Durability of Zeolite Against Repeated Activation Treatments with Microwave Heating

The durability of zeolite X against repeated treatments with microwave heating was studied, and properties of the zeolite as desiccant were compared and assessed with those of the most popular commercial desiccants (calcium chloride) for home use. Mixed cationic forms of zeolite with a ratio of Na-X/Ca-X = 5 g/45 g in a full hydration was used to achieve desirable properties. The mixture was activated by microwave (2.45 GHz) radiation for 15 min with 500 W, and after full hydration it was reactivated under the same conditions. The treatment was repeated up to twenty-five times. The adsorption capacity of the zeolite for water decreased with increasing number of treatments. Analyzing the curve of decreasing water capacity, the degradation degree at every treatment was determined to be 0.013. From this value, the number of treatments at which the adsorption capacity becomes one half of its original capacity was calculated to be 54 (defined as lifetime) and it was estimated that the zeolite could adsorb 10.7 times of its own dry weight of water by its lifetime. The rates of uptake of commercial desiccants for water were followed for two months and the uptake curves were analyzed. The desiccants reached their lifetimes in ca. 120 days and absorbed 0.8–0.9 times of their own weights of water by their lifetime. The total amount of adsorption by the zeolite is 10 times greater when compared to the commercial desiccants. Since the zeolite desiccant by using the microwave activation method exhibits higher water adsorption abilities, it is promising as a repeatedly usable desiccant for home use and other areas.     

Mechanism of Microwave Heating of Zeolite A

The mechanism of microwave heating of A zeolite was studied by comparing the heating properties, cation distributions and dielectric properties of 3A, 4A and 5A zeolites. It was easy to heat hydrated 4A zeolite to a glowing (melting) temperature by microwave (2.45 GHz) radiation from room temperature but was difficult to heat the same zeolite with little hydration. When 4A zeolite was preheated to 120°C, it could be easily heated by microwave radiation. However, 3A zeolite was not heated by microwaves under the above condition used for 4A zeolite. 3A zeolite with little hydration at room temperature could not be heated by microwaves but could be heated after hydrating it to 5 H₂O per unit cell (puc) or preheating 3A to 254°C. 5A zeolite could not be heated at all. The easiness of microwave heating was in the order of 4A < 3A 5A. There are differences in the cation distribution among these zeolites, i.e., 5A zeolite has no cations on the 4- and 8-membered oxygen ring sites but the other two have. It was expected from dielectric properties reported so far that the cation on 4-ring site can absorb microwave at <450°C with a higher efficiency but cations in other locations are ineffective for absorption. The following mechanism for the microwave heating was proposed: In the initial period, the hydratedzeolite absorbs the microwaves through its adsorbed water and its temperature rises. The adsorbed water completes desorption by ca. 400–470°C. In this temperature range the zeolite begins to absorb microwaves and the absorption efficiency becomes high with increasing temperature. When zeolite reaches 450–500°C thermal runaway starts. 5A zeolite cannot reach thermal runaway conditions because of absence of cation on 4-ring site. The adsorbed water plays the role of preheating agent in the initial period of microwave heating. Its role, however, can be substituted by other ways, e.g., preheating by conventional heating.     

微波加热化学活化法制备活性炭的优化工艺研究

研究了微波加热条件下碳酸钾活化制备活性炭的工艺流程。以碳酸钾为活化剂,微波为热源,采用正交试验,研究了浸渍时间、活化剂浓度、微波功率、微波加热时间对活性炭产品性能碘吸附值、亚甲基蓝吸附值、得率的影响规律,得到了最佳工艺条件,即微波功率600 W、微波加热时间6 min、碳酸钾浓度0.20 g/mL、浸渍时间24 h。制得活性炭的碘吸附值可达1189.68 mg/g、亚甲基蓝吸附值190 mL/g、得率29.48%,在该工艺条件下,制备的活性炭试样比表面积为1186.10 m²/g,总孔容积0.624 cm³/g,微孔容积0.407 cm³/g,吸附性能较国家标准有所提高。     

Importance of Site III Cation of Zeolite A in Microwave Heating

Properties of dehydrated Na_{12 – 2x} Ca _x -A zeolites with x = 0, 1.1 and 4 in microwave heating were experimentally and theoretically investigated and compared with one another. Final heating temperatures of zeolites by microwave radiation were measured against radiation time and the easiness of heating was in the order of Na₁₂-A Na₁₀Ca₁-A > Na₄Ca₄-A for every irradiating condition studied. Microwave (relative) absorption efficiencies of the zeolites were calculated as a function of temperature with a simple method by using dielectric properties of the dehydrated states. In every temperature calculated, the order of absorption efficiency was Na₁₂-A Na₁₀Ca₁-A Na₄Ca₄-A. From these results, it was clearly verified that Na⁺ ion on the site III played the most important role in absorbing microwaves because Na₁₂-A has one Na⁺ ion on the site III but Na₁₀Ca₁-A and Na₄Ca₄-A have no cations on the site.     

微波加热用于活性炭的制备、再生和改性

从微波加热的应用着手,阐述了微波辐照的热效应、微波在活性炭的制备、再生和改性过程中的作用机理;指出了微波加热处理活性炭有待进一步研究的问题。     

频率和功率对轮胎微波加热的影响

在双波导入射功率均为5 k W时,分别对(915±25)MHz频率范围和925 MHz频率时的双波导不同功率分配下的微波加热效率以及轮胎温度场分布进行了模拟。结果表明:微波加热效率随微波频率的变化呈类似于正/余弦曲线波动,在微波作用频率为925 MHz时,微波加热效果最好;双波导功率分配越趋近于一致,微波加热效率越高,轮胎温度场分布越均匀。     

波导对橡胶微波加热硫化的影响

采用ANSYS有限元分析软件分别模拟橡胶在圆波导和同轴波导两种模式下的微波加热硫化过程。结果表明:同轴波导模式下胶料的微波加热效率低于圆波导模式,但同轴波导模式下胶料经微波加热后,胶料的最高和最低温度的差值较小,即同轴波导模式下加热胶料内的温度分布较均匀。     

微波消解法测定水中高锰酸盐指数的最佳条件

讨论了微波消解功率、消解时间、酸度等条件对测定水样中的高锰酸盐指数分析结果的影响,建立起来了利用微波消解法快速测定水中高锰酸盐指数的最佳试验条件,并测定了该方法抗Cl-干扰的能力、精密度及准确度,为利用该方法测定水样中的高锰酸盐指数提供了依据。     

微波介电热效应在化学合成中的应用

介绍微波介电热效应原理及其在化学合成中的应用.利用微波介电热效应不仅能加快化学反应速度,缩短反应时间,而且还能合成出一些新的化合物.     

油茶壳用微波加热磷酸法制活性炭

以油茶果壳为原料,用磷酸作活化剂,采用微波加热法制备粉状活性炭。按4因素3水平的正交表设计试验方案,研究磷酸浓度、料液混合比、活化温度、活化时间等4个因素对产品亚甲基蓝吸附值的影响。在磷酸质量分数60%,料液质量比1:2.0,活化温度550℃,活化时间75 min的条件下,活性炭的亚甲基蓝吸附值可达226 mg/g,A法焦糖脱色率达100%以上,灰分为4.6%~5.2%。油茶果壳可用微波加热磷酸活化法制取液相脱色活性炭。     

苯酚作用下竹粉微波液化的工艺研究

以苯酚为液化剂,浓硫酸为催化剂,采用微波加热的方式对竹粉进行了液化处理,探讨了酚／竹固液比、催化剂用量、反应时间等因素对液化的影响。结果表明,当微波功率为500W、酚／竹固液比为4：1、浓硫酸为8％、液化温度为150℃、反应时间为8min时,液化效果最优,所得产物的残渣率仅为O．289％。采用红外光谱对竹粉液化前后官能团变化进行了分析,结果表明,经过苯酚液化后芳环被引入到竹粉的分子结构中。     

微波加热褐铁矿的脱水反应动力学

研究了微波加热褐铁矿的脱水过程,利用SEM和XRD分析了褐铁矿脱除结晶水前后矿相的转变. 根据升温和失重变化曲线,采用微分法和积分法计算褐铁矿结晶水热分解过程的动力学参数,确定了褐铁矿在微波加热条件下脱水的反应机制. 结果表明,该矿的化学式为2Fe2O3·3H2O;在脱去结晶水后转变为赤铁矿,Fe2O3和SiO2含量增加,晶粒尺寸减小,矿相相对变纯. 褐铁矿在470~650 K内脱水反应的表观活化能为17.39~19.33 kJ/mol,低于常规加热脱水反应的活化能,说明微波加热能降低反应的活化能;且其脱水反应机理符合Maple单行法则,属于随机成核和随后生长的化学反应控制.     

陶瓷材料微波加热特性计算分析

为更清楚和准确了解材料微波加热行为,提出了球形陶瓷材料微波加热升温过程的一个数学模型。用有限差分隐式格式推导了离散方程,通过编程进行了数值迭代计算,得到了Si C陶瓷球加热升温过程动态温度曲线,并分析了其加热基本特性。在此基础上,探讨了材料热导率和微波功率的影响。计算结果表明,微波体积加热效应决定了物体内部温度分布比较均匀;与普通加热方式不同,微波加热的物体内部温差随时间逐渐增加,加热初期温差比较小,这一特性决定了微波加热特别适合快速加热;对每一微波功率,有一个最大稳定温度值,因此烧结不同材料,所用微波功率应不同。材料热导率越大,物体内部温度分布越均匀,但能达到的稳定温度越低;微波功率越大,物体能达到的稳定温度越高,但物体内部温度均匀性越差,因此,为保证材料均匀烧结,不宜用大功率。     

利用微波介电加热和微波干燥水解法制备TiO2微粒

利用微波介电加热和微波干燥条件下TiCl4直接水解的方法制备出平均尺寸为40m，粒径分布窄，均为球形且形态均一，团聚较少，金红石型的TiO2纳米粒子，其内部品粒平均大小为17nm。而传统加热和干燥条件下形成的纳米微粒平均为60nm，粒经大小不均一，形态较不规则，团聚严重。微波加热和干燥方法具有清洁、快速均匀高效、环境友好的优点，推广前景良好。TiCl4水解法经济便利，适于工业化生产。     

微波加热酸、碱、盐改性沸石对亚铁离子的吸附研究

采用微波加热技术分别结合酸、碱、盐对沸石进行活化改性处理,研究了微波功率、微波辐射时间、酸、碱、盐浓度对改性沸石去除地下水中Fe2+效果的影响。结果表明:NaOH改性沸石去除水中Fe2+的效果优于NaCl改性沸石和HCl改性沸石,在微波功率为640W、微波辐射时间为5min、NaOH浓度为0.8mol·L-1时,NaOH改性沸石对Fe2+的去除率可达96.88%。     

响应面分析法优化木材微波液化的工艺研究

以醇解的聚对苯二甲酸乙二酯(PET)饮料瓶为液化剂,甘油为辅助液化剂,微波辅助加热,用2.5%H2SO4催化液化木材。采用Design-Expert7.1软件对木粉微波液化试验进行了方案设计和试验结果分析。选取液化温度、液化时间、液固比和微波辐射加热功率等四个因素进行中心组合设计;运用响应面法对木材微波液化工艺参数进行优化,得到了综合液化率与试验影响因素之间的定量数学关系模型,以及各个单因素和交互作用对液化率的影响结果,给出了木粉液化率的残差分布以及不同操作变量之间的综合液化率等值线和三维关系。木粉的微波液化实验最优条件为:反应时间10.51min,液固质量比3.93,液化温度154.7℃,微波辅助加热功率3.71kW,该条件下能使木粉完全液化。     

微波加热制备纳米ZnO粉体及其表征

以硝酸锌和氢氧化钠为原料,三乙醇胺为表面活性剂,采用微波加热沸腾回流,在不同的反应条件下制备出了平均粒径为25～80nm的纳米级ZnO粉体。采用X射线衍射(XRD)、扫描电镜(SEM)及粒度分布仪等测试手段,对产品的物相、形貌和粒度分布进行了表征。实验结果表明,利用微波加热制备出的纳米ZnO粉体结晶性能良好,粒径大小均匀;三乙醇胺的加入,明显地改变了氧化锌的结晶行为,晶体形貌由原来的棒状变为准球形,粒径减小到纳米级。     

多孔硅颗粒在微波加热诱导下荧光增强效果研究

本文主要研究了在丙醇体系中,不同微波加热条件(反应时间和温度)对于多孔硅颗粒的荧光强度的调控和其相应的机理.结果显示,随着微波时间和温度增加,多孔硅颗粒的荧光强度也得到相应的增加.为了进一步研究其荧光增强机理,我们利用红外光谱和扫描电子显微镜,研究了微波前后的多孔硅颗粒的化学组分和形貌,其结果表明,在微波辐照下,多孔硅颗粒粒径变小,同时其表面氧化也增加,这些因素协同作用导致了多孔硅颗粒的荧光强度有效增加.     

微波加热水蒸气活化再生乙酸乙烯用废活性炭的研究

提出了用微波辐射加热水蒸气活化法再生乙酸乙烯用废活性炭的新工艺.采用正交实验确定最佳工艺条件为:微波功率700 W、活化时间40 min、水蒸气流量2.1 g·min-1.在此条件下制得的活性炭碘吸附值为1193.85 mg·g-1、亚甲基蓝吸附值为19 mL·(0.1 g)-1、得率为65.36%.对活性炭的微孔分布和全孔分布进行了研究,活性炭比表面积为1547.47 m2·g-1、总孔容为0.8 mL·g-1.     

木质粉状活性炭的微波加热再生研究

对微波加热再生活性炭新工艺进行了研究，提出了优惠工艺条件。