Fractionation of air by zeolites

Oxygen recovery from ozone generators by adsorption processes

As a triatomic allotrope of oxygen, ozone has many industrial and consumer applications because of its high oxidation potential and disinfectant properties. Most of the ozone is currently produced by corona discharge reactors using high-purity oxygen as the feed gas, where the conversion to ozone is typically 6−15 wt%. Given the high operating costs associated with the unreacted oxygen, it is essential to recover the oxygen for recycling to the ozone generator. This paper aims for the first time to design, simulate and assess cyclic adsorption processes for recovering oxygen from a mixture of ozone and oxygen (O3:O2 = 10:90 wt%) produced by a commercial ozone generator. A 2-bed, 2-step cycle was first investigated in which ozone is selectively adsorbed at high pressure and then desorbed by dry air used as a sweep gas. However, it was found that the O2 purity in the recycle stream was too low because of the nitrogen build up from air. Thus, two additional cycles, namely a 3-bed, 3-step cycle incorporating an oxygen purge step and a 3-bed, 4-step cycle incorporating a vacuum blowdown step, were evaluated with the purpose of removing nitrogen from the bed after the desorption step. Both adsorption cycles achieved a satisfactory O2 purity of 98+% in the recycle stream with a sacrifice of O2 recovery and an increase in energy consumption, respectively. As a result, the adsorption processes devised in this study could serve to significantly reduce the oxygen consumption in industrial ozone generators.

Zeolites in Adsorption Processes: State of the Art and Future Prospects

Zeolites have been widely used as catalysts, ion exchangers, and adsorbents since their industrial breakthrough in the 1950s and continue to be state-of the-art adsorbents in many separation processes. Furthermore, their properties make them materials of choice for developing and emerging separation applications. The aim of this review is to put into context the relevance of zeolites and their use and prospects in adsorption technology. It has been divided into three different sections, i.e., zeolites, adsorption on nanoporous materials, and chemical separations by zeolites. In the first section, zeolites are explained in terms of their structure, composition, preparation, and properties, and a brief review of their applications is given. In the second section, the fundamentals of adsorption science are presented, with special attention to its industrial application and our case of interest, which is adsorption on zeolites. Finally, the state-of-the-art relevant separations related to chemical and energy production, in which zeolites have a practical or potential applicability, are presented. The replacement of some of the current separation methods by optimized adsorption processes using zeolites could mean an improvement in terms of sustainability and energy savings. Different separation mechanisms and the underlying adsorption properties that make zeolites interesting for these applications are discussed.

Flexible oxygen concentrators for medical applications

Medical oxygen concentrators (MOCs) are used for supplying medical grade oxygen to prevent hypoxemia-related complications related to COVID-19, chronic obstructive pulmonary disease (COPD), chronic bronchitis and pneumonia. MOCs often use a technology called pressure swing adsorption (PSA), which relies on nitrogen-selective adsorbents for producing oxygen from ambient air. MOCs are often designed for fixed product specifications, thereby limiting their use in meeting varying product specifications caused by a change in patient's medical condition or activity. To address this limitation, we design and optimize flexible single-bed MOC systems that are capable of meeting varying product specification requirements. Specifically, we employ a simulation-based optimization framework for optimizing flexible PSA- and pressure vacuum swing adsorption (PVSA)-based MOC systems. Detailed optimization studies are performed to benchmark the performance limits of LiX, LiLSX and 5A zeolite adsorbents. The results indicate that LiLSX outperforms both LiX and 5A, and can produce 90% pure oxygen at 21.7 L/min. Moreover, the LiLSX-based flexible PVSA system can manufacture varying levels of oxygen purity and flow rate in the range 93-95.7% and 1-15 L/min, respectively. The flexible MOC technology paves way for transitioning to an envisioned cyber-physical system with real-time oxygen demand sensing and delivery for improved patient care.

Effect of Li, Na and K Modification of Alumina on its Physical and Chemical Properties and Water Adsorption Ability

The effect of alkali metal (Li, Na, K) incorporation on the morphology and water vapor uptake properties of mesoporous Al₂O₃ has been studied. The modification of the raw material, pseudoboehmite, represented a mixture of low-temperature phases (γ + η + χ)-Al₂O₃, and has been done at low-temperature that does not change the phase ratio. A decrease in specific surface values and an average pores size increase were observed as a result of the introduction of metal cations by impregnation and subsequent thermal treatment. The influence of the content of the modifying metal on the adsorption ability of the obtained samples in relation to water vapours has been studied. It has been established that alkaline modification Al₂O₃ with the lithium cations did not result in adsorption ability improvement, whereas samples that were modified with sodium or potassium in the amount of 1.2 weight % and 2.6 weight %, respectively, possess a higher equilibrium capacity (by ~40%), as compared to that of the initial sample (Al₂O₃), and a sufficiently high adsorption rate.

Applications of Gas Separation by Adsorption for the Future

The separation and purification of gas mixtures by adsorption has found numerous industrial applications during the past 30 years. The very active research and development in this field is driven by (a) the highly flexible nature of cyclic adsorptive process designs, (b) the availability of many adsorbents for the separation and (c) the multiple choice of adsorbent–process design combinations for achieving the desired separation goals. The trend is to improve the product quality and separation efficiency, as well as to increase the scale of application of this technology. The design of processes using faster cycles and the use of innovative adsorber configurations are two new directions. Hybrid gas separation and production concepts such as adsorbent membranes and simultaneous sorption–reaction schemes are emerging areas that may open new frontiers of application for this technology.