A new apparatus to enhance the rate of gas hydrate formation: Application to capture of carbon dioxide. Linga, Praveen; Kumar, Rajnish; Lee, Ju Dong; Ripmeester, John; Englezos, Peter
IntroductionClathrate hydrate crystallization has been regarded as a potential unit operation for seawater desalination, gas fractionation, gas storage and other applications (Chatti et al., 2005;Davidson, 1973;Englezos, 1993;Makogon, 1981). During the past 15 years the emphasis has been on natural gas storage and transportation (Gudmundsson et al., 2000;Matsuda et al., 2006;Thomas and Dawe, 2003) and on carbon dioxide capture from flue and fuel gases (Aaron and Tsouris, 2005;Kang and Lee, 2000;Klara and Srivastava, 2002;Linga et al., 2007a;Seo et al., 2005). Hydrate formation is also a factor when considering injection of CO 2 into the ocean (Lee et al., 2003;Tsouris et al., 2004Tsouris et al., , 2007. If hydrate is to be formed from liquid water then the efficient contacting of the gas with water plays a key role in the above applications. This is because agglomeration of the hydrate crystals creates a barrier to increased conversion in stirred tank reactors (Englezos, 1996). A schematic illustrating how agglomeration of floating crystals creates a barrier to efficient gas/water contacting which in turn limits the conversion in a stirred tank reactor is provided by Linga (2009). Therefore, the search for efficient gas hydrate formation vessels or reactors is ongoing.Although there are several configurations and patents available in the literature for production of gas hydrates, the choice of the best multi phase reactor is still unknown (Heinemann et al., 2001;Iwasaki et al., 2002;Mori, 2003;Waycuilis and York, 2002;Yamasaki et al., 2003). Mori (2003) reviewed the subject and concluded that there is a need to focus on developing hydrate reactors with much improved hydrate forming efficiencies. One of the new approaches underway to enhance the kinetics of hydrate formation is to employ a fixed bed column with silica gel as a medium to capture CO 2 from flue and fuel gases via hydrate crystallization (Adeyemo et al., in press;Seo et al., 2005) or to employ a slurry bubble column (fluidized bed) arrangement to enhance the rate of hydrate formation (Hashemi, 2009) or use a non-stirred batch reactor with cyclopentane as a promoter (Zhang and Lee, 2009).A small size (volume = 323 cm 3 ) stirred vessel was used in our laboratory to demonstrate how hydrate crystallization can be employed to capture CO 2 from flue and fuel gases (Kumar et al., 2009c;Linga et al., 2007a Linga et al., ,b, 2008. It has also been used to assess the storage potential of natural gas in structure H hydrate systems . The kinetics of gas hydrate formation in this vessel is influenced by mass transfer in a short period of time due to agglomeration of hydrates at gas/liquid interface (Linga, 2009). The need for the enhancement of the rate of gas hydrate formation is more acute when additives are used. For the CO 2 capture applications additives such as tetrahydro...