The Development, Modeling and Partial Validation of a Continuous Process for the Production of PIX-Sulfate

Abstract

Kemira Kemia AB produces a water treatment chemical named ”PIX-Sulfate”,
where “PI” stands for “poly iron x”, and the “x” represents a conjugate ion, such
as chloride or sulfate, in this case, sulfate. The main process for producing PIX
Sulfate at Kemira’s plants today is to dissolve magnetite in diluted sulfuric acid and
to oxidize the resulting liquid using oxygen. Currently, this process is carried out
by producing PIX-Sulfate in batches. However, by instead utilizing a continuous
production mode, a more efficient process can be acquired.
Therefore, a new and continuous process was developed using simulations and phys
ical experiments at laboratory and pilot scales. The proposed process has three
main units: a sulfuric acid mixing unit, a dissolution unit, and an oxidation unit.
The sulfuric acid mixing unit is a continuous stirred-tank reactor in which sulfuric
acid and water are mixed. The dissolution unit is a column, containing a packed
bed of magnetite. The diluted sulfuric acid enters the column at the bottom and
passes through the voids of the magnetite bed. Meanwhile, magnetite is dissolved
and forms a PIX-Sulfate intermediate. This intermediate exits at the top of the
column. The oxidation unit is a column which contains a number of trays. The
intermediate enters at the top and trickles downwards from tray to tray via overflow
spouts. Above each tray, there is a gap in which oxygen gas resides, allowing it to
react with the intermediate, forming the final PIX-Sulfate product.
Experimental work on the dissolution unit demonstrated practical feasibility and
significantly higher production capacity per reactor volume compared to the batch
process. A mathematical model for the continuous dissolution column was devel
oped and validated with pilot-scale data, showing generally good agreement, though
deviations due to non-ideal flow characteristics did appear. An adiabatic reactor de
sign was identified as optimal for industrial applications due to its lower complexity
in construction and control. Further, the flow distribution across the column’s cross
sectional area was identified as one of the most critical design parameters.
For the oxidation unit, reaction kinetics from the literature were reviewed to con
struct a model, leading to an optimal continuous oxidation unit design which was
simulated under various scenarios. It was found that the efficiency of this unit is
highly dependent on the mass transfer rate of oxygen from the gas to the liquid
phase, emphasizing the importance of tray design as a critical parameter.
A data collection system was successfully implemented for automated data acqui
sition, and the possibility of using absorbance measurements to estimate the iron
concentration in the PIX-Sulfate product was demonstrated. Finally, a complete
process design with heat integration was presented, based on a production capacity
of 9 m3/h of PIX-Sulfate. While the proposed process appears promising, further
real-world testing is required to determine whether it is practically feasible.

Popular Abstract

Approximately 80% of the world’s wastewater is discharged into natural water bod
ies without adequate treatment, posing significant environmental and health risks.
To address this growing concern, factories that produce water treatment chemicals
are being constructed worldwide. Thus, there’s a pressing need to make these fac
tories more efficient, energy-saving, and sustainable. One crucial chemical in water
treatment is PIX-Sulfate, a black, thick liquid containing a large amount of iron.
When added to contaminated water, it effectively removes impurities, helping to
purify the water. One of the most common methods for producing PIX-Sulfate to
day is by dissolving an iron mineral, magnetite, in sulfuric acid mixed with water
and then treating the resulting liquid with oxygen gas. Traditionally, PIX-Sulfate
is produced this way by using a batch process, which can be less efficient and more
energy-intensive.
In this master’s thesis, a more efficient factory design for producing PIX-Sulfate was
developed and proposed. This new design adopts a continuous production method.
Instead of producing the chemical in separate batches, raw materials continuously
f
low into the factory, and the PIX-Sulfate product exits at a constant rate. This
approach allows a factory of similar size to produce more product while consuming
less energy compared to the batch process. To validate the new design, approxi
mately half of it was tested in real-world conditions through laboratory experiments
and a mini-factory setup. Computer simulations were also utilized to predict the
performance of these components in a full-scale factory. The remaining parts of the
design were assessed using simulations alone, identifying critical features necessary
for the factory to function as intended.
In summary, the new continuous production design for PIX-Sulfate shows signifi
cant promise in enhancing efficiency and sustainability in water treatment chemical
manufacturing. While the initial results are promising, further testing is required
to determine its feasibility for full-scale factory operations.

• author: Gudmundsson, Theodor
• supervisor: Niklas Andersson
• organization: Chemical Engineering (M.Sc.Eng.)
• course: KETM05 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: chemical engineering, industrial water treatment chemical, poly iron, conjugate ion
• language: English
• id: 9177248
• date added to LUP: 2025-01-27 13:53:47
• date last changed: 2025-01-27 13:53:47