DEVELOPMENT OF A CO2 SEQUESTRATION MODULE BY INTEGRATING MINERAL ACTIVATION AND AQUEOUS CARBONATION

Maroto-Valer, M. Mercedes ; Andresen, John M. ; Alexander, George

Pennsylvania State University

关键词: Surface Area;    Chemical Activation;    Titration;    Comminution;    Dissolution;   

DOI  :  10.2172/836207
RP-ID  :  NONE
RP-ID  :  FG26-03NT41809
RP-ID  :  836207

美国|英语

来源: UNT Digital Library

【 摘 要 】

Mineral carbonation is a promising concept for permanent CO{sub 2} sequestration due to the vast natural abundance of the raw minerals, the permanent storage of CO{sub 2} in solid form as carbonates, and the overall reaction being exothermic. However, the primary drawback to mineral carbonation is the reaction kinetics. To accelerate the reaction, aqueous carbonation processes are preferred, where the minerals are firstly dissolved in solution. In aqueous carbonation, the key step is the dissolution rate of the mineral, where the mineral dissolution reaction is likely to be surface controlled. In order to accelerate the dissolution process, the serpentine can be ground to very fine particle size (<37 {micro}m), but this is a very energy intensive process. Alternatively, magnesium could be chemically extracted in aqueous solution. Phase I showed that chemical surface activation helps to dissolve the magnesium from the serpentine minerals (particle size {approx}100 {micro}m), and furthermore, the carbonation reaction can be conducted under mild conditions (20 C and 650 psig) compared to previous studies that required >185 C, >1850 psig and <37 {micro}m particle size. Phase I also showed that over 70% of the magnesium can be extracted at ambient temperature leaving amorphous SiO{sub 2} with surface areas {approx} 330m{sup 2}/g. The overall objective of Phase 2 of this research program is to optimize the active carbonation process developed in Phase I in order to design an integrated CO{sub 2} sequestration module. During the current reporting period, Task 1 ''Mineral activation'' was initiated and focused on a parametric study to optimize the operation conditions for the mineral activation, where serpentine and sulfuric acid were reacted, as following the results from Phase 1. Several experimental factors were outlined as having a potential influence on the mineral activation. This study has focused to date on the effects of varying the acid concentration, particle size, and the reaction time. The reaction yields and the characterization of the reaction products by ICP/AES, TGA, and BET analyses were used to describe the influence of each of the experimental variables. The reaction yield was as high as 48% with a 5M acid concentration, with lower values directly corresponding to lower acid concentrations. ICP/AES results are indicative of the selective dissolution of magnesium with reaction yields. Significant improvements in the removal of moisture, as observed from TGA studies, as well as in the dissolution can be realized with the comminution of particles to a D{sub 50} less than 125 {micro}m. A minimum threshold value of 3M concentration of sulfuric acid was determined to exist in terms of the removal of moisture from serpentine. Contrary to expected, the reaction time, within this design of experiments, has been shown to be insignificant. Potentially coupled with this unexpected result are low BET surface areas of the treated serpentine. These results are issues of further consideration to be addressed under the carbonation studies. The remaining results are as expected, including the dissolution of magnesium, which is to be utilized within the carbonation unit. Phase 1 studies have shown that carbonation reactions could be carried out under a milder regime through the implementation of NaOH titration with the magnesium solution. The optimization of acid concentration, particle size, and reaction temperature will ultimately be determined according to the carbonation efficiencies. Therefore and according to the planned project schedule, research efforts are moving into Task 2 ''Aqueous carbonation'' as the redesign of the reactor unit is nearly completed.