A review of fluorocarbon sorption on porous materials
Graphical abstract
Introduction
Global refrigerant usage encompasses a growing number of applications that are critical to modern society. The past two centuries have seen the birth and rapid growth of refrigerant technologies, starting with Jacob Perkins who created a vapor-compression refrigeration cycle using liquid ammonia in the 1830s (first-generation refrigerant) [1]. By the 1930s, Thomas Midgely, Albert L. Henne, and Robert R. McNary had discovered fluorocarbon refrigerants, leading to the widespread use of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants (second-generation refrigerants) [1]. However, by the mid-1980s, CFCs were linked to the depletion of the Earth's ozone layer [2]. In 1987, the Montreal Protocol was signed limiting the production of ozone depleting substances such as CFCs [1,3]. In 1992, the Copenhagen amendment to the Montreal protocol called for the phaseout of HCFCs by the year 2030 [3]. The phaseout of CFCs and HCFCs led to the development of hydrofluorocarbon (HFC) refrigerants which have zero ozone depletion potential (ODP) [1]. HFCs are considered third-generation refrigerants and have been in production and use for the past thirty years.
Today, concerns over the global warming potential (GWP) of HFCs has become an issue [1]. In fact, some HFCs contribute thousands of times more to global warming than carbon dioxide on an equivalent mass basis. A list of some common HFCs and their GWPs is given in Table 1. In the global effort to mitigate climate change, a series of legislative actions have been taken that affects HFC use and production. The Kyoto Protocol in 2005 [1], F-gas regulations by the European Union in 2014 [1], the Kigali Amendment to the Montreal Protocol in 2016 [4], and the American Innovation and Manufacturing (AIM) act in 2020 [5] are among the most recent actions taken to phase out and limit the use of HFCs. As a result of the phaseout of HFCs, the transition to fourth-generation refrigerants is currently underway. Many of these refrigerants are based on hydrofluoroolefins (HFOs) that have a zero ODP and low GWP (Table 1) [1].
As the air-conditioning and refrigeration (RAC) industry transitions to HFOs, something must be done with the estimated 2800 ktons of refrigerant currently in use globally [6]. Opposed to venting or incinerating these high GWP refrigerants, a more preferable route would be to reclaim, separate, and recycle them. However, this process is becoming more difficult due to the similar thermophysical properties of HFC mixture components and the azeotropic nature of many of these HFC blends. Cryogenic distillation can perform some separations but is highly energy intensive and not effective at separating azeotropic compositions [[7], [8], [9], [10]]. However, the use of zeolites and activated carbons has been reported in the patent literature for separating azeotropic refrigerant mixtures [7]. Wanigarathna et al. have recently shown that it is possible to use both zeolites and metal-organic frameworks (MOFs) to separate azeotropic HFC refrigerant mixtures [[11], [12], [13]].
The use of sorbents for the separation of HFC refrigerant mixtures based on differences in molecular size and interactions is a promising, less energy-intensive alternative to conventional distillation processes. An extensive literature search has been performed for fluorocarbon sorption on porous materials. Literature and patent data have been found on the sorption of fluorocarbons including CFCs, chlorofluoroolefins (CFOs), HCFCs, hydrochlorofluoroolefins (HCFOs), HFCs, HFOs, perfluorocarbons (PFCs), and perfluoroolefins (PFOs) in porous materials such as zeolites, activated carbons, and metal organic frameworks (MOFs). Only one known review article has been found for fluorocarbon sorption and the scope is limited to sorption and separation of CFCs, HCFCs, HFCs, and PFCs with MOFs [14].
This review is organized such that the reader can easily find the topic of interest. For example, discussion on HFC sorption using zeolites is provided in Sections 7.1 (applications) and 7.2 (sorption behavior). These sections are further divded by specific applications (Sections 1 Introduction, 2 Sorbents, 3 Overview of literature, 4 Refrigerant nomenclature, 5 Chlorofluorocarbons (CFCs), 6 Hydrochlorofluorocarbons (HCFCs) and hydrochlorofluoroolefins (HCFOs), 7 Hydrofluorocarbons (HFCs)), molecular interactions (Section 7.2.1), isotherm modeling (Section 7.2.2), and reactivity (Section 7.2.3). Sections 5 Chlorofluorocarbons (CFCs), 6 Hydrochlorofluorocarbons (HCFCs) and hydrochlorofluoroolefins (HCFOs), 8 Hydrofluoroolefins (HFOs), 9 Perfluorocarbons (PFCs) and perfluoroolefins (PFOs) follow similar formatting for CFCs, HCFCs and HCFOs, HFOs, and PFCs and PFOs, respectively. This review article provides a comprehensive overview of fluorocarbon sorption and separation that can be valuable to researchers both new to the field and those having years of experience. Sorbents offer a wide range of tunable physical and chemical properties and provide an opportunity to lower the energy required for separation of fluorocarbons.
Section snippets
Sorbents
The most common sorbents found for fluorocarbon sorption include activated carbons, zeolites, and metal-organic frameworks (MOFs). A brief description about each type of sorbent is provided to familiarize the reader with some key attributes for each material. A section is also included to highlight features of sorbents that influence sorption. A comparison among zeolites, activated carbons, and MOFs is provided in Table 2. Other sorbents found less frequently in the literature for fluorocarbon
Overview of literature
An extensive literature search was conducted for fluorocarbon sorption from both academic papers and patent literature with a primary focus on sorption of straight-chain paraffinic and olefinic fluorocarbons. In this context, fluorocarbons refer to species having the following chemical formula:
Fluorocarbons are hydrocarbon-based species that contain at least one fluorine atom, but can also contain hydrogen atoms, chlorine atoms, both, or neither.
The frequency for which zeolites,
Refrigerant nomenclature
Fluorocarbons are frequently referred to by a nomenclature developed by DuPont and adopted by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) [36]. This nomenclature will be used throughout this review article and thus it is worth briefly mentioning here. A fluorocarbon can be referred to by one of the following formats:
R-X
Fluorocarbon Code-X
Here, “Fluorocarbon Code” is the type of fluorocarbon i.e., CFC, CFO, HCFC, HCFO, HFC, HFO, PFC, or PFO. Both of
Chlorofluorocarbons (CFCs)
A sampling of representative CFCs is tabulated and provided in the Supplementary Material along with values for gas-phase dipole moment (μg) and the polarizability (α) (see Table S2). CFCs are found to have much lower permanent dipole moments compared with other fluorocarbons; however, CFCs tend to have much greater polarizability, which arises from the chlorine atoms. The lack of dipole moment results from the fact that chlorine and fluorine atoms have similar electronegativities. A list of
Hydrochlorofluorocarbons (HCFCs) and hydrochlorofluoroolefins (HCFOs)
Examples of HCFCs and an HCFOs are provided in the Supplementary Material with values for gas-phase dipole moment (μg) and polarizability (α) (see Table S7). The dipole moments of HCFCs are much larger than CFCs and slightly less than HFCs on average. HCFCs also have polarizabilities slightly lower than CFCs and much larger than HFCs. HCFCs exhibit molecular properties of both CFCs and HFCs. A list of reported sorbents for HCFC and HCFO sorption and applications is provided in Table 4. Only two
Hydrofluorocarbons (HFCs)
Examples of HFCs are provided in the Supplementary Material with values for gas-phase dipole moment (μg) and polarizability (α) (see Table S12). HFCs have among the largest dipole moments and the smallest polarizabilities of the fluorocarbons and can be considered as rigid, hard spheres and ovals with distinct positive and negative ends. A list of reported sorbents for HFC sorption with applications is presented in Table 5. A breakdown of the sources that report the use of zeolites, activated
Hydrofluoroolefins (HFOs)
Examples of HFOs are provided in the Supplementary Material with values for gas-phase dipole moment (μg) and polarizability (α) (see Table S18). HFOs generally have both the largest dipole moments and polarizabilities among the fluorocarbons discussed. The large dipole moments result from the large electronegativity difference between hydrogen and fluorine atoms (as is the case with HFCs). The double bonds of HFOs contribute toward large polarizability. A list of reported sorbents for HFO
Perfluorocarbons (PFCs) and perfluoroolefins (PFOs)
Examples of PFCs and PFOs are provided in the Supplementary Material with values for gas-phase dipole moment (μg) and polarizability (α) (see Table S20). PFCs contain only carbon and fluorine atoms and are symmetrical giving them zero permanent dipole moments. PFOs are not always symmetrical and can therefore have weak permanent dipole moments. The polarizability of PFCs and PFOs increases with an increasing number of fluorine atoms.
A list of sorbents for PFC and PFO sorption along with
Discussion of chemical interactions
Molecular interactions have been discussed for zeolites, activated carbons, and MOFs with CFCs, HCFCs, HCFOs, HFCs, HFOs, and PFCs. Both dipole moment and polarizability were often used to justify sorption behavior and will now be used to highlight sorption trends noticed from previous discussion. Basic zeolites (e.g., 5A and 13X) and MOFs with high density OMSs (e.g., Ni-MOF-74) generally had greater affinity toward species with larger dipole moments, that is, HFCs, HFOs, and some HCFCs. The
Mixtures
The following section discusses separations of mixtures consisting of two or more fluorocarbons and provides multiple examples of sorbents in practical use. Examining the outcome of separated mixtures is also useful for understanding the effects of molecular interactions between fluorocarbons and sorbents. For example, Section 10 noted that untreated activated carbons generally have greater affinity for CFCs over HFCs; therefore, under normal conditions the retention time should be greater for
Conclusion
This review article explores the applications, molecular interactions, isotherm modeling, and reactivity of various sorbents and fluorocarbons as well as the separation and purification of fluorocarbon mixtures. Fluorocarbon sorption was found to be a well-studied field starting in the 1940s and continues today. A common theme found throughout fluorocarbon sorption literature and patents was environmental remediation, which has directly influenced a majority of the studies. Academic papers have
CRediT authorship contribution statement
Andrew D. Yancey: Conceptualization, Methodology, Investigation, Data Curation, Writing-Original Draft, Writing-Review & Editing, Visualization. Sophia J. Terian: Conceptualization, Writing-Original Draft. Benjamin J. Shaw: Data Curation. Tiana M. Bish: Data Curation. David R. Corbin: Conceptualization, Methodology, Supervision, Writing-Review & Editing. Mark B. Shiflett: Conceptualization, Methodology, Supervision, Funding Acquisition, Writing-Review & Editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This material is based upon work supported by the National Science Foundation under grant no. 2029354.
References (352)
The next generation of refrigerants – historical review, considerations, and outlook
Int. J. Refrig.
(2008)- et al.
Metal organic frameworks for adsorption-based separation of fluorocompounds: a review
Mater. Adv.
(2020) - et al.
Monolayer adsorption of gas mixtures on homogeneous and heterogeneous solids
Chem. Eng. Sci.
(1967) - et al.
A review on surface modification of activated carbon for carbon dioxide adsorption,
J. Anal. Appl. Pyrol.
(2010) Acidity and basicity of zeolites: a fundamental approach
Micropor. Mesopor. Mat.
(2017)- et al.
Chlorofluorocarbons adsorption structures and energetic over faujasite type zeolites—a first principle study
J. Mol. Struct. THEOCHEM
(2003) - et al.
Predicting adsorption of n-perfluorohexane (n-C6F14) on BCR-704 zeolite using the first principle force field method
Fluid Phase Equil.
(2014) - et al.
Reactivity of some halogenated alkanes on 13X molecular sieve
J. Catal.
(1977) - et al.
A computational investigation of zeolite-chlorofluorocarbon interactions
Zeolites
(1996) - et al.
Alkylations of benzene, alkylbenzenes, and halobenzenes catalyzed by protonated mordenite pretreated with chlorofluorocarbons
J. Catal.
(1991)
Improvement of platinum-supported zeolite catalysts for n-hexane aromatization by halocarbon treatment and alkaline soaking
Appl. Catal. A Gen.
Atomistic mechanism of the adsorption of CFCs in zeolite as investigated by Monte Carlo simulation
Stud. Surf. Sci. Catal.
A study on adsorption of trichloromonofluoroethane by an activated carbon pellet
Carbon
Adsorption of chlorofluorocarbons on microporous carbon fiber
Carbon
The effect of presorbed water on the adsorption of CFC-113 by a carbon adsorbent
Carbon
The recovery of chlorofluorocarbons and chlorofluorocarbon replacements by surface modified activated carbon
J. Colloid Interface Sci.
Adsorption properties of CFC and CFC replacements on activated carbon containing introduced ionic fluoride and chloride
J. Colloid Interface Sci.
Adsorption equilibrium and catalytic reaction of CFC-115 on Pd/activated carbon powder
Carbon
Adsorption dynamics of trichlorofluoromethane in activated carbon fiber beds
J. Hazard Mater.
Environmental friendly automated line for recovering the cabinet of waste refrigerator
Waste Manag.
The volume Adsorption capacity of activated carbon for selected trace contaminates
Carbon
Stratospheric ozone destruction by man-made chlorofluoromethanes
Science
A critical review of the successful CFC phase-out versus the delayed methyl bromide phase-out in the Montreal Protocol, Int. Environ. Agreem
The development of environmentally acceptable fluorocarbons
Crit. Rev. Toxicol.
H. R. 133, One Hundred Sixteenth Congress of the United States of America
Refrigerants: Market Trends and Supply Chain Assessment; NREL/TP-5500-70207
Refrigerant separation
Colcard Pty. Limited
Process for purifying pentafluoroethane, process for producing the same, and use thereof
Showa Denko K.K
Separation of chloropentafluoroethane from pentafluoroethane
E. I. du Pont de Nemours and Company
Purification Process. Imperial Chemical Industries Plc
Adsorption separation of R-22, R-32 and R-125 fluorocarbons using 4A molecular sieve zeolite
ChemistrySelect
Adsorption separation of R134a, R125 and R143a fluorocarbon mixtures using 13X and surface modified 5A zeolites
AIChE J.
Fluorocarbon separation in a thermally robust zirconium carboxylate metal-organic framework
Chem. Asian J.
Charcoal is one of the most important substances ever discovered
Office for Science and Society
History, method of production, structure and applications of activated carbon
IJERT
Activated carbon: fundamentals and new applications
Zeolite Molecular Sieves: Structure, Chemistry, and Use
The distribution of aluminum in the tetrahedra of silicates and aluminates
Am. Mineral.
Acidity in zeolites and their characterization by different spectroscopic methods
Indian J. Chem. Technol.
Competitive adsorption mechanism study of CHClF2 and CHF3 in FAU zeolite
ACS Sustain. Chem. Eng.
Adsorption of chlorofluorocarbons in nanoporous solids; a combined powder neutron diffraction and computational study of CFCl3 in NaY zeolite
Phys. Chem. Chem. Phys.
Discovery of optimal zeolites for challenging separations and chemical transformations using predictive materials modeling
Nat. Commun.
Fundamentals and Applications
The chemistry and applications of metal-organic frameworks
Science
Coordinatively unsaturated metal sites (open metal sites) in metal-organic frameworks: design and applications
Chem. Soc. Rev.
Adsorption and Diffusion, Springer-Verlag, Berlin/Heidelberg
Coadsorption of organic compounds and water vapor on BPL activated carbon. 2. 1,1,2-Trichloro-1,2,2-trifluoroethane and dichloromethane
Ind. Eng. Chem. Res.
Chemical Reactor Analysis and Design Fundamnetals
Refrigerating, and air-conditioning engineers; designation and safety classification of refrigerants
ANSI/ASHRAE Standard
Cited by (27)
Modeling of multi-temperature Type I and II benzene/ammonia adsorption isotherms: Dual LF model and linearized DR model
2024, Separation and Purification TechnologyLife cycle assessment of fluorinated gas recovery from waste refrigerants through vacuum swing adsorption
2024, Sustainable Materials and TechnologiesDynamic adsorption behavior of 1.1.1.2-tetrafluoroethane (R134a) on activated carbon beds under different humidity and moisture levels
2024, Separation and Purification TechnologyThe effect of relative humidity on multicomponent organic vapor adsorption on composite beds with micro-fibrous entrapped activated carbon
2023, Journal of Environmental Chemical EngineeringData science for thermodynamic modeling: Case study for ionic liquid and hydrofluorocarbon refrigerant mixtures
2023, Fluid Phase Equilibria