Investigating the molecular dissolution process of binary solid dispersions by molecular dynamics simulations

Dissolution molecular mechanism of solid dispersions still remains unclear despite thousands of reports about this technique. The aim of current research was to investigate the molecular dissolution mechanism of solid dispersions by molecular dynamics simulations. The formation of ibuprofen/polymer solid dispersions was modeled by the simulated annealing method. After that, the models of solid dispersions were immersed into the water box with 25–30 ? thicknesses and 50–100 ns MD simulations were performed to all systems.Simulation results showed various dissolution behaviors in different particle sizes and various polymers of solid dispersions. Small-sized particles of solid dispersions dissolved quickly in the water, while the large particles of PEG or PVP-containing solid dispersions gradually swelled in the dissolution process and drug molecules may aggregate together. In the dissolution process, the carboxylic groups of ibuprofen molecules turned its direction from polymer molecules to external water box and then the drug molecules left the polymer coils.At the same time, polymer coils gradually relaxed and became free polymer chains in the solution. In addition, solid dispersion with poloxamer could prevent the precipitate of drug molecules in the dissolution process, which is different from those of PEG or PVPcontaining systems. This research provided us clear images of dissolution process of solid dispersions at the molecular level.

Optimization of the Extraction Process of Astaxanthin from Haematococcus pluvialis with Oil Dissolution Method

[ Objective ] This study aimed to optimize the extraction process of astaxanthin from Haematococcus pluvialis with oil dissolution method. [ Method ] Small amounts of acetone or ethanol were separately added into soybean oil for astaxanthin extraction. The extraction efficiency of astaxanthin from H. pluvialis with different methods was compared. [ Result] The extraction efficiency of astaxanthin from H. pluvialis with acetone, acetone ＋ soybean oil, ethanol ＋ soybean oil, soybean oil was 20.46, 21.65, 20.85 mg/g and 13.05 mg/g, respectively. According to the results, acetone ＋ soybean oil led to the highest extraction rate, which was approximately twice that of soybean oil and higher than that of acetone. [ Conclusion ] This study laid the foundation for large-scale production of astaxanthin.

Properties and corrosion behavior of Al based nanocomposite foams produced by the sintering-dissolution process

The properties orAl based nanocomposite metal foams and their corrosion behaviors were investigated in this study. For this, the composite metal foams with different relative densities （porosity） reinforced with alumina nanoparticles were prepared using a powder me- tallurgy-based sintering-dissolution process （SDP） and NaC1 particles were used as space holders. Then, the effect of nanoparticle rein- forcement and different amounts of NaC1 space holders （corresponding porosity） on the microstructure, morphology, density, hardness, and electrochemical specifications of the samples were investigated. It was found that as the relative density increased from 60% to 70%, the wall thickness increased from about 200 to 300 pro, which led to a decrease in pore size. Also, the addition of nanoparticle reinforcement and the increased relative density result in increasing metal foam hardness. Moreover, electrochemical test results indicated that increasing the A1203 content reduced the corrosion rate, but increasing the porosity enhanced it.

Dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in sodium hydroxide solution under atmospheric pressure

The crystal structure, morphology, dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in Na OH solution under atmospheric pressure were systematically investigated by XRD and SEM. The results show that the size of single crystal of gibbsite in gibbsitic bauxite is smaller than that in pure gibbsite, but the interplanar distance is larger than that of pure gibbsite, which result in more defects in the crystal and less energy needed to dissolve in alkaline solution for the gibbsitic bauxite. The dissolution kinetic equations of gibbsitic bauxite and pure gibbsite were established, and the corresponding activation energies were calculated to be 99.144 and 115.149 k J/mol, respectively.

Analysis and modeling of alumina dissolution based on heat and mass transfer

A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was used to calculate the size dissolution rate, dissolution time and mass of alumina dissolved employing commercial software and custom algorithm based on the shrinking sphere assumption. The effects of some convection and thermal condition parameters on the dissolution process were studied. The calculated results show that the decrease of alumina content or the increase of alumina diffusion coefficient is beneficial for the increase of size dissolution rate and the decrease of dissolution time of non-agglomerated particles. The increase of bath superheat or alumina preheating temperature results in the increase of size dissolution rate and the decrease of dissolution time of agglomerated particles. The calculated dissolution curve of alumina（mass fraction of alumina dissolved） for a 300 k A aluminum reduction cell is in well accordance with the experimental results. The analysis shows that the dissolution process of alumina can be divided into two distinct stages： the fast dissolution stage of non-agglomerated particles and the slow dissolution stage of agglomerated particles, with the dissolution time in the order of 10 and 100 s, respectively. The agglomerated particles were identified to be the most important factor limiting the dissolution process.

Dissolution kinetics and removal mechanism of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure

A new chemical pre-desilication process of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure was proposed.The dissolution kinetics and mechanism were studied by chemical analysis,XRD and SEM.The kinetic results of dissolution process show that the kaolinite is symbiotic with diaspore but without cladding.The dissolution ratio of kaolinite is close to 100%at 100℃for 90 min.The dissolution kinetic equation is 1-(1-α)^1/3=7.88×10^6 exp[-64434/(RT)]t.With the low L/S(L/S=10:1),the dissolution ratio of kaolinite decreases to 55%.This is due to the formation of lamellar hydroxyl-sodalite(OH-SOD)which is deposited on the surface of kaolinite and hinders the further dissolution of kaolinite.Under the optimum conditions,the A/S(mass ratio of Al2 O3 to SiO2)of dissolved residues is increased to 8.55,while the A/S of the bauxite is only 4.97.

Effect of ferrite content on dissolution kinetics of gibbsitic bauxite under atmospheric pressure in NaOH solution

The dissolution property of high-ferrite gibbsitic bauxite and the effect of ferrite content on the dissolution kinetics of gibbsitic bauxites in sodium hydroxide solution under atmospheric pressure from 50 to 90 °C were systematically investigated.The dissolution property of high-ferrite gibbsitic bauxite is increased by increasing the dissolution temperature and the Na OH concentration or decreasing the particle size of bauxite,which is easy to dissolve under atmospheric pressure.The kinetic equations of gibbsitic bauxites with different ferrite contents during the dissolution process at different temperatures for different times were established,and the corresponding activation energies were calculated.The ferrite in the gibbsitic bauxite reduces the dissolution speed and increases the activation energy of dissolution,the diffusion process of which is the rate-controlling step.

The space time CE/SE method for solving one-dimensional batch crystallization model with fines dissolution

This article is concerned with the numerical investigation of one-dimensional population balance models for batch crystallization process with fines dissolution.In batch crystallization,dissolution of smaller unwanted nuclei below some critical size is of vital importance as it improves the quality of product.The crystal growth rates for both size-independent and size-dependent cases are considered.A delay in recycle pipe is also included in the model.The space–time conservation element and solution element method,originally derived for non-reacting flows,is used to solve the model.This scheme has already been applied to a range of PDEs,mainly in the area of fluid mechanics.The numerical results are compared with those obtained from the Koren scheme,showing that the proposed scheme is more efficient.

Thermal Analysis of Precipitate Dissolution in Binary Al-Li Alloy

In this paper,the activation energy for precipi- tate dissolution in binary AI-Li alloy has been in- vestigated by considering precipitate dissolution in Al-Li alloy,continuously heated as a thermally ac- tivated process.The proposed calculation was car- ried out by changing the scanning rate in DSC measurement.The results show that the formation of GP zone is easy because the activation energy for its dissolution is smaller than that for Li atom diffu- sion in the matrix.The δ′dissolution consists of two steps:the first step needs larger thermal activation to break down the superlattice structure,and the second is much easier like GP zone dissolution.The phase is the most stable,which needs much larger thermal activation to disappear.

Characterisation of a novel, multifunctional, co-processed excipient and its effect on release profile of paracetamol from tablets prepared by direct compression

Objective: To characterise a novel multifunctional pharmaceutical excipient and investigate its ef ect on paracetamol release from tablets prepared by direct compression.Methods: The excipient was prepared by co-processing gelatinized maize starch with sodium carboxymethyl cellulose and microcrystalline cellulose in a ratio of 2:1:1, dried and pulverized into powder. The excipient formulated was characterized using Fourier transform infrared spectroscopy and dif erential scanning calorimetry. The excipient was used to prepare batches of tablets by direct compression with drug-excipient ratios of 1:1, 1:2, 1:3 and 1:4. Parameters evaluated on tablets include crushing strength, friability and in vitro dissolution studies. Results: Differential scanning calorimetry analysis revealed a crystalline excipient while Fourier transform infrared spectroscopy showed no interaction between the excipient and paracetamol. Tablets from all the batches gave average crushing strength values between 3.47 and 4.88 kp. The 1:1 and 1:2 tablet batches were comparable to each other while 1:3 and 1:4 were also comparable to one another in their dissolution proi les. The dissolution parameters of the 1:4 batch was faster with- m∞(90.5%), t50%(3.5 min), t70%(11.6 min) while that of ratio 1:1 was the least with- m∞(48.6%), m5min(23.8%). Their release kinetics followed a KorsmeyerPeppas model with a super case-II transport mechanism.Conclusions: The drug-excipient ratios of 1:3 and 1:4 gave pharmaceutically acceptable tablets that met the British Pharmacopoeia specii cations. The t50% value of the 1:4 batch of tablets may i nd its usefulness in formulating drugs for which a fast onset of action is desired.

硝酸浓度对临界安全的影响研究

在核燃料溶解过程中,通常使用硝酸对核燃料进行溶解。针对核燃料溶解过程中的临界安全问题,在中试厂核临界安全实验装置上开展了硝酸浓度影响效应临界实验,在保持核燃料溶液浓度不变的情况下改变硝酸浓度,完成临界实验。获取了核燃料溶解过程酸度影响效应临界实验数据,通过3种临界方法得到的实验数据相对误差平均值为0.068%。同时使用蒙特卡罗程序进行了模拟计算,临界实验测量结果与理论计算值的相对偏差平均值为0.39%。研究结果表明,随着硝酸浓度的减小,系统的反应性逐渐增大,因此燃料溶解过程中需考虑由于硝酸浓度变化引起的反应性变化情况,其对乏燃料溶解过程的临界安全具有较大影响,需引起高度重视。

铝灰碱法烧结熟料溶出过程及超声协同作用研究

二次铝灰碱法烧结熟料溶出过程是回收氧化铝的重要环节,当溶出过程关键参数控制不当,会造成氧化铝溶出率低、能耗较高。为了提高氧化铝溶出率,了解氧化铝溶出机制,降低溶出过程能耗,探究了二次铝灰碱法焙烧熟料常压溶出过程中温度、时间、液固比与熟料中氧化铝溶出率的关系及熟料中NaAlO_(2)溶出过程动力学,考察了施加超声对氧化铝溶出率的影响。结果表明:熟料溶出过程优化参数为溶出温度为80℃、溶出时间为15 min、液固比(体积质量比,mL/g)为15,氧化铝溶出率可达92.3%;溶出动力学表明,NaAlO_(2)溶出过程受内扩散控制,表观活化能为13.45 kJ/mol;发现施加超声可在相同氧化铝溶出率下降低溶出温度至70℃并缩短溶出时间至9 min。该研究结果可为二次铝灰碱性焙烧熟料溶出过程降低能耗和提高效率提供新的理论参考和基础数据。

卷烟缩水糖料的分组制备工艺研究

针对卷烟糖料制备工艺缺少行业规范的现状,设置溶解分组类别、预处理方法、工艺条件等参数,构建卷烟缩水糖料的分组制备工艺。以A牌号卷烟糖料为研究对象,对糖料中各单体的溶解、分散特性展开研究,按照配方用量,设计溶剂组别、加料顺序、溶剂量分配、溶剂温度、溶解时间等参数,形成6种不同的A牌号卷烟缩水糖料分组制备工艺方案,并对方案进行论证试验和比对分析。采用分组制备工艺,糖料样品中的不溶物质含量比采用传统制备工艺时平均降低64.14%;且优选方案制备出的料液样品中不溶解物含量降低66.67%,成品糖料经放置48 h,流动性良好,料液均匀、稳定,达到预期效果,满足生产应用。与传统的糖料制备工艺相比,分组制备工艺具有显著优势。且可将分组制备工艺研究思路推广应用到其他类型的糖料制备工艺中。

乏燃料后处理碱性流程的研究进展

乏燃料后处理碱性流程是用碳酸盐、氢氧化物等碱性物质的溶液作为介质进行乏燃料的溶解及铀、钚等元素的分离与纯化的方法。碱性条件下,乏燃料中的大部分裂变产物和次锕系元素并不溶解或者在溶解过程中转变为碳酸盐、氢氧化物沉淀。与已经实现工业化的PUREX(plutonium uranium redox extraction)酸性流程相比,碱性流程具有腐蚀性更小、流程更简单等潜在的优点。鉴于碱性流程的优点及其在乏燃料后处理中的潜在应用,日本、美国、俄罗斯、韩国等国家的科研人员已经围绕该流程开展了一些研究工作。本文首先介绍了各国建议的碱性流程的技术路线;然后逐一介绍了与主要工艺环节相关的基础研究的进展,包括乏燃料的氧化溶解、核素分离、试剂的回收等;最后对该领域面临的挑战和前景进行了讨论。

川东向阳岩溶隧道水化学特征及成因机制研究

研究目的:涌突水是岩溶富水隧道的主要工程灾害,其研究具有重要现实意义。本文以向阳隧道为例,基于向阳隧道共计采集7个地表水样本和35个地下水样本开展水化学分析,研究西南岩溶山地深长隧道涌突水成因机制,为该线路岩溶隧道涌突水防治提供科学依据。研究结论:(1)隧址区水体的水化学类型主要以HCO_(3)—Ca为主,水质偏弱碱性,矿化度较低,地表水和地下水的化学性质相近,水力联系紧密;(2)水化学成分主要受硅酸盐岩和碳酸盐岩的风化溶解以及阳离子交换作用的影响;(3)地下水和地表水中Ca^(2+)、Mg^(2+)主要来源于岩溶地层中方解石和白云石矿物的溶解、碎屑砂岩中的长石矿物风化;(4)Na^(+)来源于大气降水以及硅酸盐矿物的风化;(5)碳酸盐矿物在岩石风化溶解中占据主导地位;(6)本文相关研究成果可为岩溶地区隧道线路设计提供参考。

高含硫天然气中元素硫溶解理论分析

目的通过高含硫天然气中元素硫溶解度的测试数据分析元素硫溶解过程。方法依据化学反应的物料平衡理论计算物料比例和化学反应产物占比,论证元素硫溶解过程是否适用化学溶解理论。结果元素硫溶解过程物料比例不满足化学反应的要求,化学溶解占比通常在10%以下,不适用化学溶解理论。元素硫在H_(2)S、CH_(4)、CO_(2)、含H_(2)S天然气中溶解度随着压力的升高而增大,适用物理溶解理论。结论高含硫天然气中元素硫溶解过程适用物理溶解理论。

水热法活化钾长石工艺过程优化

对氧化钙和钾长石水热化学法提钾的工艺过程进行了研究和条件优化。在对反应助剂进行筛选的基础上,探讨了反应时间、反应温度、液固比和n Ca/n(Si+Al)对钾长石活化提钾的影响。通过正交实验,确定了钾长石活化提钾的最优工艺。并利用X射线衍射和傅里叶红外研究了处理后的滤渣的晶型情况。结果表明,优选的碱基反应助剂CaO,在最佳的反应条件下,钾的浸取率最高为89.24%。处理后的钾长石滤渣主要由完整度和结晶度较好的钾霞石、水钙铝榴石和葡萄石构成,显示钾长石晶体结构被破坏。

废旧涤棉混纺织物脱色工艺研究

为解决染化料对废旧涤棉混纺织物再利用的影响,实现再生产品的高值化,采用N,N⁃二甲基乙酰胺(DMAc)对废旧涤棉混纺织物进行溶解脱色,再经二氧化硫脲(TD)和氢氧化钠协同作用进一步还原脱色。通过分析脱色过程中各因素对织物脱色率和强力保留率的影响,确定最优溶解⁃还原脱色工艺参数。分析了脱色前后织物的形貌结构、热力学性能、晶体结构,并对脱色后DMAc的回收再利用性能进行了分析。结果表明:溶解最优工艺参数为DMAc用量24 mL,反应温度145℃,反应时间120 min;还原最优工艺参数为TD质量浓度3.65 g/L,NaOH质量浓度10 g/L,温度90℃,处理时间60 min。在最优工艺条件下织物脱色率和强力保留率分别达到98.33%和92.04%,脱色后织物晶体结构变化较小,热力学性能较好,使用后的DMAc试剂可以至少循环回收4次,脱色率均在94.90%以上。

三氧化铀粉末溶解工艺研究

三氧化铀是乏燃料后处理厂的一种产品,可用于制备工厂开车、铀尾端调试、制备四价铀等工艺环节所需的硝酸铀酰溶液。为明确三氧化铀粉末溶解制备硝酸铀酰溶液的最优工艺条件,有针对性地提高三氧化铀溶解工艺水平,探索其溶解特性,有必要研究三氧化铀溶解过程中工艺条件对溶解过程的影响。本文研究了不同搅拌速度、温度、初始酸度条件下,硝酸溶解三氧化铀粉末的过程,分析了反应条件对溶解过程的影响方式,并得到了最优工艺条件。结果表明:提高反应温度、初始酸度均有利于三氧化铀的溶解,随着搅拌速度的提高溶解时间呈现先减小后增大的趋势。