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

[摘要] 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.

[发布机构] Stellenbosch University