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

Abstract

The drying of dichloromethane with a molecular sieve 3A packed bed process is modeled and experimentally verified. In the process, the dichloromethane is dried in the liquid phase and the adsorbent is regenerated by water desorption with dried dichloromethane product in the vapor phase. Adsorption equilibrium experiments show that dichloromethane does not compete with water adsorption, because of size exclusion; the pure water vapor isotherm from literature provides an accurate representation of the experiments. The breakthrough curves are adequately described by a mathematical model that includes external mass transfer, pore diffusion, and surface diffusion. During the desorption step, the main heat transfer mechanism is the condensation of the superheated dichloromethane vapor. The regeneration time is shortened significantly by external bed heating. Cyclic steady-state experiments demonstrate the feasibility of this novel, zero-emission drying process.

Adsorptive Removal of Dichloromethane Vapor on FAU and MFI Zeolites: Si/Al Ratio Effect and Mechanism

“…40 MFI zeolites also show a three-dimensional pore system with a window size of about 4.7 × 4.46 × 4.46 Å. 32 The kinetic diameter for DCM is 3.3 Å, 8,23,24 thus the molecular sieve effect can be excluded. In other words, the DCM molecule can readily gain entrance to the micropores of both types of zeolite.…”

“…Dichloromethane (DCM) is extensively used as a solvent in many chemical processes. The annual world production of DCM is more than 500 000 tons, of which about 77% is emitted into the atmosphere . Due to its high toxicity and carcinogenic character, combined with its contribution to global warming, depletion of the ozone layer, and the formation of photochemical smog, the removal of DCM is a major environmental concern. − …”

“…As a result, alternative adsorbents have drawn more and more interest. Metal–organic frameworks (MOFs), ,− hyper-cross-linked polymers, , and zeolites ,− are also being considered for adsorptive removal of DCM. Zeolites have proven to be advantageous for the control of chlorinated VOCs due to their nonflammable nature, thermal stability, and hydrophobic characteristics. − Schaaf et al have used a 3 Å molecular sieve to separate DCM from water by the steric effect.…”

Review: membrane materials for the removal of water from industrial solvents by pervaporation and vapor permeation

“…The most recent advances in adsorbents have come in the areas of metal‐organic framework (MOF) materials [including the subcategory of zeolitic imidazolate frameworks (ZIFs)], carbon molecular sieve (CMS) materials, and in the fabrication of molecular sieves into more efficient structures . For water adsorption from solvents, however, zeolite‐based molecular sieve particles, particularly sodium A‐type (‘NaA’ or ‘4A’) and potassium A‐type (‘KA’ or ‘3A’) aluminosilicates, are still the primary materials used …”

“…[28][29][30][31][32] For water adsorption from solvents, however, zeolite-based molecular sieve particles, particularly sodium A-type ('NaA' or '4A') and potassium A-type ('KA' or '3A') aluminosilicates, are still the primary materials used. 13,21,33,34 Other drying processes that may be suitable for industrial solvents are: reacting, salting out, coalescing, and fractional freezing. 13 For smaller scale drying applications, hydrate formation through contact with salts has been used.…”