Effect of surface potential upon crystallization kinetics of citric acid

Bu çalışmada, elektriksel yüzey potansiyelinin sitrik asit kristallerinin büyüme ve çözünme kinetiğine etkisi araştırılmıştır. Yüzey yüklerine göre sınıflandırılmış kristallerin düşük ve yüksek yüzey yüklü olanlarının büyüme ve çözünme davranışları tek kristal hücresinde incelenmiştir. Deneysel veriler, incelenen tüm kristaller için yüksek yüzey yüklü olanların büyüme hızlarının, düşük yüzey yüklülere göre daha yüksek, çözünme hızlarının ise daha düşük olduğunu göstermiştir. Tüm deney sonuçları, yüzey potansiyelinin büyüme ve çözünme davranışını etkilediğini göstermiştir. Ortaya konan teori ve elde edilen deneysel bulgular, yüzey potansiyelinin kristalin büyüme ve çözünmesi üzerine olan etkisinin Knapp etkisi ile açıklanabileceğini göstermekte, kristal büyüme ve çözünmesindeki saçılmaların nedenini açığa kavuşturabilmektedir.Anahtar Kelimeler: Elektrostatik ayırma, elektriksel yüzey potansiyel, kristal büyüme ve çözünmesinde saçılma, Knapp etkisi, sitrik asit monohidrat.The effect of an electrical surface potential upon the crystal growth and dissolution kinetics of citric acid monohydrate was studied in the present work.. At first stage of the study, citric acid crystals were classified by means of electrostatic separator in according to their electrical surface potentials. From classification it was found out that crystals with different size have their own distinctive intrinsic surface potential distributions. At the second stage, a growth and dissolution behavior of low and highly charged crystals of citric acid were examined in a single crystal growth cell measurement system. Experimental data showed that growth rates of highly charged crystals of citric acid monohydrate under the same super saturation level were much higher in comparison to low charged ones, whereas dissolution rates under the same instauration level were much lower. All single crystal experimental results obtained for citric acid monohydrate showed that the surface potential affects growth and dissolution rates of crystals. Proposed theory and obtained experimental findings show that it is possible to explain the effect of electrical surface potential upon crystal growth and dissolution kinetics by introducing Knapp?s effect and the reasons for dispersion phenomena encountered in growth and dissolution rates of citric acid monohydrate.Keywords: Crystal growth and dissolution rate dispersion, citric acid monohydrate, electrostatic separator, electrical surface potential, Knapp´s effect

Development of a new method for the boric acid production process from colemanite ore

Kolemanitten borik asit üretiminde mevcut teknolojideki temel sorun kolemanit cevheri içindeki yan minerallerin reaksiyon ortamında bozunmasıyla safsızlık sorunu yaratarak prosesten, verim düşüklüğüne neden olan çözelti deşarjı gerektirmesidir. Çalışmanın amacı, reaksiyonun sülfürik asit yanında propionik asit veya kalsiyum propionat katkılı ortamda gerçekleştirilerek proseste safsızlık kontrolünün mümkünlüğünü araştırmak, uygun proses koşullarını belirlemek ve yeni bir üretim prosesi geliştirmektir. Farklı proses alternatifleri değerlendirilerek proseste devreden bileşenin kalsiyum propionat olduğu yöntem seçilerek modellenmiştir. Kimyasal ve mineralojik yapıları belirlenmiş beş değişik tenörlü kolemanit cevherlerinin %10’luk propionik ve sülfürik asitlerle bozundurulmasıyla çözeltiye safsızlık geçişleri incelenmiş ve propionik asitli ortamda kil minerallerinin bozunmasının engellenebileceği belirlenmiştir. Değişik oranda propionik asit-sülfürik asit karışımları ve değişik tenörlü kolemanit cevherleri kullanılarak kesikli veya sürekli çalışan reaktörde reaksiyonun yürüyüşü ve çözeltiye geçen safsızlıklar izlenmiş ve reaksiyonda oluşan süspansiyonların filtrasyon hızları ölçülmüştür. Deneylerden, kalsiyum propionat varlığının çözeltiye geçen magnezyum ve silis konsantrasyonlarını önemli ölçüde azalttığı, sodyum ve potasyum geçişini ise hemen hemen engellendiği görülmüştür. Ortamdaki kalsiyum propionat oranı arttıkça, kalsiyum propionatın kil minerallerini dağıtması nedeni ile filtrasyon hızının düştüğü belirlenmiştir. Sonuç olarak, kolemanitten sülfürik asit yanında kalsiyum propionat kullanılmasına dayanan yeni borik asit üretim prosesinde çözeltiye safsızlık geçişi azaltılarak proses veriminin yükseltilebileceği gösterilmiştir.   Anahtar Kelimeler: Borik asit, kolemanit, propionik asit, proses geliştirme, safsızlık kontrolü.The most important problem of the current boric acid production process from colemanite ore is the decomposition of side minerals in colemanite ore in the reaction media, which leads to impurity problems and causes some of the process liquor to be purged, therefore process efficiency decreases and environmental problems arise. The aim of this study is to investigate the possibility of impurity control in the process by performing the reaction in the presence of propionic acid or calcium propionate beside sulfuric acid, to determine the appropriate process conditions and to develop a new process that can be an alternative to the conventional one using solely sulfuric acid. Since intake of the impurities into the solution is sourced from the side minerals in the colemanite ore in the boric acid production process, it is necessary to determine the chemical and mineralogical structure of the colemanite ores and their interaction with acids. For this purpose, firstly, chemical and mineralogical structures of different colemanite ores were determined. Subsequently, the concentration of impurities captured by the solution in the presence of solely propionic acid by decomposing these ores with 10% propionic acid solutions, and, the amount, the chemical and mineralogical structure of the remaining solid obtained from these decompositions were determined. Concentrations of impurities transferred into the solution were determined by also decomposing these ores with 10% sulfuric acid solutions. By comparing the concentrations of sodium, potassium, magnesium and aluminum in solutions obtained by decomposing ores in propionic and sulfuric acid solutions, where these impurities do not precipitate, it was concluded that in the presence of propionic acid the decomposition of clay and feldspar minerals could be prevented. After assessing alternative models, the process model in which calcium propionate is the recycling component was selected and modeled. Batch and continuous reaction and filtration experiments were performed in accordance with this model. Advance of the reaction was followed by chemical analysis, transfer rates of the impurities into the solution were determined during batch reactions of different colemanite ores with different propionic acid-sulfuric acid mixtures and the filtration rates of the suspensions obtained from the reactions were measured under constant pressure difference. It was determined that the reactions could be performed in conformity with the model, provided that the concentration of calcium propionate is lower than 3% in the production liquor in order to prevent calcium borate precipitation. Impurity concentrations captured by 18% boric acid solution in reaction conditions were determined and considered as the unavoidable impurity concentrations. By taking these unavoidable concentrations into consideration, it was shown that the concentrations of magnesium and silica transferred into the solution could dramatically be decreased and the transfer of the sodium and potassium could practically be prevented in the presence of propionic acid. Based on the filtration rate measurements of reaction products, it was determined that the filtration rates were decreased by increasing concentrations of calcium propionate in the media and the cause of this decrease was the swelling and consequently the dispersion of the clay minerals in the presence of calcium propionate. It was investigated whether the reactions are performed in accordance with the model in the reac-tions of different colemanite ores with different sulfuric acid-propionic acid mixtures in the continuous reaction system. The impurity intake of the solutions obtained from the reactions was determined. Similar to the results obtained from batch reaction experiments, it was found out that the intake of magnesium, silica, sodium and potassium to the solution was decreased dramatically. From the measurements of first and second filtration rates under constant pressure difference, similar results were obtained to those obtained from batch experiments. In conclusion, it was shown that product quality and process efficiency could be increased and the environmental impact of the process could be decreased by decreasing the impurity intake of the solution in the new boric acid production process based on the reaction of colemanite ore with sulfuric acid in the presence of calcium propionate.  Keywords: Boric acid, colemanite, propionic acid, process development, impurity control

Effect of surface potential upon the crystal growth and dissolution rates of potassium chloride

Bir maddenin aynı boyuta sahip kristallerinin aynı ortam ve şartlarda birbirlerinden farklı hızlarda büyüdükleri uzun zamandır bilinmektedir. Bu olay, büyüme hızındaki saçılma (Growth Rate Dispersion) olarak tanımlanır. Çözeltide bulunan anyon ya da katyonların kristal yüzeyine seçimli adsorpsiyonları nedeniyle kristaller farklı yüzey potansiyelleri kazanırlar. Bu olay büyüme hız saçılımının nedenlerinden bir tanesidir. Bu çalışmada büyümede saçılım gösterdiği bilinen KCl kristallerinin büyüme ve çözünme hızları üzerine yüzey potansiyelinin etkisi durgun ortam tek kristal ölçüm sisteminde incelenmiştir. Deneylerde, elektrostatik ayırıcıda sırasıyla 1, 3, 5, 9 ve 16 kV ayırma voltajları uygulanarak yüzey potansiyellerine göre sınıflandırılmış olan (-425+300) μm boyut bölgesindeki KCl aşı kristalleri kullanılmıştır. Saf ortamda gerçekleştirilen deneylerde, büyüme ve çözünmenin olmadığı bir ölü bölgenin varlığı tespit edilmiştir. Deneylerde elde edilen bir diğer sonuç, büyümenin başladığı duruma göre nispeten düşük sayılabilecek aşırı doygunluklarda dentritik büyüme görülürken, yüksek aşırı doygunluklarda çok farklı bir büyüme mekanizmasının ortaya çıkmasıdır. Yüksek aşırı doygunluklarda dentritik büyüme yanında yüzeye dik olarak fışkıran uzun ve çok ince iğnecikler zamanla büyüyerek çok farklı büyümüş kristal görünümünü ortaya çıkartmaktadır. Bu davranışla farklı voltajlarda ayrılan tüm kristallerde karşılaşılmıştır. Bu tip büyüme davranışının, artan ayırma voltajının artışına bağlı olarak azalma gösterdiği görülmüştür. Yapılan bu deneysel çalışma ile, KCl kristallerinin sahip oldukları yüzey potansiyellerinin büyüme ve çözünme hızları üzerinde önemli rol oynadıkları gösterilmiştir. Anahtar Kelimeler: Kristalizasyon, yüzey potansiyeli, büyüme hız saçılımı, elektrostatik ayırma, KCl.Crystallization is a very complex operation. The main reason of this complexity is the number of mass transfer steps involved in the process. In a supersaturated solution, the first step is the creation of a new surface by nucleation; then solvated growth units diffuse to the surface and are adsorbed onto it. Surface migration then occurs followed by desorption back into solution or incorporate into the crystal lattice (Davey, 1976). These steps are governed by different physical laws which are not explained completely. Growth rate dispersion (GRD) is one of the phenomena which is difficult to explain. Growth rate dispersion can be described as the difference in the growth rate of crystals which are of the same size at the time when the growth process was started (Ulrich, 1989). Explanation of this difference is based on a well-known BCF theory developed by  Burton et al., (1951). They suggested that the different growth rates were resulted from the distribution of dislocation sites on the crystal surfaces. Dislocation sites which have low attachment energy lead to the formation of the specific ion adsorption on the surface. The probable reason of specific ion adsorption is the different hydrated diameters of the ions. Details of this double layer formation can be found elsewhere (Kuşkay and Bulutcu, 2003).  The surface potential resulting from electrical double layer formation  dominates the growth and dissolution behavior through two different mechanisms. The first mechanism was explained by Knapp (1922). According to this theory, the higher the surface potential, the lower the equilibrium concentration. For this reason, crystals having higher surface potential will grow relatively in higher supersaturated conditions. The second mechanism was related to electrical double layer. The surface potential acts as an additional resistance to mass transfer, so that it will reduce the growth rate of the crystals. Surface charge can be measured easily in the case of sparingly soluble substances. But in the case of highly soluble salts it is difficult or sometimes impossible to measure it by the present technologies. But its effect can be still detected by indirect methods; such as changing the crystal growth rates in the presence of polyelectrolytes in different charge density (Sayan, 1995; Titiz, 1995).  Measuring the crystal growth rates of crystals separated with respect to their surface potential is another indirect method. Şahin and Bulutcu (2001) and İlyaskarov (2002) made experiments systematically using different types of crystals which were separated in an electrostatic separator and the crystal growth /dissolution rates were determined in each crystal group having different surface potential. KCl is one of the crystalline material showing surface potential distributions originating from specific ion adsorption (or desorption) to defected sites on the crystal surface, in its own solution. The aim of this work is to investigate the effect of surface potential on the growth rate and growth behavior of KCl in pure KCl solution. Closely sized KCl crystals were separated to sub fractions in an electrostatic separator at different voltages in the range of 0-1, 1-3, 3-5, 5-9 and 16 kV and separation voltages were taken as a measure of surface potential of each sub fraction. Crystal growth and dissolution rates of these crystal fractions were measured at around 20 oC in a stagnant type single crystal cell using an image analyzer system. Experiment showed that growth and dissolution rates versus supersaturation plots had a dead zone in which no detectable growth was observed. Widths of dead zone were slightly different for the crystals having different surface potential. During the growth of KCl crystals surface nucleation was always dominant, even at very low supersaturations. At moderate and high supersaturation levels very unusual growth behavior were observed. In this region growth of crystals were dominated by the very thin but very long rod-like crystal branches growing perpendicular to the surface and their separately growing products on the brances. For this reason, seed crystals lost their original shape during the growth process. Frequency of the formation of branches from growing surface was the function of supersaturation and surface potential. From the experimental data the role of surface potential was shown to explain the reason of growth and dissolution rates dispersions of KCl. Keywords: Crystallization, surface charge, growth rate dispertion, electrostatic separation, KCl

Effects of the noncompetitive N‐methyl‐d‐aspartate receptor antagonists ketamine and MK‐801 on pain‐stimulated and pain‐depressed behaviour in rats

BackgroundPain is a significant public health concern, and current pharmacological treatments have problematic side effects and limited effectiveness. N‐methyl‐d‐aspartate (NMDA) glutamate receptor antagonists have emerged as one class of candidate treatments for pain because of the significant contribution of glutamate signalling in nociceptive processing.MethodsThis study compared effects of the NMDA receptor antagonists ketamine and MK‐801 in assays of pain‐stimulated and pain‐depressed behaviour in rats. The nonsteroidal anti‐inflammatory drug ketoprofen was examined for comparison as a positive control. Intraperitoneal injection of dilute acid served as an acute visceral noxious stimulus to stimulate a stretching response or depress intracranial self‐stimulation (ICSS) in male Sprague–Dawley rats.ResultsKetamine (1.0–10.0 mg/kg) blocked acid‐stimulated stretching but failed to block acid‐induced depression of ICSS, whereas MK‐801 (0.01–0.1 mg/kg) blocked both acid‐stimulated stretching and acid‐induced depression of ICSS. These doses of ketamine and MK‐801 did not alter control ICSS in the absence of the noxious stimulus; however, higher doses of ketamine (10 mg/kg) and MK‐801 (0.32 mg/kg) depressed all behaviour. Ketoprofen (1.0 mg/kg) blocked both acid‐induced stimulation of stretching and depression of ICSS without altering control ICSS.ConclusionThese results support further consideration of NMDA receptor antagonists as analgesics; however, some NMDA receptor antagonists are more efficacious at attenuating pain‐depressed behaviours.What does this study addNMDA receptor antagonists produce dissociable effects on pain‐depressed behaviour.Provides evidence that pain‐depressed behaviours should be considered and evaluated when determining the antinociceptive effects of NMDA receptor antagonists.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134264/1/ejp847_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134264/2/ejp847.pd

The growth and dissolution of ammonium perchlorate crystals in a fluidized bed crystallizer

The growth and the dissolution of ammonium perchlorate crystals were studied in pure and in sodium chloride containing aqueous solutions, in a fluidized bed crystallizer. The presence of sodium chloride in the solution reduced the growth and the dissolution rates of ammonium perchlorate crystals. The growth rates were interpreted in terms of supersaturation levels. The orders and rate constants were reported. The effectiveness factors were estimated from the growth rate data to evaluate the relative magnitude of the two resistances in series, diffusion and integration. The controlling mechanism is mainly by diffusion for the crystal growth of ammonium perchlorate in pure aqueous solution. However, both diffusion and integration steps affect the growth of ammonium perchlorate crystals in the presence of sodium chloride in solution. (C) 1998 Elsevier Science B.V. All rights reserved

Crystallization kinetics of ammonium perchlorate in MSMPR crystallizer

The effects of supersaturation level, sodium chloride (NaCl) as impurity, and the suspension density of the crystallizer content on the crystallization kinetics of ammonium perchlorate (AP) were studied in a mixed-suspension mixed-product removal crystallizer. The product crystals have a plate-like morphology. The crystal size distribution is not affected by the supersaturation level. There was a deviation from the ideal population density where the growth rate of pure AP crystallization was size dependent with the order of 0.4 according to Abegg, Stevens and Larson (ASL) model, However, the ASL model was not found to be suitable to express the growth rate of the crystals in NaCl containing AP solution. Also when suspension density of the crystallizer increased, secondary nucleation was observed