Use of multifunctional nanoporous TiO(OH) 2 for catalytic NaHCO 3 decomposition-eventually for Na 2 CO 3 /NaHCO 3 based CO 2 separation technology Bryce Dutcher a , Maohong Fan a,⇑ , Brian Leonard b a Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 72071, USA b Department of Chemistry, University of Wyoming, Laramie, WY 72071, USA article info Article history: Received 15 April 2011 Received in revised form 10 May 2011 Accepted 20 May 2011 Available online 27 May 2011 Keywords: CO 2 capture CO 2 desorption Na 2 CO 3 NaHCO 3 NaHCO 3 decomposition TiO(OH) 2 abstract In general, CO 2 capture from flue gas is a costly procedure, usually due to the energy required for regen- eration of the capture medium. One potential medium which could reduce such an energy consumption, however, is Na 2 CO 3 . It has been well studied as a sorbent, and it is understood that the theoretical energy penalty of use of Na 2 CO 3 for CO 2 separation is low, due to the relatively low heat of reaction and low heat capacity of the material. While it offers some advantages over other methods, its primary downfall is the slow reaction with CO 2 during adsorption and the slow Na 2 CO 3 regeneration process. In an effort to reduce the energy penalty of post-combustion CO 2 capture, the catalytic decomposition of NaHCO 3 is studied. Nanoporous TiO(OH) 2 is examined as a potential catalytic support for a cyclic Na 2 CO 3 /NaHCO 3 based CO 2 capture process. FT-IR, SEM, and XRD characterization of NaHCO 3 supported on nanoporous TiO(OH) 2 treated with different processes indicate that TiO(OH) 2 is stable within the temperature range necessary for such a process, up to about 200 °C. More importantly, the TiO(OH) 2 has a catalytic effect on the decomposition of NaHCO 3 , reducing the activation energy from about 80 to 36 kJ/mol. This significant drop in activation energy could translate into a much lower operating cost for regenerating Na 2 CO 3 . The reaction rate of NaHCO 3 decomposition, or CO 2 desorption, is observed to increase by as much as a factor of ten due to this decrease in activation energy. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Anthropogenic CO 2 is considered a major contributor to global warming. One of the primary sources of anthropogenic CO 2 is the flue gas from fossil fuel-fired power plants. As such, an ideal meth- od of CO 2 abatement is to remove CO 2 from flue gas. Several tech- niques exist to accomplish this, including absorption using liquid solvents, membrane separation, cryogenic separation, and adsorp- tion onto solid sorbents [1–9]. Each technique has its own advan- tages and disadvantages. Currently, the most developed and commercially viable CO 2 separation technology is stripping CO 2 with aqueous amine solu- tions. Due to its many advantages, this technology has been com- monly used to remove CO 2 and other acid gases as impurities from natural gas for over 60 years [1,5]. Study on its use for CO 2 separation from flue gas is fairly recent, however. The solvents have typically been designed for low temperature absorption, be- low the temperatures of typical flue gas, and as such, have poor thermal stability [1,5,10]. The amines cannot only be poisoned by common impurities in the flue gas, such as SO x and NO x gases, but also oxygen [1,5]. Some of the amine can be lost through evap- oration to the gas stream during use, thus requiring replacement [10,11]. Moreover, amines are toxic and corrosive, and therefore are pollutants to the environment. Because of their corrosive prop- erties, amines typically need to be diluted with water; with more water present, more energy is required for desorption of CO 2 . This dilution also lowers the CO 2 capture capacities of amine solutions [1,5,10,11]. In an alternative liquid absorption process, CO 2 is captured by an aqueous alkali metal carbonate solution via the reaction M 2 CO 3 þ CO 2 þ H 2 O $ 2MHCO 3 ðR1Þ where M represents the alkali metal, primarily sodium and potas- sium. In this reversible reaction, carbonation occurs at tempera- tures typical of flue gas, 50–80 °C, and decarbonation is achieved by boiling the solution [12–19]. When M is sodium, R1 can be spe- cifically written as Na 2 CO 3 þ CO 2 þ H 2 O $ 2NaHCO 3 ðR2Þ Using alkali carbonates has several advantages. The primary one is their capital costs; alkali carbonates are readily available and less expensive. Another one is that they are thermally stable; Na 2 CO 3 , for instance, decomposes at temperatures over 800 °C, while some 1383-5866/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2011.05.022 ⇑ Corresponding author. Address: Department of Chemical and Petroleum Engineering, University of Wyoming, 1000 E Univ. Ave., Laramie, WY 72071, USA. Tel.: +1 307 766 5633; fax: +1 307 766 6777. E-mail address: mfan@uwyo.edu (M. Fan). Separation and Purification Technology 80 (2011) 364–374 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur