Search

Fluid catalytic cracking (FCC) is one of the most important processes in gasoline/diesel oil production, but the strong endothermic effect accompanied by this reaction often results in the deactivation of the catalyst. In this paper, a novel multifunctional phase change material (PCM)@Catalyst composite was designed and constructed, in which the PCM could be used to store waste heat and regulate the temperature for enhancing the catalytic efficiency of the FCC catalyst. Firstly, a core/shell Al-12wt%Si@Al2O3 was prepared via subsequent vapor treatment and high-temperature calcination of an Al-12wt%Si sphere. The Al species in the Al-12wt%Si served as the source of metal ions and was transformed in situ into a well-defined Al2O3 shell, which greatly improved the thermal stability and prevented the leaking of the Al-12wt% Si core in the high-temperature situation. The PCMs@Catalyst composite was then fabricated by casting the mixed powder of Al-12wt%Si@Al2O3 and Y zeolite into a granulated structure. The FCC results demonstrate that Al-12wt%Si@Al2O3/Y zeolite can optimize product distribution and reduce coke yield. This design concept and synthesis strategy can be extended to the production of a wide variety of hierarchical PCM@Catalyst composites for other reactions. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) can alleviate concerns over energy to some extent by reversibly storing a tremendous amount of renewable and sustainable thermal energy. However, the low thermal conductivity, low electrical conductivity, and weak photoabsorption of pure PCMs hinder their wider applicability and development. To overcome these deficiencies and improve the utilization efficiency of thermal energy, versatile carbon materials have been increasingly considered as supporting materials to construct shape‐stabilized composite PCMs. Despite some carbon‐based composite PCMs reviews regarding thermal conductivity enhancement, a comprehensive review of carbon‐based composite PCMs does not exist. Herein, a systematic overview of recent carbon‐based composite PCMs for thermal storage, transfer, conversion (solar‐to‐thermal, electro‐to‐thermal and magnetic‐to‐thermal), and advanced multifunctional applications, including novel metal organic framework (MOF)‐derived carbon materials are provided. The current challenges and future opportunities are also highlighted. The authors hope this review can provide in‐depth insights and serve as a useful guide for the targeted design of high‐performance carbon‐based composite PCMs. [ABSTRACT FROM AUTHOR]

Electro‐thermal phase‐change materials (PCMs) enable continuous operation of heating‐related processes, which is urgently required for modern thermal‐management devices. Driven by the unmet needs to develop promising electro‐thermal PCMs with low operation voltage and high electro‐thermal storage efficiency simultaneously, unique ZIF@MOF‐derived carbon‐nanotube (CNT)‐penetrated porous carbon supports for electro‐thermal PCMs are introduced. The network structure of the support decreases the resistivity of the composite and ensures a low operation voltage. Furthermore, abundant CNT cores in porous carbon shells facilitate interfacial interaction between the PCMs and the support and realize a rapid heat transformation. It is noted that low thermal conductive porous carbon shells prevent convective heat dissipation at the CNT‐air interface to a great degree which leads to enhanced electro‐thermal storage efficiency. Consequently, the obtained electro‐thermal PCMs exhibit a low operation voltage of 1.1 V and a record‐high electro‐thermal storage efficiency of 94.5%, which shows great potential in thermal management of electronic devices. [ABSTRACT FROM AUTHOR]

• Highly flexible CNTs based monolithic support was constructed via a directional freezing method. • Monolithic CNTs based composite PCM exhibits superior mechanical and thermal properties. • Flexible mechanism of monolithic CNTs based composite PCM is proposed. • This design strategy provides a new direction for future wearable fitting-skin temperature-controlled materials. Currently, most reported composite phase change materials (PCMs) are powdery shape, which require secondary processing for practical applications. Although some monolithic composite PCMs have been developed, their flexibility usually undergoes a remarkable reduction or even complete disappearance when supporting material s are infiltrated with PCMs. To solve this problem, we fabricated a flexible supporting material with a folded layer-bridge network structure by dispersing carbon nanotubes (CNTs) in acetic acid solution of chitosan (CS) with poly(vinyl alcohol) (PVA) using a directional freezing method. Then CS/PVA/CNTs (CPC) scaffold was infiltrated with polyethylene glycol (PEG) to prepare PEG@CPC composite PCM. The resulting flexible composite PCM displays excellent mechanical properties, such as high tensile strength of 2.42 MPa and bending resistance of >100 cycles. Moreover, it displays outstanding thermal properties, such as high crystallinity of close to 100% and encapsulation ratio of 92.6 wt%. This work provides a simple method for preparation of flexible monolithic composite PCMs for many potential applications, such as wearable fitting-skin temperature-controlled materials. [ABSTRACT FROM AUTHOR]

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m−1 K−1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124°) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs. Image 1 • An in situ one-step strategy was proposed to synthesize monolithic silica aerogel-based composite PCMs. • This in situ one-step strategy is universal for the encapsulation of diverse PCMs. • Monolithic silica aerogel-based composite PCMs possess excellent shape stability and high compressive strength (11 MPa). • The silica aerogel-based composite PCMs have low thermal conductivity (0.12 W m−1 K−1) and high latent heat (127.73 J/g). [ABSTRACT FROM AUTHOR]

The leakage of the liquid phase above the melting point and the low thermal conductivity of phase change materials (PCMs), are the major barriers that currently prevent the practical applications of organic PCMs. In this work, a novel supporting material with mutual interpenetrating network structure was developed by the heterogeneous decorations of Cr-MIL-101-NH 2 metal–organic frameworks (MOFs) nanoparticles on the surfaces of carbon nanotubes (CNTs). PCMs, absorbed by capillary force of porous structure and anchored by hydrogen bond interaction of amino groups, were stabilized by the MOFs nanoparticles. The close integration between CNTs and MOFs nanoparticles was conductive to the construction of three-dimensional (3D) and mutual interpenetrating network structured supporting material, which provided continuous heat transfer paths, increased mean free paths for phonons transmission and promoted effectively the reduction of interfacial thermal resistance between the PCM molecules and supporting materials. The thermal conductivity of PEG2000/CNT@Cr-MIL-101-NH 2 shape-stabilized PCM composite was improved by 100.9% over PEG2000/Cr-MIL-101-NH 2 PCM composite. Furthermore, the obtained PEG/CNT@Cr-MIL-101-NH 2 PCM composite showed large phase change enthalpy, good chemical stability and excellent thermal cycling stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The recent efforts concerning porous ss-PCMs were reviewed. • The effects of different porous materials on the phase change behaviors of ss-PCMs are discussed. • This review will lead to a better understanding on the designing and constructing of efficient ss-PCMs. Abstract Phase change materials (PCMs) are widely utilized in latent thermal energy storage and thermal management systems due to their high-energy storage density, high latent heats and excellent capabilities of maintaining almost constant temperature. However, the formidable challenge still seriously limited the performance of PCMs in thermal energy storage systems, such as their leakage and low thermal conductivities. Therefore, appropriate approaches to construct shape-stabilized PCMs (ss-PCMs) and effectively enhance the thermal conductivities are importantly necessary to realize the practical applications of PCMs. Porous supports packaged PCMs provide an effective route for constructing ss-PCMs with enhanced thermal conductivity, mechanical strength, chemical stability and flame resistance. In this review, we aim to assess the advantages/disadvantages of porous materials via summarizing the key research progress on the porous materials (e.g., metal foams, expanded graphite, graphene aerogels, carbon nanotubes, porous minerals, mesoporous silica, etc.) as ss-PCMs supports. The effects of pore size and geometry, surface modification, interaction forces, compositions, etc. on the phase change behaviors of ss-PCMs are summarized and discussed in detail by comparing the different porous materials. We believe that the summary and discussion in the review will lead to a better understanding on the designing and constructing of efficient ss-PCMs, and even shed light on the design for novel porous materials supported ss-PCMs based on the discovered interactions between the porous supports and PCMs. Finally, the future research topics and challenges on porous materials for ss-PCMs development are also prospected with emphasizing on the emergence of new design of porous materials with improved thermal conductivity, high PCMs loading amount and high thermal latent for practical applications. [ABSTRACT FROM AUTHOR]

Energy storage capacity and heat transfer ability are two important indexes for shape-stabilized phase change materials (ss-PCMs). In this paper, a core-sheath CNT@PC was prepared via carbonation of CNT@ZIF-8, simultaneously 3D structural supports were obtained due to the porous carbon (PC) sheath stabilized the CNT@PC network structure. Porous carbon (PC), derived from carbonized metal organic frameworks (MOFs), exhibited high porosity and large specific surface area. PCMs, absorbed by capillary force of porous structure, was stabilized in the pores of PC sheath. Further, the interaction between PCMs and CNTs reduced the interfacial thermal resistance greatly. Carbon nanotubes (CNTs), acting as heat transfer pathways, provided continuous channels for phonons transfer and realized rapid heat transformation between ss-PCMs and external environment. The obtained SA/CNT@PC ss-PCMs exhibited excellent thermal conductivity (1.023 W/mK), large phase change enthepy (155.7 J g −1 ) and high thermal storage capabilities (99.9%). The thermal conductivity of SA/CNT@PC was improved 222.6% and phase change enthalpy was increased 92.6% over SA/PC ss-PCM. SA/CNT@PC with large energy storage density, flexible designation, simple operation and near-constant temperature properties during phase change process shows great potential in waste heat utilization. [ABSTRACT FROM AUTHOR]

• An electro- and photo- driven thermal phase change composite was designed. • Attractive interaction was regulated to promote crystalline-amorphous state transition. • CC facilitates electron and photon penetration, and ZIF reduces the convective heat loss. • ZIF-induced chain effect between PEG and CC enhances the mechanical properties. Metal organic frameworks contain abundant empty space for selectively absorbing phase change materials (PCM) molecules and sometimes chemically transformed. However, the strong attractive interaction between metal organic frameworks and PCM severely blocks sufficient crystalline-amorphous state transition of PCM. Herein, we proposed an attractive interaction engineering strategy on hierarchical zeolitic imidazolate frameworks (ZIF) based phase change materials (polyethylene glycol/carbon cloth@ZIF, PEG/CC@ZIF) for boosting crystalline-amorphous state transition behavior and electro-/photo- driven thermal performance. Carboxyl-modified CC scaffold regulates attractive interaction between ZIF and PEG, which enhances energy storage capacity of the phase change composite. Moreover, ZIF nanoflakes deposited on the surface of CC reduce the convective heat loss at the solid–gas interface, and CC scaffold facilitates electron transportation and photon penetration, thus significantly enhancing electro- and photo- driven thermal energy storage. Furthermore, ZIF-induced chain effect between PEG and CC enhances the mechanical properties of PEG/CC@ZIF. Notably, commercially available transition metal oxide photocatalyst can be uniformly sprayed on the surface of PEG/CC@ZIF through coordination chemical engineering for multi-functional phase change composite. [ABSTRACT FROM AUTHOR]