Absorption of pure carbon-dioxide gas in a foam-bed reactor
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - Ia: Extraction & Remediation (T1-4a)
Keywords: Gas absorption, Desorption, Carbonation, Barium sulfide, Foam-bed reactor, Pure gas
Carbon dioxide is the most important of greenhouse gases. The “Global Warming Theory” predicts that increased amounts of carbon-dioxide gas in the atmosphere tend to enhance the greenhouse effect and thus contribute to the global warming. Around 24,000 million tons of carbon-dioxide gas, equivalent to about 6,500 million tons of carbon, are released per year worldwide. As per the data collected by United Nations in 2002, around 5,872 million tons of carbon-dioxide gas (24.3% of total carbon-dioxide emission) are released in the US, 3,682 million tons (15.3%) in the European Union, and 1,220 million tons (5.1%) in India. Removal of carbon-dioxide gas from large-scale gaseous emissions as from thermal power plants, etc. is a real challenge.
Foam-bed reactor offers a novel method of removal of carbon-dioxide gas. Removal of carbon-dioxide gas by treating it with aqueous barium-sulfide solution has been experimentally investigated here in a semi-batch foam-bed reactor. This carbonation reaction can be carried out using carbon-dioxide gas obtained from smoke stack furnaces or power-plant exhausts, thereby reducing the air pollution arising from these major sources. The hydrogen-sulfide gas produced in the reaction reacts faster with amines as compared to carbon-dioxide gas, and thus it can be removed with a relative ease. It can also be converted into sodium hydrosulfide by reacting with caustic solution (possibly in another foam-bed reactor), or converted into elemental sulfur in a Claus sulfur-recovery unit. Alternatively, the hydrogen-sulfide gas can be split to produce hydrogen gas. These end products would have a good market value too.
Experimental data have been generated and analyzed in this investigation to assess the role of the reverse diffusional flux of the desorbed hydrogen-sulfide gas in the actual performance of a foam-bed reactor. The experiments are carried out using pure carbon-dioxide gas, to focus on liquid-phase and interfacial resistances. The variables studied are height of foam bed, initial concentration of barium sulfide in aqueous solution, gas-flow rate, volume of the barium-sulfide solution charged into the reactor, and the surfactant type, and its concentration in the aqueous solution.
The experimental results indicate that the conversion in the reactor increases with an increase in the initial concentration of barium sulfide in the aqueous solution, and with gas-flow rate. The conversion decreases with an increase in the volume of the solution charged into the reactor. The variation of two main parameters, viz. the height of foam bed and concentration of surfactant, reveals the important role of desorption of hydrogen-sulfide gas in governing the observed performance of the foam-bed reactor. The optimum foam height was found to be 0.4 m, and the optimum surfactant concentration to be 1000 ppm. Three different types of surfactant were explored during the experimentation, namely, non-ionic (Triton X-100), cationic (CTAB), and the anionic (like SDS, LABS, stearic acid, Monoxol OT and Teepol). The aqueous solutions of barium sulfide did not foam with any of these anionic surfactants. Comparison of the performances for the non-ionic and cationic surfactants shows that the nature of surfactant does not appreciably affect the performance of the foam-bed reactor.
See the full pdf manuscript of the abstract.
Presented Wednesday 19, 12:12 to 12:30, in session Sustainable & Clean Technologies - Ia:Extraction-Remediation (T1-4a).
