Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2009, 54 (1), xxxx Progress on the gas hydrate process for CO 2 /N 2 and CO 2 /H 2 separation using a large scale apparatus Praveen Linga 1 , Rajnish Kumar 1,2 , John A. Ripmeester 2 , Peter Englezos 1 1. Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z3 2. Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, ON, Canada K1A 0R6 Introduction Energy related activities are by far the largest source of greenhouse gas emissions and more specifically carbon dioxide. Due to the emission of carbon dioxide, the production and use of energy from fossil fuels is linked to the global environmental problem known as the greenhouse effect. Separation of CO 2 from a gas mixture can be accomplished through a variety of methods such as cryogenic fractionation, selective adsorption by solid adsorbents, gas absorption and membrane separation 1-3 . Aaron and Tsouris 4 reviewed in detail all processes available for recovery of CO 2 from a flue gas mixture including some which are still at the laboratory stage and concluded the absorption with monoethaolamine (MEA) is the best method. However the regeneration of the solvent makes the absorption process energy intensive. Separation of CO 2 from a flue gas mixture and its compression are the largest contributors to the cost 5-7 . The need to reduce costs motivates further research into the subject. CO 2 capture via gas hydrate formation is among the new concepts for CO 2 capture 4,8 . Clathrate or gas hydrates are ice-like inclusion crystals formed by small molecules like methane, ethane, carbon dioxide and water at suitable temperature, pressure and material availability conditions 9-12 . When gas hydrate crystals are formed from a mixture of gases the concentration of these gases in the hydrate crystals is different than that in the original gas mixture 13 . Post combustion capture (CO 2 /N 2 separation). The input to the proposed process is a flue gas after the removal of particulates and SO X . Treated flue gas from power plants contains 15-20% CO 2 , 5-9 % O 2 and rest N 2 . Since N 2 and O 2 form hydrate crystals at approximately the same conditions the treated flue gas is considered a CO 2 /N 2 mixture. A conceptual process flow sheet was presented for recovery of carbon dioxide from a flue gas (16.9% CO 2 /rest N 2 ) mixture in three stages 14 . However, the operating pressure required for the process is high; the first stage requires 10 MPa. This problem can be alleviated by the use of additives that will lower the hydrate formation conditions without affecting the kinetics and the separation efficiency or CO 2 recovery. The need for a lower pressure process was recognized early and the addition of tetrahydrofuran (THF) was recommended for the flue gas separation based on thermodynamic measurements 8 . The addition of THF even in small quantities considerably reduces the operating pressure. Linga et al. 15 presented thermodynamic and kinetic data obtained from a semi batch stirred tank reactor studying the effect of THF on the hydrate process to capture CO 2 from a flue gas mixture. They also presented a medium pressure clathrate process operating at 273.7 K and 2.5 MPa which combines three hydrate formation stages with a membrane separation stage to recover CO 2 from a flue gas mixture. The process uses 1 mol % THF and nearly 50% of CO 2 is recovered in the first two hydrate stages and 37% in the third one. Even though, the operating pressure is reduced significantly, the rate of hydrate formation and the overall gas consumption for hydrate formation was less compared to the high pressure process without THF 14,15 . Pre-combustion Capture (CO 2 /H 2 separation). Linga et al. 14 employed a CO 2 /H 2 mixture containing 39.2 mol% CO 2 corresponding to a typical composition of a fuel gas mixture from an integrated gasification combined cycle (IGCC) to form hydrate. It was found that the hydrate crystals contained a higher percent of CO 2 on a water-free basis. A conceptual process flow sheet for recovery of carbon dioxide from a fuel gas mixture in two stages was presented. 14 However, the high operating pressure requires significant energy for compression. For the separation of CO 2 from the fuel gas mixture, a suitable additive is propane 16 . Kumar et al. 17 studied the kinetics of hydrate formation from a CO 2 (38.1%)/H 2 (59.4%)/C 3 H 8 (2.5%) gas mixture and proposed a conceptual process flow sheet to recover CO 2 and H 2 . The addition of small amount of propane (2.5%) reduces the operating pressure from 7.5 MPa to 3.8 MPa without compromising the separation efficiency. The conceptual process flow sheet for simultaneous production of CO 2 and H 2 is shown in figure 1. The only drawback is that the rate of hydrate formation and the overall gas consumption for hydrate formation was less compared to the high pressure process without propane. Increasing the separation efficiency would further reduce the amount of CO 2 leaving the lean phase from the first stage. Recently, Kumar et al. 18 based on molecular level studies reported that CO 2 /H 2 mixed hydrate exhibits a self preservation effect similar to that of CO 2 hydrate. Figure 1. Conceptual process flow sheet for simultaneous production of CO 2 and H 2 via a hybrid hydrate/membrane process 19 . The objective of this work is to demonstrate the hydrate based separation process for CO 2 capture from flue gas and fuel gas mixtures at a larger scale. A key objective of the new apparatus is to enhance the rate of hydrate formation and also to increase the CO 2 recovery or separation efficiency of the process. The rate of hydrate formation and the separation efficiency of CO 2 can be improved by having a better contact of water and gas during hydrate formation. Experimental section Apparatus. Detailed description of the apparatus (crystallizer and asssociated instrumentation and control system is available elswhere 19,20 . Procedure. Procedures to carry out hydrate kinetic experiments and CO 2 recovery determination (separation experiment) are all described in detail in the literature 13,14 . Briefly, hydrate formation kinetic experiments were conducted in a high pressure vessel