Estimation of current efficiency in ion-exchange membrane chlor-alkali cells

A generalized current efficiency equation was derived from material balance considerations to estimate the caustic current efficiency in ion exchange chlor-alkali membrane cells taking into account the presence of NaHCO₃, Na₂CO₃, and NaOH in the feed brine. The validity and the accuracy of this equation was established by comparing the ‘gas analysis’ results with the data obtained from caustic collection measurements. It is also shown that this general expression can be easily extended to deduce the current efficiency applicable for diaphragm cell operations.     

Optimization of caustic current efficiency in a zero-gap advanced chlor-alkali cell with application of genetic algorithm assisted by artificial neural networks

The effects of various process parameters on caustic current efficiency (CCE) in a zero-gap oxygen-depolarized chlor-alkali cell employing a state-of-the-art silver plated nickel screen electrode (ESNS^®) were studied. For doing a thorough research, we selected the process parameters from both cathodic and anodic compartments. Seven process parameters were studied including anolyte pH, temperature, flow rate and brine concentration from the anode side, oxygen temperature and flow rate from the cathode side and the applied current density. The effect of these parameters on CCE was determined quantitatively. A feed forward neural network model with the Levenberg–Marquardt (LM) back propagation training method was developed to predict CCE. Then genetic algorithm (GA) was implemented to neural network model. The highest CCE (98.53%) was found after 20 times running GA at the following conditions: brine concentration (287 g/L), anolyte temperature (80 °C), anolyte pH (2.7), anolyte flow rate (408 cm³/min), oxygen flow rate (841 cm³/min), oxygen temperature (79 °C), and current density (0.33 A/cm²).     

氯碱生产过程中节能降耗措施的探讨

以新疆中泰化学(集团)股份有限公司65万t/a离子膜法烧碱装置为例,分析了氯碱生产过程中降低电耗、蒸汽耗、煤耗、水耗、天然气耗、盐水精制中氯化钡消耗及提高离子膜利用效率的工艺措施及管理经验.     

A study of transport of hydroxyl ion in a chlor-alkali diaphragm

The loss of hydroxyl ions by diffusion and back migration to the anolyte compartment is the major source of efficiency loss in a chlor-alkali diaphragm cell. The transfer rate of hydroxyl ions across the diaphragm depends on diaphragm properties and electrolyte flow rate inside the diaphragm. This work examines the concentration distribution of hydroxyl ions across the diaphragm in a laboratory cell. A numerical computation is carried out to optimize the diaphragm structure and current density based on the minimum production cost of chlorine. The optimum current density is found to be 50% lower than the present operating current density in the chlor-alkali industry.Nomenclature A _p apparent cross-sectional area of the diaphragm (m²) - A _T true cross-sectional area of the pores (m²) - C _OH concentration of the hydroxyl ion at any pointx along thex-direction (kg mol m^–3) - C _K catholyte concentration (kg mol m^–3) - C dimensionless concentration given in Equation 11 - C _D unit diaphragm cost ($ kg^–1) - C _E unit direct electrical energy cost ($ kg^–1) - C ₁ unit specific investment cost ($ kg^–1) - D diffusion coefficient of the hydroxyl ion (m² s^–1) - E ₀ open circuit voltage (V) - E total cell voltage (V) - F Faraday's constants (96 487 C g equiv^–1) - i _P apparent current density based on apparent area of the diaphragm,A _P (A m^–2) - i _T true current density based on true crosssectional area of the pores,A _T (A m^–2) - I magnitude of total current through the cell (A) - (IR)_BUS voltage drop in the bus-bar (V) - (IR)_SOLN voltage drop in the solution (V) - (IR)_DIA voltage drop in the diaphragm (V) - N _OH flux of hydroxyl ion (kg mol m^–2 s^–1) - K _S average conductivity of the solution (ohm^–1 m^–1) - k ₁ energy cost ($ kWh^–1) - K ₂ capital cost of the electrolyte cell ($ m^–2) - K ₃ cost coefficient of diaphragm ($ m^–2) - K ₅ unit cost of the raw material ($ kg^–1) - l effective pore length (m) - l ₁ distance between the anode and the cathode (m) - L life period of the diaphragm (yr) - molecular weight of chlorine gas (kg) - M _NaCl molecular weight of sodium chloride (kg) - n number of years of amortization which in principle is given by the life time of the cell (yr) - N _C total number of cells (dimensionless) - p production rate of chlorine gas (kg yr^–1) - R resistance (ohm) - r ₀ resistance of the solution (ohm) - S annual interest rate (%) - U _OH– mobility of hydroxyl ion (kg mol m²V^–1 C^–1 s^–1) - electrolyte velocity along the x-direction inside diaphragm (m s^–1) - _S superficial velocity (m s^–1) - V _W volume of water lost from the catholyte compartment due to evaporation and cathodic reaction (m³ s^–1) - x axial coordinate - Z valence of hydroxyl ion (kg equiv kg^–1 mol^–1) - diaphragm thickness (m) - porosity (%) - current efficiency (dimensionless) - _a anodic overpotential (V) - _c cathodic overpotential (V) - tortuosity factor (dimensionless)     

Electrodeposition of silver powder by pulsating and reversing currents

The effect of the shape of the current wave and frequency in silver deposition by pulsating and reversing currents on the morphology of powder particles were investigated. The possibility of obtaining particles with different properties, depending on conditions of electrolysis, was demonstrated.Notation j _av average current density - j _L limiting diffusion current density - J ₀ exchange current density - p anodic/cathodic time ratio - _A overpotential amplitude - 2.3₀ slope of the cathodic Tafel line     

Palladium-Mediated Ring-Opening Reactions of Strained Cyclotetrasilanes

Room-temperature ring-opening polymerization of the strained monomer 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane mediated by palladium complexes was attempted. Examination of the reaction products between the cyclotetrasilane and the metal complex at high concentrations indicated that insertion of one cyclotetrasilane molecule between the ligand–palladium bond was followed by reductive elimination of the tetrasilane. Among the palladium complexes examined were (³-allyl)PdCp [Cp=⁵-cyclopentadienyl], [(³-allyl) PdCl]₂, (³-allyl)PdCl(PPh₃), (³-allyl)PdCl(PPh₃)₂, (³-allyl)Pd(PPh₃)₃ and PdCl₂(PPh₃)₂. Reaction of 1,1,2,3,4-pentamethyl-2,3,4-triphenylcyclotetrasilane with (³-allyl)PdCp provides similar products.     

Comparison of the critical conditions for initiation of dendritic growth and powder formation in potentiostatic and galvanostatic copper electrodeposition

Critical current densities for the initiation of dendrite growth and powder formation in potentiostatic and galvanostatic deposition are determined. Induction times for dendritic growth formation in potentiostatic and galvanostatic deposition are discussed.Nomenclature C ₀ bulk concentration - D diffusion coefficient - F Faraday constant - h height of a protrusion - h _i height of ith protrusion - h ₀ initial height of a protrusion - i current density - i _c current density at which dendrites appear instantaneously - i _i minimal current density at which dendritic growth becomes possible - i _L limiting current density - i ⁰ initial current density - i ₀ exchange current density - k proportionality factor - n number of electrons - N number of protrusions - R _t tip radius - S electrode surface area - S ₀ initial electrode surface area - t time - t _i induction time - V molar volume - thickness of the diffusion layer - overpotential - _c critical overpotential of instantaneous dendritic growth - _c,t critical overpotential of dendritic growth following non-dendritic roughness amplification - _i critical overpotential for the initiation of dendritic growth - ₀ initial overpotential - 2.3 ₀ slope of the Tafel line - quantity defined by Equation 3 - surface tension - time constant     

Chlorate Transport through Ion-Exchange Membranes

A laboratory scale chlor-alkali membrane cell was used to measure the chlorate concentration in the outlet NaOH as a function of current density, temperature, film thickness, brine strength and various membrane properties. The chlorate concentration in the NaOH increased with increasing anolyte chlorate spiking level and temperature and decreasing current density and carboxylate film thickness and was strongly dependent on the type of ion-exchange membrane used. In addition, the presence or absence of sacrificial fibers in the membrane did not measurably influence the resultant chlorate concentration. Chlorate ions were transported to the catholyte side by diffusion and electroosmotic convection and transported toward the anolyte side by migration. This balance between the three modes of transport dictates the chlorate concentration present in the NaOH product.     

Electrochemical reduction of nickel ions from diluteartificial solutions in a GBC reactor

The electrochemical reduction of nickel ions from a dilute solution has been carried out in a gas diffusion electrode packed bed electrode cell (GBC). Particle size and electrode configuration have been found to have a significant influence on the reduction process. Electrodes with a high porosity and large pores have been found to be the best for nickel deposition. The nickel current efficiency, Ni, is reported to be dependent on the current density, volumetric flow rate, nickel and boric acid concentration, and the pH. The fall in the nickel current efficiency is caused by an increase in electrode surface pH above a certain level, caused by either high bulk solution pH or high current density, leading to possibly formation of Ni(OH)2. It has been found that under conditions of exclusively metallic nickel deposition Ni/(1–Ni) is proportional to i0.69,Q10.52,CNi0.67,CBA–0.19 and pH1.0.     

Development of an artificial neural network model for prediction of cell voltage and current efficiency in a chlor-alkali membrane cell

This paper presents the development of an artificial neural network (ANN) model for the prediction of cell voltage and caustic current efficiency (CCE) versus various operating parameters in a lab scale chlor-alkali membrane cell. In order to validate the model predictions, the effects of various operating parameters on the cell voltage and current efficiency of the membrane cell were experimentally studied. The membrane cell incorporated a standard DSA/Cl₂ electrode as the anode, a nickel electrode as the cathode and a Flemion 892 polymer film as the membrane. Each of the six process parameters including anolyte pH (2–5), operating temperature (25–90 °C), electrolyte velocity (2.2–5.9 cm/s), brine concentration (200–300 g/L), current density (1–4 kA/m²), and run time were thoroughly studied at four levels and low caustic concentrations (5–22 g/L). The predictions of ANN model as well as those from other statistical methods were evaluated versus the measured values of cell voltages.

The developed ANN model is not only capable to predict the cell voltage and caustic current efficiency but also to reflect the impacts of process parameters on the same functions. The predicted cell voltages and current efficiencies using ANN modeling were found to be close to the measured values, particularly at higher current densities.     

烧碱装置中新技术发展概况

介绍近年来我国氯碱行业的盐水精制、除硝、离子膜法烧碱电解、氯氢处理、液氯、蒸发等工序新技术的应用情况,分析氯碱技术进展趋势.     

Surface-mediated stereoselective hydrogenation of dienes over chromium subcarbonyls encaged in zeolite

Tricarbonyl chromium (0) species encaged in LiX or NaX was found to be highly efficient and stereoselective for the hydrogenation of butadiene at > 230 K. The selectivity to cis-2-butene depended both on the reaction temperature and butadiene pressure. The reaction mechanism is proposed, in which cis-2-butene is formed via (⁴-C₄H₆)Cr(CO)₃, while 1-butene via (²-C₄H₆)Cr(CO)₃ and (²-C₄H₆)₂Cr(CO)₃.     

Correlation between configuration/conformation of zirconocenes on the stereoselectivity of the propylene polymerization reaction

Summary The catalytic performance (activity and polymer properties) of metallocenes with different symmetries in combination with methylaluminoxane (MAO) in the polymerization of propylene has been investigated at different temperatures, under standardized reaction conditions. The zirconocene rac-ethylene (⁵-1-indenyl) zirconium (IV) dichloride, with C₂ symmetry, produces isotatic polypropylene and isopropylidene(⁵-cyclopentadienyl (⁵-9-fluorenyl) zirconium (IV) dichloride, with C _S symmetry, syndiotactic polypropylene. The degree of the tacticity of these polymers increases with decreasing polymerization temperature. Only atactic polypropylene was formed with the unbridged zirconocenes bis(⁵-cyclopentadienyl) zirconium (IV) dichloride and bis(⁵-indenyl zirconium (IV) dichloride at any temperature investigated (10–60°C).     

Ferrocenylenesilylene Polymers as Coatings for Tapered Optical-Fiber Gas Sensors

In this paper we report the use of ferrocenylenesilylene polymers as coatings for tapered optical-fiber sensors. The principle of operation of this device is based upon environmentally induced changes in the refractive index of the polymer layer which change the power transmitted through the tapered fiber. The results for two sensor arrays fabricated using the ferrocenylenesilylene polymer [( ⁵-C₅H₄)Fe( ⁵-C₅H₄)MePhSi] _m and copolymer {[( ⁵-C₅H₄)Fe( ⁵-C₅H₄)SiPhMe] _n [( ⁵-C₅H₄)Fe( ⁵-C₅H₄)Me₂Si] _m are presented. We also show that the sensitivity of this device is a function of the taper beat length.     

12万t/a离子膜法烧碱技改总结

山东德州实华化工有限公司将5万t/a隔膜法烧碱改造为离子膜法生产装置,形成12万t/a离子膜法烧碱规模.改造中,充分挖掘、利用原有装置,2套系统公用盐水高位槽、碱液高位槽和脱氯塔,优化了产品结构,获得了良好的经济效益和社会效益.     

氯碱生产工艺研究探讨

对目前隔膜法和离子膜法生产烧碱分别进行了阐述,不仅详细分析了生产过程中对主要原料盐水的要求、电解反应过程、烧碱产品质量,而且对两种方法的优缺点进行了系统比较对比,并提出了自己的观点,以期为氯碱生产的提供参考。     

离子膜法和隔膜法烧碱装置共存时的做法

自贡鸿鹤化工集团公司氯碱厂在同时存在离子膜法和隔膜法烧碱生产装置的情况下，采用离子膜淡盐水除氨、离心机冲盐、以及合理配比离子膜淡盐水和卤水等一些好的措施。并针对一次盐水易反浑、离子膜淡盐水利用不好和用卤比偏低等情况，提出改进措施。     

Photovoltaic properties and stability of I2-doped polyacetylene

Summary Polyacetylene was doped with evaporated iodine (I₂). The characteristics of A1/cis-[CHI_y]_x/Au Schottky barrier solar cell was investigated. It is found that the maximum conversion efficiency is 2.67%. The solar cell parameters, such as open-circuit voltage (V_oc), short-circuit current (J_sc), fill factor (F.F.), and energy conversion efficiency (), were measured under the various incident light intensity. The stability of the cell was also estimated by the variation of J-V curves in argon environment.     

Extrapolation method of determining relative viscosity of polycaproamide in sulfuric acid

Conclusions A linear dependence of the relative viscosity of polycaproamide on sulfuric acid concentration has been confirmed.Regression equations have been found which make it possible to reduce the obtained using 93.5–96.5% sulfuric acid by wt. and using a variable sample weight of polycaproamide to a standardized relative viscosity st.Metrological certification of the extrapolated st method has been performed; the attainable accuracy is 0.010–0.015 when the number of determinations is 2.Inclusion of this procedure in the branch standard will make it possible to sharply reduce labor cost for analytical control.Translated from Khimicheskie Volokna, No. 4, pp. 58–60, July–August, 1988.     

A mathematical model of the viscosity of dilute solutions of rigid-chain polymers

Conclusions A procedure has been developed for identifying and discriminating between competing viscosity models from experimental data, plus a complex of programs for identifying models and discriminating between competing hypotheses.For the systems poly-p-phenyleneterephthalmaide-sulfuric acid (96.3 or 99.3%), the best results in prediction were given by the Martin model [K₅=0.435 (0.36)] and the Budatov model [K₇=0.16 (0.21)]; the temperature for both of the investigated systems was 274.25°K.In the investigated concentration region, a linear dependence is observed between sp and [], which is convenient for transition from specific viscosity to inherent viscosity. Adequate equations for expressing this relationship have been obtained from the experimental data.Translated from Khimicheskie Volokna, No. 2, pp. 20–24, March–April, 1985.