| Sodium carbonate,commonly known as soda ash,is one of the largest in-volume chemicals produced around the globe,it is also a type of essential raw material consumed in downstream industrial market.Manufacturers typically follow one of the three process routes to produce soda ash,they are the Solvay process,Hou's process and the Trona process.China is the largest soda ash producer with an annual production capacity of around 20 million metric tons,and Solvay process is the mostly adopted among all.However,over the past century,there is very less evolutionary progress towards renovating soda ash processes to address environmental concerns,especially due regard to the high consumption of energy.This research presents an energy-saving,modified Solvay process to replace the high-temperature calcination step of NaHCO3.Monoethanolamine(MEA)is used as an antisolvent to control the phase transition from sodium bicarbonate to carbonate.This research primarily focuses on the development of the novel process and the chemical modeling for the alkanolamine-inorganic salt-water systems.Proprietary results are summarized as below:(1)An experimental set-up was built prior to experimentations.Chemical models were successfully constructed after the determination of solubilities via the dissolution method,and through data regression for NaHCO3,Na2CO3,as well as other inorganic salts in alkanolamine solutions.The Mixed-Solvent-Electrolyte activity coefficient model was selected for adjusting the ion-ion interaction parameters.The newly constructed model can be used to calculate thermodynamic properties for the described system such as solubility,the activity coefficient of electrolytes,water activity,speciation behaviors etc.(2)Based on the preliminary solubility results,the phase transition process,and the crystallization behavior of NaHCO3 in MEA solution were thoroughly researched In particular,the phase transition mechanisms and relevant thermodynamics theories were fully addressed.Experimental results unveiled that NaHCO3 undergoes a complete phase transition into the anhydrous,Na2CO3 phase under 80? in a mixed solvent containing 65 wt.%of(MEA).The obtained solids were in the form of saleable,dense soda ash products;bulk densities up to 1.01 g/cm3 were achieved in the laboratory.It was found for the first time that MEA significantly lowers the water activity if added into water,an influential factor to propel the phase transition process from sodium bicarbonate to anhydrous sodium carbonate.(3)To improve the efficiency for a typical CO2 scrubbing process in a potash solution using MEA or DEA,a chemical model was constructed for the solid-liquid-gas system containing K-CO3-HCO3-MEA/DEA-CO2-H2O,after which a simulation study was conducted using OLI Analyzer.It was found that the absorption efficiency of CO2 can be greatly enhanced if DEA is added into a concentrated carbonate solution,or to use potassium carbonate as a promotor and add into a concentrated DEA solution.(4)To address the environmental concern due to the dumping of soda residues/sludges,this work presents a novel design for the direct preparation of high strength CaSO4·0.5H2O(?-gypsum)using soda residues and waste sulfuric acid.The rich calcium content embedded in soda residues ultimately forms into a type of valuable construction material.Experiment conditions such as temperature,duration of reaction,solid/liquid ratio of sludge,concentration of acids,and the amount of seeded crystals added all played roles in fostering the particle size growth of the produced gypsum crystals.A higher temperature and a longer duration of reaction are required to obtain the preferred morphological structure.By the addition of salt additives,high-strength a-gypsum can be prepared in calcium chloride medium without the need to react under a high temperature,or a pressurized reaction environment. |
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