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－　　－39Morpholine Derivatives as Thermoresponsive Draw Solutes forForward Osmosis DesalinationDue to the rapid increase in the world＇s population, the shortage of fresh water has become a serious sustainability problem. During the past decade, the forward osmosis (FO) process has been proposed and has attracted attention as one solution to this problem The driving force behind transferring water molecules in the FO process is an osmotic pressure gradient, in which water molecules are spontaneously transferred from a lower solute concentration solution (feed solution (FS)) with lower osmotic pressure, to a higher solute concentration solution (draw solution (DS)) with higher osmotic pressure through a semipermeable membrane. The FO process has a great advantage compared with pressure-driven processes such as the reverse osmosis (RO) process, because it can be operated at low or no hydraulic pressure conditions. The FO process also has the potential to achieve a higher water recovery ratio, energy efficiency, and lower fouling. To develop a forward osmosis (FO) process, the selection of draw solutes (DSs) is a critical factor in determining the water permeability of the process. In this search for novel high-performance DSs, various morpholine derivatives were investigated for their thermoresponsive potential. 4-Butylmorpholine (BuMP) showed a preferable minimum lower critical solution temperature for the FO process (31.7°C). The dilute phase of BuMP after phase separa-tion at 70°C showed a low concentration (3.3 wt %) and low osmotic pressure (3.16 bar). In the FO flux test, the water permeability and reverse solute flux of BuMP (55.0 wt %, 28 bar) against water were Jw 2.09 L m-2 h-1 and Js 14.0 g m-2 h-1, respectively. Using 0.6 M NaCl (model seawater) as the feed solution, BuMP (94.6 wt %) could extract water from this model seawater (Jw 0.56 L m-2 h-1). These results indicate a high potential for MP derivatives as DSs and provide new guidance for their development for FO desalination.Keywords : Forward osmosis process, Draw solutes, Seawater desalination, lower critical solution temperature正浸透海水淡水化に向けた温度応答性駆動溶質としてのモルホリン誘導体　世界人口の急激な増加に伴い，淡水の不足が深刻な問題となっている。この問題を解決する一つの方法として，過去 10年間に正浸透（FO）プロセスが提案され注目されてきた。FOプロセスにおける水分子の移動の駆動力は浸透圧勾配であり，半透膜を介して浸透圧の低い供給液（FS）から浸透圧の高い駆動溶液（DS）へと水分子が自発的に移動する 。FOプロセスは，逆浸透（RO）プロセス のような圧力駆動型のプロセスに比べて，低水圧または無水圧の状態で運転できるという大きな利点がある。FOプロセスを開発においては，DSの選択がプロセスの水透過性を決定する重要な要素である。そこで，新たな高性能DSを求めて，様々なモルホリン誘導体の温度応答性について調査を行った。4-Butylmorpholine（BuMP）は，FOプロセスにおいて好ましい下限臨界溶液温度（31.7 ℃）を示した。70 ℃で相分離した後のBuMPの希釈相は，低濃度（3.3 wt%），低浸透圧（3.16 bar）であった。FO流束試験では，BuMP（55.0 wt%, 28 bar）の純水（供給液）に対する透水性Jwは2.09 L m-2 h-1，逆溶質流束Jsは 14.0 g m-2 h-1であった。また，0.6 M NaCl（モデル海水）を供給溶液として用いた場合，BuMP（94.6 wt%）はモデル海水から水を抽出することが可能であった（Jw 0.56 L m-2 h-1）。これらの結果は，MP誘導体のDSとしての高い可能性を示しており，FO脱塩のための開発に新たな指針を与えるものである。キーワード：正浸透プロセス，駆動溶液，海水淡水化，下限臨界溶液温度Journal（掲載誌）Industrial & Engineering Chemistry Research, Vol. 58, No. 27, 12253-12260, June 2019Published PaperAsuka INADA, Tomoki TAKAHASHI, Kazuo KUMAGAI and Hideto MATSUYAMA