Adsorptive Water Removal from Organic Solvents in the ppm‐Region

Abstract

Highly pure organic solvents gain more and more importance in optical, electronical, pharmaceutical and chemical industry. In this context the removal of water in the lower ppm-and ppb-range is a major challenge since water is always present, e. g., air humidity, and leads to catalyst poisoning and undesired side reactions. One technique to remove water is by adsorption on zeolites, silica gels or aluminas. Despite single technical solutions already existing, systematic measurements of influencing parameters are still missing. The research project adresses the adsorption of water from different organic solvents. In the following experiments with linear primary alcohols and acetic acid esters are discussed as these solvents are often used in industry in low water content qualities. State of the ArtBurfield et al. investigated the drying of aromatic hydrocarbons, ethers, alcohols, amines and dipolar aprotic solvents such as acetone with molecular sieves, activated aluminas and silica gels. Chemicals such as calcium chloride, phosphorous pentoxide, sodium, potassium hydroxide, sodium sulphate, calcium sulphate and magnesium sulphate were also tested. They observed that high water solubilities and high dielectric constants lead to a poor drying performance, while low water solubilities in combination with low dielectric constants lead to good drying results with molecular sieves [1].Basmadjian [4] published a literature review on adsorptive drying of gases and liquids. He postulates that the isotherm for water removal from organic solvents on molecular sieves is independent from the solvent, as long as the solvent molecules cannot be adsorbed in the pores, i.e., there should be only one isotherm for a certain type of molecular sieve. As none of the isotherms he reviewed coincided perfectly with the water vapour isotherm, Basmadjian attributed the differences to reasons like regeneration of zeolites, non-equilibrium in measurements, coadsorption of solvent molecules in macropores and errors in water concentration measurement.Several authors investigated the adsorptive water removal from alcohols with molecular sieves. Teo and Ruthven [5] studied the system water/ethanol/zeolite 3A, Jain and Gupta [6] examined water/isopropanol/zeolite 4A, Paderewski and Gabrus [7] described water/n-butanol/zeolite 4A. All authors found nearly rectangular shaped isotherms typical for adsorption on zeolites. ExperimentalFor screening experiments as well as the measurement of adsorption isotherms the shaking table method was applied. Between 0.1 and 0.5 g of adsorbent were filled into an Erlenmeyer flask with 50 mL of solvent. The flasks were tightly sealed and shaken in an incubator at 20°C and 150 rpm until equilibrium was reached. A blind sample, consisting of a flask only filled with solvent, was used to detect potential water contamination from the surrounding atmosphere. Before adsorption experiments all adsorbents were prepared thermally according to manufacturer's guidelines. Sample flasks were dried in an oven prior to use. The...

Adsorptive Water Removal from Dichloromethane and Vapor-Phase Regeneration of a Molecular Sieve 3A Packed Bed

“…These results are in accordance with the findings of adsorptive drying of higher alcohols (>C4) and esters. 7 , 8 According to Basmadjian, 2 if solvent molecules cannot penetrate the pores of the molecular sieves, the water adsorption isotherm is independent of the solvent and is the same as a pure water vapor isotherm.…”

“…Adsorption is one of the possible methods for obtaining ultrapure solvents. 2 Because of their high hygroscopicity, molecular sieves have already demonstrated their adsorption capability for the drying of ethanol, 3 , 4 higher alcohols 5 , 6 and esters, 7 , 8 toluene, 9 and other hydrocarbons 10 and solvents. 11 The general conclusion is that hydrophobic solvents are easier to dry.…”

Adsorption of aromatic trace compounds from organic solvents on activated carbons—experimental results and modeling of adsorption equilibria

“…In food industry liquid phase adsorption is used today for the cleaning of sugar and alcoholic beverages (Singleton and Draper 1962;Gula and Paillat 2005). Other examples for industrial applications are the removal of the polymerization inhibitor 4-tert-butylcatechol from the monomer styrene on Al 2 O 3 (River et al 2002) and the adsorptive removal of water from organic solvents in the lower ppm-and ppb-range (Pahl et al 2011).…”

Comparison of Water-Removal Efficiency of Molecular Sieves Vibrating by Rotary Shaking and Electromagnetic Stirring from Feedstock Oil for Biofuel Production

“…After water absorption, the twisted structure of the molecular sieve swiftly expands to become cross-linked cubes full of water molecules [30]. Water content in feedstock oil might retard the transesterification reaction, leading to deteriorated fuel characteristics of the biofuel product [31]. The water-removal process is hence a necessity to enhance the reaction process for biofuel production.…”