Role of oxidant during phosphoric acid activation of lignocellulosic material

Lignin-based and wood-based activated carbons were prepared by phosphoric acid activation conducted using the oxidant ammonium persulfate ((NH₄)₂S₂O₈) as the activation additive. Results showed that at a (NH₄)₂S₂O₈ dosage of less than 10%, the oxidant increased the activated carbon yield and promoted pore development. However, at a (NH₄)₂S₂O₈ dosage of higher than 10%, an over-oxidation condition was created so that the activated carbon yield was reduced and pore development was negatively affected. It is suggested that oxidants play two roles during phosphoric activation, promotion of phosphate ester formation on the matrix and over-oxidation of carbon.     

Effects of the crystallinity of lignocellulosic material on the porosity of phosphoric acid-activated carbon

Activated carbons were prepared from three different lignocellulosic materials or in various lengths of impregnation time by phosphoric acid activation. The porous texture of activated carbon was analyzed in terms of the adsorption isotherm of nitrogen, and the crystallinity of lignocellulosic material was measured by X-ray diffraction method. The results showed that decreasing the crystallinity of lignocellulosic material promotes pore development, especially of mesopores. However, excessive impregnation is detrimental to activation. Impregnation and the selection of parent lignocellulosic material have a similar effect on developing porosity during phosphoric acid activation.     

Significance of the carbonization of volatile pyrolytic products on the properties of activated carbons from phosphoric acid activation of lignocellulosic material

Two series of activated carbons derived from China fir (Cunninghamia lanceolata) wood impregnated with phosphoric acid were prepared in a cylindrical container that was kept in a closed state covered with a lid (the covered case) or in an open state. The effects of the carbonization of volatile pyrolytic products of starting materials on the properties of activated carbon were investigated in the process of phosphoric acid activation. Elemental analysis and SEM observation showed that both activating in the covered case and increasing the mass of starting material used favored the carbonization of volatile pyrolytic products. An investigation of N₂ adsorption isotherms revealed that the carbonization of volatile pyrolytic products significantly enhanced mesopore development in the final carbons, especially pores with a size range from 2.5 to 30 nm, with little influence on micropores, and therefore produced a large increase in the adsorption capacity to Vitamin B12 (with a molecular size of 2.09 nm). Activated carbons with highly developed mesopores could be obtained in the covered case. The carbonization mechanism of volatiles was discussed and two different carbonization pathways (in solid and gas phases) were proposed during phosphoric acid activation.     

Surface area and pore development during lignite activation

Samples of five Louisiana lignites were steam activated for up to eight hours at atmospheric pressure over a temperature range of 750–900 °C. The products were characterized in terms of their structural properties — specific surface area, pore volume, and pore size distribution. Pore volume increased monotonically with increasing activation temperature and time. Specific surface area reached a maximum of approximately 460 m²/g at 850 °C and three hours activation; further activation reduced the surface area. The average pore radius of approximately 20 Å was essentially independent of activation temperature or time. A separate pyrolysis step preceding activation slowed the rate of activation but did not change significantly the product structural properties when compared at equal burnoff values.     

用加热磷酸生产粉状磷酸一铵

红磷分公司磷铵厂采用低压蒸汽加热原料磷酸生产粉状磷酸一铵,介绍磷酸加热工艺流程及设备,分析了磷酸加热对中和反应及产品的影响。实践表明:磷酸加热可有效提高水分蒸发量、反应温度及料浆流动性,对控制产品养分和保证产品颜色也有一定作用。     

Effects of thermal history on structural recovery of glasses during isobaric heating

The response of glass-forming systems to isobaric three-step thermal cycles involving cooling, isothermal annealing, and subsequent reheating has been investigated comprehensively using numerous combinations of the experimental and material parameters. The latter include the retardation spectrum or response function and the parameter x which determines the relative contributions of temperature and structure to the retardation times. The results show that, on heating, multiparameter systems can display three kinds of peak in the expansion coefficient α or the heat capacity C_p originating from the interactions of the elementary retardation processes with the thermal history of the glass. The conditions under which these peaks occur, their shifts with x, and the experimental variables have been investigated in detail. In particular, it has been shown that for a thoroughly stabilized glass reheated rapidly, the temperature at which the main peak occurs is strongly dependent on the experimental variables and on x, and that this dependence can lead to an estimate of the value of x. For poorly stabilized glasses reheated slowly, on the other hand, the main peak apparently vanishes and allows an upper peak to appear, which is small and insensitive to x and the experimental variables. Intermediate situations in which the main and the upper peaks occur separately give rise to a range of effects which may become quite complicated as the two peaks approach each other. The occurrence of such multiple peaks, which has usually been overlooked or misinterpreted in the past, is discussed and explained in detail and is compared with some experimental observations reported in the literature.     

回转窑窑法磷酸工艺开发的进展

我国回转窑窑法磷酸生产技术开发已进入工业化试验阶段,取得的成果显著。总结10kt／aw（H3PO4）85％回转窑窑法磷酸试验装置的生产成果,同时对试验装置中存在的诸如回转窑熔融结圈等问题进行讨论,提出了下一步技术开发的主攻方向。     

磷酸活化烟草杆制备中孔活性炭的研究

以烟草杆为原料,以磷酸为活化剂,采用一步炭化法制备了活性炭。采用正交实验研究了磷酸质量分数、浸渍时间、炭化温度及保温时间对活性炭得率和吸附性能的影响,在最佳工艺条件(磷酸质量分数30%,浸渍时间48 h,炭化温度750℃,保温时间20 min)下,所制备的活性炭其碘吸附值为889.36 mg/g,亚甲基蓝吸附值为21.5 mL/(0.1 g),得率为36.90%。同时测定了该活性炭的液氮吸附等温线,并通过BET、H K方程、D A方程和密度函数理论(DFT)表征了活性炭的孔结构。结果表明,该活性炭为中孔型,BET比表面积为892 m2/g,总孔体积为0.467 8 mL/g,微孔占总孔体积的37.06%,中孔占62.85%,大孔占0.07%。最后采用电子探针和透射电镜分析了活性炭的微观结构,其结构与氮吸附测定的结果较为一致。     

窑法磷酸工业生产试验进展

介绍了窑法磷酸工业生产试验的成果。与现有热法磷酸生产比较,窑法磷酸产品品质可与之相媲美,生产能耗却大幅降低,产品的性价比有较强的竞争力;窑法磷酸可以直接利用中低品位磷矿,甚至是一些磷矿选矿后丢弃的尾矿,且"三废"排放亦有所改善。该工艺将有良好的发展前景。     

磷酸生产技术及其发展方向

介绍了磷酸的用途和磷酸生产的工艺路线，着重介绍了湿法磷酸工艺中的盐酸法及溶剂萃取净化磷酸技术的开发状况，并就每一种方法的优缺点作了分析。通过对不同的生产方法进行比较。并结合我国磷矿日益贫化。地区分布不平衡。能源紧缺及环境保护的要求，作者认为溶剂萃取盐酸法工艺是今后磷酸生产的发展方向。     

磷酸萃取反应时间和过滤温度对过滤效果及稀磷酸成分的影响

在实验室中模拟磷矿与硫酸反应制稀磷酸工艺条件,通过分析稀磷酸(滤液)、磷石膏中成分的变化来确定反应时间、过滤温度对稀磷酸制取过程的影响。研究结果表明,反应时间充分,有利于磷酸萃取及磷石膏生长,使料浆过滤更容易;低温下过滤,所得稀磷酸不易结垢。     

磷酸活化法制备花生壳活性炭工艺

采用正交试验方法探讨了以花生壳为原料,通过磷酸活化法制备的高效活性炭吸附剂。以活性炭的收率和Pb2+吸附容量为考察指标,选择了磷酸质量浓度、浸渍质量比和活化温度3个因素,3个水平的正交试验方法。结果表明,对活性炭收率影响最大的因素是活化温度,对活性炭吸附Pb2+容量影响最大的是磷酸活化剂的质量浓度。综合考察各影响因素,得出在磷酸活化剂质量浓度为1 220 kg/m3,浸渍质量比为150%和活化温度为400℃时可以在保持活性炭收率较高的情况下制备高Pb2+吸附容量的花生壳活性炭吸附剂,该活性炭的比表面为1 018.5 m2/g,总孔容积为0.754 m3/g,平均孔径为2.961 nm,对低质量浓度含铅废水中铅离子的去除率接近100%,是合适的液相吸附用活性炭材料。     

磷石膏浮选脱硅回水对磷酸萃取的影响

研究以渣场酸性池水和磷石膏浮选脱硅回水作为部分二洗水进入磷酸萃取系统的评价试验。结果表明,产品w(P_2O_5)为25%左右时,磷矿分解率96.5%,洗涤率99%,石膏(干基)过滤强度600 kg/(m~2·h);吨P2O5消耗磷矿粉(w(P_2O_5)30%)3.46 t,硫酸(w(H_2SO_4)100%)2.84 t;渣场池水和磷石膏浮选脱硅回水对湿法磷酸生产过程中的分解率、洗涤率以及过滤强度没有影响;浮选脱硅回水比渣场酸性池水更容易使磷酸萃取过程中产生泡沫,添加一定量消泡剂后,可达消泡效果。     

Effects of ionic impurities on the crystal morphology of phosphoric acid hemihydrate

The adsorption of foreign molecules on the crystal surface is generally believed to contribute to modify crystal morphology and the different adsorption energies on different crystal faces may lead to different modifications of crystal morphologies. In order to obtain a deep understanding of the face growth intervening mechanism, phosphoric acid hemihydrate (H₃PO₄·0.5H₂O) is taken as an example to investigate the influence of several typical ionic impurities on its crystal morphology by applying a molecular simulation study using Cerius 2 software. The absolute values of the calculated binding energies for cations are larger than that for anions. Therefore, it is concluded from the simulation that cations inhibit the growth of some crystal faces, while anions has no significant inhibition to a particular crystal surface, which is in good agreement with the experimental observation. It is also noticed that significant differences of binding energies to the different crystal faces will lead to obvious modifications of crystal morphologies and higher charged cations have more obvious effects than lower charged cations on the crystal morphology modification.     

磷酸活化法制备污泥含碳吸附材料的研究

研究了磷酸活化法制备污泥含碳吸附剂的工艺条件,探讨了活化剂质量分数、活化温度、活化时间和浸渍质量比对活化效果的影响.结果表明,在磷酸质量分数为50%、活化温度450℃、活化时间1 h、浸渍质量比1.5:1的条件下,制得的含碳吸附剂碘值在210 mg/g以上,产品收率50%,应用该吸附材料处理废水效果较好.     

Study of chemical activation process of a lignocellulosic material with KOH by XPS and XRD

Chemical activation of carbons is currently a very common method for obtaining activated carbons with very high surface areas. KOH is one of the most effective agents employed for this purpose. However, the reaction mechanism of this kind of activation it is not yet completely elucidated, although some models have been proposed. In this paper, an activated charcoal was obtained from a lignocellulosic material by impregnation with different amounts of KOH. The activation process was studied by X-ray photoelectron spectroscopy and X-ray diffraction. These techniques point to the formation of different potassium compounds at the carbon surface (mainly K₂CO₃ and different oxides) and show the dependence between surface area development in the carbons and the amount of K₂CO₃ formed during the activation process.     

Control of pore development during CO2 and steam activation of olive stones

Several series of activated carbons were prepared from olive stones by means of carbonization followed by activation with carbon dioxide, water steam and a mixture of them, under different experimental conditions. The changes in porosity of the original char during activation were studied by adsorption of N₂ at 77 K, CO₂ at 273 K and Hg porosimetry. The study was carried out covering a wide range of burn-off (19–83%) using activation times of 20–120 min, and temperatures between 650 and 950 °C. It is shown quantitatively how the individual factors influence the development of microporosity. It was found that in general terms, increasing activation produces a continuous increase in the volume of micropores and mesopores. However, this development occurs in a different proportion whether CO₂ or steam are used: while CO₂ produces narrow micropores on the carbons and widens them as time is increased, steam yields pores of all the sizes from the early stages of the process. The simultaneous use of these two activating agents resulted positive at times higher than 1 h, since it yielded carbons with higher volumes of pores.