2,040 research outputs found
Scaling-Up Eutectic Freeze Crystallization
No full textA novel crystallization technology, Eutectic Freeze Crystallization (EFC) has been investigated and further developed in this thesis work. EFC operates around the eutectic temperature and composition of aqueous solutions and can be used for recovery of (valuable) dissolved salts (and/or or acids) and water from a wide variety of aqueous process streams. Using EFC, processes producing large quantities of saline solutions could be carried out in an ecologically and economically attractive way. An introduction and a brief summary of earlier work are given in Chapter 1. The experimental study on pilot scale Cooled Disc Column Crystallizer (CDCC-2) designed for continuous EFC operation is presented in Chapter 2. CDCC-2 was tested for an industrial MgSO4 stream and evaluated in terms of heat transfer, ice and salt sizes, production and growth rates. Application of conductivity and refractive index measurement techniques for inline concentration and supersaturation measurements of MgSO4 solution was studied in Chapter 3. Chapter 4 presents the CDCC-3 and Skid Mounted Unit, designed and constructed for 130 ton/year MgSO4.7H2O and water production capacities. MgSO4 salt crystal structure at eutectic conditions was studied and reported in Chapter 5. The MgSO4 crystal hydrate formed below approximately 0 oC was proven to be MgSO4.11H2O instead of the common reported MgSO4.12H2O. Crystal structure analysis and the molecular arrangement of these crystals were determined using single crystal X-ray diffraction. Raman spectroscopy was used for characterizing MgSO4.11H2O and for comparing the vibrational spectra with MgSO4.7H2O. Thermo gravimetric analysis confirmed the stochiometry of MgSO4.11H2O. Additionally the Miller indices of the major faces of MgSO4.11H2O crystals were defined. Chapter 6 covers the discovery of the natural occurrence of the MgSO4.11H2O new mineral -Meridianiite- as salt inclusions in sea ice from Saroma Lake-Japan and in Antarctic ice. In Chapter 7 nucleation and crystal growth of MgSO4 aqueous solution on a cooled surface were studied theoretically and experimentally. Coupled heat and mass flux equations from non-equilibrium thermodynamics (Onsager theory with reciprocal relations) were defined for crystal growth and the temperature jump at the interface of the growing crystal. Chapter 8 aims to describe the Cyclic Innovation Model (CIM) and to set a path for commercialization of the EFC technology.Mechanical Maritime and Materials Engineerin
Development of Supported Liquid Membrane Extraction Processes for Slurry Treatment
No full textMechanical Maritime and Materials Engineerin
Removal and Recovery of Phosphonate Antiscalants
No full textIn reverse osmosis (RO) desalination processes, the use of phosphonates prevents scaling, thus allowing for a higher product water recovery, which increases the efficiency of the process. However, a major concern associated with their use in RO desalination is the high cost and environmental impacts associated with the discharge of the waste brine or membrane concentrate containing phosphonates. Therefore, technologies are needed that can remove and recover phosphonate antiscalants from membrane concentrates. Chapters 2 to 5 of this thesis describe a process for the removal and recovery of phosphonate antiscalants by using adsorption technology. In Chapter 2 the phosphonate adsorption capacities of two commercially available anion exchange resins and activated carbon were compared to that of the cheap waste material iron-coated waste filtration sand (WFS). The results presented showed that, in contrast to the exchange resins, the equilibrium adsorption of nitrilotris(methylene phosphonic acid) (NTMP) on WFS is not suppressed at increasing ionic strength and is much less affected by the competitive anions carbonate and sulfate. The strong affinity of phosphonate with the iron oxy-hydroxide in the coating resulted in a relatively high adsorption capacity for NTMP of this waste material. Iron oxy-hydroxides perform very well in adsorbing phosphonates from membrane concentrates. Therefore, an iron oxy-hydroxide was selected that, in contrast with WFS, has a high purity and can be obtained commercially. Granular ferric hydroxide (GFH) was investigated as an adsorbent for NTMP in Chapter 3. Both the equilibrium and kinetics of NTMP adsorption on GFH were investigated. The adsorption kinetics were predicted fairly well with two models that considered either combined film-pore or combined film-surface diffusion as the main mechanisms for mass transport. It was demonstrated that phosphonate is preferentially adsorbed over sulfate by GFH and that the presence of calcium is beneficial for the adsorption process. Calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Spent GFH is reusable after regeneration with a sodium hydroxide solution, showing that NTMP can be recovered from the RO concentrate. In analogy with Chapter 3, the adsorption and desorption of NTMP from RO membrane concentrate on iron-coated waste filtration sand (WFS) has been investigated in Chapter 4. Equilibrium adsorption was described well with a Langmuir isotherm. Although the low cost and on-site availability of WFS is advantageous over GFH, the results revealed some drawbacks. WFS appeared to have a much lower adsorption capacity compared to GFH, which was related to the presence of impurities, the presence of manganese oxides, and aging of the ferrihydrite phase in the coating of WFS. The aim of Chapter 5 was to employ GFH in a packed bed adsorption column. The effective diffusivities and external film mass transfer coefficients estimated in Chapter 3 were used to predict the concentration of phosphonate in the effluent. Also, the regeneration of the saturated column with sodium hydroxide solution was investigated. In addition, it was investigated whether the regeneration solution containing the recovered phosphonate could be further concentrated by using a nano-filtration or a calcium-phosphonate precipitation step. The use of nano-filtration seemed to be more attractive. The first five chapters show that adsorptive removal of phosphonate antiscalants offers a viable way to improve RO concentrate treatment processes and enables the recovery of the phosphonate for reuse in the RO desalination process. Another way of tackling the unwanted discharge of phosphonates is minimizing their use. Smart sensors that predict the risk of scaling at an early stage can help to control the dosage of phosphonate antiscalants. This will allow for minimum usage of phosphonates without the risk of scaling. Chapters 6, 7, and 8 contribute to the development of such a sensor. Focus was on the development of the actuator part of the sensor that enhances crystal growth and precipitation by ultrasonic irradiation. In Chapter 6 the effect of ultrasonic irradiation on the crystallization of calcite was investigated. Seeded calcite growth experiments were conducted under constant composition conditions while the applied ultrasonic irradiation created cavitation bubbles throughout the suspension. In this way it was demonstrated that ultrasound enhances the crystallization rate of calcite substantially (i.e., 46 %), due to the ability of the generated cavitation bubbles altering the crystals’ habit and size. The increased surface area available for crystal growth resulted in enhancement of the observed crystallization rate. In Chapter 7, the cavitation phenomena that are responsible for the previously observed volumetric crystallization rate enhancement were visualized using high speed photography. Cavitation clusters cause attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation causes deagglomeration only. Cavitation inception on the surface gave the small crystals momentum. However, it was shown that breakage of accelerated crystals by interparticle collisions is unrealistic because, upon bubble collapse, they subsequently experienced a deceleration much stronger than expected from drag forces. These direct observations contradict the general assumption that interparticle collisions always play an important role in particle attrition by cavitation. Scanning electron microscopy pictures of irradiated calcite crystals showed deep circular indentations, possibly caused by shockwave induced jet impingement. Moreover, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures. The possibility of using ultrasound as a tool to enhance the demineralization of supersaturated calcium carbonate solutions (e.g., membrane concentrates) containing growth inhibitors was investigated in Chapter 8. The inhibiting effect of the phosphonate NTMP on crystal growth can be mitigated by ultrasonic irradiation. The results can be explained in part by breakage and attrition of poisoned crystals, resulting in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that ultrasound can also degrade NTMP. These observations confirm in part the hypothesis that ultrasound can be used as actuator. As an alternative to the removal of phosphonates or minimizing their use by smart sensoring techniques, phosphonates may also entirely be replaced by environmental friendly antiscalants, which is the subject of Chapter 9. The effectiveness of such an alternative, carboxymethyl inulin (CMI) biopolymers, in inhibiting calcium carbonate crystallization was compared to two phosphonate antiscalants. Compared to the phosphonates, the biopolymers exhibited a stronger inhibitory effect on the crystal growth of calcite. It was shown that the ability of the biopolymers to mitigate the spontaneous precipitation of calcium carbonate is controlled by their degree of carboxylation. The biopolymers can affect the crystal habit similar to the phosphonates, which suggests that their function as crystal growth inhibitor is comparable. These results demonstrate that CMI biopolymers are effective calcium carbonate crystallization inhibitors, indicating they can replace phosphonates as antiscalant. In Chapter 10, the results presented in this work are being discussed and, where possible, placed into perspective of future desalination developments.Process and EnergyMechanical, Maritime and Materials Engineerin
Development of scraped eutectic crystallizers
No full textMechanical Maritime and Materials Engineerin
Mixed Solvent Reactive Recrystallization of Sodium Carbonate
No full textInvestigation of the reactive recrystallization of trona (sodium sesquicarbonate) and sodium bicarbonate to sodium carbonate (soda) in a mixed solvent led to the design of several alternative, less energy consumptive, economically very attractive process routes for the production of soda from all principal sodium carbonate sources. The kinetics of the recrystallization as well as of the superimposed chemical reaction, the decomposition of the bicarbonate ion, have been measured, a thermodynamic model for the prediction of the transition temperatures for hydrate recrystallization is presented and the different occurring recrystallization mechanisms are explained in detail. In addition, several inline purification processes for the recycle of the mixed solvent have been investigated: electrodialysis, ion exchange and reactive extraction. The formed soda of mixed solvent reactive recrystallization was also found to possess higher chemical purity, higher mechanical stability and lower bulk density than commercially available soda (dense soda ash).Design, Engineering and Productio
Supercritical Fluid Extraction of Metals from Contaminated Solid Matrices
No full textMechanical Maritime and Materials Engineerin
Effect of Ultrasound on Calcium Carbonate Crystallization
No full textScaling comprises the formation of hard mineral deposits on process or membrane equipment and calcium carbonate is the most common scaling salt. Especially in reverse osmosis (RO) membrane systems, scale formation has always been a serious limitation, causing flux decline, membrane degradation, loss of production and elevated operating costs. In this work a novel concept is proposed for the prediction of scale formation tendency. By enhancing the crystallization (kinetics) locally and monitoring the process itself, scaling can be predicted accurately before it occurs in the bulk solution. This will result in better scaling risk assessment, improving chemical dosage (preventing overdosing) and prevent the necessity of cleaning or membrane replacement. Ultrasound is selected as possible method for crystallization enhancement. Consequently, the topic of this research is the effect of ultrasound on crystallization of calcium carbonate.BiotechnologyApplied Science
Cotton Dyeing in Supercritical Carbon Dioxide
No full textMechanical Maritime and Materials Engineerin
Towards Zero Liquid Discharge in drinking water production
No full textNanofiltration (NF) and reverse osmosis (RO) membranes are used to produce clean water, but also produce a concentrate stream which contains most of the contaminants. Discharging concentrate streams to the environment is hindered by regulations, which are becoming more strict, and by the desire of recovering every single valuable atom. Therefore, the minimization of the concentrate volume to almost zero, is required in order to make treatment of the concentrate feasible. Currently several research studies are being conducted to find smart zero liquid discharge (ZLD) strategies in water desalination. In this PhD work the feasibility of reaching very high recovery (which equals a very low volume of concentrate) in a system consisting of cation exchange pretreatment, NF and RO (with the RO implemented on the NF concentrate to increase feed water recovery) was studied. The outcome of this research indicates that the nearly ZLD concept is technically possible, with the right combination of techniques. The studied system could be applied for the production of drinking water from ground water or surface water with high concentrations of bivalent cations, silica and/or organic micropollutants.BiotechnologyApplied Science
Dry-cleaning with high-pressure carbon dioxide
No full textDry-cleaning is a process for removing soils and stains from fabrics and garments which uses a non-aqueous solvent with detergent added. The currently most used dry-cleaning solvent is perchloroethylene (PER), which is toxic, environmentally harmful and suspected to be carcinogenic. Carbon dioxide could be an ideal solvent to replace PER; carbon dioxide is non-toxic, non-flammable, ecologically sound, cheap, non-corrosive, available on a large scale, and can therefore serve as a permanent sustainable alternative for the currently used solvents. In this work, a dry-cleaning process using high-pressure carbon dioxide has been investigated and optimized. A disadvantage of CO2 is its limited ability to dissolve polar molecules. However, the characteristics of CO2 can be modified by the addition of a co-solvent. Various co-solvents have been investigated of which 2 propanol (IPA) was the most suitable. For most non-particulate soils, the results using CO2, water and IPA were comparable to the results using PER. For particulate soils, however, the cleaning-results using CO2, water and IPA were worse than with PER. Particulate soils can be removed from textile by mechanical action and/or surfactants. Only relatively large particles (>20 µm) could be removed in CO2 by increasing the mechanical action. Unfortunately, increasing the mechanical action had no positive influence on the removal of small particles (<20 µm). In order to remove small particles in CO2, surfactants have to be used. Amino acid based surfactants have been studied. For the production of amino acid based surfactants, renewable, low-cost raw materials are used. Furthermore, these surfactants have a low toxicity, are biodegradable and are not irritating to the skin. These characteristics make the amino acid based surfactants attractive for dry-cleaning with carbon dioxide. The amino acid based surfactants gave good results for dry-cleaning with liquid CO2. The surfactant Amihope LL (N lauroyl L lysine) gave the best cleaning-results. An important process parameter using this surfactant was the addition of water. The addition of water is required for sufficient removal of non-particulate soils. However, when no water was added to the system, there was a large increase in particle removal. Therefore, a 2-bath process was proposed. The first bath is for particulate soil removal and has optimal conditions for particulate soil removal; the second bath has optimal conditions for non-particulate soil removal. The 2-bath process using Amihope LL gave good results: the result for particulate soil removal was 84 % compared to the results for PER, the result for non-particulate soil removal was 98 % compared to PER and the overall result was 92 % compared to PER. All surfactants that gave good results for particulate soil removal (anionic, amine and amino acid based surfactants) were, surprisingly, hardly soluble in CO2 and were (largely) present as solid particles. The mechanisms that may play a role in particulate soil removal using the surfactant Amihope LL were investigated. The cleaning action of the surfactant is probably a combination of adsorption and mechanical action. An economic evaluation shows that the costs for dry-cleaning using the optimized CO2-process are equal to the costs of the PER-process. Recycling of the surfactant and the co-solvent can lower the costs of the CO2-process further.Design, Engineering and Productio
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