Comparison of Solid-Liquid and Liquid-Liquid Mass Transfer

Abstract

Mass transfer from solutions of m-acetotoluide, phenacetin and salicylamide into a stationary solvent, water, was studied. A sharp concentration jump was found at the leading solute front for all three liquid-liquid systmes. A comparison was made between the mass transferred in solid-liquid and liquid-liquid systems. The dissolution of m-acetotoluide, phenacetin and salicylamide was compared with mass transfer of solute from solutions with concentrations C_i, 2C_i and C_s into the pure solvent. In all cases, the amount dissolved from the solid was approximated by the C_i or the 2C_i-solvent system with the amount transferred in the C_s-solvent system approximately 100 fold greater than was dissolved from the solid. It was concluded that a concentration much less than saturation exists at the solid-liquid interface and that dissolution of the three compounds studied is controlled by the rate of solvent interaction at the solid surface.     

Influence of Certain Additives on the Diffusion Rate of Aspirin, Salicylamide and Phenacetin Through the Rat's Ileum

The diffusion rate of aspirin, salicylamide and phenacetin through the rat's ileum was found to be concentration dependent. The presence of glucoseamine hydrochloride decreased the amount diffused from each drug. The higher diffusion rate of aspirin was happened in presence of 0.01% w/v Myrj 59, followed by Brij 58 and then cetrimide. While that of salicylamide increased in presence of 0.01% w/v Tween 80. The more convenient increase in the diffusion rate of phenacetin produced in presence of 0.01% w/v Tween 20 and 0.3% w/v sodium lauryl sulfate. The other tested surfactants either reduced the amounts of drugs diffused or produced insignificant effect. With regard to the effect of aliphatic acids-drugs solid dispersions, tartaric acid increased the diffusion rate of aspirin; citric, tar taric and succinic acids as well as PEG 4000 increased the diffusion rate of salicylamide while, succinic acid increased the diffusion rate of phenacetin through the rat's ileum.     

A study on liquid-liquid distribution based on single picoliter droplets and in situ electrochemical measurements

A microelectrode technique combined with the microcapillary injection/manipulation of a single organic droplet in water was developed. The technique was applied to the study of the distribution of a ferrocene derivative across a single-picoliter-nitrobenzene-droplet/water interface and to the simultaneous in situ electrochemical determination of the distributed solute in the picomole-femtomole range. The liquid-liquid distribution processes were discussed in terms of droplet size and solute concentration (in water) dependencies of the interfacial mass transfer rate.     

Kinetic approach to the release of vinyl chloride monomer from polymer films,as related to diffusional theories

Monomer-release kinetics from polyvinyl chloride films, previously saturated by equilibration with monomer solutions in $\text{n}$-hexane, ethylene glycol monomethylether, methanol, and water, were measured by extraction with these model solvents, at 10–50 °C. Solute desorption rate data fitted a linear plot of total amount of solute released $\text{vs}$. the square root of time. Their analysis, in terms of diffusional release theory of a dissolved solute from a polymer matrix with initial solute loading given by the solubility limit, allowed one to obtain diffusivities of vinyl chloride in the polymer as a function of temperature, from which an activation energy of 11.9 ± 0.9 Kcal/mol could be calculated. Release kinetics were practically controlled by the low diffusivities, without any resistance to solute transport due to external mass transfer coefficients. The accelerating influence of solvents, relative to solvent-free experiments reported in the literature, may be compared to a plasticizing penetrant effect, which, however, does not appear to be susceptible, as to its bearing on diffusivities, to the chemical nature of the solvent used.     

Improved Dissolution of Indomethacin in Coprecipitates with Phospholipids-I

Indomethacin powders were blended with phospholipids to prepare physical mixtures or made into solid dispersions by the solvent method and their comparative dissolution profiles were studied. Indomethacin exhibited significantly improved dissolution rates in phospholipid coprecipitates compared to either the physical mixtures or the pure indomethacin. The coprecipitates of lecithin-indomethacin 1:16 weight ratio had a 6.5 fold greater initial dissolution rate, and the total amount dissolved after 60 minutes was 140% greater compared to indomethacin alone. Increasing the lecithin content to 1:4 resulted in only a modest additional increase in the initial dissolution rate (40%) and the limiting concentration (14%)     

考虑微观结构影响的混凝土界面过渡区裂隙渗流-溶蚀耦合模型

根据四参数随机生长法生成了混凝土界面过渡区(ITZ)的微观结构,基于格子Boltzmann方法,采用双分布函数分别模拟渗流速度场和溶质浓度场的演化,建立了考虑微观结构影响的ITZ裂隙渗流-溶蚀耦合过程的数值模型。结合2个经典算例,验证了计算模型在处理溶质对流-扩散及反应-扩散问题方面的准确性。最后讨论了渗流流速、Ca(OH)₂含量以及Ca(OH)₂排布状态等因素对ITZ裂隙渗流-溶蚀耦合作用特性的影响。研究表明:裂隙初始渗流流速越快,壁面的溶蚀速率越快,其整体孔隙率增加越快。ITZ的Ca(OH)₂含量越高,在壁面处其与流体的接触面积越大,溶蚀现象越易发生,并导致裂隙内Ca2+浓度也相应的增加。如果溶蚀出来的Ca2+得不到及时运移,将反过来抑制Ca(OH)₂的进一步溶蚀,故ITZ裂隙的渗流-溶蚀过程受控于Ca(OH)₂含量与Ca2+浓度的综合作用。对于Ca(OH)₂不同排布状态的ITZ裂隙,由于渗流受到微观结构的影响,溶蚀过程稳定后其相对渗透率水平生长最大,均匀生长次之,竖向生长最小。     

A New Approach for Enhancing the Dissolution Rate of Phenacetin

Numerous attempts are conducted so as to develop a rapid dissolution rate for those poorly water-soluble drugs. A new approach for enhancing the intrinsic dissolution rate of phenacetin is ascribed. This technique is based on the concept of the recrystallization of phencetin from different surfactants concentrations. The observed enhancing effect in the dissolution rate of phenacetin, using this technique, may be cue to wetting and/or deaggregation effect. The dissolution rate study was investigated in 0.1 N HC1 at 37°C and 50 r.p.m. The experimental study showed that the dissolution rate, during the first few minutes, is markedly affected by this technique. The relative area under the curve from 0 to 30 minutes (R.A.U.C.) was used as a parameter to 0-30 compare the different dissolution rates of the drug after being recrystallized from 1% w/v of each surfactant solution. The extent, in the dissolution rate enhancing effect, was found to range from 2.66 to 3.25 times of that of the control. This technique is valuable as a preformulation phase of phenacetin in solid dosage forms.     

A New Approach for Enhancing the Dissolution Rate of Phenacetin

Abstract

Numerous attempts are conducted so as to develop a rapid dissolution rate for those poorly water-soluble drugs. A new approach for enhancing the intrinsic dissolution rate of phenacetin is ascribed. This technique is based on the concept of the recrystallization of phencetin from different surfactants concentrations. The observed enhancing effect in the dissolution rate of phenacetin, using this technique, may be cue to wetting and/or deaggregation effect. The dissolution rate study was investigated in 0.1 N HC1 at 37°C and 50 r.p.m. The experimental study showed that the dissolution rate, during the first few minutes, is markedly affected by this technique. The relative area under the curve from 0 to 30 minutes (R.A.U.C.) was used as a parameter to 0–30 compare the different dissolution rates of the drug after being recrystallized from 1% w/v of each surfactant solution. The extent, in the dissolution rate enhancing effect, was found to range from 2.66 to 3.25 times of that of the control. This technique is valuable as a preformulation phase of phenacetin in solid dosage forms.     

An Improved Method for Scheduling Independent Tasks

A computationally efficient algorithm is developed for scheduling an independent task set, characterized by deterministic processing times and due dates, on a single processor so that total tardiness is minimized. The performance index is assumed to be a loss function of the form max (0, C_i - D_i) where C_i is the calendar completion time of task i and D_i, is its due date. The method is in general sub-optimal, but conditions are given for which an optimal schedule is always obtained. In addition, a technique is presented for improving suboptimal solutions by merely interchanging certain nonadjacent pairs of tasks.     

Continuous extraction and destruction of chloro-organics in wastewater using ozone-loaded Volasiltrade mark245 solvent

Extracting waterborne contaminants to ozone-loaded Volasiltrade mark245 (a siloxane solvent in which ozone is ten times more soluble than water) has been studied as a means of enhancing reaction kinetics and thus, providing more rapid wastewater decontamination. Investigation was carried out with respect to 2-chlorophenol and dichloromethane. Using a pilot scale continuous flow liquid-liquid/ozone water treatment system, 2-chlorophenol was extracted to the ozone-loaded solvent phase and considerable extents of destruction were achieved. However, the approach was demonstrated to yield slightly less destruction than direct gas contact for the same utilization of ozone and enhanced reaction kinetics were not shown to occur. This was suggested to be due to increased interfacial mass transfer resistance and/or the promotion of less destructive reaction pathways. Modification of the existing pilot system, by conversion from co- to counter-current solvent-loading, enabled greater dissolved ozone concentrations to be achieved within the solvent. Increasing the counter-current exchange column height to approximately 2.5m was suggested for achieving a near optimum level of performance. The liquid-liquid/ozone approach was demonstrated to be an effective means of indirectly exposing wastewater contaminants to concentrated ozone. As such the technology may be applicable as an alternative to direct gas contact in instances where the avoidance of contaminant sparging is desired (i.e. where contaminants are highly volatile, pungent and/or toxic) or foaming occurs.     

Carbamazepine and Polyethylene Glycol Solid Dispersions: Preparation, in Vitro Dissolution, and Characterization

The objective of this study was to prepare solid dispersions of carbamazepine (CBZ) using polyethylene glycol (PEG) 4000 and PEG 6000, measure the dissolution, and characterize using x-ray diffraction, DSC, and IR spectroscopy. Solid dispersions were prepared by either the melt or solvent methods. A comparison of dissolution profiles of the solid dispersions indicated dramatic increases in the rate and extent of CBZ dissolution from solid dispersions. The dissolution of physical mixtures provided evidence of the solubilizing effects of PEGs. Untreated CBZ exhibited 10.09 ± 2.92% dissolution in 10 min (D_l0); whereas, a melt of PEG 6000 and CBZ at a ratio of 6: 1 provided 36.49 ± 1.97% and a melt of PEG 4000 and CBZ at a ratio of 6: 1 gave a D₁₀ of 23.59 ± 1.45%. The rate and extent of dissolution of CBZ were significantly higher when blends of the PEGs were employed to prepare solid dispersion. The melt method provided significantly higher rate and extent of dissolution of CBZ than the solvent method. Also, the rate and extent of dissolution of CBZ were significantly greater when the solid dispersion was cooled at room temperature as opposed to with ice (faster). X-ray diffractometry revealed almost a complete loss of crystallinity of CBZ in solid dispersions. IR spectrometry indicated an increase in amorphocity of the PEGs after melting. IR spectra suggested that no complexation occurred between the PEGs and CBZ. Alterations in the crystallinity of the system were also supported by the DSC thermograms. Decreasing heats of fusion implied decrease in crystallinity, which would be expected to provide greater dissolution rates. Peak melting temperatures obtained from the thermograms ruled out the possibility of the formation of a eutectic mixture. However, the formation of solid solution could also be a possible mechanism for the increase in dissolution.     

Purification process by solution zone passages

The travelling heater zone-refining process and its relation to the travelling solvent and travelling heater methods of growing single crystals are described. The variation of the zone composition during the zone passage is derived, proceeding from the solute-impurity-solvent diagrams, and the impurity distribution along the crystallisate, after a zone passage, is derived, by considering that the solute and the impurity form either a solid solution or an eutectic. The influence of the parameters which determine the distribution is discussed. The impurity distribution along the crystallisate after a number of zone passages is derived. The application of the process is suitable in the case of a sub-unity distribution coefficient, the zone passage efficiency being higher, the smaller the distribution coefficient and the steeper the slope of the dissolution straight line. The process is particularly advantageous when the solute and the impurity form an eutectic. It is advantageous to select a high dissolution temperature, close to the solvent boiling temperature, and a crystallisation temperature as near as possible to the dissolution temperature, when the solute and the impurity form either a solid solution or an eutectic.     

Supercritical Antisolvent Versus Coevaporation— Preparation and Characterization of Solid Dispersions

The objective of this work was to improve the dissolution rate and aqueous solubility of oxeglitazar. Solid dispersions of oxeglitazar in PVP K17 (polyvinilpyrrolidone) and poloxamer 407 (polyoxyethylene-polyoxypropylene block copolymer) were prepared by supercritical antisolvent (SAS) and coevaporation (CoE) methods. Drug-carrier formulations were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, gas chromatography, UV/VIS spectroscopy and in vitro dissolution tests. The highest dissolution rate (nearly 3-fold higher than raw drug) was achieved by preparation of drug/PVP K17 coevaporate. Oxeglitazar/PVP K17 solid dispersions were stabilized by hydrogen bonding but contained higher amount of residual dichloromethane (DCM) than poloxamer 407 formulations regardless of the method of preparation. SAS prepared oxeglitazar/poloxamer 407 dissolved more than two times faster than raw drug. However, unlike PVP K17, poloxamer 407 did not form a single phase amorphous solid solution with oxeglitazar which has been manifested in higher degrees of crystallinity, too. Among the two techniques, evaluated in this work, conventional coevaporation resulted in higher amorphous content but SAS reduced residual solvent content more efficiently.     

Supercritical antisolvent versus coevaporation: preparation and characterization of solid dispersions

The objective of this work was to improve the dissolution rate and aqueous solubility of oxeglitazar. Solid dispersions of oxeglitazar in PVP K17 (polyvinilpyrrolidone) and poloxamer 407 (polyoxyethylene-polyoxypropylene block copolymer) were prepared by supercritical antisolvent (SAS) and coevaporation (CoE) methods. Drug-carrier formulations were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, gas chromatography, UV/VIS spectroscopy and in vitro dissolution tests. The highest dissolution rate (nearly 3-fold higher than raw drug) was achieved by preparation of drug/PVP K17 coevaporate. Oxeglitazar/PVP K17 solid dispersions were stabilized by hydrogen bonding but contained higher amount of residual dichloromethane (DCM) than poloxamer 407 formulations regardless of the method of preparation. SAS prepared oxeglitazar/poloxamer 407 dissolved more than two times faster than raw drug. However, unlike PVP K17, poloxamer 407 did not form a single phase amorphous solid solution with oxeglitazar which has been manifested in higher degrees of crystallinity, too. Among the two techniques, evaluated in this work, conventional coevaporation resulted in higher amorphous content but SAS reduced residual solvent content more efficiently.     

Preparation and characterization of coenzyme Q10-Eudragit solid dispersion

A solid dispersion of Coenzyme Q10 and Eudragit L 100-55 was prepared using solvent evaporation method. Solid dispersion, physical mixture, and pure compound were then characterized using differential scanning calorimetry and powder x-ray diffraction. Solubility of CoQ10 in different surfactant media was measured, and a suitable dissolution medium was developed to compare the dissolution patterns of the solid dispersion, physical mixture, and the pure compound. Combining labrasol with different surfactants in dissolution media demonstrated an additive effect on CoQ10 solubility. The solubility of CoQ10 in a 4% Labrasol/2% Cremophor EL solution was 562 microg/ml, which was five times higher than the combined solubility in 5% Labrasol (91 microg/ml) and 5% Cremophor EL (7.8 microg/ml). Moderate change in the crystalline pattern of CoQ10 was observed, which was attributed to solvent displacement rather than the degree of crystallinity change. The dissolution test indicated that the in-vitro release of Coenzyme Q10 from its solid dispersion was much faster than its physical mixture, which in turn was faster than the pure drug. The amount of drug released in 12 hours from solid dispersion, physical mixture, and the pure drug was 100, 26.5 and 12.5% respectively. CoQ10 was photostable throughout the dissolution experiments.     

Effect of water-soluble carriers on dissolution characteristics of nifedipine solid dispersions

Solid dispersions of nifedipine (NP) with polyethylene glycols (PEG4000 and PEG6000), hydroxypropyl-β-cyclodextrin (HPβCD), and poloxamer 407 (PXM 407) in four mixing ratios were prepared by melting, solvent, and kneading methods in order to improve the dissolution of NP. The enhancement of the dissolution rate and the time for 80% NP dissolution T_80% depended on the mixing ratio and the preparation method. The highest dissolution rate and the T_80% as short as 15 min were obtained from PXM 407 solid dispersion prepared by the melting method at the mixing ratio of 1:10. The X-ray diffraction (XRD) patterns of solid dispersions at higher proportions of carriers demonstrated consistent with the results from differential scanning calorimetric (DSC) thermograms that NP existed in the amorphous state. The wettability and solubility were markedly improved in the PXM 407 system. The presence of intermolecular hydrogen bonding between NP and PEGs and between HPβCD and PXM 407 was shown by infrared (IR) spectroscopy.     

Small-Angle Neutron Scattering and Photon Correlation Spectroscopy Investigation on Buckminsterfullerene Solutions

Small-Angle Neutron Scattering (SANS) and Photon Correlation Spectroscopy (PCS) findings on Buckminsterfullerene (C₆₀) solutions are presented. The analysis of SANS data allows to characterize the shape and to determine the value of the gyration radius of C₆₀ dissolved in CS₂, a solvent capable to guarantee a good contrast for the neutron probe. We obtained information about the conformation of fullerene in solution, and, by means of comparisons with experimental and theoretical data existing in literature, we found a confirmation that the gyration radius R_g is independent on concentration. PCS measurements were performed on fullerene/organic solvents (toluene, chloroform and CCl₄) solutions. Since the diffusion coefficient is related, through the Stokes-Einstein relation, to the scatterer hydrodynamic radius, R_H, we have obtained information about the conformation of fullerene in solution and about the character of the structural and hydrodynamic interaction.     

Segregation of solutes in Al-Ni and Al-Sn alloys and its influence on their mechanical properties

A study was made of the intensity of scattering of monochromatic X-rays at small angles from Al-3.6 at. % Ni and Al-0.26 at. % Sn solid solutions, in order to determine if the solutes are really dispersed. Electron-microscopic examinations were also carried out. Both alloys were obtained by rapid quenching from the melt in order to obtain the optimum dissolution. However, perfectly homogeneous solid solutions were not obtained, but agglomerations of solute atoms were detected. The evolution of clusters during annealing was examined. Their influence on microhardness and microstrain properties is discussed.     

Enhancement of Dissolution of Ethopropazine Using Solid Dispersions Prepared with Phospholipid and/or Polyethylene Glycol

The purpose of this study was to improve the dissolution properties of a poorly water soluble and bioavailable drug, ethopropazine HCl (ET), by incorporating the drug in three different types of solid dispersion systems. Solid dispersions of ET were prepared using 1:1 (w/w) ratios of (1) phospholipid (1,2 dimyristoyl-sn-glycerophosphocholine) (DMPC), (2) polyethylene glycol 8000 (PEG8000), and (3) a novel combination of both DMPC and PEG8000. Using the solvent method of preparation, ET and DMPC and/or PEG were dissolved in chloroform, and solvent subsequently was evaporated using nitrogen gas. The resulting solid dispersion(s) was passed through a 60-mesh sieve. Characterization of ET/DMPC solid dispersion was performed by differential scanning calorimetry (DSC) and X-ray diffractometry studies. Dissolution studies conducted in phosphate buffered saline (PBS) (pH 7.4, 37°C ± 0.5°C) using the USP type II (paddle) dissolution apparatus showed significant increases in the dissolution rate of ET with all the solid dispersions in this study. Specifically, within the first 5 min (D5), solid dispersions containing ET/DMPC (1:1) showed an eightfold increase in dissolution; in combination with DMPC and PEG8000 (1:1), there was an approximately sixfold increase; and a fourfold increase was observed with PEG8000 (1:1). Complete dissolution of all solid dispersions occurred within 60 min (D60) of the run. Storage of the ET/DMPC sample for over 4.5 months revealed a decrease in the dissolution rate when compared to freshly prepared sample. Overall, it was concluded that the dissolution rate of ET significantly improved when dispersed in all the selected carrier systems. However, the solid dispersion of ET/DMPC was observed to be superior to the other combinations used.