添加木质素对污泥热解过程氮转化的影响

利用热重-质谱联用仪(TG-MS)在线检测添加不同比例木质素的污泥热解和主要含氮气体释放特性,并利用傅里叶红外光谱仪(FTIR)在线检测热解过程固体残焦表面官能团的变化规律,分析木质素对污泥热解过程氮转化的影响,从而揭示氮的迁移机理。结果表明:污泥热解过程NH_3的生成主要来自蛋白质的脱氨作用,加入木质素后热解过程中产生了大量羰基,抑制了氨基酸的分子内环化和分子间缩聚反应,而促进了直链酰胺的生成,最终在OH自由基攻击下转化成HNCO和HCN;NH_3的增加并非来自HCN和OH的反应,而是由未缩合的氨基脱除生成;另外,添加40%左右的木质素对于减少污泥热解过程中NO_x前驱物的排放有积极意义。     

城市污泥慢速热解过程中氮的转化规律

利用热重-质谱联用(TG-MS)技术研究城市污泥慢速热解特性及含氮气体产物的生成规律,同时利用原位红外光谱仪实时检测固体表面官能团的变化。研究结果表明:初沉污泥在500℃之前热解已基本完成,二沉污泥由于添加了矿物质盐类,在700℃左右仍有一个较大的失重峰;二沉污泥热解过程HCN和NH₃总生成量均小于初沉污泥,即二沉污泥所加矿物质抑制了HCN和NH₃释放;但温度大于400℃时所加矿物质对HNCO生成具有一定促进作用;污泥中蛋白质热分解会产生环酰胺类物质、含氮杂环化合物和腈类物质,并最终转化为HCN,这是污泥热解过程中HCN的主要来源;400℃以下NH₃主要来自铵盐分解和HCN转化,蛋白质热分解对于NH₃生成贡献很小;400℃以上基本检测不到NH₃生成,即较高温度下挥发分二次反应对NH₃生成几乎没有影响;300~480℃,污泥中木质素裂解产生了大量含氧自由基,促使HCN转化为N₂O,HNCO则最终转化成了NO。     

流化床煤燃烧过程不同气氛下的气态氮释放特征

利用微型流化床反应装置,结合快速过程质谱仪,在850~940℃操作温度下,研究了三种不同粒度分布烟煤和无烟煤在热解、气化和燃烧反应条件下四种主要气态氮产物HCN、NH₃、NO和NO₂的释放规律。结果表明,微型流化床可以实时检测挥发分氮和焦炭氮的动态释放序和类型,热解、气化和燃烧反应气氛的改变主要影响HCN和NH₃的释放量。热解产物的气态氮主要是来自于挥发分,燃烧反应的HCN和NH₃的释放量与温度有明显关系,而气化反应的各类气态氮释放量随温度变化波动不大。煤颗粒尺寸和温度变化对烟煤和无烟煤中各类气态氮释放量产生影响比较复杂,其中NH₃的释放特性是区分挥发分N释放和半焦N释放的重要特征。     

铬革屑热解NO、NH3和HCN的释放特性

采用傅里叶变换红外光谱仪对铬革屑热解过程中NO、NH₃以及HCN的释放特性规律进行研究,探讨了随着时间的变化,热解温度对这3种含氮气体释放特性的影响。结果表明,热解过程中NO、NH₃以及HCN的释放随温度的升高呈现不同的规律。在热解温度较低的情况下含N气体的释放较少,其中NH₃的释放占主导。随着温度的升高,NO、HCN的释放量上升,尤其在550℃,HCN的释放率反超NH₃,释放的浓度达到500 ml·m^-3以上,NH₃的释放率维持在10%~15%。高温区HCN的释放存在迅速升高的过程,NO的释放量相对较少。NH₃的释放主要与胶原蛋白中氨基结构的破坏有关,如酰胺及酰胺带结构,而HCN主要来自于焦含氮结构的二次裂解,以及热解液体中含氮杂环物质的分解。NO的释放主要与C=O,C-O/C-O-C等含氧基团的变化以及原料中的N/O比例有关。     

Fe2O3对甘氨酸热解特性及氮转化的影响

选用污泥中典型氨基酸-甘氨酸（Gly）为研究对象,利用差式热值分析-质谱联用技术（DSC-MS）和固定床实验研究了Fe₂O₃对甘氨酸热解特性、NO _x 前驱物生成规律以及氮转化特性的影响。结果表明：热解特性实验中,由于Fe₂O₃将Gly的第一热失重阶段一分为二,导致其热解过程由2个阶段增至3个;Fe₂O₃使Gly热解起始温度及气体析出温度降低50℃,并通过促进半焦的二次裂解反应使Gly失重率增加23%。与Fe₂O₃对Gly热解过程的影响一致,Fe₂O₃将含N气体析出过程同样分成3个独立的阶段。固定床实验中,在Fe₂O₃/N=0.5时,Fe₂O₃最大程度地抑制了NO _x 前驱物（NH₃和HCN）析出,使其减少30%。由于Fe₂O₃促进肽脱水缩合、环化和芳香化反应,使得更多P-N、N-5和N-6固定在半焦中,半焦氮残留率增加5%。     

O2浓度对污泥燃烧还原性气体产生及还原NO的双重影响

在模拟水泥预分解炉装置上研究污泥燃烧过程中还原性气体的产生及其对NO的还原,并系统研究了O₂浓度（体积分数为0～5%）对还原性气体产生及NO还原的双重影响。TG-FTIR特征分析表明,污泥燃烧产生的还原性气体主要为HCN、NH₃、CO和CH₄。进一步实验研究发现O₂浓度对HCN和NH₃的产生有明显影响,HCN和NH₃在O₂体积分数为3%时产生速率最大。同时,O₂浓度对污泥燃烧还原NO有较大影响。在污泥燃烧温度为900℃,烟气中CO₂体积分数为25%、NO浓度为600mg/m³、SO₂浓度为200mg/m³、O₂体积分数为3%时,NO还原率可达到最大（55.8%）。通过还原性物质（NH₃、CO、CH₄和污泥焦）对NO的还原实验研究进一步发现,NH₃和CO是污泥燃烧过程中NO还原的关键物质,且NH₃对NO的还原随着O₂浓度的增加而增加,而CO对NO的还原受O₂浓度的限制。综合分析表明,O₂浓度对污泥燃烧NO还原的影响主要是由NH₃的产生速率差异、NH₃和CO对NO的还原起主导作用且受O₂浓度影响较大等多种因素综合导致。采用污泥作为还原剂进行NO还原是一种高效的方法,在水泥生产中可通过控制O₂浓度获得较高的NO还原率。     

无烟煤化学链燃烧过程燃料氮转化释放特性

基于赤铁矿石载氧体,在小型单流化床反应器上,开展煤挥发分和焦炭的化学链燃烧研究,探讨挥发分氮和焦氮在化学链燃烧过程中的转化特性。研究表明:燃料氮释放的中间产物HCN和NH₃与铁矿石载氧体具有较高的化学反应亲和性,易于被载氧体氧化生成N₂和NO。淮北无烟煤挥发分氮转化过程中,NO是唯一的氮氧化物,反应器出口中间产物NH₃的释放份额略高于HCN。在煤焦化学链燃烧还原过程中,部分燃料氮释放的中间产物HCN和NH₃被铁矿石氧化导致少量NO的生成,还原过程中无N₂O的释放;较高的还原反应温度加速了NO的生成。减少进入载氧体氧化再生过程的焦炭量可减少空气反应器NO和N₂O的生成。     

准东煤与污泥共热解过程中NOx前驱物释放规律

借助热重-质谱联用（TG-MS）、电感耦合等离子体发射光谱（ICP-OES）以及原位漫反射傅里叶变换红外光谱（in situ DRIFT）等实验手段对准东煤与污泥的混合物进行共热解实验,研究了污泥质量百分比为25%、50%、75%时混合物热解主要NO_x前驱物的释放规律,探讨了准东煤中矿物质以及混合物中官能团的变化对NO_x前驱物释放的影响。实验结果表明：混合热解过程中NH₃、HCN的产率不随污泥掺混比的增大而增加,掺混比为50%左右时NO_x前驱物的释放量相对较低。准东煤内在碱金属及碱土金属以及混合热解过程中各官能团的协同效应对NO_x前驱物释放具有抑制效果。     

热解时间对污泥生物炭活化过硫酸盐的影响研究

污泥热解制备生物炭是一种污泥有效处理处置与资源化利用方法。通过控制热解时间,调控污泥生物炭表面的活性位点,改变过一硫酸盐（PMS）体系中的活性物种组成,可实现环丙沙星（CIP）的高效降解。研究发现,热解温度为700℃、热解时间为120 min时,污泥生物炭具有较高的PMS活化性能,对CIP的去除率近90%。机理探究表明,¹O₂在体系中发挥主要作用。C==O、吡咯氮和—OH位点有利于¹O₂产生,C—O、吡啶氮、晶格氧和Fe位点促进·OH和SO₄^·-释放,石墨氮可促进PMS活化产生SO₄^·-。     

三水磷酸钾耦合CaO对樟木粉热解特性及NOx前体释放特性的影响

利用生物质催化热解生产高附加值化学品具有广阔的应用前景,但热解过程中排放的NO_x会对环境造成不利影响。本文利用热重-质谱联用技术（TG-MS）探究樟木粉热解特性及热解过程中主要NO_x前体的释放特性,对比分析CaO耦合磷酸盐对樟木粉热解过程中NO_x前体生成的反应过程的影响。实验结果显示,随着三水磷酸钾和CaO的加入,樟木粉热解过程中挥发性产物的释放量有所增加而固相产物的产率有所减少;同时,混合热解过程中生成的主要NO_x前体的离子流强度曲线有所降低。这表明,三水磷酸钾和CaO的耦合作用,一方面能够改善樟木粉的热解特性,使热解过程更加彻底;另一方面能够有效抑制樟木粉中含氮化合物的一次裂解,延缓NH₃等NO_x前体的生成、减少HCN等NO_x前体的释放。     

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part I. Effects of reactor configuration on the determined yields of HCN and NH3 during pyrolysis

The formation of HCN and NH₃ during the pyrolysis of a biomass (bagasse) and a set of rank-ordered coal samples has been studied in a novel reactor. The reactor has some features of both a drop-tube reactor and a fixed-bed reactor: the reactor allows the coal/biomass particles to be heated up rapidly as well as to be held for a pre-specified period of time at peak temperature. The experimental results obtained suggest that a considerable amount of the nitrogen in the nascent char could be converted into HCN and NH₃ if the char is held at high temperatures for long time. The formation of NH₃ from the thermal cracking of char was seen to last for more than an hour even at temperatures as high as 700–900°C. The formation of HCN went to completion much more rapidly than that of NH₃. Compared with the results in the literature from the pyrolysis of coals in a fluidised-bed reactor, the reactor configuration used in this study allows the effects of fuel rank to be studied on an unbiased basis towards the type of fuel. The yields of HCN and NH₃ from the present study decrease with increasing rank. The experimental results suggest that the differences in reactor configurations used by various researchers would account at least partially for some of the discrepancies in the literature regarding the formation of HCN and NH₃ during the pyrolysis of coals.     

CaO对大豆蛋白热解特性及NH3等含氮化合物释放的影响

利用热重-质谱联用技术研究CaO对大豆蛋白热解特性及NH₃等含氮化合物释放的影响,根据TG与DTG曲线求出不同CaO含量的大豆蛋白在热解过程中的挥发分指数D。结果表明:随着CaO含量的增加,大豆蛋白的挥发分释放剧烈程度不断下降,但是未对热失重速率峰值对应温度产生影响;CaO的加入会抑制大豆蛋白热解挥发分的析出,且CaO的含量越多,抑制效果越强;在CaO与大豆蛋白质量比为0:10、1:10、2:10、3:10、4:10和5:10六种工况下,CaO对NH₃等含氮化合物释放的影响为抑制作用,且在CaO与大豆蛋白比为4:10时抑制效果达到最好。     

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part III. Further discussion on the formation of HCN and NH3 during pyrolysis

The formation of HCN and NH₃ from the pyrolysis of coal (and biomass) is discussed based on our experimental data as well as the data in the literature, including the pyrolysis of N-containing pyrrolic and pyridinic model compounds reported in the literature. The pyrolysis of the model compounds and the thermal cracking of coal pyrolysis volatiles appear to be in good qualitative agreement in terms of the onset decomposition temperature, the main intermediates and the final N-containing product (HCN). The formation of NH₃ requires the presence of condensed phase(s) of carbonaceous materials rich in hydrogen. Direct hydrogenation of the N-sites by the H radicals generated in situ in the pyrolysing solid is the main source of NH₃ from the solid. The initiation of the N-containing heteroaromatic ring by radical(s) is the first step for the formation of both HCN and NH₃. While the thermally less stable N-containing structures are mainly responsible for the formation of HCN, the thermally more stable N-containing structures may be hydrogenated slowly by the H radicals to NH₃. The formation of NH₃ and the formation of HCN are controlled by the local availability of radicals, particularly the H radicals, in the pyrolysing solid. The increased yield of NH₃ (and HCN) with increasing heating rate can be explained by the rapid generation of the H radicals at high heating rates, favouring the formation of NH₃ (and HCN) over the combination of N-containing ring systems within the coal/char matrix. The size of the N-containing heteroaromatic ring systems and the types of substitutional groups also play important roles in the formation of HCN and NH₃.     

A theoretical investigation on the thermal decomposition of pyridine and the effect of H2O on the formation of NOx precursors

Pyridine is one of the main nitrogen-containing compounds in coal, and its pyrolytic mechanism to generate NO_x precursors (mainly NH₃ and HCN) remains unclear. In this work, the possible pathways for the pyrolysis of pyridine to form HCN and/or NH₃ were investigated by the density functional theory method, and the effects of H₂O on pyridine pyrolysis were also investigated. The results show that there are two possible reactions for the initial pyridine pyrolysis, i.e., internal hydrogen transfer and C–H bond homolysis, and that internal hydrogen transfer is more favorable. Nine possible reaction pathways following internal hydrogen transfer are obtained and analyzed. Among these pathways, pyridine prefers to produce HCN instead of NH₃. The existence of H₂O has significant effects on the decomposition of pyridine, as it participates in pyridine pyrolysis to form NH₃ rather than HCN as the major product.     

不同氨基修饰条件对NH2-MIL-53(Al)CO2吸附性能的影响

采用水热合成法,通过改变配体中2-氨基对苯二甲酸的含量制备了不同氨基含量的NH₂-MIL-53（Al）,考察了氨基含量,氨基功能化方法和氨基种类对NH₂-MIL-53（Al）的CO₂吸附性能的影响。傅里叶变换红外光谱表征（IR）发现在3500～3900 cm^-1处存在-NH₂基的伸缩振动带,氨基修饰成功。低压下,NH₂-MIL-53（Al）的CO₂吸附容量随氨基含量的增加而增大,且当氨基含量100%时,其CO₂吸附性能优于直接合成的NH₂-MIL-53（Al）。合成前修饰比合成后修饰,更有利于提高CO₂吸附容量。采用乙醇胺、1,8-二氮杂二环[5.4.0]十一碳-7-烯、N,N'-二亚乙基三胺进行后氨基功能化都不能提高MIL-53的CO₂吸附能力。     

Nitrogen release during high temperature pyrolysis of coals and catalytic role of calcium in N2 formation

Pyrolysis of 10 coals with carbon contents of less than 80 wt%(daf) has been studied with a fixed bed quartz reactor to examine mainly nitrogen release from char-N without volatile matters. When temperature is raised from 1000 to 1350 °C, N₂ yield increases but char-N decreases for all the coals used. There is a strong reverse correlation between N₂ and char-N, which points out that most of N₂ arises from char-N via solid phase reactions. NH₃ is also formed from char-N at high temperatures of ≥1000 °C. In the pyrolysis of low rank coals, demineralization by HCl washing increases yields of tar-N, HCN and char-N, but decreases NH₃ and N₂. The addition of 3 wt% Ca to the demineralized coals shows almost the reverse effect. The XRD measurements after pyrolysis at 1000–1350 °C reveal that the Ca exists predominantly as CaO with the average crystallite size of 25–65 nm and promotes carbon crystallization. As the extent of crystallized carbon increases, N₂ yield increases remarkably. It is likely that the highly dispersed CaO catalyzes efficiently conversion reactions of char-N to N₂ in the process of carbon crystallization. The reaction mechanism is discussed in term of interactions between CaO particles and char-N.     

Change of nitrogen functionality of N-enriched condensation products during pyrolysis

Changes in the nitrogen functionality of ¹⁵N-enriched condensation products prepared from glucose and ¹⁵N-glycine were investigated during pyrolysis at 600–1000 °C. The structural changes in the condensation products were studied by means of solid-state ¹³C and ¹⁵N NMR spectroscopies. During pyrolysis, the aliphatic moieties of the condensation products decomposed and evolved as gas and tar. At pyrolysis temperatures above 600 °C, almost all the carbon in the chars were converted to aromatic carbon. After pyrolysis, large amounts of nitrogen remained in the chars as char nitrogen (char-N), and about 30% of the nitrogen was eliminated from the chars as HCN and NH₃. With increasing temperature, the production of HCN and NH₃ increased and the amount of char-N decreased. By combining X-ray photoelectron spectroscopy and NMR results, detailed results for nitrogen fractions in chars were obtained. During pyrolysis, the fraction of unsubstituted pyrrole-N decreased and the fraction of quaternary-N increased. The fraction of pyridine-N remained almost constant at temperatures below 800 °C, but at 900 °C and above, the fraction of pyridine-N decreased. The fraction of substituted pyrrole-N showed minimum at 800 °C. On the basis of these results, structural changes of nitrogen functional groups during pyrolysis are discussed.