【作者】 蒋明；

【导师】 宁平；

【作者基本信息】 昆明理工大学 ， 环境工程， 2013， 博士

【摘要】 氰化氢(HCN)是一种来源广泛的“非常规”有毒有害气态污染物。废气中HCN深度净化是目前我国化工、冶金、碳纤维、化工中间体等重要行业为适应更为严格的环境保护要求而急需解决的技术问题。尤其在乙炔化工行业产生的密闭电石炉尾气中,CO含量高,O2含量低,是一类典型的含高浓度CO的工业废气(CO占70～90%),且伴有HCN、H2S、PH3、COS等有毒有害气态污染物,尾气成分复杂,净化和利用难度大。目前专门针对含HCN废气开发的净化技术较少,尤其是对含高浓度CO工业废气中HCN的脱除,国内外未见报道。应用吸附剂对模拟废气中低浓度HCN进行低温吸附(吸附温度<100℃),可在解决HCN高效净化的同时满足电石炉尾气深度净化和资源化需要,又可节约净化工艺带来的能耗,是较有应用前景的HCN净化技术。鉴于此,论文以密闭电石炉尾气中低浓度HCN为研究对象,模拟尾气中HCN浓度范围,开发出分子筛型和活性炭纤维(ACF)型系列低温吸附剂,研究了其吸附性能和对HCN的低温吸附净化机理。通过载体的选择实验、活性组分的筛选实验制备出分子筛型和ACF型吸附剂,讨论了制备条件和操作条件对吸附剂性能的影响,并进行了吸附剂的优化和再生；同时通过吸附剂的等温吸附实验得到其吸附等温线,并通过其计算得到等量吸附热、从而判定HCN在吸附剂上的吸附类型；然后通过TG、SEM/EDS、N2-BET、XRD、XPS对吸附HCN前后的吸附剂进行表征,探讨吸附剂在制备过程和吸附过程中结构的变化和失活机理。最后应用真实电石炉尾气对吸附剂的低温净化脱除HCN的性能进行了检验。研究结果表明,Zn(NO3)2可选择作为较优的改性剂制备用于脱除含高浓度CO气体中HCN的分子筛型吸附剂。21.34%的Zn为Zn/13X吸附剂的最佳负载量,15000h-1的空速、3%的氧含量、20℃的吸附温度为吸附HCN的最佳操作条件,Freundlich等温方程适用于该吸附剂吸附等温线的拟合,等量吸附热为29.71～62.71kJ/mol. ZnO是Zn/13X型吸附剂用于吸附脱除HCN的活性组分,吸附温度越高,气流中的CO在吸附剂表面越容易发生歧化分解积碳,HCN和积碳分解产生的CO2能与活性组分ZnO发生竞争化学吸附,吸附生成物ZnCO3、Zn(CN)2与歧化分解产物C共同堵塞、填充了吸附剂孔径为59.5A-133.8A的中孔,造成Zn/13X吸附剂失活。以ACF作为载体制备吸附剂时,Zn(NO3)2、Cu(NO3)2复合改性后的ACF型吸附剂对HCN可达到最佳的吸附效果。Zn(NO3)2、Cu(NO3)2改性剂浓度均为0.1mol/L、 Zn/Cu=5:1、焙烧时间为0.5h、焙烧温度为300℃时,Zn/Cu/ACF复合型吸附剂的制备性能达到最佳,20。C的吸附温度和2%的氧含量为吸附HCN试验时的最佳操作条件。Freundlich等温方程较适合于描述HCN在该吸附剂上的吸附过程,等量吸附热大小为43.99-67.54kJ/mol。改性液与ACF载体之间存在较强的相互作用,能使改性ACF吸附剂的热稳定性降低。ZnO和CuO为Zn/Cu/ACF型吸附剂用于吸附脱除HCN的主要活性组分,化学吸附后的产物Zn(CN)2和Cu(CN)2共同堵塞、填充了吸附剂孔径为24.2A～120A的中孔上的吸附活性位。失活的分子筛型和ACF型吸附剂的再生后,ACF型吸附剂的再生效率较高,平均再生效率可达80.2%。而两种类型的吸附剂均可进行多次再生使用。经过真实电石炉尾气净化的小试、中试实验,表明前期研究的活性炭型和现阶段研究的Zn/13X型吸附剂均能用于低温下尾气中HCN的净化脱除,而Zn/13X型吸附剂的净化效率较优。工业应用表明：活性炭型吸附剂的净化密闭电石炉尾气时,吸附剂使用寿命长,稳定性高,净化后尾气中杂质含量均低于0.5mg/m3。更多还原

【Abstract】 Hydrogen cyanide (HCN) is an unconventional, toxic and hazardous gaseous pollutant and generated in multitudinous sources. Deeply removed HCN from exhaust gas is needed to solve technical problems in China’s chemical industry, metallurgy, carbon fiber, chemical intermediates and other important industries for meeting environmental requirements. Closed calcium carbide furnace off-gas is a kind of typical exhaust gas which contained a large amount of CO (70-90%). The off-gas can not be recycled due to the existence of HCN, H2S, PH3, COS and other impurities. Nowadays, there is a less purification technology to remove HCN from off-gas. Especially, at low temperatures, HCN removal from industrial off-gas, which contains high concentration of CO, has not been reported. For low-concentration HCN in model off-gas low temperature adsorption (adsorption temperature<100℃), some typical adsorbents can resolve HCN efficient removing from calcium carbide furnace off-gas while meeting the needs of deep purification and recycle, but also bring energy savings. Therefore, the low temperature adsorption technical is possessing broad application prospect.In view of this, the paper took removal of low-concentration HCN in calcium carbide furnace off-gas as the research object, and developed series of adsorbents, such as molecular sieve adsorbent and activated carbon fiber (ACF) adsorbent, studied its adsorption properties and the purification mechanism of HCN at low temperature. Molecular sieve adsorbent and ACF adsorbent were prepared through selecting experiment of supports and active components, and discussed the influence of the preparation conditions and operation conditions on the properties of the adsorbents, and optimized and regenerated the adsorbents. The adsorption isotherms is also obtained by isothermal adsorption experiment of adsorbents. and the adsorption isosteric heat was got by calculation, thus the type of adsorption of HCN on the adsorbent was determined. Then adsorbents before and after adsorbing HCN were characterized by TG, SEM/EDS, N2-BET, XRD, XPS. The structure of adsorbents in the preparation process, adsorption process, and deactivation mechanism were discussed. Finally, the real calcium carbide furnace off-gas was used to test the properties of the adsorbent for removing HCN at low temperature.The results show that, Zn (NO3)2can be selected as relatively optimal modifier for preparation of molecular sieve adsorbent used for removing HCN from the tail gas which contains high concentration of CO. The highest performance of Zn/13X adsorbent is observed at the Zn loading on13X is21.34%(w/w), the optimal conditions are as follows: space velocity is15000h’’, oxygen content is3%, adsorption temperature is20℃. The adsorption isotherm of the adsorbent is conformed to the Freundlich isotherm equation, and isosteric heat is29.71-62.71kJ/mol. ZnO is the active component in Zn/13X adsorbent for removing HCN. CO is more likely to disproportionate and decompose produce carbon(C) and carbon dioxide(CO2) in the adsorbent surface with higher adsorption temperature in gas flow. And CO2can compete with HCN in reacting and adsorbing with ZnO, the adsorption products ZnCO3, Zn (CN)2and C jointly block and fill the mesopore with pore diameter ranging from59.5A to133.8A in the adsorbent, thus Zn/13X adsorbent deactivate.ACF type of adsorbent can reach the highest adsorption efficiency for adsorbing HCN through modifying with ACF as support, Zn (NO3)2and Cu (NO3)2as modifier. Zn/Cu/ACF composite adsorbent reaches the optimal performance, when the preparation conditions are as follows:both the concentration of Zn (NOs)2and Cu (NO3)2are0.2mol/L, Zn/Cu=5:l,0.5h of calcination time, calcination temperature of300℃. The optimal operating conditions are that adsorption temperature is20℃and oxygen content is2%. The Freundlich isotherm equation was suitable for describing the adsorption process of HCN on the adsorbent, and the isosteric heat is between43.99kJ/mol and67.54kJ/mol. There is a strong interaction between the modified solution and ACF support, it decrease the heat stability of the modified ACF adsorbent. ZnO and CuO are the main active component of Zn/Cu/ACF adsorbent for removing HCN, the chemical adsorption products are Zn (CN)2and Cu (CN)2which block and fill the active adsorption sites on the mesopore with pore diameter ranging from24.2A to120A.After regeneration of deactivated adsorbents, ACF type adsorbent has a high regeneration rate reaching80.2%. And both the two adsorbents can be reutilized many times.The field small and pilot-plant experiment of the calcium carbide furnace off-gas have been studied. The results show that activated carbon (AC) adsorbent gained from previous studies and Zn/13X type adsorbent obtained at the present stage can be used for removal of low-concentration HCN in calcium carbide furnace off-gas at low temperature. Zn/13X adsorbent has a ideal purification efficiency. When AC adsorbent was used to purify calcium carbide furnace off-gas, the adsorbent has a long lifetime and high stability. After the purification, the outlet concentration of all impurities in calcium carbide furnace off-gas was less than0.5mg/m3.更多还原