Effects of cyclodextrins (CD) on hydrate formation kinetics were investigated. Several kinds of cyclodextrins, such as α-CD, β-CD, β-CD polymers, and β-CD modified with methyl and triacetyl groups were tested as additives for hydrate formation of xenon, with a concentration range of 0−5 wt %. Induction time for hydrate formation was reduced by the addition of any of the CDs; however, no clear relationship between the structure of CDs and the reduction effect was observed. The three-phase equilibrium pressure (H−V−L w) was unaffected by the addition of the CDs, except for β-CDs modified with methyl or triacetyl groups. The hydrate formation rate, which was expressed as a rate constant based on the chemical potential, increased with the addition of α-CD, β-CD, and β-CD polymers. β-CD polymer showed the highest acceleration effect on the xenon hydrate at about 1 wt %; the rate constant was about three times larger than that for pure water. Contrastingly, modified β-CD and dextrin with a straight chain structure reduced the hydrate formation rate. β-CD polymer was subsequently applied as an acceleration additive for the methane hydrate formation process, and it was found that the addition of β-CD polymer increased the methane hydrate formation rate up to five times as compared to that for pure water.
A new process was proposed for the total recycling of shellfish wastes combining the carbonate production with a high-pressure carbon dioxide aqueous solution and methane fermentation. The shell part of shellfish, mainly composed of calcium carbonate was dissolved into the aqueous solution of carbon dioxide at about 30 bar or acetic acid, and will be separated from the flesh part. On the other hand, the flesh part can be anaerobically fermented to produce biogas mainly composed of methane. Two options can be considered for the treatment of the carbonate solution; recovered as pure calcium carbonate, or disposed of into the ocean as a carbon sequestration process. Process feasibility was examined by obtaining key parameters through laboratory-scale experimental studies. The dissolution kinetics of blue mussel samples was examined with a high-pressure CO 2 solution and acetic acid to elucidate the influences of CO 2 pressure, temperature, stirring speed, and the sample size on the dissolution kinetics. The biogas production rate was examined with the flesh part of the sample mussel either treated with an acid solution or untreated. The biogas production rate was found to be almost unaffected by the acid exposure. Based on the experimental results, the process design and evaluation was carried out. The cost of the process with CO 2 treatment and recovery of calcium carbonate was about 21,000 JPY/tshellfish waste, that of ocean disposal process was 44,000 JPY/t-shellfish waste, and that of acetic acid treatment process was 16,000 JPY/t-shellfish waste, respectively. The proposed processes are competitive with the conventional waste disposal cost, while being simpler and more environmentally benign.
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