-alkohol adsorpsie; en, ʼn ondersoek van interaksie in die binêre 1-alkoholsisteme. Adsorpsiedata is gemeet met ‘n banktoetsskaal lotadsorpsiesisteem. Die eksperimentele prosedure behels bekers wat alkohol-alkaanoplossings (1-alkoholkonsentrasie < 3.3 massa%) en adsorbeermiddel bevat, in ʼn waterbad te dompel en die verandering in alkoholkonsentrasie oor tyd te meet. Die waterbad word gehandhaaf by spesifieke temperature (25 °C en 45 °C). Wanneer die adsorbeermiddels vergelyk word, vertoon Selexsorb CDx® en Selexsorb CD® groter adsorbeerladings as Geaktiveerde Alumina F220 vir meeste sisteme, met algehele ekwilibrium adsorbeerladings van ongeveer 110 tot 130 mg/g vir die enkelkomponentsisteme en effens meer, 128 tot 150 mg/g vir die binêre komponentsisteme. Oor die geheel het verhoogde temperatuur ʼn korresponderende verhoging in adsorbeerlading vertoon. Adsorbeerlading is gevind om toe te neem met toenemende aanvanklike alkoholkonsentrasie tot en met ʼn konsentrasie van ongeveer 1 tot 1.2 massa% nadat die ekwilibrium adsorbeerladings relatief konstant gebly het. Die alkoholkoolstofkettinglengte het minimale effek op adsorpsie gehad, met sommige gevalle wat toenemende tempo van adsorpsie vir die korter ketting alkohole vertoon het. Wanneer die adsorpsie van ʼn 1-alkohol in ʼn enkel- en binêre komponentsisteem (met die spesifieke 1-alkohol wat ʼn gelyke aanvanklike konsentrasie in beide sisteme het) vergelyk word, is die adsorbeerlading van die 1-alkohol in die binêre komponentsisteem merkbaar minder as in die korresponderende enkelkomponentsisteem. Vervolgens is antagonistiese/kompeterende gedrag gevind om oorwegend in die aanvanklike adsorbeerkonsentrasiebestek van 1 tot 1.5 massa% te wees. Vir die enkel- en binêre komponentsisteme is die Redlich-Peterson (R2 > 0.96) en Uitgebreide Freundlich modelle (R2 > 0.85 vir meeste sisteme) gevind om die beste korrelasie van die ekwilibrium data te gee, onderskeidelik. Die binêre komponent isotermmodelle, het egter swakker korrelasie van die data gegee. Die enkel- en binêre komponent adsorpsiekinetika is gevind om baie soortgelyk aan mekaar te wees, met die pseudo-tweede-orde model wat ʼn goeie korrelasie van die kinetiese data (R2 > 0.96 vir meeste sisteme) gee. Die intrapartikel diffusiemodel was amper net so gepas vir die data. Die adsorpsie van enkel- en binêre 1-alkohole van n-dekaan deur geaktiveerde alumina adsorbeermiddels te gebruik, is gevind om ʼn tegnies uitvoerbare proses te wees, met adsorpsie voorgestel om gedomineer te word deur ʼn swakker chemisorpsie, en kompeterende adsorpsie wat korter koolstofketting alkohole effens verkies.

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