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Citation: Lu, Z. Comprehensive
Investigation of Cooling, Heating,
and Power Generation Performance
in Adsorption Systems Using
Compound Adsorbents:
Experimental and Computational
Analysis. Sustainability 2023,15,
15202. https://doi.org/10.3390/
su152115202
Academic Editor: Luca Cioccolanti
Received: 12 September 2023
Revised: 15 October 2023
Accepted: 16 October 2023
Published: 24 October 2023
Copyright: © 2023 by the author.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
sustainability
Article
Comprehensive Investigation of Cooling, Heating, and Power
Generation Performance in Adsorption Systems Using
Compound Adsorbents: Experimental and
Computational Analysis
Zisheng Lu
Chongqing Research Institute, Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University,
Dongchuan Rd. 800#, Shanghai 200240, China; zslu@sjtu.edu.cn; Tel.: +86-21-3420-6309
Abstract:
The extensive utilization of petrochemical energy sources has led to greenhouse gas emis-
sions, the greenhouse effect, the frequent occurrence of extreme weather events, and the severe
degradation of Earth’s ecosystems. The development of renewable energy technologies has become
an inevitable trend. This paper investigates an adsorption-based cooling/heating/power generation
technology driven by low-grade solar thermal energy. The research results demonstrate that the
adsorption performance of vermiculite compound adsorbents impregnated with LiCl solution is
superior to those impregnated with CaCl
2
solution, with the former exhibiting adsorption at lower
p/po partial pressure ratios. Furthermore, at an adsorption bed temperature of 25
◦
C and a p/po
partial pressure of 0.8, the adsorption cooling performance of Comp. 2 compound adsorbent im-
pregnated with LiCl solution reaches 5760.7 kJ/kg, with a coefficient of performance (COP) of 0.75,
heating performance of 9920.8 kJ/kg, COPh of 1.51, and power generation capacity of 10.6 kJ/kg.
This research contributes to the advancement of sustainable energy technologies and the mitigation
of environmental impacts associated with petrochemical energy sources.
Keywords: compound adsorbents; water; cooling; heating; power generation
1. Introduction
The pressing need to discover sustainable and renewable energy sources has arisen
due to the stark contrast between the rapid surge in energy demand and the dwindling
reserves of conventional fossil fuels. Renewable energy and residual heat emerge as highly
appealing alternatives to conventional fossil fuels, offering a sustainable and ecologically
friendly energy reservoir that holds the potential to curtail greenhouse gas emissions and
alleviate the repercussions of climate change. Unlike fossil fuels, which are finite and
progressively challenging to extract, renewable energy sources such as solar and wind
are abundant and widely accessible. Simultaneously, residual heat stands as an accessible
resource within numerous industrial processes, which can be effectively harnessed to
generate electricity or supply heating services. These resources, encompassing renewable
energy sources and residual heat, have the capacity to generate electricity, cooling, or
heating with minimal to negligible greenhouse gas emissions, thereby diminishing air
pollution and attenuating the adverse effects of climate change [1,2].
Numerous researchers have delved into the investigation of advanced adsorbents,
notably metal–organic frameworks (MOFs), and their applications in various domains,
including adsorption-based cooling systems. For instance, in the work of M. Rezk et al.,
a dedicated effort is made to enhance adsorption systems for cooling and desalination
by leveraging advanced materials and innovative adsorbent bed configurations. Their
study employs computational methodologies to assess the performance of a heat exchanger
incorporating a copper-foamed adsorbent bed packed with MOF-801 adsorbent, juxta-
posed against a baseline adsorbent comprising silica gel. Employing a multi-objective
Sustainability 2023,15, 15202. https://doi.org/10.3390/su152115202 https://www.mdpi.com/journal/sustainability
Sustainability 2023,15, 15202 2 of 16
optimization approach, the research aims to attain the optimal balance between coefficient
of performance, specific cooling power, and clean water productivity. The outcomes un-
equivocally demonstrate that the MOF-801-based system surpasses its silica gel counterpart
in terms of clean water production and specific cooling power. However, it’s noteworthy
that the latter exhibits superior cooling capacity and coefficient of performance, primarily
attributable to its higher packing density [3].
In a similar vein, the research undertaken by S. Chumnanwat et al., explores the
application of an innovative adsorbent coating technique on aluminum fins within an
adsorption-based heat pump or chiller system. The methodology involves immersing an
aluminum substrate into a solution containing the adsorbent, resulting in the formation of
a compound adsorbent layer on the surface. The study rigorously evaluates the adhesion
properties of this layer through a peeling test. Notably, the investigation identifies specific
anodization conditions and the utilization of zeolite AQSOA-Z01 as the adsorbent, resulting
in the formation of a thin aluminum oxide film layer with commendable adhesion strength
and specific cooling capacity, making it a promising option for adsorption heat pump and
chiller applications [4].
H. Banda’s research delves into the exploration of graphene oxide’s applicability as an
adsorbent material within adsorption systems, drawing a comparative analysis against the
performance of silica gel. The findings unequivocally underscore the considerable enhance-
ments realized with graphene oxide, with a remarkable 44% boost in thermal efficiency,
up to 57% improvement in adsorption capabilities, as well as notable advancements in
specific daily water production, specific cooling power, coefficient of performance, and
energy efficiency when juxtaposed with silica gel [5].
In the realm of experimental investigations, a hybrid adsorption system, strategically
coupling a pretreatment module tailored for heavy metal removal with a unit focused on
desalination and cooling, underwent scrutiny. This multifaceted system harnessed a trio of
adsorbents, namely activated carbon, zeolite, and aluminum fumarate MOF. The outcomes
attest to the system’s impressive efficacy in the removal of heavy metals, yielding a prolific
daily production of distilled water exceeding 260 L and generating a robust 6.9 kW of
cooling power while boasting a commendable coefficient of performance of 0.26. These
findings collectively emphasize the system’s potential as a promising solution, not only for
water purification but also for the eco-friendly production of clean cooling resources [6].
To elevate the adsorption efficacy of adsorbents, extensive scholarly investigations
have delved into the realms of adsorption performance, heat and mass transfer character-
istics, and the optimization of efficient sorption processes, particularly with compound
adsorbents comprising physical adsorbents such as MOFs and hygroscopic salts. For
instance, H. Zhao embarks on an exploration of MIL-100(Fe)’s water vapor adsorption
properties within the context of sorption-based atmospheric water harvesting (SAWH).
This endeavor involves a comparative analysis between methods involving solvents and
those devoid of solvents for the preparation of MIL-100(Fe). The findings emanating from
this study unequivocally indicate that MIL-100(Fe) synthesized in a solvent-free manner,
alongside its compound adsorbent counterpart, MgCl
2
@MIL-100(Fe), exhibits notable
enhancements in adsorption performance and desorption characteristics. These improve-
ments manifest through higher equilibrium adsorption capacities when contrasted with
the conventional solvent-based synthesis approach. These insightful results not only un-
derscore the potential application of solvent-free MIL-100(Fe) and its associated compound
adsorbent within the realm of SAWH systems but also provide a compelling avenue for
future research and technological advancement [7].
Throughout their investigation, the research team unearthed pivotal revelations.
Specifically, they ascertained that MOF-801 displayed significantly superior adsorption
(desorption) capacities in comparison to both silica gel and the 13X molecular sieve. The
enhancements amounted to a substantial increase, respectively. In parallel, the scholarly
endeavors led by Bo Han and his collaborators have been dedicated to a multifaceted ex-
ploration of adsorption-based thermal energy storage [
8
]. This domain holds vast potential
Sustainability 2023,15, 15202 3 of 16
as a foundational cornerstone for diverse heat-related processes encompassing cooling,
heat pumps, desalination, power generation, water harvesting, and dehumidification.
Their comprehensive investigation yielded remarkable findings: targeted modifications
to the original MOFs, particularly the MIL-53 (Al) MOFs, resulted in alterations in hy-
drophilicity and hydrophobicity, leading to an enhancement in water loadings of up to
0.9 g/g. This augmentation was further exemplified through the accelerated water transfer
facilitated by functionalized and protonated MIL-53 (Al) MOFs, demonstrating enhanced
kinetics when compared to their unmodified counterparts. Notably, the ligand-extended
MIL-53 (Al) MOFs showcased impressive capabilities, particularly in transferring water
between environments characterized by high humidity (80% to 90% relative humidity)
and those undergoing regeneration (30% relative humidity). This innovative approach
yielded a promising thermal energy storage density (TESD) reaching up to 1.54 MJ/L.
Sandra Jose and her colleagues undertook a comprehensive review focused on energy
storage applications, with particular emphasis on compounds comprised of conducting
polymers and metal-organic frameworks (CP/MOF). The findings underscore the versatil-
ity of CP/MOF compounds, indicating their potential extension into a range of domains,
including electrochemical sensors, water splitting, and carbon dioxide reduction [
9
]. In
a distinctive investigation, Fan Luo and colleagues delved into an innovative monolithic
adsorbent derived from bi-metallic MOFs, designed specifically for solar-triggered atmo-
spheric water harvesting. This bimetallic MOF exhibited an impressive specific surface
area of
1203 m2.g−1
and a substantial pore volume measuring 0.51 cm
3
.g
−1
. Their efforts
culminated in the successful fabrication of an advanced water harvesting system, ultimately
showcasing a remarkable daily water yield of up to 1.9 g/g through the purpose-built
monolithic adsorbent [
10
]. Majdi Amin’s research revolved around the scrutiny of sorption-
ejector systems, emphasizing the imperative need for further experimental validation of
theoretical data. Within integrated sorption-ejector configurations, notable enhancements
came to the fore: a noteworthy 9.8% reduction in power consumption, a 13.6% decrease in
cooling capacity, and a substantial 8–60% improvement in the coefficient of performance
compared to standalone sorption systems. Moreover, the overall coefficient of performance
(COP) for combined adsorption-ejector systems exhibited a significant increase, registering
increments of 0.33 and 1.47, respectively [
11
]. Turning attention towards energy storage,
Jingwei Chao and their team harnessed zeolite/MgCl
2
compound sorbents with the aim of
augmenting energy storage density. Their outcomes revealed impressive average energy
densities, notably peaking at 686.86 kJ/kg for heat storage and 597.13 kJ/kg for cold stor-
age [
12
]. In another exploration led by Suboohi Shervani and their associates, the focus was
on harnessing the potential of vermiculite/LiCl compound adsorbents for thermal energy
storage. The results underscored a substantial enhancement in energy storage performance
facilitated by this compound adsorbent. Significantly, the energy storage density could
reach an impressive 159 kWh/m
3
under specific regeneration conditions, particularly at
a temperature of 120
◦
C [
13
]. Finally, Faraz Ege and other research teams embarked on
an assessment of MIL-101(Cr)-coated microchannels as adsorbents to amplify adsorption
performance. The experimental findings vividly demonstrated the superior performance of
these meticulously characterized coated channels across various domains, encompassing
adsorption as well as adsorption-driven heating and cooling capabilities
[14–18]
. Efficient
adsorbents are applied in adsorption systems for seawater desalination and adsorption
refrigeration. For instance, activated carbon and zeolite are used as adsorbents, and
MOF is coated on the adsorbents. Research results demonstrate a desalination capacity
of 260 L/day and a refrigeration power of 6.9 kW [
6
]. In order to enhance the overall
performance coefficient of the adsorption system, researchers utilized oxidized graphene
as the adsorption material for adsorption refrigeration and seawater desalination. Research
findings reveal that, compared to the silica gel system, the seawater desalination capacity
of the oxidized graphene system increased by 44.4%, and the refrigeration performance
improved by 29.5% [
5
]. The researchers employed an aluminum fumarate metal-organic
framework, or SAPO-34/CPO-27(Ni) as the adsorption material for the study of adsorption-
Sustainability 2023,15, 15202 4 of 16
based seawater desalination and adsorption refrigeration. Research findings demonstrate a
significant enhancement in the coefficient of performance of the system [19,20].
As mentioned previously, numerous scholars have actively conducted research in the
domains of adsorbents, adsorption cooling, and adsorption energy storage. Nevertheless,
there has been a conspicuous dearth of comprehensive investigations into the innovative ad-
sorption system capable of concurrently facilitating cooling, heating, and power generation
through the utilization of compound adsorbents. The primary objectives of this research
paper encompass the following aspects: Firstly, the development of a series of compound
adsorbents is undertaken, accompanied by a comparative analysis of their structural char-
acteristics and adsorption performance. Secondly, a thorough examination is conducted to
assess their cooling capabilities, heating performance, and power generation efficiency.
The innovative aspects of this paper are primarily reflected in the following areas:
(1) Novel High-Efficiency Composite Adsorbents: This study investigates high-porosity
zeolites and immerses them in hygroscopic salt solutions such as calcium chloride and
lithium chloride to create innovative composite adsorbents. Their high porosity enables
the storage of a greater quantity of adsorbate solution. Calcium chloride enhances ad-
sorption performance while considering the cost-effectiveness of composite adsorbent
production. Lithium chloride effectively lowers desorption temperatures and improves
adsorption capabilities. (2) Innovative Composite Cycle: Due to the enhanced adsorption
performance of the novel composite adsorbents, this paper presents the possibility of
constructing a composite cycle. This composite cycle can facilitate adsorption-based refrig-
eration, adsorption-based heating, adsorption-based desalination, and adsorption-based
power generation. This approach can significantly enhance the overall cycle efficiency.
(3) Expanded Application Scenarios: The system can be powered by both solar energy
and industrial waste heat, making it suitable for a variety of applications, including island
environments, deserts, and industrial settings. This versatility contributes to economic and
environmental benefits.
2. Matrix-Salt Adsorbents and Test Setup
This paper outlines the fabrication process of four distinct matrix-salt adsorbents.
These adsorbents feature porous media composed of activated carbon, vermiculite, and
activated carbon/silica diatomite. To prepare them, the porous media were submerged in
salt solutions with precise concentrations for a 12-h period. For comparison, two different
salt solutions were utilized, and their respective parameters can be found in Table 1.
Following immersion, the adsorbents underwent further treatment in an oven at 130
◦
C for
12 h, culminating in the formation of the matrix-salt adsorbents, as illustrated in Figure 1.
Table 1. Main components of matrix-salt adsorbents and parameters of immersion salt solutions.
Type Matrix
Salt Solution Components
CaCl2% LiCl% MgCl2% MIL101%
Matrix-salt 1 Activated carbon 10.9 14.8 0 1.8
Matrix-salt 2 Vermiculite 10.9 14.8 0 1.8
Matrix-salt 3 AC/Diatomite 10.9 14.8 0 1.8
Matrix-salt 4 Vermiculite 30% 0 0 0
The examination of the matrix-salt adsorbents was conducted employing a confocal
microscope. When scrutinizing these materials, distinct characteristics emerged. Activated
carbon displayed a relatively consistent pore size distribution, while activated carbon/silica
diatomite exhibited a more varied pore structure, encompassing fine micropores to larger
macropores. In contrast, vermiculite showcased a markedly dissimilar morphology com-
pared to porous substances like activated carbon. Vermiculite assumed a “worm-like”
configuration and featured a stratified structure characterized by a relatively substantial
pore volume.
Sustainability 2023,15, 15202 5 of 16
Sustainability 2023, 15, x FOR PEER REVIEW 5 of 17
Figure 1. Photograph and confocal microscopy images of matrix-salt adsorbent.
The examination of the matrix-salt adsorbents was conducted employing a confocal
microscope. When scrutinizing these materials, distinct characteristics emerged. Acti-
vated carbon displayed a relatively consistent pore size distribution, while activated car-
bon/silica diatomite exhibited a more varied pore structure, encompassing fine mi-
cropores to larger macropores. In contrast, vermiculite showcased a markedly dissimilar
morphology compared to porous substances like activated carbon. Vermiculite assumed
a “worm-like” configuration and featured a stratified structure characterized by a rela-
tively substantial pore volume.
To assess the adsorption capacity of the matrix-salt adsorbents, we employed an
ASAP 2020 (Norcross, GA, USA) device, as depicted in Figure 2. The ASAP 2020 serves as
a high-performance adsorption analyzer, facilitating the measurement of surface area,
pore size, pore volume, and adsorption capacity of the matrix-salt adsorbents. Addition-
ally, the pore structure of these matrix-salts was thoroughly analyzed utilizing a confocal
microscopy device known as Smartproof 5 (White Plains, NY, USA). Smartproof 5 har-
nesses confocal imaging principles to achieve a remarkable 1.4-fold enhancement in tra-
ditional optical resolution. It boasts XY direction line resolution of up to 120 nm and a
minimum Z-axis step accuracy of 1 nm.
(a) (b)
Figure 2. Experimental instrument: ASAP adsorption analyzer; (a) block diagram; (b) experimental
setup.
Figure 1. Photograph and confocal microscopy images of matrix-salt adsorbent.
To assess the adsorption capacity of the matrix-salt adsorbents, we employed an ASAP
2020 (Norcross, GA, USA) device, as depicted in Figure 2. The ASAP 2020 serves as a high-
performance adsorption analyzer, facilitating the measurement of surface area, pore size,
pore volume, and adsorption capacity of the matrix-salt adsorbents. Additionally, the pore
structure of these matrix-salts was thoroughly analyzed utilizing a confocal microscopy
device known as Smartproof 5 (White Plains, NY, USA). Smartproof 5 harnesses confocal
imaging principles to achieve a remarkable 1.4-fold enhancement in traditional optical
resolution. It boasts XY direction line resolution of up to 120 nm and a minimum Z-axis
step accuracy of 1 nm.
Sustainability 2023, 15, x FOR PEER REVIEW 5 of 17
Figure 1. Photograph and confocal microscopy images of matrix-salt adsorbent.
The examination of the matrix-salt adsorbents was conducted employing a confocal
microscope. When scrutinizing these materials, distinct characteristics emerged. Acti-
vated carbon displayed a relatively consistent pore size distribution, while activated car-
bon/silica diatomite exhibited a more varied pore structure, encompassing fine mi-
cropores to larger macropores. In contrast, vermiculite showcased a markedly dissimilar
morphology compared to porous substances like activated carbon. Vermiculite assumed
a “worm-like” configuration and featured a stratified structure characterized by a rela-
tively substantial pore volume.
To assess the adsorption capacity of the matrix-salt adsorbents, we employed an
ASAP 2020 (Norcross, GA, USA) device, as depicted in Figure 2. The ASAP 2020 serves as
a high-performance adsorption analyzer, facilitating the measurement of surface area,
pore size, pore volume, and adsorption capacity of the matrix-salt adsorbents. Addition-
ally, the pore structure of these matrix-salts was thoroughly analyzed utilizing a confocal
microscopy device known as Smartproof 5 (White Plains, NY, USA). Smartproof 5 har-
nesses confocal imaging principles to achieve a remarkable 1.4-fold enhancement in tra-
ditional optical resolution. It boasts XY direction line resolution of up to 120 nm and a
minimum Z-axis step accuracy of 1 nm.
(a) (b)
Figure 2. Experimental instrument: ASAP adsorption analyzer; (a) block diagram; (b) experimental
setup.
Figure 2.
Experimental instrument: ASAP adsorption analyzer; (
a
) block diagram; (
b
) experimen-
tal setup.
For assessing adsorption performance and overall system performance, the following
equations can be employed:
x=x0e
−k[ln p(Ts)
p(Ta)]n
(1)
where
x
is the adsorption capacity, kg/kg;
x0
is the maximum adsorption capacity, kg/kg;
k
is a constant;
p(Ts)
is the pressure at saturation temperature, Pa;
p(Ts)
is the pressure at
adsorption temperature, Pa; and nis a constant.
The equation for evaporation heat (Qeva porat ) is given by:
Sustainability 2023,15, 15202 6 of 16
Qeva por at =madsorben xadsorptio.,end −xadsorptio.,begin·hv aporizatio +Cp,wateTcondensatio −Teva poratio (2)
where
Qeva por at
is the cooling capacity, kJ;
madsorben
is the adsorbent mass, kg;
xadsorptio.,end
is
the adsorption uptake at the end of the cycle, kg/kg;
xadsorptio.,begin
is the adsorption uptake
at the beginning of the cycle, kg/kg;
hvapori zatio
is the latent heat of vaporization, kJ/kg;
Cp,wate
is the specific heat capacity, kJ/(kg.K);
Tcondensatio
is the condensation temperature,
K; and Tevaporatio is the evaporation temperature, K.
The adsorption cooling capacity (Qcooling) equation is given by:
Qcool ing =madsorbedCpTcondensation −Tevaporation +madsorbedhvapor (3)
where
Qcool ing
is the adsorption cooling capacity, kJ/kg;
madsorbed
is the mass of adsorbate
adsorbed, kg/kg;
Cp
is the specific heat capacity of the adsorbate, kJ/(kg.
◦
C);
Tcondens ation
is the condensation temperature,
◦
C;
Tevaporation
is the evaporation temperature,
◦
C; and
hvapor is the latent heat of vaporization, kJ/kg.
The equation for heating (Qheating) is given by:
Qheating =mbed Cp,bedTdesor ption −Tadsor ption +ZTdesor pti on,end
Tdesorp tion,s tart
madsorbed Cp,adsorbatedT +madsorbed hdesorptio n (4)
where
Qheating
is the heating capacity, kJ/kg;
mbed
is the mass of the bed, kg;
Cp,bed
is the
specific heat capacity of the adsorbate, kJ/(kg.
◦
C);
Tdesorptio n
is the desorption temperature,
◦
C;
Tadsor ption
is the adsorption temperature,
◦
C;
Cp,adsorbate
is the specific heat capacity of
the adsorbate, kJ/(kg.
◦
C);
madsorbed
is the mass of adsorbate adsorbed, kg/kg; and
hdesorption
is the heat of desorption, kJ/kg.
The equation for the cooling power of the cooling water (Qcool,water ) is given by:
Qcool ,water =mbedCp,bedTdesor ption −Tadsorptio n+ZTadsor ptio n,end
Tadsor ption ,start
madsorbed Cp,adsorbatedT +madsorbed hdesorptio n (5)
where
Qcool ,water
is the cooling power of the cooling water, kJ/kg;
mbed
is the mass of the
bed, kg;
Cp,bed
is the specific heat capacity of the adsorbate, kJ/(kg.
◦
C);
Tevaporation
is the
evaporation temperature,
◦
C;
Tadsor ption
is the adsorption temperature,
◦
C;
Cp,adsorbate
is
the specific heat capacity of the adsorbate, kJ/(kg.
◦
C);
madsorbed
is the mass of adsorbate
adsorbed, kg/kg; and hdesorption is the heat of desorption, kJ/kg.
The coefficient of performance (COP) equation for an adsorption cooling system is
defined as:
COP =Qco oling
Qheating
(6)
where
COP
is the coefficient of performance;
Qcool ing
is the cooling capacity, kJ/kg; and
Qheating is the heating capacity, kJ/kg.
The condensation capacity (Qcondens atio n) equation can be expressed as:
Qcondensation =mcndensedCpTdesor ption −Tcondensation+mcndensedhcondensation (7)
where
Qcondensation
is the condensation capacity, kJ/kg;
mcndensed
is the mass of condensate
water, kg;
Cp
is the specific heat capacity of the condensate, kJ/kg;
Tdesorptio n
is the desorp-
tion temperature,
◦
C;
Tcondens ation
is the condensation temperature,
◦
C; and
hcondensation
is
the heat of condensation, kJ/kg.
The coefficient of performance for heating (
COPh
) equation in an adsorption heating
system is given by:
COPh=Qcondensation+Qcool ,water
Qheating
(8)
where COPhis the coefficient of performance for heating.
Sustainability 2023,15, 15202 7 of 16
The power generation (COPh) equation is given by:
welectricity =cvapor,water ·mvapor,water ·Tdesor ption −Tcondensation·µex pender ·µgenerator (9)
where
welectricity
is the power generation capacity, kJ/kg;
cvapor,w ater
is the specific heat
capacity of the adsorbate, kJ/(kg.
◦
C);
mvapor,w ater
is the mass flow of the water vapor,
kg/s;
Tdesorptio n
is the desorption temperature,
◦
C;
Tcondens ation
is the condensation temper-
ature,
◦
C;
µex pender
is the efficiency of the expender; and
µgenerator
is the efficiency of the
power generator.
The advantages of matrix-salt adsorbents are shown as follows: Matrix-salt adsorbents,
also known as hybrid adsorbents, offer a multitude of advantages in various applications,
ranging from environmental remediation to industrial processes. These innovative ma-
terials combine different adsorbent components to create synergistic effects that enhance
their performance. Below, we explore the numerous benefits associated with matrix-salt
adsorbents. Enhanced Adsorption Capacity: Matrix-salt adsorbents often exhibit higher
adsorption capacities compared to single-component adsorbents. This increased capacity
results from the combination of multiple adsorbent materials, each with its own unique
adsorption characteristics. Improved Selectivity: Tailoring matrix-salt adsorbents by care-
fully selecting their components allows for enhanced selectivity. This feature is particularly
valuable in separating target matrix-salts from complex mixtures. Versatility: Matrix-salt
adsorbents can be designed to target specific pollutants or contaminants, making them
versatile tools for various applications, such as wastewater treatment, air purification,
and gas separation. Regenerability: Many matrix-salt adsorbents are readily regenerable,
allowing for multiple usage cycles. This property reduces operational costs and environ-
mental impacts compared to one-time-use adsorbents. Faster Adsorption Kinetics: The
synergistic effects of matrix-salt adsorbents can result in faster adsorption kinetics, enabling
more efficient pollutant removal or gas separation processes. Improved Stability: The
combination of different adsorbent materials often enhances the stability and durability of
the matrix-salt adsorbents, ensuring a longer service life. Cost-Effectiveness: Matrix-salt
adsorbents can be designed to use readily available and cost-effective materials, making
them an economically viable option for various industries. Tailored for Specific Applica-
tions: These adsorbents can be tailored to suit specific application requirements, allowing
engineers and researchers to design solutions that meet their unique needs. Reduced
Environmental Impact: Matrix-salt adsorbents can help reduce the environmental impact
of various processes by effectively removing harmful substances and minimizing waste
generation. Innovation and Research Opportunities: The development of matrix-salt ad-
sorbents continues to drive innovation in materials, science, and engineering, offering
researchers exciting opportunities to explore new combinations and applications. Scalabil-
ity: Matrix-salt adsorbents can be designed for scalability, making them suitable for both
small-scale and large-scale operations. Compatibility with Existing Systems: In many cases,
matrix-salt adsorbents can be integrated into existing treatment or separation systems with
minimal modifications, providing a seamless upgrade option. Wide Range of Applications:
Matrix-salt adsorbents find applications in diverse fields, including water purification,
gas separation, pharmaceutical manufacturing, and more, making them indispensable in
modern industries. Matrix-salt adsorbents represent a promising and versatile class of
materials that offer numerous advantages across a wide spectrum of applications. Their
ability to combine the strengths of different adsorbent components makes them a vital tool
for addressing environmental and industrial challenges while promoting sustainability and
cost-effectiveness. Continued research and development in this field promise to unlock
even more potential benefits in the future.
The model and specification of the equipment are shown in Table 2. The schematic
diagram of the adsorption cooling/heating/electricity generation system is depicted in
Figure 3
. The main working principle of the experimental system is based on the adsor-
bent’s adsorption or desorption of the adsorbate. The adsorbent can be heated by heat
Sustainability 2023,15, 15202 8 of 16
sources at different temperatures or cooled by cooling water at different temperatures. The
adsorbate can evaporate at different temperatures or be condensed into a liquid. Under
different operating conditions, the adsorption capacity of the adsorbent for the adsorbate
varies. From the diagram, it is evident that it mainly consists of two constant-temperature
water baths, an adsorption bed, an evaporative condenser, a vacuum pump, a pressure
storage tank, a power generation device, and more. Its operating principle is as follows:
Firstly, during the adsorption bed heating and desorption process, hot water from constant-
temperature water bath 1 heats the adsorption bed, causing the matrix-salt adsorbent
within the bed to desorb water vapor. Secondly, in the condensation process, water vapor
is condensed into pure water within the evaporative condenser, and the condensation heat
is carried away by constant-temperature water bath 2. Thirdly, during the cooling and
adsorption process, cold water from constant-temperature water bath 1 cools the adsorption
bed, and the adsorbent within the bed adsorbs the vapor evaporated from the evaporative
condenser. At the same time, the adsorption bed releases adsorption heat, which is carried
away by constant-temperature water bath 1. Fourthly, in the evaporative cooling process,
the adsorbate water evaporates in the evaporative condenser, simultaneously generating
cooling capacity, which is carried away by constant-temperature water bath 2. Fifthly, in the
vortex power generation process, the high-pressure water vapor resulting from adsorption
bed desorption is stored in the pressure storage tank, and this steam can drive a vortex
generator for electricity generation. The experimental setup is illustrated in Figure 4.
Table 2. Model and specification of the equipment.
No. Name Model Specification Accuracy
1Temperature sensor
(Garland, TX, USA) OMEGATJ36 K type 0–1200 ◦C 0.4%
2Pressure sensor
(Mainz, Germany) WIKA S-20 0–6 MPa 0.12%
3Mass flowmeter
(Monterey, CA, USA) LONTROL DN15 0.6–3.6 m3/h 0.5%
Sustainability 2023, 15, x FOR PEER REVIEW 9 of 17
Figure 3. The adsorption cooling/heating/power generation system.
Figure 4. The setup of the adsorption cooling/heating/power generation system.
3. Results of Performance of Cooling, Heating and Power Generation
3.1. Performance of Cooling
The outcomes of adsorption performance assessments for the matrix-salt adsorbents
are visually depicted in Figure 5. Upon a careful examination of the graph, it becomes
apparent that the adsorption performance of matrix-salt adsorbents employing vermicu-
lite as the porous medium demonstrates a relatively favorable performance and follows a
comparable adsorption trend. It is essential to note, however, that the adsorption perfor-
mance of vermiculite-based matrix-salt adsorbents impregnated with CaCl2 exhibits a
slight lag in comparison to those impregnated with LiCl and other adsorbents. This ob-
served difference can primarily be aributed to the lower moisture sorption capacity of
CaCl2 when contrasted with LiCl. Furthermore, the graph reveals that at lower p/po (rel-
ative pressure) values, matrix-salt 2 exhibits a higher adsorption capacity when
Figure 3. The adsorption cooling/heating/power generation system.
Sustainability 2023,15, 15202 9 of 16
Sustainability 2023, 15, x FOR PEER REVIEW 9 of 17
Figure 3. The adsorption cooling/heating/power generation system.
Figure 4. The setup of the adsorption cooling/heating/power generation system.
3. Results of Performance of Cooling, Heating and Power Generation
3.1. Performance of Cooling
The outcomes of adsorption performance assessments for the matrix-salt adsorbents
are visually depicted in Figure 5. Upon a careful examination of the graph, it becomes
apparent that the adsorption performance of matrix-salt adsorbents employing vermicu-
lite as the porous medium demonstrates a relatively favorable performance and follows a
comparable adsorption trend. It is essential to note, however, that the adsorption perfor-
mance of vermiculite-based matrix-salt adsorbents impregnated with CaCl2 exhibits a
slight lag in comparison to those impregnated with LiCl and other adsorbents. This ob-
served difference can primarily be aributed to the lower moisture sorption capacity of
CaCl2 when contrasted with LiCl. Furthermore, the graph reveals that at lower p/po (rel-
ative pressure) values, matrix-salt 2 exhibits a higher adsorption capacity when
Figure 4. The setup of the adsorption cooling/heating/power generation system.
3. Results of Performance of Cooling, Heating and Power Generation
3.1. Performance of Cooling
The outcomes of adsorption performance assessments for the matrix-salt adsorbents
are visually depicted in Figure 5. Upon a careful examination of the graph, it becomes
apparent that the adsorption performance of matrix-salt adsorbents employing vermiculite
as the porous medium demonstrates a relatively favorable performance and follows a
comparable adsorption trend. It is essential to note, however, that the adsorption perfor-
mance of vermiculite-based matrix-salt adsorbents impregnated with CaCl
2
exhibits a slight
lag in comparison to those impregnated with LiCl and other adsorbents. This observed
difference can primarily be attributed to the lower moisture sorption capacity of CaCl
2
when contrasted with LiCl. Furthermore, the graph reveals that at lower p/po (relative
pressure) values, matrix-salt 2 exhibits a higher adsorption capacity when juxtaposed with
matrix-salt 4. Additionally, matrix-salt 4 showcases a more fragmented adsorption curve
in contrast to matrix-salt 2. This distinction can be ascribed to the broader spectrum of
hydrates formed by CaCl
2
as opposed to those generated by LiCl. Figure 5provides a
visual representation of the adsorption performance of various matrix-salt adsorbents.
Notably, vermiculite-based adsorbents demonstrate favorable performance trends, albeit
with variations attributed to the choice of impregnating agent. Additionally, the differences
in adsorption capacity and curve characteristics between matrix-salt 2 and matrix-salt 4
are elucidated, shedding light on the influence of the impregnation agent’s properties on
adsorption behavior. These findings contribute valuable insights to the understanding of
matrix-salt adsorbents’ performance in different configurations.
Figure 6provides a graphical depiction of the cooling performance of the matrix-salt
adsorbents, while Figure 7furnishes valuable insights into the coefficient of performance
(COP). Within the presented graphical data, a discernible pattern emerges in which the
adsorption cooling performance exhibits an ascending trajectory with increasing evaporator
pressure. When the focus is narrowed to matrix-salt adsorbents featuring vermiculite as the
uniform porous substrate, a clear trend materializes wherein the COP tends to converge as
the partial pressure (p/po) ascends. What is particularly noteworthy is the conspicuous
prominence of matrix-salt 2, which demonstrates the most exceptional cooling performance
among the evaluated matrix-salts. In stark contrast, matrix-salt 3 exhibits the least effective
cooling performance within the defined parameters. To illustrate, at an adsorption bed
temperature of 25
◦
C and a p/po partial pressure of 0.8, matrix-salt 2 boasts a remarkable
cooling performance of 5760.7 kJ/kg, accompanied by a COP of 0.75. This is because
Sustainability 2023,15, 15202 10 of 16
matrix-salt 2 has a high porosity of zeolite, and additionally, CaCl
2
and LiCl exhibit high
hygroscopic properties. Therefore, matrix-salt 2 possesses superior adsorption capability
and adsorption refrigeration performance. Conversely, under identical conditions, matrix-
salt 3 manages to achieve only a modest cooling performance of 597.1 kJ/kg, coupled with
a significantly lower COP of 0.46. Figure 6visually encapsulates the cooling performance of
the various matrix-salt adsorbents, revealing an upward trajectory in cooling performance
as evaporator pressure increases. Moreover, a detailed examination of Figure 7underscores
the noteworthy disparities in COP among the matrix-salts, with matrix-salt 2 emerging
as the frontrunner in cooling performance, while matrix-salt 3 lags behind under the
specified operating conditions. These findings furnish crucial insights into the performance
differentials among the matrix-salt adsorbents in the context of cooling applications.
Sustainability 2023, 15, x FOR PEER REVIEW 10 of 17
juxtaposed with matrix-salt 4. Additionally, matrix-salt 4 showcases a more fragmented
adsorption curve in contrast to matrix-salt 2. This distinction can be ascribed to the
broader spectrum of hydrates formed by CaCl2 as opposed to those generated by LiCl.
Figure 5 provides a visual representation of the adsorption performance of various matrix-
salt adsorbents. Notably, vermiculite-based adsorbents demonstrate favorable perfor-
mance trends, albeit with variations aributed to the choice of impregnating agent. Addi-
tionally, the differences in adsorption capacity and curve characteristics between matrix-
salt 2 and matrix-salt 4 are elucidated, shedding light on the influence of the impregnation
agent’s properties on adsorption behavior. These findings contribute valuable insights to
the understanding of matrix-salt adsorbents’ performance in different configurations.
Figure 5. Adsorption performance of matrix-salt adsorbents (adsorption temperature: 25 °C).
Figure 6 provides a graphical depiction of the cooling performance of the matrix-salt
adsorbents, while Figure 7 furnishes valuable insights into the coefficient of performance
(COP). Within the presented graphical data, a discernible paern emerges in which the
adsorption cooling performance exhibits an ascending trajectory with increasing evapo-
rator pressure. When the focus is narrowed to matrix-salt adsorbents featuring vermicu-
lite as the uniform porous substrate, a clear trend materializes wherein the COP tends to
converge as the partial pressure (p/po) ascends. What is particularly noteworthy is the
conspicuous prominence of matrix-salt 2, which demonstrates the most exceptional cool-
ing performance among the evaluated matrix-salts. In stark contrast, matrix-salt 3 exhibits
the least effective cooling performance within the defined parameters. To illustrate, at an
adsorption bed temperature of 25 °C and a p/po partial pressure of 0.8, matrix-salt 2 boasts
a remarkable cooling performance of 5760.7 kJ/kg, accompanied by a COP of 0.75. This is
because matrix-salt 2 has a high porosity of zeolite, and additionally, CaCl2 and LiCl ex-
hibit high hygroscopic properties. Therefore, matrix-salt 2 possesses superior adsorption
capability and adsorption refrigeration performance. Conversely, under identical condi-
tions, matrix-salt 3 manages to achieve only a modest cooling performance of 597.1 kJ/kg,
coupled with a significantly lower COP of 0.46. Figure 6 visually encapsulates the cooling
performance of the various matrix-salt adsorbents, revealing an upward trajectory in
Matrix-salt 1
Matrix-salt 2
Matrix-salt 3
Matrix-salt 4
Figure 5. Adsorption performance of matrix-salt adsorbents (adsorption temperature: 25 ◦C).
Sustainability 2023, 15, x FOR PEER REVIEW 11 of 17
cooling performance as evaporator pressure increases. Moreover, a detailed examination
of Figure 7 underscores the noteworthy disparities in COP among the matrix-salts, with
matrix-salt 2 emerging as the frontrunner in cooling performance, while matrix-salt 3 lags
behind under the specified operating conditions. These findings furnish crucial insights
into the performance differentials among the matrix-salt adsorbents in the context of cool-
ing applications.
Figure 6. Cooling performance of matrix-salt adsorbents (adsorption temperature: 25 °C).
Figure 7. Coefficient of performance (COP) of matrix-salt adsorbents (adsorption temperature: 25
°C).
Matrix-salt 1
Matrix-salt 2
Matrix-salt 3
Matrix-salt 4
Figure 6. Cooling performance of matrix-salt adsorbents (adsorption temperature: 25 ◦C).
Sustainability 2023,15, 15202 11 of 16
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cooling performance as evaporator pressure increases. Moreover, a detailed examination
of Figure 7 underscores the noteworthy disparities in COP among the matrix-salts, with
matrix-salt 2 emerging as the frontrunner in cooling performance, while matrix-salt 3 lags
behind under the specified operating conditions. These findings furnish crucial insights
into the performance differentials among the matrix-salt adsorbents in the context of cool-
ing applications.
Figure 6. Cooling performance of matrix-salt adsorbents (adsorption temperature: 25 °C).
Figure 7. Coefficient of performance (COP) of matrix-salt adsorbents (adsorption temperature: 25
°C).
Matrix-salt 1
Matrix-salt 2
Matrix-salt 3
Matrix-salt 4
Figure 7.
Coefficient of performance (COP) of matrix-salt adsorbents (adsorption temperature: 25
◦
C).
3.2. Performance of Heating
Figure 8provides a visual representation of the heating performance of the matrix-salt
adsorbents, while Figure 9presents data on the heating performance coefficient (COPh). A
careful analysis of these graphs reveals that matrix-salt adsorbents featuring vermiculite
as the consistent porous substrate showcase commendable adsorption performance. It
is worth highlighting that vermiculite-based matrix-salt adsorbents treated with a LiCl
solution exhibit a slightly superior adsorption performance when compared to those treated
with a CaCl
2
solution. This observation is particularly noteworthy at lower p/po (relative
pressure) values, where matrix-salt 2 outperforms matrix-salt 4 in terms of adsorption
performance. These findings collectively suggest that vermiculite-based matrix-salt adsor-
bents, especially those impregnated with LiCl, hold significant promise for efficient heating
applications. Matrix-salt 2, in particular, stands out as a potential candidate for such applica-
tions, especially under lower-pressure conditions. These insights shed light on the potential
of these matrix-salt adsorbents in the realm of heating performance and underscore the
advantages of utilizing vermiculite and LiCl as key components in their formulation.
The graphical representations also unveil a notable trend in which the adsorption
heating performance exhibits enhancement as the evaporator pressures increase. For
matrix-salt adsorbents maintaining vermiculite as the consistent porous substrate, there
emerges a tendency for the heating performance coefficient (COPh) to converge as the
relative pressure (p/po) ascends. Of remarkable significance is the prominent position
of matrix-salt 2, which distinguishes itself with the most efficient heating performance
among the parameters considered. Conversely, matrix-salt 3 exhibits the least effective
heating performance within the specified parameters. To provide a concrete illustration, at
an adsorption bed temperature of 25
◦
C and a relative pressure (p/po) of 0.8, matrix-salt
2 achieves an impressive heating performance of 9920.8 kJ/kg, coupled with a COPh of
1.51. This is because during the adsorption heating process, both adsorption heat and
condensation heat can be utilized, resulting in a COPh greater than 1. In stark contrast,
under identical conditions, matrix-salt 3 manages to attain only a modest heating perfor-
mance of 1582.7 kJ/kg, accompanied by a significantly lower COPh of 1.22. These findings
underscore the noteworthy potential of matrix-salt 2 for efficient heating applications,
particularly under conditions of elevated pressure. The observed trends further emphasize
the advantages of employing vermiculite-based matrix-salt adsorbents in such heating
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scenarios, with matrix-salt 2 emerging as a particularly promising candidate for optimizing
heating performance.
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condensation heat can be utilized, resulting in a COPh greater than 1. In stark contrast,
under identical conditions, matrix-salt 3 manages to aain only a modest heating perfor-
mance of 1582.7 kJ/kg, accompanied by a signicantly lower COPh of 1.22. These ndings
underscore the noteworthy potential of matrix-salt 2 for ecient heating applications, par-
ticularly under conditions of elevated pressure. The observed trends further emphasize
the advantages of employing vermiculite-based matrix-salt adsorbents in such heating
scenarios, with matrix-salt 2 emerging as a particularly promising candidate for optimiz-
ing heating performance.
Figure 8. Heating performance of matrix-salt adsorbents (adsorption temperature: 25 °C).
Matrix-salt 1
Matrix-salt 2
Matrix-salt 3
Matrix-salt 4
Figure 8. Heating performance of matrix-salt adsorbents (adsorption temperature: 25 ◦C).
Sustainability 2023, 15, x FOR PEER REVIEW 13 of 17
Figure 8. Heating performance of matrix-salt adsorbents (adsorption temperature: 25 °C).
Figure 9. Coefficient of performance for heating (COPh) of matrix-salt adsorbents (adsorption tem-
perature: 25 °C).
3.3. Performance of Power Generation
The process of desorption in matrix-salt adsorbents generates high-temperature and
high-pressure steam, which can be harnessed as a valuable resource to drive a turbine
generator, thereby contributing to electricity generation. In Figure 10, we are presented
with an overview of the performance of electricity generation within this context. A
Matrix-salt 1
Matrix-salt 2
Matrix-salt 3
Matrix-salt 4
Figure 9.
Coefficient of performance for heating (COPh) of matrix-salt adsorbents (adsorption
temperature: 25 ◦C).
3.3. Performance of Power Generation
The process of desorption in matrix-salt adsorbents generates high-temperature and
high-pressure steam, which can be harnessed as a valuable resource to drive a turbine
generator, thereby contributing to electricity generation. In Figure 10, we are presented
Sustainability 2023,15, 15202 13 of 16
with an overview of the performance of electricity generation within this context. A
detailed analysis of the graph reveals that the matrix-salt adsorption system, leveraging the
pressure differential between the desorption bed and the condenser, exhibits a noteworthy
capacity for electricity generation. For instance, consider a scenario where the desorption
temperature is maintained at 95
◦
C and the condenser temperature is around 25
◦
C, with
the maximum partial pressure ratio (p/po) set at 0.8. Under these conditions, matrix-salt 1
demonstrates a commendable electricity generation capacity, reaching 10.6 kJ/kg. This is
because the high-temperature, high-pressure water vapor desorbed from the adsorption
system can drive the operation of a steam turbine, which, in turn, can drive a generator to
produce electricity. The comparison between other studies and the results of this paper is
shown in Table 3. Upon comparison, it was found that the vermiculite/CaCl
2
/LiCl system
employed in this paper exhibited superior adsorption performance, refrigeration capacity,
and COP (coefficient of performance). Its adsorption performance was 32.5% higher than
that of the activated carbon fiber/CaCl
2
/LiCl system, and its COP was 55.1% higher than
that of the zeolite 13X/CaCl2system.
Sustainability 2023, 15, x FOR PEER REVIEW 14 of 17
detailed analysis of the graph reveals that the matrix-salt adsorption system, leveraging
the pressure differential between the desorption bed and the condenser, exhibits a note-
worthy capacity for electricity generation. For instance, consider a scenario where the de-
sorption temperature is maintained at 95 °C and the condenser temperature is around 25
°C, with the maximum partial pressure ratio (p/po) set at 0.8. Under these conditions, ma-
trix-salt 1 demonstrates a commendable electricity generation capacity, reaching 10.6
kJ/kg. This is because the high-temperature, high-pressure water vapor desorbed from the
adsorption system can drive the operation of a steam turbine, which, in turn, can drive a
generator to produce electricity. The comparison between other studies and the results of
this paper is shown in Table 3. Upon comparison, it was found that the vermicu-
lite/CaCl2/LiCl system employed in this paper exhibited superior adsorption performance,
refrigeration capacity, and COP (coefficient of performance). Its adsorption performance
was 32.5% higher than that of the activated carbon fiber/CaCl2/LiCl system, and its COP
was 55.1% higher than that of the zeolite 13X/CaCl2 system.
Figure 10. Expansion work and power generation performance of matrix-salt adsorbents.
Tab l e 3. Comparison between other studies and the results of this paper.
Type Adsorbent
Salt Solution Components
Adsorption
g/g% Cooling kJ/kg Heating kJ/kg COP COPh
Matrix-salt 1 Activated carbon/CaCl2/LiCl 39.3 850.6 1996.1 0.55 1.31
Matrix-salt 2 Vermiculite/CaCl2/LiCl 266.7 5760.7 11,286.5 0.76 1.49
Matrix-salt 3 AC/Diatomite/CaCl2/LiCl 27.6 597.1 1582.7 0.46 1.22
Matrix-salt 4 Vermiculite/CaCl2 235.9 5096.4 9920.8 0.77 1.50
Reference [21] Zeolite 13X/CaCl2 / 523.4 / 0.49 /
Reference [22] FAPO4-5/CaCl2 136.6 / / / /
Reference [23] LiCl + CH3COONa)/ACF/SiO2 149.7 / / / /
Reference [24] Activated carbon fiber/CaCl2/LiCl 201.3 1476.2 / / /
Figure 10. Expansion work and power generation performance of matrix-salt adsorbents.
Table 3. Comparison between other studies and the results of this paper.
Type Adsorbent
Salt Solution Components
Adsorption
g/g%
Cooling
kJ/kg
Heating
kJ/kg COP COPh
Matrix-salt 1 Activated carbon/CaCl2/LiCl 39.3 850.6 1996.1 0.55 1.31
Matrix-salt 2 Vermiculite/CaCl2/LiCl 266.7 5760.7 11,286.5 0.76 1.49
Matrix-salt 3 AC/Diatomite/CaCl2/LiCl 27.6 597.1 1582.7 0.46 1.22
Matrix-salt 4 Vermiculite/CaCl2235.9 5096.4 9920.8 0.77 1.50
Reference [21] Zeolite 13X/CaCl2/ 523.4 / 0.49 /
Reference [22] FAPO4-5/CaCl2136.6 / / / /
Reference [23] LiCl + CH3COONa)/ACF/SiO2149.7 / / / /
Reference [24] Activated carbon fiber/CaCl2/LiCl 201.3 1476.2 / / /
Sustainability 2023,15, 15202 14 of 16
4. Discussion and Conclusions
These results demonstrate that different matrix-salt adsorbents exhibit varying ad-
sorption performance, with the zeolite-CaCl
2
/LiCl adsorbent showing the highest adsorp-
tion performance while maintaining cost-effectiveness. Furthermore, different matrix-salt
adsorption systems possess diverse refrigeration capabilities. Among them, the zeolite-
CaCl
2
/LiCl adsorption system demonstrates the highest refrigeration performance and
coefficient of performance (COP). This adsorption refrigeration system can be driven by
solar energy as well as industrial waste heat. Various matrix-salt adsorption systems also ex-
hibit distinct heating capabilities. Among them, the zeolite-CaCl
2
/LiCl adsorption system
exhibits the highest heating performance and coefficient of performance for heating (COPh).
This adsorption heating system can be utilized during the winter season. Additionally, the
zeolite-CaCl
2
/LiCl adsorption system can be employed for both desalination of seawater
and electricity generation. It is evident that the zeolite-CaCl
2
/LiCl adsorption system
can fulfill multiple functions, making it a practical, cost-effective, and environmentally
friendly solution.
This study represents a comprehensive exploration of the development and charac-
terization of four distinct matrix-salt adsorbents, employing advanced techniques and
rigorous measurements. Confocal microscopy was employed to unveil detailed micro-scale
insights into the structural attributes of these matrix-salt adsorbents. Additionally, an
adsorption analyzer was utilized to conduct exhaustive tests, meticulously assessing the
adsorption performance of these multifaceted materials. Subsequently, a systematic analy-
sis was undertaken to evaluate the cooling, heating, and electricity generation capabilities
of these matrix-salt adsorbents, yielding valuable insights into their potential applications.
To begin, the vermiculite-based matrix-salt adsorbents were found to possess a distinc-
tive morphology, characterized by a “worm-like” structure, layered architecture, and a
notably substantial pore volume. Moreover, it was evident that vermiculite matrix-salt
adsorbents treated with a LiCl solution outperformed their counterparts treated with a
CaCl2solution in terms of adsorption performance. However, the use of calcium chloride
can effectively enhance the economic viability of the adsorption system, given that the
price of calcium chloride is approximately one-thirteenth that of lithium chloride. This
performance superiority was particularly pronounced at lower p/po (partial pressure ratio)
values, underscoring the favorable adsorption characteristics of LiCl-impregnated vermi-
culite matrix-salt adsorbents. Furthermore, under specific operational conditions featuring
an adsorption bed temperature of 25
◦
C and a p/po partial pressure of 0.8, matrix-salt
2 exhibited remarkable adsorption cooling performance, achieving a cooling capacity of
5760.7 kJ/kg with a coefficient of performance (COP) of 0.75. Additionally, it showcased an
impressive heating capacity of 9920.8 kJ/kg with a heating COPh of 1.51, along with a note-
worthy electricity generation capacity of 10.6 kJ/kg. These collective findings underscore
the multifaceted and promising applications of these matrix-salt adsorbents across various
energy domains, including cooling, heating, and electricity generation. This positions them
as compelling candidates for the development of sustainable and efficient energy systems,
showcasing their potential to contribute significantly to the advancement of clean and
renewable energy technologies.
Funding:
This work was sponsored by the National Natural Science Foundation Project (52271323),
Natural Science Foundation of Chongqing, China (cstc2021jcyj-msxmX1092), the Ministry of Edu-
cation Industry-University Cooperation Collaborative Education (220606517274858, 202102168008,
202102464053), key projects in teaching research and practice of energy and power in higher education
institutions (NDJZW2021Z-21), Shanghai Jiao Tong University Decision Consulting (JCZXSJA2022-
05), Shanghai Jiao Tong University innovation and Entrepreneurship Special Fund, responsible
person, construction of innovation and entrepreneurship talent training system, (CTLD23C 0006 &
CTLD23J0033), Shanghai Jiao Tong University Overseas Student Research Practice Base, Projects for
Higher Education Scientific Research Planning (23SYS0104), PRP Projects, and software of Simdroid.
Institutional Review Board Statement: Not applicable.
Sustainability 2023,15, 15202 15 of 16
Informed Consent Statement: Not applicable.
Data Availability Statement:
The raw/processed data required to reproduce the above findings
cannot be shared at this time as the data also forms part of an ongoing study.
Acknowledgments:
We Thank W.L. Luo, K. Xia, A.F. Cai, H.Y. Shao, W.S. Chen, Y.H. Wang, and A.
Rehman for the test and experiment setup.
Conflicts of Interest:
The author declares that he has no known competing financial interests or
personal relationships that could have appeared to influence the work reported in this paper.
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