Abstract
Deep eutectic solvents (DES) are compounds of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) that contain a depressed melting point compared to their individual constituents. DES have been studied for their use as carbon capture media and biogas upgrading. However, contaminants’ presence in biogas might affect the carbon capture by DES. In this study, conductor-like screening model for real solvents (COSMO-RS) was used to determine the effect of temperature, pressure, and selective contaminants on five DES’ namely, choline chloride-urea, choline chloride-ethylene glycol, tetra butyl ammonium chloride-ethylene glycol, tetra butyl ammonium bromide-decanoic acid, and tetra octyl ammonium chloride-decanoic acid. Impurities studied in this paper are hydrogen sulfide, ammonia, water, nitrogen, octamethyltrisiloxane, and decamethylcyclopentasiloxane. At infinite dilution, CO2 solubility dependence upon temperature in each DES was examined by means of Henry’s Law constants. Next, the systems were modeled from infinite dilution to equilibrium using the modified Raoults’ Law, where CO2 solubility dependence upon pressure was examined. Finally, solubility of CO2 and CH4 in the various DES were explored with the presence of varying mole percent of selective contaminants. Among the parameters studied, it was found that the HBD of the solvent is the most determinant factor for the effectiveness of CO2 solubility. Other factors affecting the solubility are alkyl chain length of the HBA, the associated halogen, and the resulting polarity of the DES. It was also found that choline chloride-urea is the most selective to CO2, but has the lowest CO2 solubility, and is the most polar among other solvents. On the other hand, tetraoctylammonium chloride-decanoic acid is the least selective, has the highest maximum CO2 solubility, is the least polar, and is the least affected by its environment.
Highlights
Anaerobic digestion (AD) is the process of breaking down organic substances in anoxic conditions by bacteria [1]
The results of this study contain important preliminary data regarding the implementation of Deep eutectic solvents (DES) in biogas upgrading systems
It has been shown that the polarity of a solvent, its size, and its constituents are factors contributing to solubility, but the main determinant is the hydrogen bond donor (HBD) selection
Summary
Anaerobic digestion (AD) is the process of breaking down organic substances in anoxic conditions by bacteria [1]. Organic macro-molecules such as fats, carbohydrates, and proteins are digested into micro-molecules during AD, which results in a nutrient-rich solid for plants (fertilizer) and biogas [2]. This process occurs naturally in landfills, and in a controlled environment in equipment called anaerobic digestors. The feedstock for AD are materials that are otherwise considered waste, such as agricultural waste, manure, organic waste from animal processing plants, food waste, and many others [3,4]. During AD, several reactions occur, but the process can be categorized into four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Long-chain polymers like cellulose are hydrolyzed into fermentable forms like glucose
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