Progress of polymer reaction engineering:From process engineering to product engineering

Polymer reaction engineering studies the design,operation,and optimization of reactors for industrial scale polymerization,based on the theory of polymerization kinetics and transfer processes(e.g.,flow,heat and mass transfer).Although the foundation and development of this discipline are less than80 years,the global production of polymers has exceeded 400 million tons per annum.It demonstrates that polymer reaction engineering is of vital importance to the polymer industry.Along with the matu rity of production processes and market saturation for bulk polymers,emerging industries such as information technology,modern transportation,biomedicine,and new energy have continued to develop.As a result,the research objective for polymer reaction engineering has gradually shifted from maximizing the efficiency of the polymerization process to the precise regulation of high-end product-oriented macro molecules and their aggregation structures,i.e.,from polymer process engineering to polymer product engineering.In this review,the frontiers of polymer reaction engineering are introduced,including the precise regulation of polymer chain structure,the control of primary aggregation structure,and the rational design of polymer products.We narrow down the topic to the polymerization reaction engineering of vinyl monomers.Moreover,the future prospects are provided for the field of polymer reaction engineering.

Modulation doping of p-type Cu_(12)Sb_(4)S_(13)toward improving thermoelectric performance

The commercial viability of thermoelectric(TE)devices relies heavily on two factors:cost reduction and efficiency enhancement.In this study,we first produce p-type Cu_(12)Sb_(4)S_(16-x)(x=0,3,4)using a low-temperature bottom-up approach and demonstrate Cu_(12)Sb_(4)S_(13)to show the best TE performance among the three tested compositions.Subsequently,the TE energy conversion efficiency of Cu_(12)Sb_(4)S_(13)is further enhanced by optimizing its electronic band structure through the incorporation of small amounts of tel-lurium.At an optimal Te content of 5 mol%,more than a twofold increase in the TE figure of merit(zT)is obtained.To gain insight into the mechanism of improvement on the transport properties of the mate-rial,we compare the interphase transport mechanism by incorporating nanodomains of different metals(Ag and Cu)into the Cu_(12)Sb_(4)S_(13)matrix.The improved electrical conductivity obtained with Cu_(12)Sb_(4)S_(13)-Te nanocomposites is attributed to a charge flooding of the Cu_(12)Sb_(4)S_(13)surface.In contrast,excessive down-ward band-bending at the interphases of Ag/Cu metal-semiconductor drastically reduces the electrical conductivity.Besides,a weighted mobility(μw)analysis shows a dominant thermal activation of carri-ers in Cu_(12)Sb_(4)S_(13)-Te nanocomposites.In this material,a strong decrease in lattice thermal conductivity is also found,which is associated with a phonon-carrier scattering mechanism.Our work shows the impor-tance of proper band-engineering in TE nanocomposites to decouple electrical and thermal transport to enhance TE performance,and the efficacy ofμw for electrical and thermal transport analysis.

Chemical recycling of polyolefin waste: from the perspective of efficient pyrolysis reactors

Polyolefins,widely used for packaging,construction,and electronics,facilitate daily life but cause severe environmental pollution when discarded after usage.Chemical recycling of polyolefins has received widespread attention for eliminating polyolefin pollution,as it is promising to convert polyolefin wastes to high-value chemicals(e.g.,fuels,light olefins,aromatic hydrocarbons).However,the chemical recycling of polyolefins typically involves high-viscosity,high-temperature and high-pressure,and its efficiency depends on the catalytic materials,reaction conditions,and more essentially,on the reactors which are overlooked in previous studies.Herein,this review first introduces the mechanisms and influencing factors of polyolefin waste upcycling,followed by a brief overview of in situ and ex situ processes.Emphatically,the review focuses on the various reactors used in polyolefin recycling(i.e.,batch/semi-batch reactor,fixed bed reactor,fluidized bed reactor,conical spouted bed reactor,screw reactor,molten metal bed reactor,vertical falling film reactor,rotary kiln reactor and microwave-assisted reactor)and their respective merits and demerits.Nevertheless,challenges remain in developing highly efficient reacting techniques to realize the practical application.In light of this,the review is concluded with recommendations and prospects to enlighten the future of polyolefin upcycling.