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Hede, P.D., Bach, P., Jensen, A.D.
"Top-spray fluid bed coating: Scale-up in terms of relative droplet size and drying force"
Powder Technology, 184 (3), pp. 318-332. (2008)


Top-spray fluid bed coating scale-up experiments have been performed in three scales in order to test the validity of two parameters as possible scaling parameters: The drying force and the relative droplet size. The aim was to be able to reproduce the degree of agglomeration as well as the mechanical properties of the coated granules across scale. Two types of placebo enzyme granule cores were tested being non-porous glass ballotini cores (180-350 μm) and low porosity sodium sulphate cores (180-350 μm). Both types of core materials were coated with aqueous solutions of Na2SO4 using Dextrin as binder. Coating experiments were repeated for various drying force and relative droplet size values in three top-spray fluid bed scales being a small-scale (Type: GEA Aeromatic-Fielder Strea-1), medium-scale (Type: Niro MP-1) and large-scale (Type: GEA MP-2/3). The tendency of agglomeration was assessed in terms of particle size fractions larger than 425 μm determined by sieve analysis. Results indicated that the particle size distribution may be reproduced across scale with statistical valid precision by keeping the drying force and the relative droplet size constant across scale. It is also shown that none of the two parameters alone may be used for successful scaling. Morphology and microscope studies indicated that the coating layer is homogenous and has similar structures across scale only when both the drying force and the relative droplet size were fixed. Impact and attrition tests indicated that it is possible to produce granules with similar attrition and impact strength across scale and that the two types of mechanical properties are inversely related. © 2007 Elsevier B.V. All rights reserved.


Sloth, J., Bach, P., Jensen, A.D., Kiil, S.
"Evaluation method for the drying performance of enzyme containing formulations"
Biochemical Engineering Journal, 40 (1), pp. 121-129. (2008)


A method is presented for fast and cheap evaluation of the performance of enzyme containing formulations in terms of preserving the highest enzyme activity during spray drying. The method is based on modeling the kinetics of the thermal inactivation reaction which occurs during the drying process. Relevant kinetic parameters are determined from differential scanning calorimeter (DSC) experiments and the model is used to simulate the severity of the inactivation reaction for temperatures and moisture levels relevant for spray drying. After conducting experiments and subsequent simulations for a number of different formulations it may be deduced which formulation performs best. This is illustrated by a formulation design study where 4 different enzyme containing formulations are evaluated. The method is validated by comparison to pilot scale spray dryer experiments. © 2007 Elsevier B.V. All rights reserved.


Hede, P.D., Bach, P., Jensen, A.D.
"Validation of the flux number as scaling parameter for top-spray fluidised bed systems"
Chemical Engineering Science, 63 (3), pp. 815-828. (2008)


Top-spray fluidised bed coating scale-up experiments have been performed in three scales in order to test and validate the Akkermans flux number as possible scale-up parameter. Coating operations were performed on low porosity sodium sulphate cores (180 - 350 μ m) coated with aqueous solutions of Na2 SO4 using Dextrin as binder in three top-spray fluidised bed scales, i.e. a small-scale (type: GEA Aeromatic-Fielder Strea-1), medium-scale (type: Niro MP-1) and large-scale (type: GEA MP-2/3). Following the parameter guidelines adapted from the original patent description, the flux number was tested in the preferred range of 3.5-4.5 as well as with a value of 4.7 in a total of 24 experiments. The agglomeration tendency was observed to decrease with increasing flux number on an overall basis, but coating conditions with flux number values below 4.5 resulted in a complete collapse of the bed. Coating conditions with flux number values of 4.5 and 4.7 were however successful in terms of agglomeration tendency and match of particle size fractions, but indicated in addition a strong influence of nozzle pressure. The present paper suggests even narrower boundaries for the flux number compared to the patent descriptions, and adds further new guidelines for the successful scale-up of top-spray fluidised bed coating systems in terms of the flux number. © 2007 Elsevier Ltd. All rights reserved.


Nielsen, L.K., Simonsen, O.
"Chapter 5 Design of liquid enzyme products with built-in liquid detergent stabilization system"
Computer Aided Chemical Engineering, 23, pp. 149-163. (2007)

Enevoldsen, A.D., Hansen, E.B., Jonsson, G.
"Electro-ultrafiltration of amylase enzymes: Process design and economy"
Chemical Engineering Science, 62 (23), pp. 6716-6725. (2007)


Electro-ultrafiltration (EUF) has previously resulted in flux improvements in the order of 3-7 times during filtration of amylase enzymes [Enevoldsen, A.D., Hansen, E.B., Jonsson, G., 2007. Electro-ultrafiltration of industrial enzyme solutions. Journal of Membrane Science 299, 28-37]. To determine the energy balance for EUF, the influence of TMP, crossflow velocity and conductivity of the enzyme solution is studied and compared to conventional ultrafiltration (UF). EUF is favorable when filtering solutions of high concentration, while UF is favorable when filtering solutions of low concentration. The dimension of the feed channel, especially the height and the conductivity are crucial for the feasibility of the EUF process. The channel height should be below 1.0 mm and the conductivity less that 2 mS/cm before EUF is economically feasible. © 2007 Elsevier Ltd. All rights reserved.


Beier, S.P., Enevoldsen, A.D., Kontogeorgis, G.M., Hansen, E.B., Jonsson, G.
"Adsorption of amylase enzyme on ultrafiltration membranes"
Langmuir, 23 (18), pp. 9341-9351. (2007)


A method to measure the static adsorption on membrane surfaces has been developed and described. The static adsorption of amylase-F has been measured on two different ultrafiltration membranes, both with a cutoff value of 10 kDa (a PES membrane and the ETNA10PP membrane, which is a surface-modified PVDF membrane). The adsorption follows the Langmuir adsorption theory. Thus, the static adsorption consists of monolayer coverage and is expressed both as a permeability drop and an adsorption resistance. From the adsorption isotherms, the maximum static permeability drops and the maximum static adsorption resistances are determined. The maximum static permeability drop for the hydrophobic PES membrane is 75%, and the maximum static adsorption resistance is 0.014 m2·h·bar/L. The maximum static permeability drop for the hydrophilic surface-modified PVDF membrane (ETNA10PP) is 23%, and the maximum static adsorption resistance is 0.0046 m2·h· bar/L. The difference in maximum static adsorption, by a factor of around 3, affects the performance during the filtration of a 5 g/L amylase-F solution at 2 bar. The two membranes behave very similarly during filtration with almost equal fluxes and retentions even though the initial water permeability of the PES membrane is around 3 times larger than the initial water permeability of the ETNA10PP membrane. This is mainly attributed to the larger maximum static adsorption of the PES membrane. The permeability drop during filtration exceeds the maximum static permeability drop, indicating that the buildup layer on the membranes during filtration exceeds monolayer coverage, which is also seen by the increase in fouling resistance during filtration. The accumulated layer on the membrane surface can be described as a continually increasing cake-layer thickness, which is independent of the membrane type. At higher concentrations of enzyme, concentration polarization effects cannot be neglected. Therefore, stagnant film theory and the osmotic pressure model can describe the relationship between flux and bulk concentration. © 2007 American Chemical Society.


Enevoldsen, A.D., Hansen, E.B., Jonsson, G.
"Electro-ultrafiltration of industrial enzyme solutions"
Journal of Membrane Science, 299 (1-2), pp. 28-37. (2007)


To reduce the problems with fouling and concentration polarization during crossflow ultrafiltration of industrial enzyme solutions an electric field is applied across the membrane. The filtration performance during electro-ultrafiltration (EUF) has been tested with several enzymes. Results show that EUF is an effective method to filter high concentrated solutions at low crossflow. The flux improved 3-7 times for enzymes with a significant surface charge at an electric field strength of 1600 V/m compared to conventional UF. The greatest improvement is observed at high concentration. Not all enzymes can be filtered with EUF, mainly due to a low surface charge and impurities in the feed solution. Using a pulsed electric field did not improve the flux compared to a constant field. Gel electrophoresis experiments of the enzymes appear to be a useful method for estimating the influence of the electric field. © 2007 Elsevier B.V. All rights reserved.


Hede, P.D., Bach, P., Jensen, A.D.
"Small-scale top-spray fluidised bed coating: Granule impact strength, agglomeration tendency and coating layer morphology"
Powder Technology, 176 (2-3), pp. 156-167. (2007)


The degree of agglomeration and impact strength of Na2SO4 cores (all in the size range of 200-300 μm) coated with aqueous solutions of sodium sulphate and dextrin as a function of several process and formulation variables have been investigated. The coating process was performed in a modified small-scale GEA Aeromatic-Fielder Strea-1 top-spray fluidised bed, and the impact strength was tested in bulks using a Pneumatic Impact Gun, in which granule samples of 0.5 g were exposed to ten repeated impacts at 10 m/s. Using an unreplicated double 24 - 1 fractional factor design, two regression models were derived from experimental data describing quantitatively the degree of agglomeration and impact strength respectively. The agglomeration model suggests in accordance with previous studies that increasing the nozzle pressure as well as coating-solution-dry-matter-concentration decreases the tendency of agglomeration. The consistency between the agglomeration model and new experimental data is concluded to be satisfactory. The impact strength model indicates increasing impact strength with increasing nozzle pressure, coating solution-dry-matter-concentration and bed temperature. These tendencies may be influenced by the large extent of droplet penetration, as observed in additional coating droplet penetration and coating layer morphology studies in the present paper. The validation of the impact strength model shows that the model clearly follows overall experimental tendencies. The derivation of these quantitative models may be seen as a first step towards the development of processes for production of unagglomerated enzyme granules with high mechanical strength and contribute to an improved understanding of fluid bed processes and products. © 2007 Elsevier B.V. All rights reserved.


Enevoldsen, A.D., Hansen, E., Jonsson, G.
"Enzyme recovery by crossflow electro-ultrafiltration"
Desalination, 199 (1-3), pp. 55-56. (2006)

Jørgensen, K., Jensen, A.D., Sloth, J., Dam-Johansen, K., Bach, P.
"Comments to "analysis of constant rate period of spray drying of slurry" by Liang et al., 2001"
Chemical Engineering Science, 61 (6), pp. 2096-2100. (2006)


In the study by Liang et al. [2001. Analysis of constant rate period of spray drying of slurry. Chemical Engineering Science 56, 2205-2213] the Darcy flow of liquid through a pore system of primary particles to the surface of a slurry droplet was applied for the constant rate period. Steep primary particle concentration gradients inside ∼25μm droplets with a primary particle size of 0.2μm were observed. Unfortunately, the boundary condition at the droplet surface for the parabolic second-order PDE did not conserve the solid mass in the droplet, and the plots for the primary particle concentration profiles in the droplets were incorrect. In this letter we derive the correct boundary condition equation. Furthermore, we show that the primary particle concentration profiles inside the droplets are flat when the primary particles have a size of 0.2μm . We conclude that the model presented by Liang et al. is unable to predict the formation of hollow particles. © 2005 Elsevier Ltd. All rights reserved.


Jørgensen, K., Bach, P., Jensen, A.D.
"Impact and attrition shear breakage of enzyme granules and placebo particles-application to particle design and formulation"
Powder Technology, 149 (2-3), pp. 157-167. (2005)


The strength and breakage mechanisms of detergent enzyme granules and typical core materials used for enzyme granules (all of size 500-600 μm) have been investigated under impact and shear stress conditions to simulate the stresses experienced in a detergent factory. In an Impact Tester, single-particle experiments were performed at impact velocities of 8-25 m/s. Multiple (bulk) particle experiments were performed in an Attrition Shear Cell (ASC), where the particles were exposed to shear strains of about 1250 and normal stresses of 1-30 kPa. For coated enzyme granules the results indicate that the primary breakage mechanism after repeated impacts at 10 m/s is chipping associated with local delamination. Damages to the coating layer may expose the underlying enzyme-containing layer or core and lead to the release of enzyme-active dust. Markedly lower enzyme dust release was obtained by incorporating the enzyme into the core of the granule as compared to a layer-structured enzyme distribution. Furthermore, the results indicated that stronger enzyme granule core materials provide a better impact resistance of the final enzyme granule towards the release of enzyme-active dust. Coating layers of inorganic salts and water-soluble polymers are observed to enhance the breakage resistance of the enzyme granules tremendously. The impact and shear resistance of four different placebo enzyme granule core particles were investigated. A transition from chipping to fragmentation as the main breakage mechanism was observed at impact velocities from 8 to 20 m/s. Experiments performed with attrition shearing indicated that the extent of breakage depend on surface friction and particle sphericity as well as intraparticular forces. The results obtained in this work are of importance for the design and formulation of mechanically resistant enzyme granules. © 2004 Elsevier B.V. All rights reserved.