An energy‐saving, modified Solvay process for dense soda ash production was proposed to replace the high‐temperature, calcination step of NaHCO3. We found NaHCO3 completely decomposed into anhydrous, Na2CO3 at 353 K in a mixed‐solvent containing at least 65 wt% of monoethanolamine (MEA), which is an amine‐absorbent prevalently used for CO2 capture. A chemical model was built after the determination of solubilities and through data regression for the solid–liquid system: Na‐Cl‐NH4‐CO3‐HCO3‐MEA‐H2O. Reparameterization for paired‐ion interactions were performed via the mixed‐solvent electrolyte model. Thermodynamic analysis elucidated the shift in ion dominance from HCO3− to CO32+, thereby providing the phase transition mechanisms. An exploratory, fed‐batch experiment was implemented to verify the accuracy of the model, for which 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.
To advance the state of knowledge and the conventional method of processing soda residues/sludges, this work presents a novel design for the preparation of high-strength CaSO 4 •0.5H 2 O (a-gypsum). The two steps included are to (1) produce CaSO 4 •2H 2 O (dihydrate, DH) using the discharged soda residues and H 2 SO 4 and (2) transform DH into a-gypsum in a mixed solution with additives at 368 K. A critical step was included to reduce the iron content of the discharged liquor. Thermodynamic properties and phase transition mechanisms were investigated for the solid−liquid systems that involve CaSO 4 . The composition of the obtained raw soda residues, containing mostly CaCO 3 (∼60%), was quantified. The influence of the following parameters was studied on the obtained CaSO 4 •2H 2 O crystals: the duration of the reaction (1.5−3 h), temperature (333− 353 K), solid/liquid ratio of sludge (1:2−1:4), concentration of acids (0.95−2.54 mol/L), and amount of seeded crystals added (5−10%). Marked effects on the evolution of particle sizes and morphological structures were examined. The produced a-gypsum crystals possess an elongated-prismatic or spherical structure, much favored for their excellent injectability and high compressive strength. The most optimal conditions deduced from these experiments can be applied to aid in real industrial design and for the scale-up of the mass production of a-gypsum.
In
this work, the solubility behavior of salts NaCl and NH4Cl was investigated in aqueous diethanolamine (DEA) solution
by varying both temperature and the solvent composition. DEA has been
prevalently used in the postcombustion process to capture CO2, but a limited amount of references can be found pertaining to any
solid–liquid system containing DEA. It was experimentally determined
that the solubility of NaCl decreases, whereas the solubility of NH4Cl increases with the addition of DEA (x′DEA = 0–0.2). The solubility of both salts increases
if temperature is raised from 283 to 353 K. The common-ion effect
was examined for the quaternary system when both salts are present
in the solution. By the regression of solubility data with the Mixed
Solvent Electrolyte model, we proved that readjusting the middle-range
interaction parameters between Cl–-DEA and DEAH+-Cl– would lower the relative deviation
(within 5%) for each proposed ternary system. A comprehensive chemical
model was further constructed based on the newly adjusted interaction
parameters, provided to further analyze system equilibria, as well
as the activity coefficients for aqueous electrolytes.
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