Reactivities of Various Silicates with Calcium Hydroxide and Water

The reactivity of oxides and silicates with alkaline solutions is especially important in cement chemistry and is closely related to the pozzolanic reaction, the alkali-aggregate reaction, and to glass fiber reinforcement of hardened cement. Thus, the rate of the hydration reaction between several silicates and Ca(OH)₂ or portland cement at 20° and 80°C was studied. Results showed that essentially high reactivity in the reaction with Ca(OH)₂ was found in Italian pozzolan, metakaolin, and silica gel in which the first two have very high Blaine surface areas. The pozzolanic reaction of typical oxides and silicates was considered from a thermodynamic point of view.     

Investigation into the Mechanism of Interaction of Calcium and Magnesium Silicates with Carbon Dioxide in the Course of Mechanical Activation

A prolonged grinding of diopside, akermanite, sphene, wollastonite, and enstatite is accompanied by absorption of CO₂ from the environment (carbonation) along with amorphization and hydration. The IR spectra of ground minerals contain bands of distorted carbonate groups due to absorption of carbon dioxide. If the mechanical activation is not attended by the distortion of the crystal lattice, the sorption of carbon dioxide results in the formation of undistorted [CO₃ ^2–] groups.     

Reaction of Beta-Dicalcium Silicate and Tricalcium Silicate with Carbon Dioxide and Water Vapor

The carbonation-reaction kinetics of beta-dicalcium silicate (2CaO·SiO₂ or β-C₂S) and tricalcium silicate (3CaO. SiO₂ or C₃S) powders were determined as a function of material parameters and reaction conditions and an equation was developed which predicted the degree of reaction. The effect of relative humidity, partial pressure of CO₂, surface area, reaction temperature, and reaction time on the degree of reaction was determined. Carbonation followed a decreasing-volume, diffusion-controlled kinetic model. The activation energies for carbonation of β-C₂S and C₃S were 16.9 and 9.8 kcal/mol, respectively. Aragonite was the principal carbonate formed during the reaction and the rate of carbonate formation was coincident with depletion of the calcium silicates; C-S-H gel formation was minimal.     

Reaction Calorimetry in Supercritical Carbon Dioxide

Summary: Reaction calorimetry is an efficient tool used to obtain kinetic, thermodynamic and safety data. A reaction calorimeter, RC1e‐HP350, developed in collaboration with Mettler‐Toledo GmbH, allows investigating chemical reactions under supercritical conditions. The main technical difference, compared with a classical liquid system, is that the whole reactor volume is occupied by the media. Heat transfer analysis in supercritical carbon dioxide (scCO₂) by the Wilson plot method shows that the behavior of the internal heat transfer coefficient in scCO₂ is the opposite of the one observed for classical liquid. In scCO₂ the lower the temperature (above the critical point) the better the internal heat transfer coefficient. The evolution of scCO₂ thermodynamical and transport properties near the critical point are responsible for this behavior. The dispersion polymerization of methyl methacrylate in scCO₂, with the polydimethylsiloxane monomethacrylate as stabilizer, is used as a model reaction. A polymerization reaction enthalpy of ?56.9 ± 2.2 kJ · mol^?1 is determined, being in good agreement with previously reported data. The results presented illustrate the accuracy of the heat balance model used and emphasize the potential of reaction calorimetry for the promotion of supercritical fluids technologies.

Technical comparison between liquid and supercritical reaction calorimetry.     

秸秆炭固定二氧化碳反应的动力学研究

在固定床中,氨水改性秸秆炭对吸附二氧化碳气体的吸附特性进行了测定,分别考察了浸渍时间（1～4 h）、浸渍温度（30～45℃）、浸渍浓度（10%～25%）对氨水改性的秸秆炭吸附二氧化碳性能的影响,结果表明：浸渍氨水浓度越高,吸附性能越好;吸附量随浸渍时间的增加,呈先增大后减小的趋势,存在较强的浸渍时间;浸渍温度升高对吸附性能影响不大。依据吸附反应的基本原理,建立了吸附动力学模型。模型计算得到的穿透曲线,与实验结果吻合较好。     

Calcium Carbonate Decomposition in Carbon Dioxide Atmosphere

Calcite crystal fragments of known surface area were decomposed in controlled carbon dioxide atmospheres. The decomposing sample was weighed continuously on an automatically recording thermobalance and a rate of weight loss per unit area was obtained. A rate expression involving actual and equilibrium CO₂ pressures and the decomposition rate in pure nitrogen was derived. The mechanism of the decomposition is pictured as being a two-stage phenomenon. Initially the CO₂ leaves the CaCO₃ cell and the residue of the CaO apparently assumes a metastable rhombohedral configuration similar to the original CaCO₃. The second step of the reaction is the formation of well-crystallized CaO from the active CaO. The active CaO thus acts as a bridge for this reversible reaction.     

超临界二氧化碳中的不饱和聚酯树脂固化反应

本文研究了超临界二氧化碳对不饱和聚酯树脂固化反应的影响。结果表明超临界二氧化碳能够使不饱和聚酯树脂体系的固体时间有明显的缩短,达到原来固体时间的53.8%。随着超临界二氧化碳的加入,双键反应率有明显降低,但是双键反应率并没有随着压力的升高继续减小。     

超临界二氧化碳/水复合发泡体系制备聚苯乙烯发泡材料

采用超临界二氧化碳和水作为复合发泡剂,制备聚苯乙烯发泡材料,分析发泡剂的吸附过程,并通过观测扫描电镜照片研究发泡样品的泡孔结构.通过比较发泡剂吸附量、泡孔直径、泡孔密度和表观密度4个参数,分析使用复合发泡剂对聚苯乙烯发泡制品性能的影响.结果表明:使用二氧化碳和水作为复合发泡剂,聚苯乙烯中吸附的发泡剂含量增加,发泡制品表观密度降低,泡孔直径增大,泡孔密度减小.     

Synthesis of Calcium Hexaboride Powder via the Reaction of Calcium Carbonate with Boron Carbide and Carbon

The synthesis of calcium hexaboride (CaB₆) powder via the reaction of calcium carbonate (CaCO₃) with boron carbide (B₄C) and carbon has been investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products have been studied using X-ray diffractometry, and the morphologies of CaB₆ obtained at various temperatures and holding times have been investigated via scanning electron microscopy. The interaction in the CaCO₃–B₄C–carbon system by which CaB₆ is formed is a solid-phase process that passes through the transition phases Ca₃B₂O₆ and CaB₂C₂. The optimal conditions for CaB₆ synthesis are a holding time of 2.5 h at a temperature of 1673 K, under vacuum (a pressure of 10⁻² Pa). CaB₆ powder has the same morphology as B₄C, and the properties and the shape of CaB₆ powders can be improved by choosing good-quality raw materials.     

Crystal Chemistry of Hydrous Calcium Silicates: II, Characterization of Interlayer Water

Examination of tobermorite, 4–SCaO.5SiO₂.-5H₂O, and xonotlite, 5CaO.5SiO₂.H₂O, by infrared absorption revealed striking structural similarities and differences in the two phases. In the 8- to 15- μ region, the absorption was the same for both; the differences arose from the manner in which water and hydroxyl ions were bonded. Tobermorite exhibited strong absorption at 6.2 μ , a band which is generally associated with interlayer water, and at 2.9 μ , a band generally attributed to bonded (OH). The mineral xonotlite did not show these two bands but contained the band at 2.75 μ generally associated with free (OH). Synthetic xonotlite prepared at 300°C. was essentially the same as the mineral, but samples prepared at progressively lower temperatures exhibited the 2.9- μ band in increasing intensity. The fibrous form of tobermorite showed a band at 6.5 to 7.0 μ which increased in intensity with increasing amount of CaO in the solid; this band was also found in the 14-a.u. 1.0 CaO: SiO₂ hydrate, but not in xonotlite. The great volume stability of xonotlite during drying and wetting is readily explained on the basis of the present results. Shrinkage of tobermorite during drying at temperatures up to 650°C. may be due to removal of both interlayer water and bonded (OH). The changes in absorption during drying at room temperature were too small, however, to permit drawing any conclusions. Similarities and differences between tobermorite and certain clays are discussed.     

超临界二氧化碳中的甲苯选择性氧化反应

考察了甲苯选择性氧化反应中反应物及产物在超临界二氧化碳中的溶解性质。结果表明,甲苯在超临界二氧化碳中的溶解度较大,在反应条件下能与二氧化碳形成均相;苯甲醇、苯甲醛和苯甲酸在超临界二氧化碳中的溶解度随着物质极性的增强而降低。利用不同产物的溶解性差异,可实现超临界二氧化碳中甲苯的选择性氧化。同时考察了超临界二氧化碳中甲苯选择性氧化反应过程中,反应时间、反应压力、反应温度以及n(甲苯)/n(氧气)对反应选择性的影响。     

Water Solubility of Carbon Dioxide under Supercritical and Subcritical Conditions

The solubility of carbon dioxide in water at t = 25, 50, 100, and 150°C and p = 10–80 MPa is studied experimentally by a static method in a constant-volume cell. The results are described by the entropy method of similarity theory. The calculated and experimental data are in satisfactory agreement.     

拜耳法赤泥固化CO2反应特征的研究

以拜耳法赤泥为CO2固化剂,研究了不同压力下赤泥对CO2的固化封存能力,以及固化CO2过程中矿物物相的化学转化行为.探讨了温度、液固比、粒径、时间等因素对赤泥固化CO2效率的影响以及赤泥固化CO2过程Na、K的浸出特性变化.结果表明,CO2压力为0.6 MPa、1 MPa、1.6 MPa时,赤泥固化CO2的饱和增重率分别达到2.36％、2.70％、3.07％.随反应时间的变化,赤泥浆液的pH值不断下降,最后稳定在6.40左右.液固比减小,赤泥粒径减小,在2060℃之间温度升高,有助于赤泥固化CO2效率的提高.赤泥固化CO2后Na、K的浸出量增加.XRD和红外光谱分析显示赤泥固化CO2后主要形成的矿物相是钙霞石(cancrinite)和方解石(CaCO3).不同压力下赤泥对CO2的固化反应符合准一级动力学方程.     

超临界CO2络合萃取乳酸钙中痕量重金属离子的研究

以乙醇为改性剂,超临界CO2络合萃取乳酸钙中痕量重金属离子.考察了络合剂种类及用量、乙醇用量、温度、压力、萃取时间等对萃取效果的影响.结果表明,不同络合剂对不同金属离子的萃取效果有明显差异;乙醇用量对金属离子的萃取效果影响不明显;温度在50℃时,金属离子总萃取率可达80%以上;萃取时间比萃取压力的影响更为显著,表明络合反应控制着该过程.确定优化的萃取工艺条件如下:10 mL乙醇作改性剂、温度50℃、CO2流速13 L·h-1、压力20 MPa、萃取时间90 min、二乙基二硫代氨基甲酸钠与四丁基溴化铵复配物用量为样品质量的2%.     

废弃物制备钙基二氧化碳吸附剂的研究进展

新世纪以来人类活动产生了极大的碳排放量和大量废弃物,还造成了严重的资源浪费,环境成为经济发展的代价.利用二氧化碳吸附剂减少二氧化碳排放,是目前工业最有效的手段.高温钙基二氧化碳吸附剂以其成本低、性能好受到了广泛应用.利用废弃物改性制备二氧化碳吸附剂达到以废治废是一种资源节约、环境友好的研究方向.从不同钙源和不同掺杂剂的方面分类介绍了目前国内外关于废弃物改性钙基二氧化碳吸附剂的研究,对于改性后的钙基吸附剂的碳酸化转化率、循环吸附性能、作用特点等方面进行了详细阐述.     

煤清洁利用新途径——煤焦二氧化碳气化法

探讨了煤焦二氧化碳气化工艺研究现状及其作为煤清洁利用途径的优势。目前,还没有单独用纯二氧化碳参与煤焦大规模气化的研究。该工艺可以减少大气中二氧化碳,是一种煤清洁利用的手段,具有很好的经济、社会和生态效益。     

CO2、CH4气体对循环水系统的影响

介绍CO2、CH4气体漏入循环水气体后对水质的影响，影响的原因及其危害。     

高二氧化碳浓度下石灰石的热分解反应动力学

用热重分析仪,在升温速率5～20K/min范围内,研究CO2浓度对石灰石热分解反应动力学参数的影响及高CO2浓度气氛下两种化学成分与矿物组成不同的石灰石的热分解反应动力学。采用改进的双外推法计算这两种石灰石的热分解反应动力学参数。结果表明:石灰石热分解反应的活化能与气氛中的CO2浓度呈指数增加关系;在高CO2浓度气氛条件下石灰石的热分解过程机理模型为随机成核和随后生长模型,得到了反应机理函数,CO2浓度不同,反应级数不同,反应级数的变化范围为2/5～2/3;CO2浓度越高,石灰石热分解的活化能越高,反应级数越大;在相同CO2浓度气氛条件下,石灰石中含有一定量白云石有助于其分解反应的进行。     

磷石膏制备纳米氧化钙基二氧化碳吸附剂工艺的优化

随着化学工艺的发展和成熟,磷石膏制取氧化钙逐渐成为常见的制备方法。对此技术工艺优化,对反应时间、反应温度、二氧化碳通量、搅拌速度进行单因素实验,得出不同因素对纳米氧化钙二氧化碳吸附颗粒的影响。得出结论:搅拌速率越慢越好,杂质含量越少越好;纳米氧化钙基二氧化碳吸附剂的粒径越小,其吸附量就越大,吸附速率也越快,其稳定性也就越高。     

Extraction of Furfural with Carbon Dioxide

Abstract

A new approach to separate furfural from aqueous waste has been investigated. Recovery of furfural and acetic acid from aqueous effluents of a paper mill has successfully been applied on an industrial scale since 1981.

The process is based on the extraction of furfural and acetic acid by the solvent trooctylphosphineoxide (TOPO). Common extraction of both substances may cause the formation of resin residues. Improvement was expected by selective extraction of furfural with chlorinated hydrocarbons, but ecological reasons stopped further development of this project.

The current investigation is centered in the evaluation of extraction of furfural by supercritical carbon dioxide. The influence of temperature and pressure on the extraction properties has been worked out. The investigation has considered the multi-component system furfural-acetic acid-water-carbon dioxide. Solubility of furfural in liquid and supercritical carbon dioxide has been measured, and equilibrium data for the ternary system furfural-water-CO₂ as well as for the quaternary system furfuralacetic acid-water-CO₂ have been determined. A high-pressure extraction column has been used for evaluation of mass transfer rates.