泥炭基活性炭的制备及孔结构演化与调控研究

城市的发展不可避免会产生大量生活垃圾,焚烧处理可对垃圾有效减容减重,但垃圾焚烧会产生"三致"物质二噁英.工程上广泛采用活性炭净化垃圾焚烧厂烟道气,吸附脱除二噁英,发达的2～5 nm孔隙是活性炭高效吸附二噁英的前提,但其吸附二噁英的作用机制还不够清晰.泥炭作为煤化学意义上的"准年轻煤"和林产学意义上的"年老生物质",是制备煤基活性炭或木质活性炭的优良大宗原料.目前,工业生产活性炭主要采用的物理活化法和化学活化法,所涉及的中孔调控技术对2～5 nm孔的适用性和针对性明显不足,孔结构演化的作用机制尚不够明晰.论文采用分子模拟方法(Materials Studio,MD)研究活性炭的二噁英吸附过程;以贵州毕节泥炭为原料,采用物理活化法(水蒸气活化,二氧化碳活化)和磷酸化学活化法制备泥炭基活性炭,利用热重分析(TGA)考察泥炭炭化/活化过程的热解/气化反应性,采用X衍射(XRD)分析炭化料的微晶结构,通过解析活性炭的N2吸脱附等温线表征活性炭的孔结构,以激光拉曼光谱(Raman),傅里叶变换红外光谱(FTIR),扫描电子显微镜(SEM)表征炭化料和活性炭的碳结构,表面化学,微观形貌.论文开展的研究工作主要包括:1)活性炭2～5 nm孔径吸附二噁英的作用机理,适于吸附二噁英的活性炭孔结构特征;2)泥炭的炭化和气体活化反应性,炭化料经物理活化形成活性炭过程中组成,结构的演变特征及对活性炭孔结构,吸附性能的影响;3)物理活化制备泥炭基活性炭的孔结构演化规律和作用机制,2～5 nm孔的调控途径;4)磷酸在泥炭炭化/活化过程中的作用机理,磷酸活化制备泥炭基活性炭的孔结构演化规律和2～5 nm孔的调控途径.论文研究形成的主要结论有:1.活性炭的2～5 nm孔隙具有良好的二噁英吸附能力,其原因在于此范围孔的内部具有较大的吸附作用势;适于吸附净化二噁英的活性炭应具有发达的中孔(2～50 nm),尤其是2～5 nm的孔隙.有毒二噁英异构体2,3,7,8-四氯代二苯并-对-二噁英(TCDD)分子与活性炭狭缝孔壁间的作用势有两个以孔中心为轴对称分布的能量最低点,孔径为2～5 nm特别是2～4 nm时孔中心和孔壁面附近均有较大的作用势,吸附过程中TCDD分子与活性炭的相互作用能在孔径大于2 nm后的强度分布逐渐向低吸附能区偏移,孔隙对TCDD分子的吸附能力逐渐减弱.在120～200℃温度范围内,活性炭对TCDD分子的吸附性能与中孔的发达程度呈正增长关系,中大孔率相近时,2～5 nm孔隙发达的活性炭利于二噁英的吸附,中孔发达,具有较高2～5 nm孔容的活性炭的TCDD扩散系数值及相同温度条件下的Henry常数值,吸附量最大.2.泥炭在不同炭化条件下形成了组成和结构差异较大的炭素前驱体,是炭化阶段调控泥炭基活性炭孔结构的基础.泥炭炭化的主要温度区间为200～600℃,最大失重速率出现在300℃,增加炭化温度和时间利于形成挥发分产率Vdaf低,石墨化度g高的炭化料;炭化料发生气体活化反应的主要温度区间为740～900℃,活化过程以消耗无序炭和微晶外围活性位点碳为主,表面官能团种类不变,含量降低;随炭化料炭化程度的加深,活性炭的孔结构演化先后经历"跃变区"(炭化温度小于500℃)和"平台区"(炭化温度大于500℃),比表面积SBET,总孔容Vt,中孔容Vmeso和微孔容Vmicro在"跃变区"发生大幅升/降变化,在"平台区"基本稳定,过高的炭化程度(炭化温度大于550℃)会降低2～5 nm孔容和孔容率.3.活化过程碳结构的烧蚀是物理活化法制备泥炭基活性炭时孔结构发育的主要作用和调控途径.水蒸气活化下,随活化温度的升高,活性炭的孔结构先后经历造孔(750～800℃),扩孔(800～850℃),孔塌陷(850～900℃),炭表面烧蚀(900～950℃)的演化过程;随活化时间的增加,先后经历充分发育期(60～120min),过度发育期(120～150 min);水蒸气通量的增加仅产生扩孔作用.2～5 nm孔的发育规律与微孔趋于一致,有效的调孔以全程清除无序炭,部分消耗缺陷微晶炭,少量激活活性位点碳来实现.二氧化碳活化下,随活化温度,活化时间,CO2流量的增加,活性炭分别在900℃,120 min,200 m L/min取得微孔容Vmicro和中孔容Vmeso的极大值.2～5 nm孔的发育程度取决于活性炭总体孔隙结构的发育程度,且主要伴随中孔生长而增大.晶化碳的烧蚀利于活性炭孔隙的发育,非晶化碳的烧蚀则具有相反的效果.4.磷酸化学活化法制备泥炭基活性炭时,泥炭的活化反应性和活性炭的孔结构发育主要受磷酸-泥炭交联反应作用的影响.泥炭在磷酸存在下的炭化/活化过程中发生了交联反应,炭化/活化最大失重速率出现的温度从300℃附近降低至200℃附近,最大失重速率随磷酸浸渍比的增加而降低,低升温速率利于炭化/活化反应充分进行,高磷酸浸渍比利于微晶结构无序化.磷酸浸渍比的增加促进了交联反应量的增多,活性炭的2～5 nm孔容先伴随微孔增长(浸渍比0.7～1.0),后伴随中孔增长(浸渍比1.0～1.5);活化温度的增加促进了交联反应强度的增强,孔隙结构先逐渐收缩(400～550℃),后发生破坏(600℃),2～5 nm孔容递减;交联反应需>120 min才能完成,活化时间对2～5 nm孔的发育无明显影响.论文在优化的物理活化工艺参数条件下(炭化温度450℃,活化温度800℃,活化时间120 min,水蒸气通量0.5 g/(g·char·h)),制得泥炭基活性炭样品的2～5nm孔容为0.129 cm3/g,2～5nm孔容率为21.83%,中孔率为73.94%;在优化的化学活化工艺参数条件下(磷酸浸渍比1.5,活化温度400℃,活化时间150 min),制得泥炭基活性炭样品的2～5 nm孔容为0.158 cm3/g,2～5 nm孔容率为32.62%,中孔率为51.03%,孔结构优于或接近于市售国际品牌垃圾焚烧烟道气净化用活性炭.水蒸气活化法更利于中孔发育,可作为开发泥炭基垃圾焚烧烟道气净化用活性炭的优选制备途径.

水处理活性炭的超声波再生技术

为研究水处理活性炭的再生,利用超声波处理技术,以甲基橙为有机化合物模型,进行吸附饱和木质活性炭的超声处理再生实验.结果表明,Fe2+,Cu2+的加入明显提高了超声反应的脱色率.在pH值为1.0,温度为30℃,声能密度为180 W/L,Fe2+和Cu2+的投加量为0.6 g/L的条件下,超声反应30m in后,脱色率都可达到95.5%.

水处理活性炭的超声波再生技术

根据活性炭吸附机理,利用超声波处理技术,以甲基橙为有机化合物模型,进行吸附饱和木质活性炭的超声处理再生.试验结果表明,Fc2+、Cu2+的加入明显提高了超声反应的脱色率,在pH值为1.0、温度为30℃、声强为180W·L-1 Fe2+、Cu2+的投加量为0.6g·L-1的条件下超声反应30min后,脱色率都可达到95%.

高吸附性能木质活性炭的研究

以水解木素炭为原料,用碱类化合物A作活化剂,研究了活化温度、活化时间及活化剂用量对活性炭的亚甲基蓝脱色力、碘值和活化得率的影响。试验结果表明,活化的最佳工艺条件为:活化温度750℃,活化时间1/4小时,活化剂用量为8:1。在此条件下制得的活性炭具有亚甲基蓝脱色力35.3ml/0.1g,碘值2514mg/g,活化得率为62.3%。

棉秆与污泥共热解制备生物炭工艺优化及其结构与吸附性能

随着经济的发展,产量巨大的棉秆与污泥亟需找到新的资源化方式.该研究利用污泥与棉秆共热解制备炭,采用正交试验法全面考察与分析了各因素对污泥-棉秆炭吸附性能以及表面结构的影响.结果表明,污泥质量分数,KOH浓度,微波功率,辐照时间以及装填量均会显著影响污泥-棉秆炭的吸附性能,表面官能团以及孔结构.优化工艺参数为:污泥质量分数30%,微波功率280 W,辐照时间24 min,KOH质量分数50%,装填量150 g,在该工艺条件可制备获得综合吸附性能较优的污泥-棉秆炭,其亚甲基蓝,酸性品红,硫酸铜以及碘的吸附值分别达到157.80,293.39,272.12,1281.93 mg/g.污泥-棉秆炭的吸附性能可达到或超过国家木质净水用活性炭一级品的标准,但吸附质与炭的结构特性均会影响其吸附性能.酸性官能团总量与孔容分别与酸性品红吸附值及硫酸铜吸附值显著相关,其他结构参数与吸附性能相关性不显著,污泥-棉秆炭对污染物的吸附并不只是单一的物理吸附或化学吸附.该研究结果对于定向设计高效的棉秆-污泥炭基吸附剂具有参考价值.%The production of sludge and cotton stalk arise along with the rapid development of China's economy. Currently the most common methods for sludge and cotton stalk disposal are landfilling, incineration, and application in land in China. And incineration of cotton stalk may bring new air pollution problems; it may contaminate soils and ground water when sludge is used in land as fertilizer. Therefore, it is necessary to find an efficient way for the sludge and cotton stalk recycling. As alternative technology for the common sludge and cotton stalk treatment methods, the pyrolysis has been researched. But there are few researches on the effect of reaction conditions on surface structure properties of chars obtained from co-pyrolysis of sludge and biomass, as well as the research on the relationship between surface structure and adsorption properties. In this study, the pore structure properties (BET surface area, total pore volume and average pore width), the abundance of surface functional groups and the adsorption capacities of sludge and cotton stalk chars (SCA) were analyzed under 5 different reaction conditions. The reaction conditions included sludge content, concentration of KOH (potassium hydroxide) solution, radiation power, radiation time and loading amount. Chars were made from the mixtures of cotton stalk and sludge by microwave heating via KOH activation. The adsorption capacities of SCA were measured by removing methylene blue (MB), acid fuchsin (AF), iodine and copper sulphate (CuSO4) in aqueous solution. The correlations between the structure parameters and the adsorption capacities were calculated to test if the structure would affect the adsorption properties of chars. The results showed that all reaction conditions influenced the pore structure properties, and the abundance of surface chemical groups of chars significantly. On the same structure parameter, the effects of 5 conditions were not the same. For all pore or chemical structure parameters, each of these factors showed the influence with different capacities, and all the responses showed different trend with the change of condition levels. The adsorption capacity of SCA could reach the national stand of wooden activated carbon. All reaction conditions influenced the adsorption capacities to the MB and the CuSO4 significantly, but its influence on the adsorption capacities to AF and iodine was not significant. And for the same adsorption capacity, the reaction conditions showed different influence. The composite index, which was calculated by the adsorption capacity to MB, AF, iodine and CuSO4, was used to optimize the preparation process of the char, and the optimal parameters were as follows: the sludge content of 30%, the concentration of KOH solution of 50%, the radiation power of 280 W, the radiation time of 24 min and the loading amount of 150 g. The adsorption capacities of the SCA to MB, AF, iodine and CuSO4 obtained at the optimal parameters were 157.80, 293.39, 1281.93 and 272.12 mg/g, respectively. The effects of the reaction condition on composite index were as follows: load amount > radiation time > sludge content > radiation power > KOH concentration. The chemical and pore structure properties of the chars and the characteristics of the adsorbate influenced the adsorption properties of SCA significantly. The number of total acidic groups and total pore volume had significant correlation with the adsorption capacity to AF and CuSO4respectively. But other single structure characteristic did not significantly correlate with the adsorption capacity of SCA. The adsorption of SCA to the po

活性炭吸附处理高盐农药废水的研究

采用活性炭吸附预处理后的莠去津农药废水中的有机物,研究了活性炭种类、溶液pH值、盐含量对吸附的影响,测定了吸附等温线,并探讨了活性炭的再生性能.结果发现:pH值小于3时粉状木质活性炭对农药废水的吸附效果最好;废水中的盐含量越高,越有利于吸附;Freundlich模型比Langmuir模型能更好地拟合吸附等温线,pH值为3时的最大吸附量为250 mg/g.碱液可以将吸附在活性炭上的有机物解吸下来,再生后活性炭的吸附量可达到新鲜活性炭的98%以上.

水体净化用木质素基活性炭的制备及其吸附动力学

In order to study the adsorption mechanism of lignin-based activated carbon, Kraft lignin/cellulose acetate composite membrane (KL/CA-M) was prepared through solution mixing and immersion precipitation phase conversion coating technology followed by high temperature carbonization and phosphoric acid activation to form ligninbased activated carbon with excellent adsorption performance. The structure 3 thermal property and adsorption property of activated carbon were tested and analyzed. The results showed that the obtained lignin-based activated carbon had stable structure and excellent adsorption property. The optimum technological conditions for preparing the lignin-based activated carbon were 50% lignin content for the initial membrane, 800 T! for carbonization activation temperature, 60 min for activation time and the mass ratio of phosphoric acid to initial membrane with the number of 1. Thus, the resulting lignin-based activated carbon is with the specific surface area of 1 375.649 m2/g, the micropore volume of 0.714 m3/gCand the adsorption capacity for Methylene Blue of 157.24 mg/gCwhich were higher than the one of commercial activated carbon. The adsorption of Methylene Blue onto lignin -based activated carbon was an exothermic process involving monolayer and multilayer adsorption. The lignin-based activated carbon absorbed Methylene Blue via both physical adsorption and chemical adsorption and the adsorption process was controlled by multiple diffusion.