Nutrient release characteristics and coating homogeneity of biopolymer coated urea as a function of fluidized bed process variables

Abstract

The present study investigates the effect of fluid‐bed process parameters on the diffusion coefficient of nitrogen release and coating homogeneity of controlled‐release urea (CRU) produced in a rotary fluidized bed using polyvinyl‐alcohol‐modified starch as a coating material. An existing mathematical model was used to estimate the diffusion coefficient. The coefficient of variance of size distribution and coating mass variation are reported as a measure of coating homogeneity. Statistical analysis suggested that the most influential process variables that govern urea release characteristics and coating homogeneity were (a) fluidizing gas temperature and (b) coating time. A moderate spray rate combined with longer coating time yielded the lowest diffusion coefficient for nutrient release. Elutriation as the result of elevated fluidizing gas temperature allowed a higher diffusion coefficient due to lower coating thickness. Burst release patterns were observed for granules with coating imperfections. The augmented temperature of fluidizing gas had a negative effect on coating mass and size distribution of CRU granules but the influence of longer coating time was positive.

Experimental methods in chemical engineering: Preface

“…We identified and collated keywords that represent physical and physicochemical properties (pressure, temperature, time), instruments and derived properties (XRD, XPS, viscosity, pH), [4][5][6][7] mathematical methods (CFD, tomography), [8,9] and statistical tests, and experimental design like response surface methodologies. [10,11] To illustrate relationships between the network data, we generated bibliometric maps with the VOSViewer software tool. [12] It identified three clusters of properties with a similar focus ( Figure 1).…”

Production and Characterization of Controlled Release Urea Using Biopolymer and Geopolymer as Coating Materials

“…The CRU based on synthetic polymers produced promising results in terms of longevity of nitrogen release [3][4][5]. However, there are many drawbacks with respect to cost, non-biodegradability, operational feasibility, and ease of application of the final product [6].…”

“…For example, different starches were modified by (i) borax/urea [13], (ii) polysulfone [14], and (iii) polyvinyl alcohol/boric acid [15], and used as coating materials to produce CRU with nitrogen release time as low as 0.05, 5.0, and 8.0 h, respectively. The development of starch based films in which urea fertilizer is impregnated into a matrix of starch (with necessary additives) is commonly reported in the literature as controlled release vehicles; however, the controlled release films have the issue of ease of application in the fields [16].The dip coating or simple immersion technique is used in various studies for the production of CRU that has the drawback of aggregates formation due to poor evaporation of solvent and the subsequent development of coating heterogeneities [6].…”

Experimental methods in chemical engineering: Reactors—fluidized beds

“…Engineers select fluidized beds to achieve economies of scale for catalytic reactions that are highly exothermic, endothermic, or explosive, for catalysts that deactivate in seconds and minutes, and for chemistry that requires multiple dosing cycles (redox reactions). Together with catalysis, other applications include combustion, filtration of particles, drying, and coating of solid particles . Despite the many advantages of fluidized beds, researchers are reluctant to study kinetics in these reactors, instead favouring fixed bed reactors.…”

“…Together with catalysis, other applications include combustion, filtration of particles, drying, and coating of solid particles. [1,2] Despite the many advantages of fluidized beds, researchers are reluctant to study kinetics in these reactors, instead favouring fixed bed reactors. Fluid beds operate isothermally while radial and axial temperature gradients complicate interpreting fixed bed kinetic data; intraparticle mass transfer resistance is orders of magnitude lower in fluidized bed powders because of the smaller particle size (although, researchers grind pellets to a smaller size to study kinetics in fixed beds); solids are completely backmixed, while in fixed beds the oxidation state or coking varies axially and radially; we sample solids on-line in a fluidized bed but is problematic in fixed beds.…”