Evaluation and comparison of the ability of three industrially relevant adsorbents to remove alcohol contaminants from an alkane solvent

Groenewald, Jomare (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Adsorption has been used successfully in many industries and has replaced the use of processes such as distillation in some cases. The adsorption process is influenced by many factors and its efficiency is largely dependent on the regeneration of the spent adsorbent. Adsorption is system specific and requires experimental adsorption and regeneration data for the system to be separated. A better understanding of adsorbent regeneration and its effects on the adsorption process also aids in improving the overall efficiency of the process. The aims of this project were to investigate the adsorption of alcohol solutes from an alkane solvent using three industrially used adsorbents and to evaluate the effects of regeneration on each adsorbent. This was achieved through the following objectives: (1) designing and constructing batch adsorption and regeneration experimental setups; (2) performing equilibrium and kinetic adsorption tests to evaluate the effect of the type of adsorbent, type of adsorbate and temperature on the adsorption process, (3) modelling this data with existing equilibrium and kinetic models; (4) Perform cyclic adsorption-regeneration batch tests. Objective one was met by designing and constructing two batch experimental setups. The adsorption setup consisted of a heated water bath housing 10 tall form beakers in which the adsorption experiments were run. The column type regeneration system included three regeneration columns, a condenser, a liquid trap and activated carbon trap. Nitrogen gas was used as the carrier gas in the system and electric heat tracing on the column inlet tubing and regeneration columns was used to heat the system to the required regeneration temperatures. Adsorption tests investigating the alcohol adsorbing capabilities were performed using 3 types of adsorbates (1-hexanol, 1-octanol and 1-decanol), 3 types of adsorbents (activated alumina F-220, Selexsorb® CD and Selexsorb® CDx) and 3 temperatures (25, 30 and 35 °C). Overall, the activated alumina F-220 adsorbent performed better than the other two adsorbents. Generally, the 1-hexanol showed higher adsorbent loadings compared to those of 1-octanol and 1-decanol. The performance of the adsorption systems appeared to favour the slightly higher adsorption temperatures, showing the largest adsorbent loadings at 35 °C. The third objective was met by applying three isotherm and three kinetic models to the equilibrium and kinetic adsorption data respectively. The isotherm modelling confirmed that all adsorption systems exhibited favourable adsorption with physical bonds formed between adsorbate and adsorbent. The kinetic modelling gave insight into the rate-limiting step of each kinetic system, indicating that the rate-limiting step of each adsorption system could not be solely defined as intra-particle diffusion or adsorption reaction, but was rather a combination of the two. Lastly, the effects of two regeneration temperatures (185 and 205 °C) were tested on the three adsorbents in 8 adsorption-regeneration cycles. All three adsorbents remained thermally stable for all 8 cycles and the activated alumina F-220 adsorbent showed the lowest decline in alcohol removal efficiency for both regeneration temperatures. At a regeneration temperature of 185 °C the adsorbents showed slightly higher initial adsorbent loadings, but a greater decline in adsorbent loading over the 8 cycles than at the 205 °C regeneration temperature. Recommended future work suggestions included investigating higher adsorption temperatures to find the optimal temperature and investigating the effect of regeneration duration on the regeneration process.

AFRIKAANSE OPSOMMING: Adsorpsie word suksesvol in baie industrieë gebruik en het die gebruik van prosesse soos distillasie in sommige gevalle vervang. Die adsorpsieproses word beïnvloed deur vele faktore en sy doeltreffendheid steun grootliks op die regenerasie van die gebruikte adsorbeermiddel. Adsorpsie is stelsel-spesifiek en vereis eksperimentele adsorpsie- en regenerasie-data vir die stelsel om geskei te word. ’n Beter begrip van adsorpsie regenerasie en sy effek op die adsorpsieproses help ook met die verbetering van die algehele doeltreffendheid van die proses. Die doel van hierdie projek was om die adsorpsie van alkohol opgeloste stowwe vanuit ʼn alkaan oplosmiddel te ondersoek deur drie adsorbeermiddels wat in die industrie gebruik word, te gebruik en die effek van regenerasie op elke adsorbeermiddel te evalueer. Dit is bereik deur die volgende doelstellings: (1) die ontwerp en bou van lotadsorpsie en regenerasie eksperimentele opstellings; (2) uitvoering van ewewig en kinetiese adsorpsietoetse om die effek van die tipe adsorbeermiddel, tipe adsorbaat en temperatuur op die adsorpsieproses te evalueer; (3) modellering van hierdie data met bestaande ewewigs- en kinetiese modelle; (4) uitvoering van sikliese adsorpsie-regenerasie lottoetse. Die eerste doel is behaal deur twee loteksperimentele opstellings te ontwerp en te bou. Die adsorpsie opstelling het uit ʼn verhitte waterbad bestaan, wat tien lang vorm bekers huisves waarin adsorpsie eksperimente gedoen is. Die kolomtipe regenerasiestelsel het drie regenerasie kolomme, ʼn kondensator, ʼn vloeistofvanger en geaktiveerde koolstofvanger ingesluit. Stikstofgas is gebruik as die draergas in die stelsel en elektriese hitte opsporing op die kolominlaatpype en regenerasiekolomme is gebruik om die stelsel na die vereiste regenerasie temperature te verhit. Adsorpsietoetse wat die alkohol adsorbering vermoë ondersoek, is uitgevoer deur drie tipes adsorbate (1-heksanol, 1-oktanol en 1-dekanol), drie tipes adsorbeermiddels (geaktiveerde alumina F-220, Selexsorb® CD en Selexsorb® CDx) en drie temperature (25 °C, 30 °C en 35 °C) te gebruik. Oor die algeheel het die geaktiveerde alumina beter doeltreffendheid as die ander twee adsorbeermiddels gehad. Gewoonlik het die 1-heksanol hoër adsorbeermiddellading in vergelyking met dié van 1-oktanol en 1-dekanol, gehad. Die werkverrigting van die adsorpsiestelsel lyk of dit die effens hoër adsorpsie temperature verkies, met die grootste adsorbeermiddelladings by 35 °C. Die derde doel is bereik deur drie isotermiese en drie kinetiese modelle op die ewewig en kinetiese adsorpsie data onderskeidelik toe te pas. Die isoterm modellering het bevestig dat alle adsorpsiestelsels gunstige adsorpsie vertoon met fisiese verbindings wat gevorm is tussen adsorbate en adsorbeermiddels. Die kinetiese modellering het insig gebied in die tempo-beperkende stap van elke kinetiese stelsel, wat aandui dat die tempo-beperkende stap van elke adsorpsiestelsel nie alleenlik gedefinieer kan word as intra-partikel diffusie of adsorpsie reaksie nie, maar dat dit eerder ʼn kombinasie van die twee is. Laastens is die effek van twee regenerasie temperature (185 °C en 205 °C) op die drie adsorbsie-regenerasiesiklusse getoets. Al drie adsorbeermiddels het termies stabiel gebly vir al agt siklusse en die geaktiveerde alumina F-220 adsorbeermiddel het die laagste vermindering in alkohol-verwydering-doeltreffendheid vir beide regenerasie temperature gewys. By ʼn regenerasie temperatuur van 185 °C het die adsorbeermiddels effens hoër aanvanklike adsorbeermiddellading gewys, maar ʼn groter afname in adsorbeermiddellading oor die agt siklusse as by die 205 °C regenerasie temperatuur. Voorstelle vir toekomstige werk sluit in die ondersoek van hoër adsorpsie temperature om die optimale temperatuur te vind en die ondersoek van die effek van regenerasie duur op die regenerasieproses.

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