Akinobu Sasaki

Design of recycling system for poly(methyl methacrylate) (PMMA). Part 1: recycling scenario analysis

IntroductionIn this series of papers, we present a poly(methyl methacrylate) (PMMA) recycling system design based on environmental impacts, chemical hazards, and resource availability. We evaluated the recycling system by life cycle assessment, environment, health, and safety method, and material flow analysis.PurposePrevious recycling systems have not focused on highly functional plastics such as PMMA, partly because of lower available volumes of waste PMMA compared with other commodity plastics such as polyethylene or polypropylene. However, with the popularization of PMMA-containing products such as liquid crystal displays, the use of PMMA is increasing and this will result in an increase in waste PMMA in the future. The design and testing of recycling systems and technologies for treating waste PMMA is therefore a high research priority. In this study, we analyze recycling of PMMA monomers under a range of scenarios.MethodsBased on the differences between PMMA grades and their life cycles, we developed a life cycle model and designed a range of scenarios for PMMA recycling. We obtained monomer recycling process inventory data based on the operational results of a pilot plant. Using this process inventory data, we quantified life cycle greenhouse gas (LC-GHG) emissions and fossil resource consumption, and we calculated the LIME single index.Results and discussionPMMA produces more than twice the amount of GHG emissions than other commodity resins. Through scenario and sensitivity analyses, we demonstrated that monomer recycling is more effective than mechanical recycling. Operational modifications in the monomer recycling process can potentially decrease LC-GHG emissions.ConclusionsHighly functional plastics should be recycled while maintaining their key functions, such as the high transparency of PMMA. Monomer recycling has the potential to achieve a closed-loop recycling of PMMA.

Bubble Characteristics of Circulating Three-Phase Fluidized Bed

The behavior of bubbles in a circulating gas-liquid-solid fluidized bed was investigated in a column of 25.4 mm ID and 5 m height with glass beads of 5 different sizes by using a bore scope. The distribution of bubble size followed the logarithmic normal distribution law. At high liquid velocity the effects of particle size and solid concentration on volume-surface mean diameter of bubbles were negligible because of liquid turbulent motion.