Fines removal in a continuous plug flow crystallizer by optimal spatial temperature profiles with controlled dissolution

This work presents a systematic study for obtaining the optimal temperature profile in a continuous plug flow crystallizer (PFC). The proposed PFC consists of multiple segments where the temperature of each segment can be controlled individually. An optimization problem is formulated for a target crystal size distribution (without fines) with the temperature of the segments as decision variables. The results indicate that for the crystallization kinetics considered, dissolution steps are necessary for the reduction of fines due to nucleation. A systematic study on the form of growth and dissolution kinetics suggested that the key factor that determines whether the dissolution steps will be successful in reducing fines, without compromising the final size of the crystals from seed, is the size dependence of the growth and dissolution kinetics. Best fines removal is achieved when the larger crystals grow faster than the smaller ones and the smaller crystals dissolve faster than the larger ones. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4582–4594, 2013     

铜冶炼尾矿砂在污酸废水中固氟除氟的研究

介绍了某铜冶炼厂利用炉渣选铜后产生的尾矿砂对污酸废水进行除氟的试验情况,确定了最佳溶解条件和尾矿砂添加量.该冶炼厂将尾矿砂溶解于含氟污酸中,降低污酸中氟离子的腐蚀活性,并强化废水处理工序的絮凝沉降效果.试验表明:尾矿砂最佳溶解温度为50~60℃,溶解时间为1.0 h,尾矿砂最佳溶解粒径为300~400目,添加量为2.5~3.0 g/L.通过高氟污酸溶解尾矿砂,模拟现有污酸废水全流程处理工艺,中和上清液中ρ(F)在20~25 mg/L,除氟效果较为明显.     

高铝煤矸石铝硅分级提取实验研究

分级研究了热活化条件下高铝煤矸石在盐酸和氢氧化钠溶液中的铝硅溶出行为。采用X射线衍射仪（XRD）、扫描电镜（SEM）和比表面积测定仪（BET）对煤矸石试样做了表征分析。通过正交实验分析了反应温度、反应时间、初始酸碱浓度和固液比对热活化处理后高铝煤矸石中Al2O3和酸浸渣SiO2溶出率的影响。结果表明：酸浸溶出Al2O3反应过程中,固液质量比和酸浸时间对溶出率的影响最为显著,酸浸过程的最优工艺条件：初始盐酸质量分数为20%、酸浸温度为90 ℃、酸浸时间为2.5 h、固液质量比为1∶6,在此条件下,Al2O3的浸取率达82.95%;强碱溶解酸浸渣溶出SiO2反应过程最优工艺条件：碱溶温度为95 ℃、碱溶时间为2.0 h、NaOH质量分数为20%、固液质量比为1∶10,在此条件下SiO2溶出率为69.74%,碱溶温度和碱液浓度对溶出率的影响最为显著。     

Nanostructuring of NiAl-Mo eutectic alloys by selective phase dissolution

A technique for the electrochemical structuring of directionally solidified NiAl-Mo eutectic by selective phase dissolution is presented. Local matrix dissolution at 200 mV SHE in 1 M HCl of pH 1 yielded the grid of Mo nanowires spanning along the central part of the sample. On the other hand, the dissolution of the fibrous minor phase while passivating the continuous NiAl matrix resulted in continuous nanopore arrays. Initially, mechanical polishing and electropolishing were employed to thin the samples. Etching time was optimized by plotting the etch time until hole formation as a function of initial sample thickness, along with plotting sample thickness versus etching time. As a next step, an investigation into the passivation behaviour of the NiAl was performed in order to determine the optimal potential for wire dissolution. A potential scan from 0 to 2500 mV SHE on a bulk sample of pure NiAl in an electrolyte of 0.1 M acetate buffer pH 6.0 indicated that a potential of 500 mV SHE, just below the breakdown potential would provide maximum driving force for wire dissolution process. Different parameters within the electrochemical system are varied in order to optimize the wire dissolution. The extent of wire dissolution is measured both quantitatively (total charge transfer) and qualitatively (optical and SEM imaging).     

新型优化策略在青霉素间歇发酵过程中的应用研究

基于全面关注间歇发酵过程中间状态的思想,提出由求解一系列端点时间不固定最优控制子问题形成的新型优化控制策略,并在优化目标函数中加入了菌体平均生长速率和流加时间间隔对发酵产量的影响因素.在此基础上提出基于遗传算法的最优控制策略实现算法,同时获得了最优流加时间间隔及相应的最优流加速率.将该方法在青霉素发酵过程进行仿真,将仿...     

不同溶液对地下水中甲基叔丁基醚溶解过程影响

采用实验室小型二维砂箱对地下水流动过程中甲基叔丁基醚(MTBE)溶解过程进行模拟实验,主要考察了非离子型表面活性剂聚乙氧基油酸山梨糖醇(Tween80)、阴离子表面活性剂十二烷基苯磺酸钠(SDBS)与助溶剂乙醇对MTBE溶解过程的影响。结果表明,Tween80在其临界胶束浓度(CMC)以上能够对MTBE起到增溶的效果而且在所研究浓度范围存在最佳增溶浓度10g/L;低于临界胶束浓度条件下的SDBS并没有增强MTBE迁移反而会延缓MTBE的溶解;乙醇可以增大MTBE的溶出浓度,而且随着含量提高增溶效果加强。通过比较各种条件下最佳的MTBE累积去除率可以得出,当MTBE去除率达到80%之前,对MTBE溶解增强效果由大到小顺序依次为:非离子型表面活性剂Tween80> 助溶剂乙醇> 水> 阴离子表面活性剂SDBS;而去除率80%以后,增溶效果的顺序则为乙醇> Tween80> 水> SDBS。     

In-situ optical emission spectrometry during galvanostatic aluminum anodising

In this study, we report on the use of optical emission spectrometry (OES) for the online detection of changes in the Al concentration ejected in a 1.0 mol dm⁻³ sulphuric acid electrolyte during galvanostatic anodising of Al thin film substrates. The technique relies on the coupling of an Inductively Coupled Plasma (ICP) spectrometer to a specially designed electrochemical flow cell. This has allowed to correlate, for the first time, the kinetics of Al dissolution to well-established morphological changes related to porous anodic oxide formation and growth. A deconvolution algorithm was first developed in order to decompose the experimental ICP/OES signal into elementary distributions, each one characteristic for a specific kinetic regime. The highest dissolution rate systematically occurred during the first step, associated with barrier oxide formation. This is followed by a systematic decrease in the rate of Al dissolution during pore formation. During steady-state porous oxide growth, the Al dissolution rate increases again, but still remains below the level established during barrier oxide growth. In each of these three kinetic regimes, a linear variation of the Al dissolution rate with current density was observed in the range 0.5–5.0 mA cm⁻², with slope values of, respectively, 35 ± 2, 24 ± 2 and 28 ± 1 μg C⁻¹. Regarding the temporal transitions between the different regimes, a desynchronisation was observed between the kinetic (dissolution) and morphological transitions, the time offset going in opposite directions for barrier and steady-state porous oxide growth. Finally, using the measured Al dissolution rates, the current density dependence of the film formation efficiency for both porous and barrier oxide growth has been established.     

二元离子液体强化秸秆预处理

为了提高生物质秸秆的溶解率、优化秸秆组分再分布,采用1-丁基-3-甲基咪唑氯盐([Bmim]Cl)和1-乙基-3-甲基咪唑醋酸盐([Emim][OAc])的二元离子液体混合体系,考察溶剂组成、反应温度和处理时间三因素对预处理的影响。结果表明,随着[Bmim]Cl在二元离子液体中摩尔比的升高,秸秆溶解率呈先上升后下降的趋势;纤维素在处理后秸秆中所占比例也遵循此规律。随着温度升高,溶解率逐渐增加,当温度超过100℃时,二元离子液体溶解液的黏度发生突变,秸秆发生变性;此外,随着处理时间的延长,溶解率逐渐升高,但是超过3 h以后,溶解效果提升并不明显。综合各因素作用效果,确定最佳反应温度为90℃,最佳处理时间3 h。在此条件下,秸秆的溶解率达到46.53%,经处理后秸秆中纤维素比例达到55.77%。     

Composition controlling of Co-Ni and Fe-Co alloys using pulse-reverse electroplating through means of experimental strategies

The optimal plating settings in the pulse-reverse electroplating mode for the non-anomalous plating of Co-Ni deposits (i.e., the metal composition of deposits is equal to that of the plating solutions) from chloride solutions were approached by using experimental strategies including fractional factorial design (FFD), path of steepest ascent and central composite design (CCD) coupled with the response surface methodology (RSM). The potentials and time period of pulse-plating were the key factors affecting the composition of Co-Ni deposits in the FFD study. The two variables were the path of the steepest ascent investigation to approach the optimal conditions for non-anomalous plating of Co-Ni deposits. The effects of pulse-plating potential and pulse-plating time on the compositions of Co-Ni deposits were further examined using a regression model in the CCD study.The variable Ni contents of Co-Ni deposits are caused by metal hydroxide on the deposit surface. After anodic dissolution process, the increasing pulse-plating time and lower pulse-plating potential can remove metal hydroxide and improve Ni ion deposition ratio on the fresh deposit.All Fe-Co deposits were equal to the composition metal ratio of plating bath while pulse-reverse-plating potential included the anodic dissolution process.     

离子液体-乙醇-水体系水热法分离毛竹组分

采用水热法与离子液体-乙醇-水体系组合处理毛竹,分析了固体产物结构. 结果表明,基本实现了毛竹全组分分离,水热法预处理选择性脱除半纤维素组分的脱除率达82.88%. 离子液体-乙醇-水体系中大部分木质素被溶解,而纤维素基本不发生水解,最佳工艺条件为：反应温度170℃,反应时间4 h,[AMIM]OAc:C2H6O:H2O=5:5:0.5(j),此条件下,水解残渣溶解率为43.14%,粗纤维素和粗木质素的纯度分别为91.38%和87.70%.     

Direct and Indirect Dissolution of Sapphire in Calcia–Magnesia–Alumina–Silica Melts: Dissolution Kinetics

The dissolution rate of sapphire into CaO-MgO-Al₂O₃-SiO₂ (CMAS) melts was investigated at 1450° and 1550°C. The effects of immersion time, specimen rotation rate, and magnesia concentration in the bulk melt on the sapphire dissolution rate and on the growth rate of magnesium aluminate spinel at the sapphire/melt interface were determined. The processes of direct and indirect sapphire dissolution into CMAS melts are discussed, with the support of kinetic and microprobe data.¹ A model of indirect sapphire dissolution^1,2 is used along with the equations of Tedmon³ to describe the kinetics of indirect dissolution and spinel layer growth during forced-convective and static sapphire dissolution.     

基于PBM的L-谷氨酸粒度分布控制优化

针对β型L-谷氨酸冷却结晶过程,为获取期望粒度分布,采用特征曲线法（MOCH）来建立关于粒度相关生长率的种群平衡方程（PBE）,然后通过对种群平衡模型（PBM）参数辨识后确定最优过饱和度及控温曲线。由于辨识模型参数的目标函数具有非线性和非凸型性,因而采用少量经济性的批量冷却结晶实验,结合图像分析晶种和产品粒度分布得到的统计数据,拟合模型参数。根据实际要求的结晶过程时间,为达到目标粒度分布,通过优化结晶过程的过饱和度获得最优调温曲线,实现基于恒定过饱和度的晶体生长过程优化控制。实验结果表明通过优化的控温曲线,实现了基于最优过饱和度控制的期望目标粒度分布。     

Kinetics of non-congruent dissolution of E-glass fiber in saturated calcium hydroxide solution

The kinetics of non-congruent dissolution of long E-glass fiber in saturated calcium hydroxide solution has been investigated at 25°C in a closed reactor adopting the rotating disc method for the sample holder. The fiber dissolution rate (), measured from the relative loss weight of the fiber after selective dissolution of the attack layer in acetic acid, is a linear function of time, what implies an interfacial dissolution process. However, the kinetics does not stay regular for a long time due to local detachment of the attack layer. The comparison between = f (t) and ′ = f (t) curves, where ′ is the formation rate of the attack layer, shows that the formation of the layer does not only imply the deposit of a bad-crystalline hydrated calcium silicate but the nucleation and growth of solid calcium hydroxide and calcium carbonate resulting from the transfert, to the interface, of ions coming from the liquid phase. This phenomenon was precedently observed by some other authors in the case of glass-fiber reinforced cement matrix.     

磷尾矿硝酸脱镁制取氢氧化镁工艺研究

实验采用硝酸对磷矿浮选尾矿进行化学脱镁,讨论了温度、pH和时间3个因素对脱镁率和磷溶解率的影响.发现在液固比为3∶1的前提下,最佳酸浸条件为:温度50℃,pH=2.5,时间150 min,在上述条件下脱镁率达到94.26％,磷溶解率为5.94％.脱镁后的酸浸液实现了Mg2+与其他金属离子的分离,并通过XRD和化学分析得知产品Mg(OH)2中MgO质量分数为64.45％.     

Real‐time control of a semi‐industrial fed‐batch evaporative crystallizer using different direct optimization strategies

This article presents a model‐based control approach for optimal operation of a seeded fed‐batch evaporative crystallizer. Various direct optimization strategies, namely, single shooting, multiple shooting, and simultaneous strategies, are used to examine real‐time implementation of the control approach on a semi‐industrial crystallizer. The dynamic optimizer utilizes a nonlinear moment model for on‐line computation of the optimal operating policy. An extended Luenberger‐type observer is designed to enable closed‐loop implementation of the dynamic optimizer. In addition, the observer estimates the unmeasured process variable, namely, the solute concentration, which is essential for the intended control application. The model‐based control approach aims to maximize the batch productivity, as satisfying the product quality requirements. Optimal control of crystal growth rate is the key to fulfill this objective. This is due to the close relation of the crystal growth rate to product attributes and batch productivity. The experimental results suggest that real‐time application of the control approach leads to a substantial increase, i.e., up to 30%, in the batch productivity. The reproducibility of batch runs with respect to the product crystal size distribution is achieved by thorough seeding. The simulation and experimental results indicate that the direct optimization strategies perform similarly in terms of optimal process operation. However, the single shooting strategy is computationally more expensive. © 2010 American Institute of Chemical Engineers AIChE J, 57: 1557–1569, 2011     

Optimal control of a batch bioreactor for the production of xanthan gum

The application of an optimal control procedure to reduce the fermentation time necessary to produce a desired amount of xanthan gum is presented. This procedure computes the temperature operating policy for the culture based on the fermentation initial conditions and the desired (target) product concentration at the final time. For that purpose, it uses biomass and product growth models proposed previously in the literature, which are dependent on the medium temperature. Computational experiments show that the optimal fermentation time to produce 15 g of gum per l is 16.3% shorter than the necessary time when the usual constant temperature of 28°C is used, and 12% shorter than the necessary time when the two-temperature strategy of other authors is used. The results also show considerable energy savings. Rules to determine a near optimum temperature profile without applying the optimization procedure are outlined and some results are presented. These rules are based on the outcome of the optimal control procedure and only require the knowledge of the initial cell and the desired final gum concentrations.     

ON-LINE OPTIMAL FEED OF SUBSTRATE DURING FED-BATCH CULTURE OF CELL MASS

In the cultivation of cell mass, a mathematical model for the specific growth rate of the cells can be used to design a strategy for the optimal feed of substrate to the culture. In this paper, a model of specific growth rate valid at both low and high cell concentration is developed for Candida utilis and Candida brassicae. An on-line control algorithm is then proposed to determine the optimal substrate concentration for the production of cell mass in fed-batch culture. An on-line estimation scheme using the sensitivity method is also included for cases in which the cell mass can not be measured. Simulation results demonstrate that the proposed method can minimize the production time of fed-batch culture.     

卡维地洛滴丸的制备工艺与表征

本文开发了一种可提高新剂型的可提高难溶性药物卡维地洛溶出的制备方法并进行表征。采用固体分散技术法制备滴丸，通过响应面试验法，按照归一值法优化指标，优选最佳工艺并验证，考察自制滴丸体外溶出度。采用差示扫描量热法（DSC）、粉末 X射线衍射法和红外吸收光谱法鉴定药物在滴丸中的存在状态。结果表明：最优制备工艺为卡维地洛与基质质量比为1∶7，PEG6000与PEG4000质量比为1∶3，滴速为54min^-1，药液温度为75℃，所建模型显著。滴丸在pH1.2的盐酸溶液中30min内释药最快，达到90%以上，其次为pH4.5、pH6.8、去离子水。所制3批滴丸重现性好，体外溶出相似（f ₂>85），稳定性好。药物在滴丸中主要以无定形状态存在，可提高难溶性药物的溶出，为卡维地洛新的口服速释剂型的开发提供参考。     

Potentiodynamic growth of anodic silver chromate layers

Silver passivation is studied in sodium chromate aqueous solutions. It is shown that the active–passive transition involves active metal dissolution followed by the precipitation of a poorly-conducting layer of silver chromate that passivates the electrode. The potentiodynamic current–potential behavior is adequately described by using the layer-pore-resistance model (LPRM). The agreement between experimental and theoretical curves is excellent and allows us to demonstrate that, after the first stages that involve active dissolution of silver and nucleation of the film, the growth of the passive layer is mainly controlled by the resistance of the electrolyte in the pores of the layer. After passivation, further growth of the film occurs under diffusion control.     

Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders

Well-crystallized cerium(IV) oxide (CeO₂) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO₂ crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO₂ crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO₂ crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains.