Rapid Refrigeration and Water Protection

This chapter defines common terms and discusses some fundamental concepts for adsorption-based refrigeration and water pollutants removal systems. It also summarizes important topics of every chapter that has been published in this book entitled, ‘Rapid Refrigeration and Water Protection—Next Generation Adsorbents.’

A set of thermal compressors (often referred to as adsorption beds) is employed in an adsorption heat pump (AHP) system to achieve the desired cooling, whereas electricity-driven compressors are used in a conventional vapor compression refrigeration system (VCRS). Although an AHP is much more environmentally friendly than VCRS, its massive size is one of the major hindrances towards its commercial application. The primary reason for this bulkiness is the huge amount of adsorbents that are being used in the adsorption beds. A remedy to this major flaw can be the use of composite adsorbents instead of loosely packed powders. Another colossal issue is the poor efficiency of this system which can be partially resolved by (i) proper selection of adsorbent, adsorbate, binder, thermal conductivity enhancer and optimizing their composition; (ii) applying optimum pressure in the consolidation process; (iii) determining the thermophysical properties of adsorbents to select the most suitable one, and (iv) ensuring efficient operation of the system by optimizing the duration of different recovery schemes. In this chapter, the synthesis technique to prepare silica gel-based high-quality consolidated adsorbents is demonstrated, a comparison of several thermophysical properties of the parent and composite adsorbents is presented, and finally, the system operation is investigated and optimized through simulation studies.

This chapter begins with the synthetization of methyl-functionalized-MOF-801 (Zr) and Aluminium Fumarate-zeolite/alkali metal cations composites. The porous structures are characterized by XRD, TGA, SEM, and N₂ adsorption analysis. Later water adsorption on these synthesized materials is measured gravimetrically. Based on the experimental results, the adsorption chiller performance adopting modified fumarate-based MOFs as adsorbents is predicted by thermodynamic modeling. Enhanced hydrophilicity and faster water adsorption kinetics are observed for MOFs-zeolite/alkali metal cations composites. It is also observed that the methyl functional groups (–CH₃) enhance the thermal stability of MOF structures as well as increases the water uptake/offtake kinetics. Under adsorption-assisted cooling system operating conditions, the water transfer per cooling cycle for methyl functionalized MOF-801 (Zr) is found 25% higher as compared with the original MOF-801 (Zr) materials. On the other hand, modified fumarate MOFs improve the water loading rates significantly up to two folds. Therefore, the SCP and COP are also found higher for modified fumarate-based MOF-801 (Zr) and Al-Fum MOFs.

Environmentally benign adsorption heat pump (AHP) and desalination (AD) systems have already attracted considerable attention for space cooling/heating and potable water production since they require no electricity and are driven by solar or waste heat. The adsorbent material is the key element of these adsorption systems. Highly porous carbon-based consolidated composites are very promising adsorbents. Specific heat capacity (c_p) of adsorbent is one of the most significant thermophysical properties. It plays a vital role in predicting the performance of the systems accurately. However, the estimation of the c_p of adsorbent materials is a demanding issue and has not been focused sufficiently yet. Therefore, this chapter will present the significance of specific heat capacity, detailed experimental procedure, and the c_p of composites, as well as the parent materials at the operating temperature range of AHP and AD systems. Finally, all the experimental data are analyzed rigorously and correlated with the established equations of c_p. The presented experimental c_p data along with the fitted parameters are crucial in the design of AHP and AD systems.

This chapter focuses on a modern characterization technique, Atomic Force Microscopy (AFM), which uses nanoprobes to extract three-dimensional (3-D) images of surfaces. These 3-D images contain both qualitative and quantitative information. Qualitative information is useful for visually understand the differences between various adsorbents that influence the physical properties. Quantitative information is suitable for determining roughness, shape, and depth of surface pores, pore size distribution, etc. However, it is quite challenging to take images of highly coarse surfaces like the porous materials usually have. Each of the materials requires different techniques for image extraction. Therefore, this work contains a brief description of the image extraction techniques for various porous materials with quantitative analysis.

The Chapter addresses two emerging adsorption processes aimed at improving the Earth's ecology, namely, water harvesting from the atmosphere and recuperation of heat and moisture in ventilation systems. Both systems are open and can be examined in a unified way by analyzing a thermodynamic cycle of the process to account for various climatic conditions. Since these conditions can significantly vary for seasons and geographic locations, they have to be correctly taken into account to formulate thermodynamic requirements to an optimal adsorbent. Special attention is paid to a) harmonization of the adsorbent and the cycle, and b) the preparation of the optimal adsorbent and its testing. Advanced adsorbents selected/developed/tested for both applications are considered

In the last decade, the amount of contaminated water resources has increased dramatically with the rapid growth in industrial sectors. Additionally, the growth in world population and the effects of climate changes have also increased the water contamination levels in several areas. Thus, there is a crucial need for effective and eco-friendly water treatment materials. The current available water treatment methods and materials have multiples drawbacks that limit their usability. Materials such as metal oxide nanoparticles, carbon nanotubes, and polymer membranes are used widely in the water treatment field. However, the efficiency of these materials is limited by the complexity of the water contaminants. Therefore, highly efficient activated carbon is introduced as a proper approach to treat contaminated water. Typically, activated carbon is produced from different types of biomass. Hence, activated carbon can be produced almost everywhere. Currently, Lignocellulosic biomass is provided as a reliable renewable resource that can be used to produce activated carbon. Indeed, Lignocellulosic biomass can be utilized to produce several materials such as biogases, biofuels, and biochar. Activated carbon is produced from biomass using different thermal conversion technologies such as pyrolysis, anaerobic digestion, torrefaction hydrothermal processing, and gasification. Historically, pyrolysis technology is used for hundreds of years to produce biofuel and char from woody biomass. This chapter focuses on the different reaction phases during pyrolysis and the effect of the reaction conditions on biomass to produce activated carbon. Moreover, the impact of technological development on the energy density of the lignocellulosic residues is covered in the chapter.

The pollution of water resources with different inorganic and organic pollutants and deterioration of drinkable water quality is pressing the need for the introduction of new and advanced material for water treatment technology. Nanomaterials are being very popular in water purification technology because of their excellent removal efficiency for a vast spectrum of pollutants via the adsorption process. Nowadays, carbon nanomaterials (carbon nanofiber, carbon nanotube, graphene, and its derivatives, etc.) have attracted great attention as adsorbents because of their extraordinary physicochemical properties for water treatment. This chapter explores the adsorption performance of carbon nanotube, carbon nanofiber, graphene, and its derivatives, etc., for organic dye, heavy metal, and pharmaceutical pollutants. It starts with the fundamental of the adsorption mechanism and isotherms. The chapter describes all the details on material from the synthesis process to the application and concisely states that adsorption performance can be improved by functionalization and modification of the pristine material. The current hurdle and prospects of the carbon nanomaterial also have been discussed. This chapter will contribute to a proper understanding of the implementation of carbon nanomaterials in the field of adsorption for environmental remediation and designing future experiments for water treatment.

Water pollution can cause severe health hazards in living organisms since most of the contaminants are toxic, mutagenic, and carcinogenic. There is a critical need to decontaminate the water from industrial effluents preceding their discharge into water bodies. The current chapter explores the potential of various nanoparticle-based adsorbents with special reference to nano zero-valent iron (NZVI), iron oxide, titanium, alumina, and silica in the field of adsorptive hosting of inorganic and organic pollutants from aqueous solutions. The nano adsorbents exhibit greater adsorption capacity, rapid adsorption rate, and competence to host various pollutants, recyclability, and reusability when compared to conventional adsorbents. These properties emphasize the relevance of nano adsorbents for the remediation of water contaminated with heavy metal ions, dyes, and chlorinated organic compounds. This chapter gives an overview of the progress and application of bare and functionalized metal and metal oxide nanoparticles for this purpose. Moreover, the mechanism of heavy metal ions, dyes, and organic chlorinated compounds removal by nanoparticles has also been discussed. The present chapter offers advanced information about the imperative characteristics of some metal and metal oxide-based nanoparticles and demonstrates their advantages as adsorbents in water remediation.