In order to obtain the basic data in cracking of PE, PP and PS (addition polymerization plastics), experimental investigation was carried out using supercritical water of density of 0.3 g/cm3 at a temperature of 430°C and a pressure of ca. 42 MPa. It was found that these plastics were easily decomposed to oily materials without coke formation and the time required for liquefaction was in the order of PE>PP>PS. The oily products obtained had the main chemical structure of polymers; normal paraffin's for PE, and 1,3,5-cyclohexane for PP. For PS, styrene monomer was first produced, with a gradual increase in ethyl benzene toluene and stable poly-phenyl hydrocarbons with 2-4 rings, which were different, from oligomer of styrene. The amount of them increased with reaction time. When a decomposition reaction occurred in alkali solution, the decomposition rate decreased, but the reaction mechanism seemed to be unchanged.
In order to clarify the mechanism and the effect of mixed-polymer treatment on the reaction rate of hydrothermal cracking in supercritical water, experimental investigation were carried out with mixtures of PE, PP and/or PS at 430°C and a pressure of ca. 42 MPa. Following results were obtained. (1) When a mixture of different kinds of plastics are treated hydrothermally, the plastics, which are more hardly decomposed, can be easily degraded into low molecular weight oily materials by attack of radicals which are generated from the plastics more easily decomposed. (2) The mechanism of attack of radicals on the plastics, which are more hardly decomposed, in the mixed treatment is effective no matter whether the cracking mechanism of these plastics is random scission or depolymerization at the end of main chain. (3) In mixed treatment, the main mechanism of degradation for each plastic is the same as that in separate treatment, so that the main composition of oily product in mixing treatment is similar to that of the mixture of oily products in each separate treatment. But some new materials were also found in the oily product. They are formed by the reaction of radicals from plastics easily decomposed and the products from plastics hardly decomposed, so that they retain the similar structures of main chain structure of the plastics. (4) In either mixed or separate treatment, the composition of oily product by thermal cracking does not differ much from that by hydrothermal cracking in supercritical water. However, much less polymerization among reactive products occurs in the hydrothermal treatment of mixture.
The performance of charcoal bricks made from beer lees (MaltCeramics, MC) was investigated as the material for purification of water breeding goldfish in order to compare with gravel and activated charcoal. The goldfish used in this study discharges 0.409 mg/D·g of TOC, 0.26 mg/D·g of NH4-N, 0.024 mg/D·g of NO3-N and 0.007 mg/D·g of T-P. It was confirmed that MC is useful for the carrier of microorganisms and it is possible to reduce soluble organic matter and soluble nitrogen compound such as NH4-N, NO3-N and NO2-N as same as activated charcoal. In the case of MC, NH4-N is decomposed to form NO2-N and NO3-N within 50 h. NO2-N and NO3-N are the decomposition products of NH4-N substrate and NO2-N is denitrated for 50-80 h. NH4-N and NO2-N are rapidly decomposed, but the denitrification of NO3-N is a very slow reaction. TOC is decreased down to the initial concentration level for 20-30 h. MC contains phosphorus at the ratio of about 2 wt%, which is soluble in water, and some minerals. It is considered that they would activate bacteria in water.
Industrial systems and daily life in Japan are shifting to a society based on recycling to reduce energy and resource consumption. To establish a society based on recycling urban resource recovery centers (mines) are important as places to reduce waste volumes, reusing and recycling valuable materials with application of mineral processing technology. The authors have reviewed applications of mineral processing in urban mines, and recent developments in common separation methods, magnetic separation, gravity separation, flotation, and agglomeration in liquid.