4 Dynamic Simulation of Technical Precipitation Processes
119
The process plant (Figs. 4 and 5) enables two different types of experiments: Bulk
and two-zone experiments.
Bulk Experiments (Experimental Setup C)
A standard semi-batch procedure is performed in bulk experiments. Therefore, the
valves to the external loop (3, 4) are closed and the feed pipe is positioned in the
tank reactor (1). Initially, 5.37 L BaCl 2 solution was poured into the tank reactor,
which corresponds to 50% of final filling. The rotational velocity was adjusted to the
target value. After the process started, the Na 2 SO 4 solution was added through the
feed pipe by using a defined feed volume flow Q prim until a total addition volume
of 5.37 L Na 2 SO 4 solution was reached. Subsequently, probes of solid product were
taken at position P in the STR.
Two-Zone Experiments (Experimental Setup D)
The feed pipe in two-zone experiments is not positioned inside the tank reactor (A).
Instead, it is positioned in the external mixing reactor (C). The valves to the external
loop were opened and Pump 2 was adjusted to the calculated value for the circulation
flow. The stirring rotational speed was always adjusted to N = 300 rpm, as the stirred
tank represented the well-mixed BF. At the start of the process, the Na 2 SO 4 solution
was added through the feed pipe into D, until a total addition volume of 5.37 L
Na 2 SO 4 solution was reached. Sampling was carried out at position P in the STR.
2.2.3 Analytics
The volume-based PSD q 3 (L)(m
−1
) for particles from steady-state experiments was
measured by dynamic light scattering (DLS) using a Zetasizer Nano ZS by Malvern.
Additionally, scanning electron microscopy (SEM) was used as a second measurement technique to calculate the number-based PSD q 0 (L)(m
−1
). Probes for SEM
analysis were centrifuged three times at 11,000 rpm, including two intermediate
washing steps with deionized water. Subsequently, the product was dried for 24 h at
50 °C in a drying cabinet and sputtered with 3.5 nm platin for the investigation in a
LEO 1530 SEM. Diameters of 500 particles at different locations were determined
by graphical evaluation to calculate the q 0 (L) distribution.
The particle sizes for dynamic semi-batch experiments exceeded the measurement
range of DLS, as the mixing intensity in the STR is several orders lower than the one
reached in CIJMs. Therefore, we measured the particle size for these experiments by
static light scattering (SLS) using Mastersizer 3000 or 3000E by Malvern. Measurements were carried out in deionized water using a Hydro EV wet dispersion system
by Malvern. Samples were measured with a laser occlusion of 10%, a refractive
index of n r = 1.643 and an absorption coefficient of α abs = 0.1.
119
The process plant (Figs. 4 and 5) enables two different types of experiments: Bulk
and two-zone experiments.
Bulk Experiments (Experimental Setup C)
A standard semi-batch procedure is performed in bulk experiments. Therefore, the
valves to the external loop (3, 4) are closed and the feed pipe is positioned in the
tank reactor (1). Initially, 5.37 L BaCl 2 solution was poured into the tank reactor,
which corresponds to 50% of final filling. The rotational velocity was adjusted to the
target value. After the process started, the Na 2 SO 4 solution was added through the
feed pipe by using a defined feed volume flow Q prim until a total addition volume
of 5.37 L Na 2 SO 4 solution was reached. Subsequently, probes of solid product were
taken at position P in the STR.
Two-Zone Experiments (Experimental Setup D)
The feed pipe in two-zone experiments is not positioned inside the tank reactor (A).
Instead, it is positioned in the external mixing reactor (C). The valves to the external
loop were opened and Pump 2 was adjusted to the calculated value for the circulation
flow. The stirring rotational speed was always adjusted to N = 300 rpm, as the stirred
tank represented the well-mixed BF. At the start of the process, the Na 2 SO 4 solution
was added through the feed pipe into D, until a total addition volume of 5.37 L
Na 2 SO 4 solution was reached. Sampling was carried out at position P in the STR.
2.2.3 Analytics
The volume-based PSD q 3 (L)(m
−1
) for particles from steady-state experiments was
measured by dynamic light scattering (DLS) using a Zetasizer Nano ZS by Malvern.
Additionally, scanning electron microscopy (SEM) was used as a second measurement technique to calculate the number-based PSD q 0 (L)(m
−1
). Probes for SEM
analysis were centrifuged three times at 11,000 rpm, including two intermediate
washing steps with deionized water. Subsequently, the product was dried for 24 h at
50 °C in a drying cabinet and sputtered with 3.5 nm platin for the investigation in a
LEO 1530 SEM. Diameters of 500 particles at different locations were determined
by graphical evaluation to calculate the q 0 (L) distribution.
The particle sizes for dynamic semi-batch experiments exceeded the measurement
range of DLS, as the mixing intensity in the STR is several orders lower than the one
reached in CIJMs. Therefore, we measured the particle size for these experiments by
static light scattering (SLS) using Mastersizer 3000 or 3000E by Malvern. Measurements were carried out in deionized water using a Hydro EV wet dispersion system
by Malvern. Samples were measured with a laser occlusion of 10%, a refractive
index of n r = 1.643 and an absorption coefficient of α abs = 0.1.