A Novel Technology for Green(er) Manufacturing of CNTs via Recycling of Waste Plastics
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A Novel Technology for Green(er) Manufacturing of CNTs via Recycling of Waste Plastics Chuanwei Zhuo1, Brendan Hall1, Yiannis Levendis1 and Henning Richter2 1 Mechanical and Industrial Engineering, Northeastern University, 334 SN, 360 Huntington Ave., Boston, MA 02115, U.S.A. 2 Nano-C, Inc., 33 Southwest Park, Westwood, MA 02090, U.S.A. ABSTRACT Costly and often highly-flammable chemicals, such as hydrogen and carbon-containing gases, are largely used for carbon supply in current carbon nanotube (CNT) synthesis technologies. To mitigate related economic and safety concerns, we have developed a versatile CNT synthesis sequence, where low-cost and safe-to-handle-and-store waste solid polymers (plastics) are used for in situ generation of hydrogen and carbon-containing gases. Introduction of different waste plastics, such as polyethylene, polypropylene and polystyrene, into a multistage pyrolysis/ combustion/synthesis reactor allows for efficient CNT formation. This process is largely exothermic and scalable. It uses low-cost stainless steel screens to serve both as substrates as well as catalysts for CNT synthesis. This technique enables a solution for both waste plastic utilization and sustainable CNT production. INTRODUCTION The expanding markets for CNT applications place continuously increasing demands on improving the quality and lowering the cost of these materials. Current technology for CNT mass production requires intensive supply of premium fuels and input of external energy [1]. Thus a more sustainable alternative would certainly increase the public acceptance of the quickly developing nano-manufacturing technology. Readily-available alternative fuels, such as existing waste streams, should be necessarily explored. Over the past fifty years the proliferation of nonbiodegradable man-made materials, such as plastics, has increased dramatically [2]. As these polymers are mass-produced and inexpensive, they are readily discarded, thereby creating a vast solid waste and pollution issue. Recycling efforts in past years have partly alleviated this problem; however, as recycled plastics are generally devalued products, i.e., they cannot be used in their original applications, the economics of this practice do not always work out [2]. Recently, a slump in the overall recycling market, following depressed commodity markets, has accentuated this problem. This threatens to erode the recycling markets, the associated infrastructure and, subsequently, the public’s mindset for recycling. Generating high value products, such as CNTs, from recycled waste plastics may not only reverse this trend and restore, even enhance, the motives for recycling, but also lower the cost of CNTs and in turn further overcome the hurdles of their large-scale use in consumer and industrial products. Moreover, such conversion into CNTs further reduces the amount of waste plastics, providing greener solutions for both environments and CNT industries. The feasibility of utilizing plastics for CNT synthesis is related to the fact that plastic main
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