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Study on Factor Involved in Multi-step Two Phase CO2 Sequestration Process

Hemmati, Azadeh | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46147 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Shaygan Salek, Jalaloddin; Kariminia, Hamid Reza
  7. Abstract:
  8. The increase in CO2 concentration and its effect on ecosystem and global warming make carbon sequestration inevitable for now and future. Ex-situ carbonation of mineral ores is one of the studied sequestration methods. This method is permanent and safe in comparison with others. This process is carried out in four steps and two phases in this dissertation. At the first stage magnesium was extracted from its mineral silicate ore (Mixture of serpentine and olivine) by hydrochloric acid (HCl) and was dissolved in liquid phase as ion. After that the resultant leachate of extraction step was purified from unwanted ions extracted from minerals in two steps by precipitation formed by increasing pH. In final step carbonation takes place by addition of Na2CO3 to purified leachate drop by drop. The white precipitate of magnesium carbonate shaped in this stage. Sodium carbonate solution can be produced from scrubbing of carbon dioxide by NaOH. Acid and base utilized in the whole process was produced from a bipolar electrodialyzer fed by NaCl. At the end of the process the liquid was recycled to the electrodialyzer. The extraction and three stages of precipitation took place in 2 and 4 litres plexiglass reactors. Magnesium extraction performed in atmospheric pressure in 80˚C. According to prevention of acid evaporation from high temperature, the extraction reactor is equipped with condenser and coated by cold water jacket. Each reactor has a three blade mechanical stirrer which can be adjust from 0 to 1000 rpm. Precipitation processes were carried out in semi batch conditions in room temperature. Various factors affected carbonation efficiency and CO2 elimination such as mineral ore particle size, precipitation temperature, the pH of the precipitation reactors outputs and reaction time. The process mass balance physical and chemical analysis of the products, pH optimization of the precipitation reactors and the extraction mechanism studies are goals of this project. The optimum pH for maximum purity and productivity of magnesium carbonate product was found to be 9 and 10 for second and third precipitation reactors respectively. The highest carbonation efficiency expressed as the conversion of Mg ions to magnesium carbonate, reached 82.5wt %. The maximum magnesium content in the final product was 99.82 wt % of MgO when the second precipitation reactor pH was equal to 9.The process mass balance shows that 3.1 tonne of hydrated magnesium carbonate is obtained for each tonne of CO2 sequestrated. And for each tonne of carbon dioxide sequestrated, about 3.74 tonnes of mineral ore are needed as a source of magnesium. At the end it was concluded that the shrinking core model (SCM) is a good match for ore particles less than 20 µm while the extraction of large particle feet to crackling core model (CCM). This thesis was done in cooperation with Institute of Chemical and Engineering Sciences (ICES) in Singapore
  9. Keywords:
  10. Carbon Dioxide ; Mineralization ; Sequestration ; Magnesium Carbonate ; Carbonation ; PH Optimization

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