STUDY ON FIXATION OF CARBON-DIOXIDE IN CLATHRATE HYDRATE

As a step in investigating the possibility of CO2 clathrate for the fixation of carbon dioxide in deep seas, experiments were performed at temperatures from 277 to 281K, stirring rate range from 300 to 1600 min-1, salt concentration range from 0 to 5.7% as NaCl and pressure range from 3.5 to 9.1 MPa. Furthermore, simulations for CO2 clathrate sedimentation in deep sea were performed. The following results were obtained. (1) The rate of CO2 clathrate formation is proportional to the difference between the fugacity of CO2 and the equilibrium fugacity at the experimental temperature and to the interfacial area. (2) Large particles of CO2 clathrates must be formed so that they should sediment to the settled deep sea bottom. In the present study, we evaluate the validity of this countermeasure from the view-points of mass balance, energy balance and dynamics. First we determined the desired amount of nutrients based on the PNC ratio in the plant biota in the ocean, and assumed several ways of fertilization. Second, we evaluated its response by a numerical box model taking the unsteady-state recirculation of the inorganic/organic carbon and nutrients, and carbon fixation by plant biota into account. The results indicated that this technique possibly can have the expected effect on the restraint of increse in atmospheric CO2 within a few years, while its effect on the oceanic organic carbon in the surface is only doubling the present thin concenration for a hundred years' fertilization. The energy evaluation also indicated that the amount of CO2 produced from the manufacture and transportation of both N and P fertilizers is no more than 9% of the amount that is expected to be taken up into the ocean from the atmosphere.