Søren Kiil

Enzyme-based antifouling coatings: a review

Abstract A systematic overview is presented of the literature that reports the antifouling (AF) protection of underwater structures via the action of enzymes. The overall aim of this review is to assess the state of the art of enzymatic AF technology, and to highlight the obstacles that have to be overcome for successful development of enzymatic AF coatings. The approaches described in the literature are divided into direct and indirect enzymatic AF, depending on the intended action of the enzymes. Direct antifouling is used when the enzymes themselves are active antifoulants. Indirect antifouling refers to the use of enzymes to release an active biocide with AF activity. For direct AF, several patents have been granted, and a commercial product has been launched. However, the achievement of an efficient broad-spectrum AF coating based on a single or a few enzymes has not yet been achieved. An indirect AF coating is not yet available commercially. The technology is mainly limited by the instability of substrate supply, whether the substrates are found in the surrounding seawater or in the coating itself. Legislative issues regarding which part(s) of an enzyme system should be regarded as biocidal for product registration purposes are also considered. The above question currently remains unanswered for technologies utilising indirect enzymatic AF.

Controlled drug delivery from swellable hydroxypropylmethylcellulose matrices: model-based analysis of observed radial front movements

This work is related to the on-going development of mathematical models describing transient drug delivery from hydroxypropylmethylcellulose (HPMC) matrices. Recently, experimental data providing a detailed mapping of radial swelling, diffusion, and erosion front movements in a high-viscosity HPMC matrix were published [J. Controlled Release 70 (2001) 383]. Using these and other data for verification of simulations, a detailed mathematical model, taking into account water-induced swelling, drug dissolution, and external and internal mass transport resistances of dissolved drug, has been developed. In contrast to earlier models, explicit equations for the rate of movement of the swelling, diffusion and erosion fronts, with the relevant physical properties of drug and HPMC matrix contained in the equations, were derived. Simulations have been compared to transient experimental data for three drugs of very different water solubility and a good agreement was found, taking into account the uncertainty of key input parameters. Furthermore, the model predicts the presence of the drug particle translocation phenomenon observed experimentally. However, continued swelling of the matrix, subsequent to the disappearance of the swelling front, could not be described by the present model. The front-tracking approach illustrated is of relevance in the development of detailed and accurate models of drug delivery from swellable cylindrical matrices involving both axial and radial diffusion.

Full-scale co-firing of straw and coal

Abstract Co-firing of biofuels and coal in power plants is considered by the Danish utilities as a potential tool in reducing CO 2 emissions. To test this, full-scale measurements were carried out for 1 week on a 250 MW e pulverized coal fired unit using 10–20% straw (thermal basis). With an increased fraction of straw in the fuel, a net decrease in NO x and SO 2 emissions was measured. The SO 2 emission decreased partly due to the lower sulfur content of the fuel per MJ, but also due to higher sulfur retention in the ash. The NO emission decreased solely due to lower conversion of fuel-N. An increased fraction of straw in the fuel blend resulted in a higher potassium content, but no significant increase in slagging or fouling was observed. Only small amounts of deposit at the lower part of the radiant superheater and little slagging at the furnace walls were observed as a result of co-firing straw and coal. No significant effects on the performance of the desulfurization plant were detected, which may be due to the short test period, probably not allowing the desulfurization process to reach steady-state operation.

Optimisation of a wet FGD pilot plant using fine limestone and organic acids

Abstract The effects of adding an organic acid or using a limestone with a fine particle size distribution (PSD) have been examined in a wet flue gas desulphurisation (FGD) pilot plant. Optimisation of the plant with respect to the degree of desulphurisation and the residual limestone content of the gypsum has been the aim of the work. In contrast to earlier investigations with organic acids, all essential process parameters (i.e. gas phase concentration profiles of SO 2 , slurry pH profiles, and residual limestone in the gypsum) were considered. Slurry concentrations of adipic acid in the range of 0– 7 mM were employed. The overall degree of desulphurisation in the plant increased from 83% at 0 mM to 90% at 3 mM and the residual limestone level was reduced from 4.6 to 1.4 wt % . Increasing the slurry concentration of adipic acid above 3 mM gave only a slightly higher degree of desulphurisation. The wet FGD model of Kiil et al. (Ind. Eng. Chem. Res., 37 (1998) 2792) was extended to include buffer systems and verified against experimental data. Subsequently, the model was used as a tool to identify the optimal organic acid dissociation constants (as pK a values) and concentration levels at different operating conditions. At a holding tank pH of 5.5 and a temperature of 50°C, simulations with Bryozo limestone and a monoprotic buffer suggested that the optimum pK a value is between 4.5–5.5 and 5.5–6.5 with respect to the degree of desulphurisation and the residual limestone level, respectively. Adipic acid has pK a values close to these ranges ( pK 1 =4.40 and pK 2 =5.41 at 50°C). Changing limestone type (in the absence of organic acids) to one with a lower average particle size (i.e. from 20 to 4 μm ) increased the overall measured degree of desulphurisation from 83 to 87% and reduced the residual limestone level from 4.6 to 1.3 wt % . Increasing the holding tank pH level from 5.5 to 5.8 affected the degree of desulphurisation and the residual limestone level only slightly. At holding tank pH levels between 5.88 and 5.90, a high degree of desulphurisation was observed, but the residual limestone content in the gypsum increased to somewhere between 19 and 30 wt % , making this pH range unsuitable for use in a full-scale plant. The investigations have shown that both the addition of organic acids and the use of a limestone with a fine PSD can be used to optimise wet FGD plants.

Presence and effects of marine microbial biofilms on biocide-based antifouling paints

Abstract Marine microorganisms are capable of successfully colonizing toxic surfaces through the formation of biofilm structures. In this article, most of the literature reporting the presence of marine biofilms on chemically-active antifouling paints is briefly reviewed. Of special concern is the influence of the dense extracellular polymeric substances (EPS) matrix on the release rate of the compounds involved in antifouling paint performance (i.e. active compounds and controlled-release binder molecules). A deeper understanding of these phenomena is of interest for both environmental legislators and paint formulators.

Mathematical Modelling of a Self-Polishing Antifouling Paint Exposed to Seawater: A Parameter Study

A fundamental mathematical model for a self-polishing antifouling paint was used to conduct a parameter study. The aims were to show how a mathematical model can reduce the amount of experimental work needed to estimate the behaviour of self-polishing antifouling paints at different conditions, and to suggest ways of controlling biocide release rates. A case study with an antifouling paint based on the well-known tributyltin self-polishing copolymer system showed that the rate of paint polishing was influenced, to various degrees, by the following parameters: seawater pH and concentration of NaCl, pigment particle size, pigment volume concentration of the paint, the rate of pigment dissolution, and the pore size distribution of the leached layer. The modelling approach can be applied to any type of self-polishing antifouling paint provided that kinetic, solubility and diffusivity data are available for the pertinent rate-influencing steps.

Active pharmaceutical ingredient (API) production involving continuous processes – A process system engineering (PSE)-assisted design framework

A systematic framework is proposed for the design of continuous pharmaceutical manufacturing processes. Specifically, the design framework focuses on organic chemistry based, active pharmaceutical ingredient (API) synthetic processes, but could potentially be extended to biocatalytic and fermentation-based products. The method exploits the synergic combination of continuous flow technologies (e.g., microfluidic techniques) and process systems engineering (PSE) methods and tools for faster process design and increased process understanding throughout the whole drug product and process development cycle. The design framework structures the many different and challenging design problems (e.g., solvent selection, reactor design, and design of separation and purification operations), driving the user from the initial drug discovery steps--where process knowledge is very limited--toward the detailed design and analysis. Examples from the literature of PSE methods and tools applied to pharmaceutical process design and novel pharmaceutical production technologies are provided along the text, assisting in the accumulation and interpretation of process knowledge. Different criteria are suggested for the selection of batch and continuous processes so that the whole design results in low capital and operational costs as well as low environmental footprint. The design framework has been applied to the retrofit of an existing batch-wise process used by H. Lundbeck A/S to produce an API: zuclopenthixol. Some of its batch operations were successfully converted into continuous mode, obtaining higher yields that allowed a significant simplification of the whole process. The material and environmental footprint of the process--evaluated through the process mass intensity index, that is, kg of material used per kg of product--was reduced to half of its initial value, with potential for further reduction. The case-study includes reaction steps typically used by the pharmaceutical industry featuring different characteristic reaction times, as well as L-L separation and distillation-based solvent exchange steps, and thus constitutes a good example of how the design framework can be useful to efficiently design novel or already existing API manufacturing processes taking advantage of continuous processes.

Dynamic simulations of a self-polishing antifouling paint exposed to seawater

A mathematical model for a self-polishing antifouling paint exposed to seawater was extended to handle dynamic simulations. The aim has been to investigate, quantitatively, the transient responses of the paint to changes in seawater temperature, pH, concentration of NaCl, and ship speed. The simulation study revealed that polishing and biocide release rates for a paint present on a ship bottom rarely reach stable conditions, because of the slow response of the paint to changes in temperature and ship speed. It was also found that the paint behavior stabilizes more rapidly from a temperature or speed increase than from temperature or speed reductions. These results are essential for the testing of paints on ships and useful information in the development of novel self-polishing antifouling paints.The modeling approach underlying the simulations can be applied to any type of self-polishing antifouling paint provided that sufficient kinetic, solubility, and diffusivity data are available for the pertinent rate steps influencing the paint behavior.

Simulation studies of the influence of HCl absorption on the performance of a wet flue gas desulphurisation pilot plant

Abstract The mathematical model of Kiil et al. (Ind. Eng. Chem. Res. 37 (1998) 2792) for a wet flue gas desulphurisation (FGD) pilot plant was extended to include the simultaneous absorption of HCl. In contrast to earlier models for wet FGD plants, the inclusion of population balance equations for the limestone particles enabled a quantitative description of the influence of HCl absorption on essential process parameters such as the degree of desulphurisation and the residual limestone level of the gypsum produced. Simulations showed that the presence of 100 ppmv HCl in the flue gas reduced the degree of desulphurisation from 85 to 84% and increased the residual limestone level of the gypsum from 2.1 to 2.4 wt %. It was found that these undesired effects from HCl absorption could be counteracted by adding adipic acid to the slurry in a concentration of about 1 mM . The influence of holding tank pH and the inlet flue gas concentration of SO2 on the degree of desulphurisation and the residual limestone level was found to be almost the same irrespective of HCl was present ( 100 ppmv ) in the flue gas or not. The results presented are of importance in the analysis of the performance of wet FGD plants installed at power plants firing coals of varying Cl contents.

Experimental Study of Drag Resistance Using a Laboratory Scale Rotary Set-up

This work covers an experimental study of the drag resistance of different painted surfaces and simulated large-scale irregularities, viz. dry spraying, weld seams, barnacle fouling and paint remains. A laboratory scale rotary set-up was used to determine the drag resistance, and the surface roughness of the samples was determined by means of two different stylus-based methods, one having a 1.6 mm ball stylus (giving the macro-roughness) and the other having a needle type stylus (giving the micro-roughness). It is demonstrated that, in the case of ideal painted surfaces (low macro-roughness), the micro-roughness is much more important than the macro-roughness. On the other hand, the study also indicates that larger scale irregularities have a much greater influence on the drag resistance compared to measurements of the paint system alone.