<p>Membrane gas absorption is a new way of contacting gas and liquid for industrial scale gas purification and offers significant advantages compared to conventional absorption towers. Due to the separation of the phases by a microporous membrane the contactor may be operated without limitations caused by flooding, foaming, channeling and liquid entrainment. Very compact hollow fiber membrane units can be made resulting in significant savings in weight and space required.</p><p>This dissertation deals with membrane gas absorption in the application of CO₂removal by aqueous alkanolamines, using microporous PTFE hollow fiber membranes. A new lab-scale apparatus was constructed and an extensive experimental study executed to determine the performance of the membrane gas absorber, with aqueous solutions of monoethanolamine (MEA) and methyldiethanolamine (MDEA) as absorbents. The important operation parameters CO₂partial pressure, gas velocity, liquid velocity, temperature and liquid CO₂ loading were systematically varied within the range typically experienced in a process for exhaust gas CO₂-removal.</p><p>The results clearly show the change in the absorption rate and the overall mass transfer coefficient related to each of the variables. An important conclusion from the experimental study is that the contribution from the gas phase in the overall mass transfer resistance is negligible for the conditions studied. Membrane mass transfer resistance corresponds to less than 12% of the total, leaving the liquid side as the totally dominating resistance term. It is found that the liquid side mass transfer is limited by component diffusivities except at low partial pressures, where the chemical reaction may be rate-limiting.</p><p>A comprehensive model for the simulation of the membrane gas absorber was developed. The model explicitly accounts for the rates of mass transfer through the membrane, diffusion and chemical reaction in the liquid phase and the corresponding heat transfer model. The important effect of radial viscosity gradients on the liquid diffusivities was also included. An equilibrium model was developed to calculate liquid speciation and equilibrium partial pressures in the chemical systems CO₂/MEA/water and CO₂/MDEA/water.</p><p>The membrane gas absorber model calculates temperature profiles and concentration profiles of all components through the length of a single membrane tube. The total absorption rate in a membrane module is calculated from a mass balance of the gas and the liquid phase. It was observed that the diffusional transport of chemically bound CO₂and other ionic reaction products is an important rate limiting step. This lead to the requirement of new correlations for these component diffusivities, developed from parameter regression on selected experiments. Model predictions of absorption rates and the effects of individual variables agree well with experimental data, with maximum deviations within 15 %. In the range of operation for an industrial contactor with CO₂ absorbing in aqueous MEA, the average model deviation is 2.8%.</p><p>The possibility of utilizing a lab-scale membrane gas absorber as a tool in measuring the kinetics of CO₂-alkanolamine reactions is discussed. It has been shown that the sensitivity to reaction kinetics can be significantly improved by reducing the contact time beyond what is possible in the present experimental set-up. This may be achieved in a membrane module with 1-5 cm tube length and a high number of tubes so that absorption fluxes can still be measured with a high level of accuracy. To verify this procedure, experiments were performed in a range with a reasonably good sensitivity to reaction kinetics in the MDEAsystem. The second order rate constant of the CO_2-MDEA reaction was regressed from the experimental data resulting in an Arrhenius expression comparable to literature values.</p>

<p>This thesis presents studies of the interactions between suspended particles and dissolved and colloidal substances (DCS) in process water. The main focus has been to determine if colloidal wood resin is adsorbed by suspended fines or fillers, and how the dissolved material influences this adsorption. The effect of some synthetic polymers on this adsorption has also been investigated.</p><p>Successive refining of mainly Norway spruce followed Successive refining of mainly Norway spruce followed by removal of the produced fines after each refining stage, resulted in fines with different physical and chemical properties. In the first refining stage mainly flake-like fines were produced, while more fibrillar fines were produced in later refining stages. The different types of fines were analysed for both the bulk and the surface composition. Variation in the chemical composition between the fines was particularly striking with regard to the surface composition. Special attention was also given to the amount and origin of charged groups since these may consume cationic additives in the papermaking process. After alkali treatment, between 80 and 90% of all the charged groups measured by polymer adsorption originated from three uronic acids.</p><p>Fines were shown to adsorb model colloidal wood resin, but the adsorption was greatly influenced by the pH or salt content. Also the amount of dissolved components in the suspension, which sterically stabilised the colloidal wood resin, was shown to strongly influence the adsorption of the colloidal wood resin to the fines. The flake-like fines adsorbed the colloidal wood resin to a higher extent than the fibrillar fines. This selectivity was also possible to obtain by using polyethyleneoxide (PEO). PEO removed the sterically stabilised colloidal wood resin more efficiently when flake-like fines rather than fibrillar fines were present. For comparison, cationic polyacrylamide (CPAM) did not have this selectivity. The selectivity of PEO was explained by a higher affinity to flake-like fines than fibrillar fines. It was shown that more PEO adsorbed to flake-like fines rather than to fibrillar ones. PEO may adsorb to extractive surfaces, but was inhibited by adsorbed components from the dissolved fraction. The degree of stabilisation was also shown to influence the adsorption of the colloidal wood resin by other particles like fillers. This adsorption, which was energetically favourable, did not occur at high concentrations of dissolved material.</p>

<p>Desizing wastewater is largely responsible for the chemical oxygen demand (COD) load in the textile industry wastewater. A larger portion of COD comes from degraded starch in desizing wastewater. Removing the starch from the wastewater by an ultrafiltration process may reduce the environmental problem caused by the textile factory. If the treatment is made in such a way that all starch components are removed from the wastewater, the treated water can be reused by the factory. If the starch in the concentrate is stable, it can also be reused as a sizing agent. This will give the factory an economic advantage.</p><p>In this thesis we have studied the fouling mechanisms involved in the ultrafiltration of solution with partially degraded starch in order to find the treatibility of such solutions. The work has mainly been directed to uncover how the different fouling mechanisms depend on the operating parameters, and to find the performance of selected membranes. In addition, different models were evaluated for their validity in predicting the performance of the membranes and the data was fitted to the model that give the best prediction and are physically more meaningful. In addition, the starch solution was concentrated, and the flux, concentration, retention and rejection profiles as a function of concentrating time were investigated.</p><p>For the study, we used a partially degraded starch solution as a model solution. The solution was prepared in the laboratory by enzymatic degradation of potato starch to different levels. In order to evaluate the reproducibility of the degraded starch, three replicates were prepared. The reproducibility was determined by comparing the molar mass distribution from HPLSEC analysis and the concentration of reducing sugar from a DNS test for the replicates. The analyses show very good reproducibility. Three starch model solutions with three different degradation levels were chosen for our ultrafiltration experiments to investigate the effect of average molar mass of the starch.</p><p>For the ultrafiltration of the solution ES625 (from PCI) and MPT-U20 (from KOCH) membranes were used. Both membranes were used in the investigation of the contribution of different fouling mechanisms to the flux decline during ultrafiltration of the solution. In the evaluation of the performance of ultrafiltration of the starch solution, however, only the ES625 membrane was used. According to the manufacturers, both membranes have nearly equal pure water flux and MWCO. But in our test, we observed a higher and different pure water flux for each type of membrane. The ES625 had a lower flux (higher retention) than the MPTU20 membrane.</p><p>In the ultrafiltration of partially degraded starch solution the permeate flux declines very fast and, for a low feed concentration, it reaches a steady state in a very short time. The steady state time was observed to increase with concentration, molar mass and transmembrane pressure drop, and to decrease with cross flow velocity. All the three fouling mechanisms (concentration polarization, adsorption and deposition) were responsible for the flux decline. The major observed contributors are, however, adsorption and deposition. Adsorption is largely responsible at low-pressure operation while the deposition fouling effect is dominant at higher pressures, near or beyond the limiting flux.</p><p>For the ES625 membrane, the contribution of adsorptive fouling increases with concentration and decreases with molar mass of the starch, temperature and pH at a given transmembrane pressure and cross flow velocity. The effect of the operating parameters on the depositional fouling is in line with literature. It increases with pressure, concentration, molar mass and temperature, and decreases with cross flow velocity. Its dependence on pressure can be expressed by a power function with exponent larger than 1.0. This seems to due to an increase in thickness and compaction of the starch gel/deposit at the membrane surface as the transmembrane pressure drop is increased. The contribution of the concentration polarization is also dependent on concentration, cross flow velocity and pressure. Its relative contribution increases with concentration while it decreases with an increase in cross flow velocity. In the turbulent flow regime the relation between the resistance contributed by concentration polarization increases almost linearly with transmembrane pressure drop. In the laminar flow regime, however, the relative contribution of the resistance due to concentration polarization increases for the lower range of pressure and decreases for the higher range of pressure. Its relative contribution also increases with temperature and decreases with increasing molar mass. But the overall fouling resistance in the ultrafiltration of the starch solution increases with feed concentration, molar mass of the starch and transmembrane pressure drop and decreases with cross flow velocity and temperature.</p><p>The trend of the flux loss due to all fouling mechanisms for MPT-U20 membrane is similar to ES625 membrane except for adsorption and concentration polarization with changes in concentration and molar mass. The difference could be a result of the difference in morphological properties between the two membranes and the experimental procedures used in determining flux data that used for calculating the contributions. From the pure water flux and the retention data, the ES625 membrane seemed to have a smaller pore size than the MPT-U20 membrane.</p><p>Among the ultrafiltration models, the resistances-in-series model was chosen for its provision to include all the fouling mechanisms into the model. When our permeate flux data was fitted to the model, it gives a good fit. However, the model fails to give realistic estimates of the contribution of the individual fouling mechanisms. In order to improve this problem, the model was modified by introducing osmotic pressure across the membrane in such a way that the effect of concentration polarization is accounted for. This modified model is more physically meaningful and gives a realistic estimate of the contribution the reversible and irreversible fraction of the overall resistance.</p><p>In concentrating mode operation, the permeate was continuously withdrawn and hence, the concentration of starch in the feed tank was increased. At an early stage of ultrafiltration, the permeate flux appeared to increase slightly, which seems, a result a shear thinning of the starch solution when the solution was pumped through the system. For the rest of the operation, the flux was decreasing, the retention was increasing and the rejection of the membrane was shifted to a lower molar mass as the solution in the feed tank got more concentrated as expected. The shift of rejection to the lower molar mass region is due to the fouling layer that reduces the accessibility of the pores of the membrane.</p><p>Generally, the flux we obtained in ultrafiltration of a partially degraded starch solution with the ES625 tubular membrane is equal or better than the reported values from an existing ultrafiltration plant that has been used in the textile industry to recover a synthetic sizing agent (PVA) from the desizing wastewater. The retention is, however, rather low. Two or more stages of treatment are needed to get all starch components removed from the wastewater and make the treated water reusable (recycled).</p>

<p>Separation of azeotropic mixtures is of great industrial importance and distillation is the dominating unit operation for such separations. However, the presence of azeotropes and non-idealities in the phase behaviour of such mixtures complicates the separation. In the pharmaceutical and fine/specialty chemical industry, the small-scale production and the requirement for flexibility indicates batch distillation as the best suited process. Among, various techniques to enhance distillation, heterogeneous azeotropic (heteroazeotropic) distillation is a very powerful and widely used one. Thus, there is a need for deeper understanding of the complex behaviour of the separation of heteroazeotropic mixtures in batch distillation columns.</p><p>This thesis is concerned with feasibility and operation aspects of heteroazeotropic distillation in different batch column configurations. Both conventional batch columns (rectifiers) and novel configurations (multivessel columns), with and without vapour bypass, are considered. The focus is on closed operations, without product removal. Batch time requirements for operation in all columns are provided for both zeotropic and heteroazeotropic mixtures. The advantages and drawbacks of each configuration are discussed and compared based on dynamic simulations. The configuration of the vapour stream in the middle vessel has an important effect on the time requirements of the process. Later on, a detailed analysis of the process is provided and previous published work concerning different operation modes and separation strategies is put under the right perspective. Simple control schemes are proposed for the practical operation of the columns and the realisation of the desired steady state results. The thesis ends with a detailed feasibility study of the process. The possibilities and limitations raised by different operational modes and separation strategies are illustrated. Simple feasibility conditions and entrainer selection rules are formulated that allow someone to investigate feasibility of the process in a systematic and comprehensive manner.</p>

<p>Chlorine as a chemical is widespread in industry and found in a great variety of processes ranging from water purification to plastic production. In this thesis, a magnesium production factory was chosen as an example because it involved both chlorine - air separation and hydrogen –hydrogen chloride separation.</p><p>Previously, various types of membrane materials have been tested out for their applicability in the chosen process. The materials previously tested either lacked sufficient membrane performance or sufficient membrane stability. As an attempt to improve both the membrane performance and stability, glass membranes are used in this thesis.</p><p>Glass membranes are prepared from a borosilicate glass, via a phase separation followed by an acid leaching route. By choosing the appropriate phase separation temperature and acid to glass ratio, the membrane can be produced with an average pore diameter of 2 nm (or 4 nm).</p><p>However, the 2 nm average pore size is still too large to separate gases with separation selectivities beyond the selectivities predicted from Knudsen diffusion theory. If the pores are narrowed, the selectivity may be raised while the flux hopefully is maintained. The narrowing of the pores was done by a silane coupling to the surface OH-groups on the glass. The silane coupling agent is of the dimethylacyl-chlorosilane type, where the length of the acyl chain varies from 1 carbon up to 18 carbons. Glass fibres are also tested in this work, which are produced without phase separation and their average pore size is smaller than the surface-modified glasses.</p><p>To be able to compare the performance of the various membranes, permeance measurements are performed and these measurements are evaluated by the separation power (product of the selectivity and the permeability of the fastest permeating compound). Because of the harsh chlorine or hydrogen chloride environment, to which the membranes are exposed in this work, the membrane stability is at least as important s factor as the perm-selectivities. To evaluate this, both short- and longterm aggressive gas exposures are performed using a special designed durability chamber. From the combination of the perm-selectivities and the durability tests, the following conclusions may be drawn (evaluated at 30°C and 1 bar): Firstly, the pure glasses have a relatively poor stability (for chlorine gas) and the perm-selectivity is too low (for both separations in question). Secondly, the C8 and C12 modified glass membranes have a relatively satisfactory perm- selectivity for chlorine separation, but the durability in chlorine is poor. Thirdly, the long-chained C18 modified glass membrane has a relatively satisfactory perm-selectivity but a fair to low chlorine stability. If the C18 membrane is applied in the hydrogen chlorine separation the perm-selectivity is a bit low, but the stability is sufficient. However, this membrane is the best choice for a low temperature HCl selective membrane.</p><p>Finally, to improve the chlorine stability, a perfluorinated version of a C1 modification is tried out. This membrane has excellent chlorine stability, and the perm-selectivity is fair. This membrane is the best choice for a chlorine selective membrane.</p><p>The stability of the fibres is comparable to that found for the pure glass tubes. However, the permeabilities in the glass fibres are several orders of magnitude lower than for the glass tubes. The pore size in the fibre is so narrow that separation occurs according to a molecular sieving mechanism. The mounting of the fibres into a labsized module is tricky and the permeabilities are at the border of detection, so the results obtained here should only serve as trends.</p>

<p>Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have attracted intense research efforts with the expectation that these materials may have many unique properties and potential applications. The most promising way for large-scale synthesis of CNFs and CNTs is chemical vapor deposition (CVD). </p><p>CNFs were synthesized on a series of hydrotalcite (HT) derived 77 wt.% Ni-Fe/Al₂O₃ catalysts in order to achieve the optimization of productivity and quality. It was found that only the Fe catalyst was active in CO disproportionation and only the Ni catalyst was active in ethylene decomposition, whereas all catalysts were active in ethylene decomposition when the reactants were a mixture of C₂H₄/CO. More control over the structure and diameter of the CNFs has been realized with the HT catalysts. At the same time, a high yield can be obtained. The synthesis process has been further studied as a function of various process parameters. It turned out that high hydrogen concentration, space velocity, and reaction temperature would enhance the production of CNFs. However, a slightly lower quality was associated with the higher productivity. The optimum CNF yield of 128 gCNF/gcat could be reached within 8 h on the HT catalyst with a Ni/Fe ratio of 6:1. Therefore, HT derived catalysts present a new promising route to large-scale controlled synthesis of CNFs. </p><p>CNTs has been synthesized from CO disproportionation on Ni-Fe/Al₂O₃ supported catalysts with metal loadings of 20 and 40 wt.%. A high space velocity resulted in a high production rate but a short lifetime and a low carbon capacity. Increasing the metal loading to 40 wt.% significantly increased the reaction rate and productivity, and produced similarly uniform CNTs. Furthermore, H₂was found to be necessary for a high productivity, and the H₂partial pressure could be changed to adjust the orientation angle of the graphite sheets. </p><p>The effects of catalyst particle size and catalyst support on the CNT growth rate during CO disproportionation were studied over SiO₂and Al₂O₃ supported Fe catalysts with varying particle sizes. It was found that there was an optimum particle size at around 13-15 nm for the maximum growth rate, and the growth rate was influenced both by the particle size and the support but the particle size was the dominating factor. The trends have been demonstrated at two different synthesis temperatures of 600 and 650°C. The effect of gas precursors on the yield and structure of carbon growth has been systematically investigated over powder Fe and Fe/Al₂O₃ catalysts. CO/H₂, CO, CH₄, and C₂H₆/H₂were the gas precursors studied. The carbon yield was higher on powder Fe from CO, but the yield was higher on Fe/Al₂O₃ from hydrocarbons. Completely different or similar carbon nanostructures were synthesized, depending on the gas precursors. It was suggested that the reactivity of gas precursors and the structures of carbon deposits are determined by the size and crystallographic faces of the catalyst particles, which are dictated by the interactions among metal particles, support, and the reactants. Controlled synthesis of CNT, platelet nanofiber, fishbone-tubular nanofiber, and onion-like carbon with high selectivity and yield was realized. A mechanism was proposed to illustrate the growth of different carbon nanostructures.</p>

Desizing wastewater is largely responsible for the chemical oxygen demand (COD) load in the textile industry wastewater. A larger portion of COD comes from degraded starch in desizing wastewater. Removing the starch from the wastewater by an ultrafiltration process may reduce the environmental problem caused by the textile factory. If the treatment is made in such a way that all starch components are removed from the wastewater, the treated water can be reused by the factory. If the starch in the concentrate is stable, it can also be reused as a sizing agent. This will give the factory an economic advantage. In this thesis we have studied the fouling mechanisms involved in the ultrafiltration of solution with partially degraded starch in order to find the treatibility of such solutions. The work has mainly been directed to uncover how the different fouling mechanisms depend on the operating parameters, and to find the performance of selected membranes. In addition, different models were evaluated for their validity in predicting the performance of the membranes and the data was fitted to the model that give the best prediction and are physically more meaningful. In addition, the starch solution was concentrated, and the flux, concentration, retention and rejection profiles as a function of concentrating time were investigated. For the study, we used a partially degraded starch solution as a model solution. The solution was prepared in the laboratory by enzymatic degradation of potato starch to different levels. In order to evaluate the reproducibility of the degraded starch, three replicates were prepared. The reproducibility was determined by comparing the molar mass distribution from HPLSEC analysis and the concentration of reducing sugar from a DNS test for the replicates. The analyses show very good reproducibility. Three starch model solutions with three different degradation levels were chosen for our ultrafiltration experiments to investigate the effect of average molar mass of the starch. For the ultrafiltration of the solution ES625 (from PCI) and MPT-U20 (from KOCH) membranes were used. Both membranes were used in the investigation of the contribution of different fouling mechanisms to the flux decline during ultrafiltration of the solution. In the evaluation of the performance of ultrafiltration of the starch solution, however, only the ES625 membrane was used. According to the manufacturers, both membranes have nearly equal pure water flux and MWCO. But in our test, we observed a higher and different pure water flux for each type of membrane. The ES625 had a lower flux (higher retention) than the MPTU20 membrane. In the ultrafiltration of partially degraded starch solution the permeate flux declines very fast and, for a low feed concentration, it reaches a steady state in a very short time. The steady state time was observed to increase with concentration, molar mass and transmembrane pressure drop, and to decrease with cross flow velocity. All the three fouling mechanisms (concentration polarization, adsorption and deposition) were responsible for the flux decline. The major observed contributors are, however, adsorption and deposition. Adsorption is largely responsible at low-pressure operation while the deposition fouling effect is dominant at higher pressures, near or beyond the limiting flux. For the ES625 membrane, the contribution of adsorptive fouling increases with concentration and decreases with molar mass of the starch, temperature and pH at a given transmembrane pressure and cross flow velocity. The effect of the operating parameters on the depositional fouling is in line with literature. It increases with pressure, concentration, molar mass and temperature, and decreases with cross flow velocity. Its dependence on pressure can be expressed by a power function with exponent larger than 1.0. This seems to due to an increase in thickness and compaction of the starch gel/deposit at the membrane surface as the transmembrane pressure drop is increased. The contribution of the concentration polarization is also dependent on concentration, cross flow velocity and pressure. Its relative contribution increases with concentration while it decreases with an increase in cross flow velocity. In the turbulent flow regime the relation between the resistance contributed by concentration polarization increases almost linearly with transmembrane pressure drop. In the laminar flow regime, however, the relative contribution of the resistance due to concentration polarization increases for the lower range of pressure and decreases for the higher range of pressure. Its relative contribution also increases with temperature and decreases with increasing molar mass. But the overall fouling resistance in the ultrafiltration of the starch solution increases with feed concentration, molar mass of the starch and transmembrane pressure drop and decreases with cross flow velocity and temperature. The trend of the flux loss due to all fouling mechanisms for MPT-U20 membrane is similar to ES625 membrane except for adsorption and concentration polarization with changes in concentration and molar mass. The difference could be a result of the difference in morphological properties between the two membranes and the experimental procedures used in determining flux data that used for calculating the contributions. From the pure water flux and the retention data, the ES625 membrane seemed to have a smaller pore size than the MPT-U20 membrane. Among the ultrafiltration models, the resistances-in-series model was chosen for its provision to include all the fouling mechanisms into the model. When our permeate flux data was fitted to the model, it gives a good fit. However, the model fails to give realistic estimates of the contribution of the individual fouling mechanisms. In order to improve this problem, the model was modified by introducing osmotic pressure across the membrane in such a way that the effect of concentration polarization is accounted for. This modified model is more physically meaningful and gives a realistic estimate of the contribution the reversible and irreversible fraction of the overall resistance. In concentrating mode operation, the permeate was continuously withdrawn and hence, the concentration of starch in the feed tank was increased. At an early stage of ultrafiltration, the permeate flux appeared to increase slightly, which seems, a result a shear thinning of the starch solution when the solution was pumped through the system. For the rest of the operation, the flux was decreasing, the retention was increasing and the rejection of the membrane was shifted to a lower molar mass as the solution in the feed tank got more concentrated as expected. The shift of rejection to the lower molar mass region is due to the fouling layer that reduces the accessibility of the pores of the membrane. Generally, the flux we obtained in ultrafiltration of a partially degraded starch solution with the ES625 tubular membrane is equal or better than the reported values from an existing ultrafiltration plant that has been used in the textile industry to recover a synthetic sizing agent (PVA) from the desizing wastewater. The retention is, however, rather low. Two or more stages of treatment are needed to get all starch components removed from the wastewater and make the treated water reusable (recycled).

Membrane gas absorption is a new way of contacting gas and liquid for industrial scale gas purification and offers significant advantages compared to conventional absorption towers. Due to the separation of the phases by a microporous membrane the contactor may be operated without limitations caused by flooding, foaming, channeling and liquid entrainment. Very compact hollow fiber membrane units can be made resulting in significant savings in weight and space required. This dissertation deals with membrane gas absorption in the application of CO2 removal by aqueous alkanolamines, using microporous PTFE hollow fiber membranes. A new lab-scale apparatus was constructed and an extensive experimental study executed to determine the performance of the membrane gas absorber, with aqueous solutions of monoethanolamine (MEA) and methyldiethanolamine (MDEA) as absorbents. The important operation parameters CO2 partial pressure, gas velocity, liquid velocity, temperature and liquid CO2 loading were systematically varied within the range typically experienced in a process for exhaust gas CO2-removal. The results clearly show the change in the absorption rate and the overall mass transfer coefficient related to each of the variables. An important conclusion from the experimental study is that the contribution from the gas phase in the overall mass transfer resistance is negligible for the conditions studied. Membrane mass transfer resistance corresponds to less than 12% of the total, leaving the liquid side as the totally dominating resistance term. It is found that the liquid side mass transfer is limited by component diffusivities except at low partial pressures, where the chemical reaction may be rate-limiting. A comprehensive model for the simulation of the membrane gas absorber was developed. The model explicitly accounts for the rates of mass transfer through the membrane, diffusion and chemical reaction in the liquid phase and the corresponding heat transfer model. The important effect of radial viscosity gradients on the liquid diffusivities was also included. An equilibrium model was developed to calculate liquid speciation and equilibrium partial pressures in the chemical systems CO2/MEA/water and CO2/MDEA/water. The membrane gas absorber model calculates temperature profiles and concentration profiles of all components through the length of a single membrane tube. The total absorption rate in a membrane module is calculated from a mass balance of the gas and the liquid phase. It was observed that the diffusional transport of chemically bound CO2 and other ionic reaction products is an important rate limiting step. This lead to the requirement of new correlations for these component diffusivities, developed from parameter regression on selected experiments. Model predictions of absorption rates and the effects of individual variables agree well with experimental data, with maximum deviations within 15 %. In the range of operation for an industrial contactor with CO2 absorbing in aqueous MEA, the average model deviation is 2.8%. The possibility of utilizing a lab-scale membrane gas absorber as a tool in measuring the kinetics of CO2-alkanolamine reactions is discussed. It has been shown that the sensitivity to reaction kinetics can be significantly improved by reducing the contact time beyond what is possible in the present experimental set-up. This may be achieved in a membrane module with 1-5 cm tube length and a high number of tubes so that absorption fluxes can still be measured with a high level of accuracy. To verify this procedure, experiments were performed in a range with a reasonably good sensitivity to reaction kinetics in the MDEAsystem. The second order rate constant of the CO2-MDEA reaction was regressed from the experimental data resulting in an Arrhenius expression comparable to literature values.

This thesis presents studies of the interactions between suspended particles and dissolved and colloidal substances (DCS) in process water. The main focus has been to determine if colloidal wood resin is adsorbed by suspended fines or fillers, and how the dissolved material influences this adsorption. The effect of some synthetic polymers on this adsorption has also been investigated. Successive refining of mainly Norway spruce followed Successive refining of mainly Norway spruce followed by removal of the produced fines after each refining stage, resulted in fines with different physical and chemical properties. In the first refining stage mainly flake-like fines were produced, while more fibrillar fines were produced in later refining stages. The different types of fines were analysed for both the bulk and the surface composition. Variation in the chemical composition between the fines was particularly striking with regard to the surface composition. Special attention was also given to the amount and origin of charged groups since these may consume cationic additives in the papermaking process. After alkali treatment, between 80 and 90% of all the charged groups measured by polymer adsorption originated from three uronic acids. Fines were shown to adsorb model colloidal wood resin, but the adsorption was greatly influenced by the pH or salt content. Also the amount of dissolved components in the suspension, which sterically stabilised the colloidal wood resin, was shown to strongly influence the adsorption of the colloidal wood resin to the fines. The flake-like fines adsorbed the colloidal wood resin to a higher extent than the fibrillar fines. This selectivity was also possible to obtain by using polyethyleneoxide (PEO). PEO removed the sterically stabilised colloidal wood resin more efficiently when flake-like fines rather than fibrillar fines were present. For comparison, cationic polyacrylamide (CPAM) did not have this selectivity. The selectivity of PEO was explained by a higher affinity to flake-like fines than fibrillar fines. It was shown that more PEO adsorbed to flake-like fines rather than to fibrillar ones. PEO may adsorb to extractive surfaces, but was inhibited by adsorbed components from the dissolved fraction. The degree of stabilisation was also shown to influence the adsorption of the colloidal wood resin by other particles like fillers. This adsorption, which was energetically favourable, did not occur at high concentrations of dissolved material.

Separation of azeotropic mixtures is of great industrial importance and distillation is the dominating unit operation for such separations. However, the presence of azeotropes and non-idealities in the phase behaviour of such mixtures complicates the separation. In the pharmaceutical and fine/specialty chemical industry, the small-scale production and the requirement for flexibility indicates batch distillation as the best suited process. Among, various techniques to enhance distillation, heterogeneous azeotropic (heteroazeotropic) distillation is a very powerful and widely used one. Thus, there is a need for deeper understanding of the complex behaviour of the separation of heteroazeotropic mixtures in batch distillation columns. This thesis is concerned with feasibility and operation aspects of heteroazeotropic distillation in different batch column configurations. Both conventional batch columns (rectifiers) and novel configurations (multivessel columns), with and without vapour bypass, are considered. The focus is on closed operations, without product removal. Batch time requirements for operation in all columns are provided for both zeotropic and heteroazeotropic mixtures. The advantages and drawbacks of each configuration are discussed and compared based on dynamic simulations. The configuration of the vapour stream in the middle vessel has an important effect on the time requirements of the process. Later on, a detailed analysis of the process is provided and previous published work concerning different operation modes and separation strategies is put under the right perspective. Simple control schemes are proposed for the practical operation of the columns and the realisation of the desired steady state results. The thesis ends with a detailed feasibility study of the process. The possibilities and limitations raised by different operational modes and separation strategies are illustrated. Simple feasibility conditions and entrainer selection rules are formulated that allow someone to investigate feasibility of the process in a systematic and comprehensive manner.