钙矾石吸附水的模型及等温式

钙矾石３ＣａＯ·Ａｌ２Ｏ３·３ＣａＳＯ４·３２Ｈ２Ｏ是水泥熟料水化的重要产物．它易被空气中的ＣＯ２ 分解,常温下的分解反应为３ＣａＯ·Ａｌ２Ｏ３·３ＣａＳＯ４·３２Ｈ２Ｏ ３ＣＯ２ →３ＣａＣＯ３ Ａｌ２Ｏ３·ｘＨ２Ｏ ３（ＣａＳＯ４·２Ｈ２Ｏ） （２６ -ｘ）Ｈ２Ｏ分解机理［１ ,２］是：Ｈ２Ｏ先吸附在钙矾石表面的活性中心上,吸附态水再吸收ＣＯ２ 成为Ｈ２ＣＯ３ ,然后碳酸与钙矾石反应,实现碳化（即分解）．其分解速率［３］为ｖ＝ｋｐｃｏ２ ｐＨ２ｏ（１）可见水的吸附是钙矾石碳化分解的关键步骤,因此探讨…     

碳化氨水法制腐植酸铵肥料

风化煤是制取腐植酸铵肥料的主要原料之一。有些风化煤由于钙、镁含量高,不能直接氨化,必须排除钙、镁干扰,才能氨化。通过我们的实践,总结出用碳化氨水与高钙、镁风化煤“一步氨化”制取腐植酸铵的工艺,方法可土可洋,产品经化验和农田试验证明,效果良好。一、方法原理此法基本原理是:碳化氨水中的碳酸铵和氢氧化氨与风化煤中的腐植酸钙、镁盐发生复分解反应。碳酸根(CO_3~(--))和氢氧根(OH~-)与钙、镁化合成难溶于水的碳酸钙和碱式碳酸镁等沉淀,使腐植酸游离出来     

富钙生物油煅烧过程中孔结构变化特性的研究

在热重分析仪上进行富钙生物油煅烧实验。结果表明,富钙生物油的煅烧过程分为三个阶段,分别是生物油部分组分的脱CO₂和H₂O阶段、有机酸钙盐分解阶段、碳酸钙分解阶段。其中,有机酸钙盐分解对煅烧产物的孔结构有重要影响。在450℃~600℃,气体析出的气蚀作用与生物油中高分子化合物的碳化沉积现象同时存在,两者共同作用,但后者占主导,高分子化合物的碳化沉积主要发生在500℃~600℃。600℃以后,碳酸钙开始分解,释放出CO₂,气蚀作用使煅烧产物内部形成新的微孔,产物具有发达的孔结构。相同煅烧温度下,富钙生物油煅烧产物的孔隙特性明显优于CaCO₃。     

准东煤灰化过程中的矿物演变及矿物添加剂对其灰熔融特性的影响

利用低温灰化、高温灰化和X射线衍射物相分析相结合的方法对准东煤中矿物质在加热过程中的演变规律进行了研究。结果表明,准东煤中原始矿物质以方解石、高岭石为主,随着燃烧温度的升高,煤灰中矿物质最终生成了铁橄榄石、硅酸钙等。此外,向准东煤中掺加不同比例的高岭土和刚玉混合添加剂,发现随着SiO2/Al2O3比值的降低,煤中生成了钙矾石、钙铝榴石等高熔点物质,准东煤的灰熔点逐步升高。     

准东煤灰化过程中的矿物演变及矿物添加剂对其灰熔融特性的影响

利用低温灰化、高温灰化和X射线衍射物相分析相结合的方法对准东煤中矿物质在加热过程中的演变规律进行了研究。结果表明,准东煤中原始矿物质以方解石、高岭石为主,随着燃烧温度的升高,煤灰中矿物质最终生成了铁橄榄石、硅酸钙等。此外,向准东煤中掺加不同比例的高岭土和刚玉混合添加剂,发现随着SiO₂/Al₂O₃比值的降低,煤中生成了钙矾石、钙铝榴石等高熔点物质,准东煤的灰熔点逐步升高。     

Mo/ZSM-5 分子筛碳化钼活性中心结构及甲烷活化机理的密度泛函理论研究

 应用密度泛函理论 (DFT) 研究了 Mo/HZSM-5 分子筛上碳化钼活性中心的几何结构和电子结构, 以及甲烷 C–H 键在该活性中心上的活化机理. 设计了两种碳化钼单体模型 Mo(CH2)2/ZSM-5 和 Mo(CH2)2CH3/ZSM-5, 两种碳化钼双体模型 Mo2(CH2)4/ZSM-5 和 Mo2(CH2)5/ZSM-5. 其中单钼模型构建在 ZSM-5 分子筛孔道交叉点 T6 位的 Brönsted 酸位上, 双钼模型构建在 T6---T6 相邻双酸位上. 这些模型中都有 Mo=CH2 键, 结构优化后得到的 Mo–C 键长与实验值吻合. 所有模型的前线分子轨道都在 Mo=CH2 的 π 键上. 甲烷活化过程是发生 C–H 键异裂, H+和 H3C–残基分别进攻 Mo=CH2 键的 C 和 Mo, 使 π 键同时断裂. 在以上 4 种碳化钼模型上, 甲烷 C–H 键活化能都在 106~196 kJ/mol, 且 Mo2(CH2)5/ZSM-5 在甲烷活化过程中显示出最高的催化活性.     

聚苯胺碳化产物表面和体相结构表征

测试分析了聚苯胺树脂碳化产物表面和体相结构。结果表明聚苯胺树脂碳化产物比表面积随碳化温度升高而下降。在700℃和1000℃还原性气氛中碳化处理的样品与620℃处理的样品相比,比表面积分别下降了约8.3%和33.7% 。在相同温度条件下,惰性气氛中碳化处理的样品比表面积低于还原性气氛中碳化处理的样品。聚苯胺树脂碳化产物表面中的氮主要以两种不同的基团结构形式存在,并且树脂碳化产物表面的氮含量随着碳化处理温度升高逐渐降低。聚苯胺620℃碳化处理时主要是树脂中的含氮基团发生变化,而其他结果基团变化较小。700℃碳化处理后则开始大规模碳化裂解。但1000℃碳化处理后的样品仍含有少量的碳氢键和氮氢键。1000℃碳处理的树脂碳化样品开始形成多碳稠环,并向有序化方向转变。     

碳化钼催化剂加氢脱氮性能研究

MoO3在CH4/H2气氛中程序升温还原碳化反应制备了Mo2C催化剂,用XRD、BET、SEM、XPS进行了表征。以吡啶/环己烷溶液为模型化合物,在高压微反装置上评价了碳化钼催化剂的吡啶加氢脱氮性能。结果表明,MoO3在CH4/H2气氛中程序升温至675℃可制得高纯度的β-Mo2C,SEM表征其形貌为板块状颗粒,平均粒径约3.9μm,比表面积达到了10.7m2/g,高于其前驱体MoO3 的2.7倍。在反应压力3.0MPa,空速为8h－1,H2/原料液体积比为500∶1,体积分数为5%的吡啶/环己烷溶液中,碳化钼催化剂在340℃下的吡啶加氢脱氮转化率达到了86.30%,高于相应MoS2约8%。随还原碳化温度的升高,碳化钼催化剂的比表面积降低,表面积炭增多,导致其吡啶加氢脱氮活性下降。确定的碳化钼催化剂的合成条件以还原碳化温度675℃、还原碳化气体空速1.8×104h－1左右较为适宜。     

制备条件对碳化钼催化剂加氢脱硫性能的影响

以MoO3为前驱体,在CH4/H2气氛中程序升温还原碳化反应制备了Mo2C催化剂,用XRD和BET进行了表征. 以二苯并噻吩/环己烷溶液为模型反应物,评价了制备条件对碳化钼催化剂加氢脱硫性能的影响. 结果表明,在还原碳化温度为675 ℃,恒温保持150 min的合成条件下可制得高纯度的a-Mo2C催化剂,该催化剂表现出了较高的加氢脱硫活性,用质量分数为0.6%的二苯并噻吩/环己烷溶液为反应物,反应压力3.0 MPa,反应空速8 h-1,反应温度330 ℃实验条件下的二苯并噻吩加氢脱硫转化率达到了73.29%. 随还原碳化温度的升高和恒温保持时间的延长,制备的碳化钼催化剂的比表面积下降,表面积炭增多,引起其二苯并噻吩加氢脱硫活性的下降. 适当增大制备过程中还原碳化气体空速,有利于还原碳化反应过程中C、 O之间局部规整反应的进行,并对其二苯并噻吩加氢脱硫活性有明显的促进作用. 实验确定的还原碳化气体空速以1.8×104h-1为宜.     

碳化终温对β-Mo2C催化喹啉加氢脱氮性能影响

以MoO_3为前驱物,CH_4/H_2为碳源,采用程序升温直接还原碳化法制备不同碳化终温(640、660、680、700和720℃)的碳化钼催化剂,通过XRD、N_2吸附-脱附、SEM、TEM、XPS和Raman表征研究碳化钼的物理性质和结构性质,并研究不同碳化终温碳化钼对喹啉加氢脱氮的催化性能。结果表明,不同碳化终温的碳化钼催化剂均为β-Mo_2C,碳化终温可显著改变碳化钼表面物种含量、平均孔径和介孔分布。碳化终温为680℃时,催化剂碳化程度较高,表面氧物种含量最低,表面C/Mo物质的量比最高,对应的催化活性也最佳,在340℃、4 MPa条件下,喹啉的转化率和脱氮率均高达99%以上,芳香族类化合物的选择性可达37.8%,显示出较低的芳环破坏性。表面组成尤其是表面氧对于β-Mo_2C上喹啉加氢脱氮反应途径的调控至关重要。     

Multicyclic study on the carbonation of CaO using different limestones

Different samples of limestones, with small differences in their stoichiometry, have been studied comparatively. The carbonation reaction has been studied for a large area of isothermal temperatures. The conditions for the multicyclic experiments of calcination/carbonation were: isothermal temperature 670°C, heating time 60 min and carrier gas CO₂. The final carbonation conversion depends mainly on the isothermal temperature of the carbonation reaction and the heating time. The final temperature of the calcination reaction depends on the percentage of CaO that it has not been conversed to CaCO₃ in the repeated carbonation experiments. The quantity of CaO that has not been carbonated, in the same sample, affects the values of the coefficients of the kinetic model that fit the calcination reaction. In the multicyclic experiments the carbonation conversion for two of the four studied samples, was high enough in comparison to other samples of calcite. At sample A the reduction of the carbonation conversion during the first five cycles is less than it is at other samples from the literature. Under the above experimental conditions — isothermal temperature and heating time — specific samples consisted mainly of calcite can absorb larger quantities of CO₂ than samples consisted mainly of dolomite.     

Theoretical Study of the AlEt3-Promoted Tandem Reductive Rearrangement of Epoxides

The AlEt3-promoted tandem reductive rearrangement reactions of epoxides was studied at B3LYP/6-31G(d,p) level. For the model compound σ-hydroxy epoxides, two possible reaction pathways I and II were calculated. The main difference is the order of ethylene release and six- to five-member ring rearrangement.The ring contraction rearrangement in pathway I is the first step and this step is the rate controlling step with a free energy barrier of 116.62 kJ/mol. For pathway II, the ethylene release occurs first, and is followed by a six-member ring opening reaction which is the rate controlling step, and the barrier is 251.38 kJ/mol.The reason for such high barrier is that the ethylene release results in the following reaction being moredifficult. The results show that pathway I (C-C rearrangement and then ethylene release) is more favorable,which is consistent with experimental results.     

钛酸锌高温煤气脱硫剂再生行为的研究

在热天平装置上研究了再生反应温度、反应气体中氧气体积分数、脱硫剂颗粒粒径对钛酸锌高温煤气脱硫剂再生行为的影响。实验结果表明,较高的反应温度和氧气体积分数,较小的颗粒粒径有利于提高脱硫剂的再生反应速率。由于二次反应的影响,脱硫剂再生过程中有硫酸盐生成,提高反应温度或降低反应气体的氧气体积分数可以减少硫酸盐的生成。利用收缩核模型对其动力学行为进行了分析,结果表明,脱硫剂的再生过程存在动力学控制步骤的转移。脱硫剂再生转化率较低（<65%）时,再生过程主要受化学反应控制;再生转化率较高（>75%）时,再生过程主要受颗粒内扩散控制。表观化学反应速率常数的指前因子为8.01×10－2 m/s,活化能为19.11 kJ/mol;有效扩散系数的指前因子为3.12×10－4 m2/s,扩散活化能为48.84 kJ/mol。     

Reaction kinetics of CO2 carbonation with Mg-rich minerals

Due to their low price, wide availability, and stability of the resulting carbonates, Mg-rich minerals are promising materials for carbonating CO(2). Direct carbonation of CO(2) with Mg-rich minerals reported in this research for the first time could be considerably superior to conventional liquid extraction processes from an energy consumption perspective due to its avoidance of the use of a large amount of water with high specific heat capacity and latent heat of vaporization. Kinetic models of the reactions of the direct CO(2) carbonation with Mg-rich minerals and within simulated flue gas environments are important to the scale-up of reactor designs. Unfortunately, such models have not been made available thus far. This research was initiated to fill that gap. Magnesium silicate (Mg(2)SiO(4)), a representative compound in Mg-rich minerals, was used to study CO(2) carbonation reaction kinetics under given simulated flue gas conditions. It was found that the chosen sorbent deactivation model fits well the experimental data collected under given conditions. A reaction order of 1 with respect to CO(2) is obtained from experimental data. The Arrhenius form of CO(2) carbonation with Mg(2)SiO(4) is established based on changes in the rate constants of the chosen deactivation model as a function of temperature.     

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

Carbonation of solid calcium oxide by gaseous carbon dioxide was monitored by thermogravimetry. A kinetic model of CaO carbonation is proposed in order to interpret the first rapid step of the reaction. By taking into account, the existence of large induction period as well as the sigmoidal shape of the kinetic curves in this kinetic-controlled region, a surface nucleation and isotropic growth kinetic model based on a single nucleus per particle is proposed, and the expressions of the fractional conversion and the reaction rate versus time are detailed. The induction period is found to have a linear variation with respect to temperature and to follow a power law with respect to CO₂ partial pressure. The areic reactivity of growth decreases with temperature increase, and increases with CO₂ partial pressure increase. A mechanism of CaCO₃ growth is proposed to account for these results and to determine a dependence of the areic reactivity of growth on the temperature and the CO₂ partial pressure.     

Thermal analysis of cyclic carbonation behavior of CaO derived from carbide slag at high temperature

In this work, CaO derived from the carbide slag (CaO?Ccarbide slag) as a kind of typical industrial waste was used to capture CO₂ during the calcination/carbonation cycles. The carbonation kinetics and cyclic carbonation behavior of CaO?Ccarbide slag were investigated in a thermogravimetric analyzer. The chemical reaction activation energy and the product layer diffusion activation energy for carbonation of CaO?Ccarbide slag are 12.46 and 36.83?kJ?mol^?1, respectively, which are significantly less than those for carbonation of CaO derived from the limestone (CaO?Climestone). CaO?Ccarbide slag shows higher carbonation conversion than CaO?Climestone after enough reaction time and at the same number of cycles. Moreover, the calcination temperature and CO₂ concentration in the carbonation atmosphere have important effect on the carbonation behavior of CaO?Ccarbide slag. The BET surface area of CaO?Ccarbide slag is 1.6 times as large as that of CaO?Climestone after 1 cycle and the average pore size of CaO?Ccarbide slag is much smaller. In addition, the carbide slag contains much more Al₂O₃ than most of the limestones. These are reasons why carbide slag as a precursor can retain greater carbonation conversion than limestone in calcination/carbonation cycles.     

DFT Study on the Origin of the Enantioselectivity of （S）-4-Hydroxylproline-Catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde

DFT-B3LYP calculations were carried out to study the enantioselectivity of the （S）-4-hydroxylproline-catalyzed direct aldol reaction between acetone and 4-nitrobenzaldehyde. Four transition structures associated with the stereo-controlling step of the reaction have been determined. They are corresponding to the anti and syn arrangements of the methylene moiety related to the carboxylic acid group in enamine intermediate and the si and re attacks to the aldehyde carbonyl carbon. The effect of DMSO solvent on the stereo-controlling step was investigated with polarized continuum model （PCM）. The computed energies of the transition states reveal the moderate enantioselectivity of the reaction.     

H+HNCO→NH2+CO的反应机理及动态学计算

用从头算方法研究了H+HNCO→NH2+CO的反应机理: 首先经过H2NCO中间体,并为反应的控制步骤。在此基础上, 计算了控制步骤的反应途径, 沿反应途径的动态学性质和正则变分过渡态理论的速率常数。结果表明, 反应存在返回效应和隧道效应, 反应途径的曲率对隧道效应影响较大, 用变分过渡态方法和小曲率近似方法分别进行校正是有效的。     

Gas generation during Cypris clay expansion

Blast furnace slag was leached using HCl to prepare lithium-based sorbents for CO₂ capture, and chemical composition and phase of the acid leaching slag were determined by X-ray fluorescence analysis. The microstructure and morphology of both sorbents were characterized by scanning electron microscope and X-ray diffraction. The absorption capacity of both sorbents was observed non-isothermally and isothermally using thermogravimetric analysis, and 12 carbonation and calcination cycles were conducted to observe cycling stability. Controlling step of absorption process was determined by fitting the isothermal graphs using a double exponential model. The results show that 98.33% amorphous SiO₂ can be obtained when the blast furnace slag was treated at 373 K for 10 h. Purified lithium-based sorbent by acid leaching slag (LBS-ALS) shows dense polyhedral particles with particle size between 25 and 120 μm. LBS-ALS shows similar absorption capacity with pure Li₄SiO₄ (P-Li₄SiO₄), but narrower absorption temperature range at non-isothermal absorption condition. The double exponential model fits well with the isothermal graphs for LBS-ALS and P-Li₄SiO₄, and diffusion of CO₂ is the controlling step of the absorption process at lower temperature. LBS-ALS shows different controlling mechanism for desorption process compared with P-Li₄SiO₄. LBS-ALS maintains higher absorption capacity after 12 cycles in 100% CO₂ flow.     

含钒钢渣碳酸化浸取提钒动力学研究

用高钙含钒钢渣经钠盐焙烧后的焙砂样品以及焦钒酸钙合成样品,在15-75℃范围内进行了碳酸化浸取动力学研究。碳酸化浸取提钒,主要是把钢渣中的碳酸钙溶解,使钒呈钒酸钠形式进入溶液,钙转变成碳酸钙沉淀。研究表明,在碱性溶液中通入CO₂气体,随着pH值的下降,首先生成Na₂CO₃,随后生成NaHCO₃。此碳酸化浸取的液-固反应过程,用颗粒表面溶解反应的收缩核心模型进行描述,在反应初期阶段是Na₂CO₃的溶浸作用,然后则主要是NaHCO₃的溶浸作用,后者的反应速度比前者快。用焦钒酸钙合成样品进行研究,证实了所推论的反应机理。在所试验的温度范围内,碳酸化浸取焦钒酸钙合成样品的反应表观活化能为25.3千焦/摩尔。