This study analyzes the absorption of pure carbon dioxide in aqueous solutions of mixtures of di-isopropanolamine (DIPA) and triethanolamine (TEA). A stirred tank batch reactor was used with a known flat interface area. The variables considered were temperature within the range 288–313 K and concentration in the interval 5–20% (in weight), being DIPA/TEA relations 75/25, 50/50, and 25/75. The temperature control for the DIPA/TEA 75/25, 50/50, 25/75 systems in the absorption experiments, at all the concentrations and temperatures assayed, showed no differences between that of the liquid phase with respect to the operation, implying that the processes occurred under isothermal conditions. The results show that for the DIPA/TEA 75/25 CO 2 was absorbed in a moderately fast reaction regime, following a second-order reaction for the total alkanolamine and a first-order reaction for the CO 2 , whereas for the DIPA/TEA 50/50 and 25/75 systems the process followed first-order kinetics with respect to CO 2 and the mixture of alkanolamines, in a moderately fast reaction regime.

The aim of this work was to produce diacylglycerols (DAG) and monoacylglycerols (MAG) with a high content of polyunsaturated fatty acids (PUFA). Rhizomucor miehei lipase mediated-hydrolysis of sardine oil was conducted at several water activities. The system was mechanistically modeled to predict the time evolution of the concentration of triacylglycerols, DAG, MAG and free fatty acids (FFA) and the concentration of saturated, mono- and polyunsaturated fatty acids. The release of the first fatty acid from the triacylglycerol was independent on the unsaturation degree. Contrary, the hydrolysis of the second one was highly affected by the degree of unsaturation, PUFA being the fatty acids that showed the highest resistance to hydrolysis. MAG percentage was maximum (7mol%) at lower water activities, while DAG content was favored at higher water activities (35mol%), achieving a 2-fold concentration of DHA.

The process of pure CO2 absorption by aqueous solutions of 2-methyl-amino-ethanol (MAE) has been studied in relation to the thermal effects of the operation. This study evaluates the consequences of heat effects during absorption and chemical reaction. The experiments were performed in a stirred tank reactor operated in batches with respect to the gas liquid phases, having a plane interfacial area. The working variables considered were the alkanolamine concentration within the interval 0.1-2.0 kmol/m(3) and the temperature in the range 288-313 K. From the results, it is deduced that the CO2 absorption at high pressures in aqueous MAE solutions, occur in the instantaneous reaction regime with high interface temperature. An expression is proposed to relate the experimental results to the initial concentration of alkanolamine and at the same time enable the determination of the interfacial temperature (T-s). In relation to temperature in the bulk liquid phase (T-B), increases (T-s-T-B) close to 43 K were determined in the experiments performed at high concentrations and in the highest temperature series.

Abstract In this work, the absorption of pure carbon dioxide by aqueous triethanolamine solutions (TEA) was studied in terms of the kinetic process. The process was made in a stirred tank reactor with a flat and known interfacial area, the operating variables being temperature (288 to 313 K) and concentration in the range 0.1-2.0 M. From the results, it was deduced that the absorption of pure carbon dioxide by aqueous triethanolamine takes place under isothermal conditions in which there is an instantaneous reaction regime at low concentrations, while at higher concentrations it takes place in a moderately fast reaction regime, following a first-order kinetic with respect to alkanolamine. In these conditions of concentrations and temperatures essayed, an expression for the constant kinetic was deduced.

The granulometric characterization of a pulverulent material requires quantification of the particle size and its distribution frequency. From these primary data, the mean size (mean diameters) of the pulverulent material is calculated and the data are adjusted to the distribution functions. In this study, the most frequent mean diameters are defined and calculated, and the application of the distribution functions to the experimental results is discussed. It is concluded that the Rosin‐Rammler distribution function and a modified Nukiyama‐Tanasawa function are the most suitable equations to fit the differential and the cumulative undersize distribution frequencies. This review is accompanied by calculations that illustrate the application of the equations related to this work.

An integral fluidodynamic model for hollow fibre (HF) has been developed and analysed. The model explains the pressure and flow profiles in three operation modes: open- and full-shell mode with forced circulation in the shell in cocurrent or countercurrent (OSFC); closed- and full-shell mode with forced recirculation in the shell in cocurrent or countercurrent (CSFR) and open- and empty-shell mode (OES). A methodology has been proposed to determine the parameters of the system and to verify the different operational systems proposed. Simple expressions have been developed to evaluate the pressures and the flows in the lumen fibres and in the shell, the transmembrane pressure, and the permeate flow for each operation mode assayed. The behaviour of the HF depends on the geometry of the module, on the operation mode chosen, and on the flows circulating through the lumen fibres and through the shell. The experimental results found with a commercial HF verified the model developed. The use of these expressions led us to choose the HF, the operation mode and the adequate flows that optimise the objective desired.

The process of pure carbon dioxide absorption is analyzed in aqueous solutions of N-methyldiethanolamine (MDEA). The experiments were made in a stirred tank reactor with a plane and known interface area. The variables considered were the MDEA concentration within the range 0.1–3.0 M and the temperature in the interval 288–313 K. From the results, we deduce that the process takes place under isothermal conditions and moderately fast regime, with second-order kinetics. We determined a reaction order of one with respect to the amine, and an expression for the kinetic constant valid throughout the entire range of temperatures and concentrations assayed ln k = 22.4 − 6243.5/T. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 204–214, 2009

ABSTRACT We have determined the density, rheological behavior and surface tension of whey protein concentrate (WPC) solutions. Densities (ρ) were measured at concentrations of 0.05–0.40 w/w at temperatures of 20–35C. The results were expressed as a function of temperature and mass fraction (w). This function fit the data with deviations of less than±0.4%. Apparent viscosities (ηa) for WPC solutions with mass fractions w ≤ 0.20 at temperatures of 10–40C and high shear rates, 50–1,200/s, were found to be independent of shear rates, implying that the rheological behavior of WPC solutions is Newtonian. Dynamic viscosity (η) data were fitted to an empirical function of the WPC mass fraction and temperature with a mean deviation of±4.7%. Surface tensions (σ) were determined for mass fractions between 0.01 and 0.30 at 25C. At this temperature and w = 0.05, there was a critical surface tension,σc = 42.5 mN/m. When w ≥ 0.10, the arithmetic mean ofσat 25C was 46.3 mN/m. The surface tension values were similar to those published for skimmed milk at 25C. In addition, for w = 0.05 and w = 0.20, we found that at temperatures between 20 and 40C, the surface tension decreased linearly with temperature. These linear equations fit our experimental data with an average deviation lower than±0.4%.PRACTICAL APPLICATIONSDensity, rheological behavior and surface tension are required to design and control processes with momentum, heat and mass transfer. The process of producing protein concentrates from milk or whey by ultrafiltration uses spiral‐wound membranes. The cross‐flow pressure drop and permeate mass flow are a function of fluid density and viscosity, which in turn depend on concentration and temperature. The ultrafiltration process used to concentrate solutions with mass fractions of about 0.10–0.20 w/w must then be treated to avoid physicochemical or microbiological alterations. Spray drying is usually used as the preservation technique. In the spray‐drying design, these physical properties are necessary to calculate the mean droplet diameter and droplet size distribution.

The growing concern for the environment is promoting the use of surfactant products from renewable sources such as fatty alcohol ethoxylates. The high production and use of these products implies the need to develop models that enable predictions of their behaviour in biodegradation processes. The biodegradation tests were carried out according to the OECD 301 E test for ready biodegradability. In this work, kinetic models of general application to surfactant biodegradation are developed, both for substrates that do not support growth and for those that do, considering a residual substrate concentration as not being biodegraded. The models were applied to three commercial non-ionic surfactants, fatty alcohol ethoxylates with different carbon-chain lengths and degrees of ethoxylation, also analysing the initial surfactant concentration.

No fundamental mechanism or model enables a theory on particle-size distribution to be built. Consequently, a wide variety of empirical models or equations have been proposed to characterize experimental particle-size distributions, such as the Rosin–Rammler model. Because the Nukiyama–Tanasawa equation uses four parameters to simulate differential distribution frequencies for particle-size diameters, the distribution function is not easy to apply in order to fit experimental data. In this paper, a modification of the Nukiyama–Tanasawa model with only two parameters has been proposed to fit the data on a particle-size distribution (PSD). The proposed normalized distribution function has been applied successfully to the PSD analysis (cork granulate and spray atomization droplets).

In this paper, the influence of pH in the 3–9 interval and NaCl concentration up to 25mM on the cross-flow microfiltration of BSA was studied. A tubular ceramic membrane with a mean pore size of 0.14μm was employed. The evolution of permeate flow and BSA transmission with time was determined at 30°C, a cross-flow velocity of 3.28m/s and a transmembrane pressure of 100kPa. The flow data were discussed by means of combination of two fouling mechanisms: complete and standard blocking when transmission of proteins occurred and complete blocking and cake formations otherwise. The effective radius of the protein and the electrostatic interactions protein–membrane explained the transmission protein values.

This work proposes a lumped kinetic model for the acidolysis of a triacylglycerol (TAG) and an odd free fatty acid (FFA) in a non-aqueous medium, catalyzed by a 1,3 specific lipase immobilized on a solid support. This model is based on the mechanism of the acidolysis reaction by considering the following hypothesis: (1) only the fatty acids in positions 1 and 3 of TAG are exchanged and these two positions in the glycerol backbone are equivalent and (2) the only intermediate of appreciable lifespan in which the enzyme participates is the acyl-enzyme complex. The kinetic equation obtained for the rate of incorporation of an odd fatty acid to TAG has been applied to the results obtained in the acidolysis of three oils (commercial triolein, cod liver oil (CLO) and a commercial oil enriched in eicosapentaenoic acid (EPA), EPAX 4510TG) with caprylic acid (CA), catalyzed by the immobilized lipase Lipozyme IM contained in a packed bed reactor (PBR). The acidolysis has been carried out by recirculating the reaction mixture through the PBR until the reaction equilibrium was reached. In these conditions it has been proved that the PBR behaves as a perfect mixed dispersion reactor and the experimental results obtained at low TAG concentrations (<100mol/m3) have been acceptably fitted to the kinetic expression obtained from the proposed model, with only two fitting parameters.However, for TAG concentrations higher than 100mol/m3, an appreciable reduction of the reaction rate was observed. This result was due to the decrease of the effective diffusivity of reactants within the pores of the support where the lipase is immobilized, since the viscosity of the reaction mixture increases appreciably when the reactant concentration also does. When this phenomenon is included in the developed kinetic model, the experimental results obtained at high TAG concentrations could also be explained, even in absence of the organic solvent (n-hexane). It is observed that the influence of diffusion into the pores increases with the degree of CA incorporation to TAG, which was due to the increase of TAG and native fatty acid concentrations in the particle pores, which determines a continuous decrease in the effective diffusivity of CA.

A two-parameter equation to reproduce the droplet size distribution (DSD) of emulsions has been developed. The equation has been applied satisfactorily to oil-in-water (O/W) emulsions with triolein and tributyrin as oil phase and gum arabic, an alkylpolyglucoside and a fatty ethoxilated alcohol as emulsifier agents. Emulsions with aging effect also have been studied. The equation reproduces satisfactorily the DSD obtained using two parameters, n and m. This equation enables to determine the distribution of the interfacial area and the oil volume in the emulsions prepared. The equation is suitable too to model the experimental results reported by different researchers.

The enzymatic hydrolysis of triglycerides in emulsion form, which involves a heterogeneous system and furthermore unstable over time, is a difficult task. This work proposes a kinetic model for the enzymatic hydrolysis of tributyrin, using the enzyme Lipolase® 100 of Novozymes. This model considers the hydrolysis reaction to take place between the enzyme and the surface ester-bonds of tributyrin. For this, the enzyme penetrates the droplet surface, bonds to a surface-ester group, and performs the hydrolytic step, this latter stage of the process being irreversible. The concentration of the hydrolysable surface bonds in the emulsion has been calculated for the application of the model. The model proved valid for low enzyme concentrations, at which the interface was not found to be saturated, and it has been applied at different temperatures. In all cases, the model succeeded in predicting the initial reaction rates with a relative deviation of less than 5%. The model also reproduces the results found for enzymatic hydrolysis as a function of reaction time up to conversions of 0.25.

An adsorption-kinetic model has been proposed to explain beta-galactosidase stability in a recirculation hollow-fibre bioreactor at different temperature. The kinetic constants of the model and its dependence on temperature have been evaluated.In addition, a study has been made of the influence of lactose and enzyme concentration on lactose hydrolysis with hollow-fibre modules made of Cuprophan and Polysulfone. The membrane surface areas assayed were between 1 and 1.95 m(2). The experimental results have been satisfactorily explained with the model proposed in a previous work. This model included the competitive inhibition of the enzyme by galactose and the enzymatic adsorption onto the membrane. The adsorption constants have been calculated, verifying the applicability of the model in the modules used. Within the experimental range analysed, the hollow-fibre module made of Polysulfone provided the least adsorption of the enzyme and therefore was the most suitable for this enzyme and reaction. (c) 2006 Elsevier Inc. All rights reserved.

In this paper, a process for the stable production of low allergenicity hydrolysates is presented. Whey protein was hydrolysed at 50 °C and pH 8.5 using a bacterial protease in a continuous stirred tank membrane reactor including a polyethersulfone plate and frame ultrafiltration module with a molecular weight cut-off of 3 kDa. The reactor was maintained in operation for 16 h. Conversion reached a steady value around 80% after 10 h of operation, while a steady permeate flow was achieved after 13 h. A slight, first order enzyme thermal inactivation was detected. A hydrolysate with an average peptide chain length around 4 amino acids was obtained. The antigenic whey protein in the product was reduced 99.97%, which suggests that it can be incorporated as nitrogen source in infant formula and enteral nutrition.

The enzymatic alcoholysis of triolein and an oil highly rich in polyunsaturated fatty acid with ethanol to obtain 2-monoacylglycerols (2-MG) was studied. Two sn-1,3 specific lipases were used to catalyze this reaction: Lipozyme® IM from Mucor miehei and lipase D from Rhizopus oryzae. The experimental results were acceptably fitted to a mechanistic kinetic model that considers the formation of an acyl–enzyme complex and the isomerization of 2-monoacylglycerols (2-MG) by acyl migration to 1(3)-monoacylglycerols (1(3)-MG). The results of the alcoholysis reaction were both qualitatively and quantitatively dependent on the lipase used. When using Lipozyme IM the process was controlled by the acyl migration of the 2-MG to 1(3)-MG, which finally gave rise to glycerol. In contrast, when using lipase D, no acyl migration occurred and the process was controlled by the formation of 1(3),2-DG and 2-MG. The yields of 2-MG obtained with lipase D (almost 80%) were therefore greater than those obtained using Lipozyme IM in the same experimental conditions. The proposed kinetic model predicted the experimental results of the alcoholysis as a function of the processing intensity (lipase amount×reaction time/reaction volume, mEt/V) irrespective of whether acyl migration took place. It also allowed the kinetic parameters of all the processes involved to be calculated.

La hidrolisis enzimatica de trigliceridos en forma de emulsion, donde interviene un sistema heterogeneo y ademas inestable en funcion del tiempo es una tarea dificil. En este trabajo se propone un modelo cinetico para la hidrolisis enzimatica de tributirina utilizando la enzima Lipolase 100 de Novo-Nordisk. Dicho modelo implica la union de la enzima a un grupo ester situado en la interfase de la emulsion y accesible para la enzima, la separacion de la acil-enzima de la fase lipidica a la acuosa y la hidrolisis posterior de la acil-enzima en la fase acuosa. Esta ultima etapa del proceso se considera irreversible. Se ha calculado la concentracion de enlaces hidrolizables superficiales en la emulsion para la aplicacion del modelo. El modelo cinetico propuesto reproduce los resultados experimentales de velocidad inicial respecto concentracion de enzima y concentracion inicial de enlaces hidrolizables con una desviacion media menor del 10%.

A general procedure has been developed to model the behaviour of enzymatic reactions in a membrane bioreactor. This procedure unifies the kinetics of the reaction and the adsorption of the enzyme or enzymatic complexes on the membrane, enabling the selection of the most appropriate kinetic model. The general procedure proposed has been particularized and applied to experimental results obtained with two enzymatic reactions carried out in a hollow-fibre reactor, enzymatic hydrolysis of lactose by β-galactosidase and glucose–fructose isomerization by glucose isomerase. The application of the general model has allowed us to determine the mechanism of the reaction for both kinetic reactions, assuming the adsorption of the enzymatic complex EGa for lactose hydrolysis and the adsorption of the free enzyme onto the membrane for glucose–fructose isomerization.