Stabilization of Gas Hydrate by Addition of Gel and its Application to Gas Storage

利用甲烷作为能源是减少CO_2产生的最佳途径之一。甲烷以甲烷水合物的形式埋藏在深海中。甲烷水合物的稳定和可控生成是其利用的关键技术之一。而对甲烷水合物生长抑制剂的研究主要集中在甲烷水合物的生长抑制剂上。例如，一类生长抑制剂是具有侧基如内酰胺环的聚合物，其在与聚合物主链相邻的每个环的顶部含有酰胺基（-N-C=O）。提出了甲烷水合物稳定化的高分子添加剂。聚合物添加剂的优点是（1）低挥发性，（2）可再循环性，和（3）它们的化学稳定性。我们制备了两种类型的添加剂，（1）水溶性高分子添加剂和（2）水不溶性添加剂。聚丙烯酸（PA）和聚芳胺盐酸盐（PAAm/HCl）不作为甲烷水合物的稳定剂。PA抑制甲烷水合物的形成。PAAm/HCl不能抑制甲烷水合物的生成。我们添加了交联的聚（苯乙烯）颗粒（c-PSt）作为水不溶性添加剂。加入c-PSt后，甲烷-水体系的温度-压力平衡曲线向低温侧移动。这表明c-PSt稳定了甲烷水合物。聚（甲基丙烯酸四氢糠酯）（PTHFMA）也稳定甲烷水合物。水不溶性高分子添加剂c-PSt和PTHFMA的稳定机理在我们的研究中尚不清楚。然而，这些结果表明，高分子添加剂和甲烷水合物表面之间的相互作用是甲烷水合物的稳定和晶体生长的重要因素。

Utilization of methane for energy sources is one of the best approaches for reducing production of CO_2. Methane is buried as methane hydrate form under the deep sea. Stabilization and controlled formation of methane hydrate is a key technology of its utilization. However, growth inhibitor of methane hydrate has been investigated mainly. For example, one class of growth inhibitors are polymers with pendant groups such as a lactam ring, containing an amide group (-N-C=O) at the top of each ring adjacent to the polymer backbone. We proposed the polymeric additives for stabilization of methane hydrate. Merits of polymeric additives are (1) low volatility, (2) recyclability, and (3) chemical stability of them. We prepared two-type additives, (1) water-soluble polymeric additives and (2) water-insoluble ones. Poly (acrylic acid) (PA) and poly (aryl amine) hydrochloride salt (PAAm/HCI) did not act as a stabilizer of methane hydrate. PA inhibited formation of methane hydrate. PAAm/HCI did not inhibit formation of methane hydrate. We added cross-linked poly (styrene) particle (c-PSt) as a water-insoluble additive. Temperature-pressure equilibrium curve of the methane-water system with c-PSt shifted to lower pressure and higher temperature side. This suggests that the c-PSt stabilized methane hydrate. Poly (tetrahydrofurfuryl methacrylate) (PTHFMA) also stabilized methane hydrate. Stabilization mechanism of the water-insoluble polymeric additives, c-PSt and PTHFMA is not clear in our investigation. However, these results suggest that interaction between the polymeric additives and the methane hydrate surface is important factor for the stabilization and crystal growth of the methane hydrate.