The reaction extraction is prospective in potassium dihydrogen phosphate (KDP) crystallization with the advantages of easy scale-up and low energy consumption. Hence, crystallization by reactive extraction is also regarded as a promising approach for the production of KDP, which is generally acknowledged in academic circles. As a result of high stirring rate, the crystals impact the wall surface and cause erosion of the wall and attrition of crystals. It is noteworthy that the particle attrition is an unneglected link in the reactive extraction crystallization. It could lead to the degradation of industrial product quality, and result in a series of environmental problems. However, the influence of the crystal attrition in the reactive extraction crystallization has long been ignored by scholars. In this study, KDP is prepared by reactive extraction from phosphoric acid and potassium chloride with trioctylamine-isoamyl alcohol (TOA) as extracting agent. The effects of the reactive extraction-crystallization process (extraction system temperature, stirring rate, and phase ratio) on the grain size of the products are quantified by single-factor experiments in order to determine the optimal conditions for the coupled process. In order to investigate the attrition degree of the extracted crystals, the attrition characteristics of KDP are investigated in a laboratory-scale stirring type crystallizer (STC). An exponential decay attrition model is proposed to describe the time-dependent attrition behavior of crystals under different conditions. This work could be helpful for the design and optimization of KDP preparation using the extraction method.

The main aim of this study is to remove lignin, which is one of the main colored substance in palm oil mill effluent (POME), by adsorption using activated carbon prepared from palm kernel shell (PKSAC) for POME decolorization in Thailand’s palm industry. First, PKSAC was prepared by a chemical activation method using orthophosphoric acid and the effects of treatment conditions on yield and characteristic of PKSAC were studied. With lower treatment temperature, the yield and specific surface area of PKSAC became higher, and PKSAC with high yield (0.8 at highest) and surface area (1,400×10³ m² kg-AC⁻¹ at highest) could be obtained without extreme elevation of treatment temperature. Second, batch equilibrium adsorption of the model POME containing lignin was conducted using the prepared PKSAC to study the adsorption performance of PKSAC. The obtained PKSAC could effectively adsorb and remove lignin in model POME (fractional removal of 0.4 at highest). The adsorption followed the Langmuir equation and the saturated adsorbed amount was correlated with the specific surface area of PKSAC. Subsequently, the feasibility of PKSAC utilization for POME treatment was discussed by a simple material balance in the palm oil production process based on the yield and adsorption performance of PKSAC obtained in the above experiments. The amount of obtained PKSAC was much larger than that necessary for the removal of all lignin in POME in the process. Consequently, the treatment of POME by PKSAC was proposed as a feasible method to remove lignin for POME decolorization in Thailand’s palm industry.

To understand the inclusion of mother liquor in crystals at different sizes, the continuous crystallization of potassium sulfate was investigated. A bench-scale crystallizer of the draft-tube type was employed for both batch cooling and continuous crystallizations. A standard solution of potassium sulfate was employed as the saturated solution at 323 K. The batch cooling crystallization was first performed at 283 K at a rate of 5 K/h, after which the continuous crystallization was performed at 283 K at two different residence times. The crystal size distribution (CSD) of potassium sulfate crystals and the inclusion ratio of mother liquor in the crystals at different sizes were measured. The average size of the crystals was approximately 400–500 µm, and the inclusion ratio was less than 1% for all sizes; however, the small and large crystals contained a considerable amount of mother liquor, and the specific crystals that exhibited the lowest inclusion ratios were investigated. Moreover, an impurity distribution model for the suspension crystals was proposed based on core-aggregation and shell-growth processes.

A pH-responsive permeation system based on a packed layer of polyacrylic acid (PAA)-coated alumina particles is reported. γ-Alumina particles coated with PAA (M_w=25,000) were synthesized using a silane coupling agent and polymerization agent. The permeation of 1.0×10⁻² mol L⁻¹ aqueous solutions through packed layers of the PAA-coated particles decreased in the following order: HCl>CH₃COOH>pure water>CH₃COONa>NaOH. The increased average specific resistance of the packed particle layer with increasing solution pH was ascribed to decreased interparticle spacing due to electrostatic repulsion of the negatively charged PAA chains upon deprotonation of the carboxyl groups at high pH values. Thus, packed layers of PAA-coated alumina particles are a simple, promising, and practical system for pH-dependent permeation.