An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl 3 solution was used to promote the conversion of calcium sulfate dihydrate (DH) to hexagonal prismatic α-HH with high strength at atmospheric pressure. The phase transition kinetics of FGD gypsum was experimentally investigated under conditions: AlCl 3 (2−2.5 m), MgCl 2 (0−0.4 m) existing in raw FGD gypsum, and the solid−liquid ratio (or solid content %) range of 0.1−2 at 363 K. It was found that increasing the concentrations of MgCl 2 in AlCl 3 solution accelerated the conversion. The uniform large hexagonal prism HH product was obtained at the folowing optimal conditions: 2.5 mol/kg AlCl 3 , 0.4 mol/kg MgCl 2 , solid−liquid ratio of 2, and equilibration time of 2 h at 363 K. The phase diagram of the AlCl 3 -MgCl 2 -H 2 O system was determined by measuring solubility of solids. The E-NRTL activity model was used to construct the phase transition diagram of CaSO 4 in AlCl 3 −MgCl 2 media and to judge the stable range of DH and HH.
The
reaction kinetics of peracetic acid from acetic acid and hydrogen
peroxide in a helical capillary microreactor was investigated and
modeled via regression of the measured conversion rate of hydrogen
peroxide. It was found that the activity of the proton in the sulfuric
acid solution played a significant role in the synthesis as a catalyst.
The activities of the proton were calculated with the ELECNRTL equation
and used to obtain a kinetic model with apparent activation energies
of peracetic acid synthesis and hydrolysis of 53.63 and 54.45 kJ/mol,
respectively. A new continuous process for industrial manufacture
of peracetic acid solution (30 wt %) was proposed, where the reacted
solution from the microreactor is distilled to separate unreacted
reactants and sulfuric acid, which are recycled as a feed. The feasibility
of the new process was validated by Aspen Plus simulation and economic
assessment.
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