2015年炭黑和白炭黑测试实验室间比对结果分析

介绍2015年炭黑和白炭黑实验室间炭黑着色强度、炭黑氮吸附比表面积和白炭黑氮吸附比表面积测试的比对结果分析。结果表明,炭黑着色强度和白炭黑氮吸附比表面积比对测试均只存在1个离群结果,炭黑氮吸附比表面积比对测试存在2个离群结果,出现离群结果的实验室应进行仪器、试剂和测试条件等的校准和修正,提高测试水平。     

低温氮吸附法测定炭黑的比表面积

研究用低温氮吸附法测定炭黑的比表面积,考察预处理方式、预处理温度、预处理时间、饱和蒸气压准确性等因素对炭黑比表面积测试结果的影响。结果表明,使用具有防污染装置的真空加热方式对炭黑进行预处理、预处理温度为200℃、预处理时间为3 h、保证饱和蒸气压的准确性,炭黑比表面积的测试结果更准确。     

新合成二氧化硅氮吸附比表面积不断变化原因探究

采用BET法氮吸附比表面积测定仪,透射电镜,CTAB法比表面积测定仪三种手段,表征一种实验室新合成二氧化硅在不同条件下随放置时间的延长各参数的变化情况,并据此进行原因的分析探究.BET法比表面积测试结果显示,刚合成的二氧化硅比表面积较大,因其中存在大量的超微孔,其对比表面积测试结果的贡献很大;随着不同条件下放置时间的延长,此类超微孔不断减少,比表面积最终达到一个相对稳定的值.透射电镜和CTAB法的测试结果证明,超微孔的存在与否,不影响二氧化硅粒径大小,此两种方法是表征此类二氧化硅粒径大小相对可靠的方法.     

不同气化条件和煤种对颗粒煤气化的残焦影响

采用自制的煤炭气化装置进行气化,研究粒度为5—10 mm的大颗粒褐煤、烟煤和无烟煤在不同气化条件下气化所得残焦的微观结构和官能团特性。结果表明:适当升高气化温度,残焦的氮吸附量和比表面积值均增大,孔容和微孔率则先增大后减小。H_2O(g)为气化剂的残焦的氮吸附量、比表面积、总孔容和微孔率均大于CO_2气化残焦的。残焦的氮吸附量、比表面积、总孔容和微孔孔容的变化均随着煤种的煤化程度降低而升高。     

煤拔头中低温快速热解烟煤半焦的孔隙结构

利用喷动载流床模拟煤拔头工艺,在550, 650, 750和850℃热解温度下对大同烟煤进行热解得到拔头半焦. 采用氮吸附法对该烟煤及其半焦的孔隙结构进行了研究. 结果表明,拔头半焦的孔隙发达度都弱于原煤;由低到高4个热解温度下挥发分析出率(Y)依次为7.89%, 21.79%, 22.12%, 39.33%,中孔尺寸随Y增加而减小,微孔和大孔尺寸及总孔体积和总孔比表面积基本随Y增加而增加;550℃时挥发分的析出对孔隙结构的发展无明显有利影响. 从原煤到半焦(热解温度由低到高),样品满足BET吸附等温式的相对压力范围依次为0.101~0.351, 0.093~0.201, 0.072~0.152, 0.032~0.053, 0.058~0.108,BET比表面积与NLDFT总孔比表面积变化趋势一致.     

活性炭粒径对吸附不同分子质量有机污染物的影响

以苯酚、聚乙二醇(PEG-6000)、腐殖酸为研究对象,采用活性炭为吸附剂,对椰壳活性炭在4组不同粒径范围(150~2 000μm)的吸附能力进行比较。结果表明:活性炭对苯酚的吸附量与微孔比表面积成正比;对PEG-6000的吸附量与中孔比表面积成正比。在吸附苯酚时,粒径小于150μm的活性炭吸附能力是粒径1 000~2 000μm活性炭的1.2倍;吸附PEG-6000和腐殖酸时,粒径小于150μm活性炭的吸附能力是粒径1000~2000μm的4倍和1.2倍。     

竹炭粒径对竹活性炭的吸附性能与孔结构的影响

研究了竹炭粒径对KOH活化法制备的竹活性炭吸附性能和孔结构的影响。结果表明,竹炭粒径0.18~0.27 mm和0.55~0.88 mm时活化得率较高。竹活性炭碘吸附值和亚甲基蓝吸附值都随竹炭粒径的减小而先减小后增大,与活性炭的比表面积BET和总孔容积变化趋势相一致;苯酚吸附值随竹炭粒径的减小而先增大后减小。竹炭粒径对竹活性炭碘吸附值和苯酚吸附值的影响较小,0.11~0.15 mm粒径竹炭制备的活性炭的亚甲基蓝吸附值最大。0.18~0.27 mm和0.55~0.88 mm粒径竹炭制备的活性炭的平均孔径较小,说明0.18~0.88 mm粒径竹炭制备的活性炭的微孔率相对较高,有利于在低分子质量气体吸附方面的应用。因此,竹炭制备高性能活性炭的较佳粒径为0.18~0.88 mm。     

煤基制备活性炭及其吸附性能研究

采用化学活化法,以太原无烟煤为原料,采用NaOH热解和活化两步法制备了高比表面积煤基活性炭。研究了NaOH与无烟煤比例对HSSAAC孔结构和吸附性能的影响,采用低温氮吸附法测定其比表面积和孔结构。结果表明,最好条件下制备样品比表面积为820.49m2/g,为高比表面积的煤基活性炭,苯酚吸附测试证实样品表现出优异的苯酚吸附性能,吸附值为298mg/g。通过NaOH化学活化方法,太原无烟煤成为具有良好吸附能力的高比表面积活性炭的良好前体。     

甲烷在成型前后活性炭上吸附的初步试验

通过对比试验,分析成型对活性炭储存甲烷特性的影响。首先,应用丙烯酸甲酯乳胶黏合剂对活性炭SAC-02成型,在温度区间268.15～338.15 K、压力范围0～15 MPa测试甲烷的吸附等温线;通过确定吸附量和等量吸附热,比较甲烷在成型前后活性炭上的吸附平衡。其次,测试储罐吸附床中心在室温、4个压力（6.5 MPa、5.5 MPa、4.5 MPa和3.5 MPa）下快速充放气过程的温度变化,分析成型对吸附过程热效应的影响。结果表明,成型活性炭的密度增大、比表面积减小、单位质量吸附剂上的甲烷吸附量减小;甲烷在成型前后活性炭上的等量吸附热均处于13～20.5kJ·mol^-1;成型活性炭吸附床中心温度在充放气过程中的变化幅度和变化速率均增大。比较试验结果时发现,选用黏合剂成型须综合考虑其对吸附床热导率、传质阻力及吸附剂微观结构的影响。     

煤基活性炭比表面积与碘吸附值相关性研究

为快速测量煤基活性炭比表面积和孔隙结构等性能指标,通过分析活性炭的碘吸附值与比表面积、孔结构之间的关系,明确BET与碘吸附值之间的相关性。结果表明,碘吸附值在50~800 mg/g时,碘吸附值与比表面积之间具有良好的线性关系,拟合度达0.933,利用碘吸附值可快速高效估算比表面积和微孔结构,还可用来预测BET,但相对吸附压力(P/P0)和常数C选择不当,将导致比表面积测量不准确;碘吸附值的大小主要表征了活性炭微孔0.8~1.2 nm孔隙的发达程度;碘分子在微孔中进行单层吸附符合由致密堆积的六方晶格组成的表面覆盖模型。碘吸附值能够实现煤基活性炭比表面积和孔结构的快速分析。     

Hydration of magnesium oxides in the presence of water vapour

The uptake of water vapour on to magnesium oxide has been studied using a silica spring technique. In the experiment reported here, porous magnesium oxides were investigated, and the amount adsorbed at equilibrium at various vapour pressures of water was determined. The magnesium oxides used were characterised using low temperature nitrogen adsorption to give a pore size distribution and a specific surface area, and chemical analysis from X-ray fluorescence data. The nitrogen adsorption isotherms obtained were a mixture of type II and type IV using the BET classification. The oxides sorbed water vapour to give an equilibrium isotherm which was sigmoid in character. Rehydration of the samples after desorption and degassing at 298 K produced samples with an enhanced capacity for water vapour sorption. This is associated with a change in the surface of the oxide from a hydrophobic to a hydrophilic character upon the second adsorption cycle. This is of importance in assessing the water sorption capacity of industrial produced porous magnesium oxides and their subsequent use as desiccants.     

Influence of pore size distribution on water adsorption on silica gels

The influence of pore size distribution on water adsorption has been analysed for a series of partially dehydroxylated silica gels with different pore structure, assessed from the analysis of nitrogen and CO₂ adsorption isotherms. It has been observed that some silica gels show water adsorption mainly in the first range of relative pressures (relative pressure from 0 up to 0.6), while other silica gels also show water adsorption at higher relative pressures. Comparison of the N₂ and water adsorption isotherms points out that only silica gels containing mesoporosity show water adsorption at relative pressures higher than 0.6. Moreover, a good correlation between the initial part of water adsorption isotherms (relative pressure from 0 up to 0.3) and CO₂ adsorption isotherms has been found (the higher the CO₂ adsorption capacity, the higher the water adsorption capacity at low pressure).     

硅胶嵌入多孔纸基对苯蒸气吸附性能

苯蒸气作为一种典型的有害VOC污染物，研究对其的高效净化处理具有重要意义。纸基材料是一种密度小、孔隙率高、机械强度高的多孔材料，分析以木浆纤维纸、陶瓷纤维纸作为多孔基材，通过多次硅溶胶浸泡的方法制得硅胶嵌入多孔纸基吸附材料样片。通过扫描电镜SEM研究两种纸基材料表面的形貌及结构，采用重量法蒸气吸附仪对不同上胶次数的两种基材样片进行吸附性能测试。测试结果表明：木浆纤维纸和陶瓷纤维纸6次上胶率高达3.38 g/g和8.66 g/g; 0.1分压苯蒸气下30 min样片吸附量即可达到最大吸附量的80%；两种硅胶嵌入多孔纸基样片吸附容量在0.8分压苯蒸气下均超过100 mg/g；在4次上胶时样片表现出最佳的苯蒸气吸附性能。此外，通过对实验结果进行分段拟合得到吸附特征曲线。     

Reliable specific surface area measurements on anhydrous cements

The specific surface area (SSA) of anhydrous cement has a direct impact on its reactivity and on the properties of fresh and hardened concrete. However, measuring this physical parameter is non-trivial.The choice of the degassing conditions (temperature, pressure and time) is essential for reliable SSA measurements by nitrogen adsorption because of the dehydration of the gypsum it contains. Such dehydration involves a significant increase of the SSA_BET, whereas Blaine test is poorly sensitive to the hydration state and structural modification of the calcium sulfate carrier. Because of this, SSA_BET values may be more variable than Blaine fineness. More consistent SSA_BET results could be obtained by degassing anhydrous cement samples at 40 °C under N₂ flow for 16 h, as at these conditions the cement composition is preserved.     

Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Silica Gel

Abstract

Adsorption isotherms of acetaldehyde, propionaldehyde, and butyraldehyde on Davison silica gel were determined gravimetrically at three temperatures. The isoteric heat of adsorption initially increased at low loading and then decreased monotonically with an increase in loading. The equilibrium adsorption data were successfully correlated by Polanyi's potential theory. The equilibrium data were also correlated with the Langmuir, BET, Freundlich, and the Hines et al. models. The Freundlich and the Hines et al. models provided the best fit to the data, while the BET equation was found to be applicable only for a relative pressure range of 0.05 to 0.2. The monolayer surface coverages of silica gel by all of the aldehydes estimated by the Langmuir equation were found to be consistently higher than those calculated from the BET equation, except for acetaldehyde at 306.5 K.     

The devolatilisation of millimetre sized coal particles at high heating rate: the influence of pressure on the structure and reactivity of the char

Most studies on the influence of pressure on the combustion of coal particles have shown that for a constant oxygen concentration, an increase of pressure leads to a decrease of combustion rate. Among the different phenomena, which can explain this behaviour, the influence of the devolatilisation pressure on the structure and reactivity of the char formed may be important. The aim of this paper was to obtain a quantitative characterisation of the physical and chemical structure of chars formed during pyrolysis under a large range of pressure. Experiments of single coal particle pyrolysis were conducted in a laser reactor with pressure ranging from 0.014 to 2.1 MPa in a nitrogen atmosphere. As expected, an increase of pressure lead to a decrease of the volatile matter yield, which can be related to the secondary reactions of volatile matter. A characterisation of the char was performed by gas adsorption methods: nitrogen adsorption, carbon dioxide adsorption and active surface area (ASA) measurement. True and apparent densities, porosities and swelling of the particles were also investigated. Although the volatile matter yield decreases, the porosity and the swelling of the char increases with increasing pyrolysis pressure. We observed an increase in surface area and microporosity with increasing pressures up to 0.6 MPa. The ASA surface also increases in this temperature range, but the ratio of ASA to CO₂ surfaces shows that the intrinsic reactivity of the surface decreases with increasing pyrolysis pressure.     

Complexity of CO2 adsorption on nanoporous sulfur-doped carbons – Is surface chemistry an important factor?

Nanoporous S-doped carbon and its composites with graphite oxide were tested as adsorbents of CO₂ (1 MPa at 0 °C) after degassing either at 120 °C or 350 °C. The adsorption capacities were over 4 mmol/g at ambient pressure and 8 mmol/g at 0.9 MPa in spite of a low volume of micropores. The nitrogen adsorption experiments showed an increase in porosity upon an increase in the degassing temperature. The extent of this effect depends on the stability of surface groups. Interestingly, the CO₂ adsorption, especially at low pressure, was not affected. The good performance is due to the presence of ultramicropores similar in sizes to CO₂ molecule and to sulfur in various functionalities. Sulfur incorporated to aromatic rings enhances CO₂ adsorption via acid–base interactions in micropores. Moreover, sulfonic acids, sulfoxides and sulfones attract CO₂ via polar interactions. Hydrogen bonding of CO₂ with acidic groups on the surface can also play an important role in the CO₂ retention. These carbons have high potential for application as CO₂ removal media owing to their high degree of pore space utilization. The results obtained also show that high degassing temperatures might result in the decomposition of surface groups and thus in changes in surface interactions.     

Adsorption of chromium by activated carbon from aqueous solution

Adsorption isotherms of Cr(III) and Cr(VI) ions on two samples of activated carbon fibres and two samples of granulated activated carbons from aqueous solutions in the concentration range 20–1000 mg/l have been studied. The adsorption isotherms have been determined after modifying the activated carbon surfaces by oxidation with nitric acid, ammonium persulphate, hydrogen peroxide and oxygen gas at 350°C and after degassing at different temperatures. The adsorption of Cr(III) ions increases on oxidation and decreases on degassing. On the other hand, the adsorption of Cr(VI) ions decreases on oxidation and increases on degassing. The increase of Cr(III) and the decrease of Cr(VI) on oxidation and the decrease of Cr(III) and the increase of Cr(VI) on degassing have been attributed to the fact that the oxidation of the carbon surface enhances the amount of acidic carbon–oxygen surface groups while degassing eliminates these surface groups. Thus while the presence of acidic surface groups enhances the adsorption of Cr(III) cations, it suppresses the adsorption of Cr(VI) anions.     

脱气预处理条件对木质活性炭比表面积和孔容积分析结果影响初探

在测定木质活性炭比表面积和孔容积前, 先对活性炭进行脱气预处理, 研究预处理条件(脱气温度和脱气时间)对活性炭的比表面积和孔容积的影响, 并将所测结果与仪器推荐条件下所测结果进行对比分析。研究结果表明: 脱气温度和脱气时间对于物理法木质活性炭比表面积和孔容积分析结果影响较小, 这是因为物理法活性炭制备温度高, 官能团少, 结构以微孔为主, 吸附类型以物理吸附为主, 吸脱附速度较快。物理法活性炭预处理条件以脱气温度150 ℃脱气3 h为宜, 相较于ASAP 2460使用说明所推荐的350 ℃和24 h的预处理条件, 明显缩短预处理时间, 降低电耗, 提高了检测效率。脱气温度和脱气时间对化学法木质活性炭比表面积和微孔分析结果影响较大, 适宜的预处理条件为300 ℃脱附12 h。主要是因为磷酸法活性炭制备温度较低, 杂原子较多, 表面化学基团丰富, 发生物理吸附的同时易发生化学吸附, 需要较高的温度和较长的时间才能脱气完全, 当脱气温度过高时, 孔道内的吸附质发生炭化形成炭质微粒堵塞孔道, 同时部分物理吸附在更高的活化能下转化为化学吸附, 使分析结果有所下降。     

Solvent-dependent adsorption of phenolic resin onto silica substrate

The solution impregnation route is commonly exploited to prepare polymer-based composites. However, the adsorption of polymer components is complicated, which is the result of interactions between reinforcement, solvent and polymer. In this study, the adsorption of phenolic resin onto silica substrate from different solvents was investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, UV-visible absorption spectroscopy and thermogravimetric analysis (TGA). Isotherms for phenolic resin adsorption from solvents onto silica substrate have been examined as a function of phenolic resin content in different solvents. The viscosity and surface tension were measured for the solution systems before and after adsorption. Hydrogen bonding interaction was considered to be operative in the resin–solvent–silica system. The adsorption of phenolic resin is dependent on its relative affinity for the solvent on one hand and for the silica surface on the other. UV-visible absorption spectroscopy results suggested that phenolic resin forms hydrogen bonds with the solvent, which competes with the hydrogen-bonding adsorption mechanism for phenolic resin occurring on silica surface. This hydrogen bonding in solution along with the competitive adsorption of solvent onto silica surface suppresses the adsorption of phenolic resin and such suppression is unfavorable in a solution impregnation process.