水热处理对褐煤含氧官能团和亲水性的影响

考察了不同水热处理条件对胜利褐煤主要含氧官能团甲氧基、羧基和酚羟基的脱除效果及其表面亲水性的影响.结果表明,提高温度、延长恒温时间以及增大初压均能不同程度地促进含氧官能团的脱除,甲氧基、羧基和酚羟基的最大脱除率分别为67.88%,89.41%和93.70%.脱除含氧官能团使水热处理后的煤样/水接触角增大,亲水性减弱.通过线性拟合,接触角与三种含氧官能团均表现出较好的相关性,其中羧基的相关性最好,说明羧基束缚水的能力要强于甲氧基和酚羟基.     

低温干燥对褐煤含氧基团及其吸水性能的影响

采用红外光谱法确定褐煤中含氧官能团的种类,利用化学法分析干燥前后褐煤表面含氧官能团的变化,吸水性能用最高内在水分来表征,研究低温干燥过程中温度、干燥程度和干燥气氛对褐煤含氧基团及其吸水性能的影响.结果表明,褐煤中羧基和酚羟基含量较高;惰性气氛低温干燥时,酚羟基含量基本不变,羧基发生少量分解;空气下干燥时,羧基含量先减小,之后在氧化作用下,羧基和酚羟基含量同时增大.随着干燥程度的加深,煤样最高内在水分先减小后增大.     

高挥发分不黏煤的预热改质与成焦行为研究

在自行设计的热处理装置中，采用不同的气氛、温度、时间对高挥发分不黏煤进行低温预热处理。研究了热处理条件对含氧官能团、煤分子结构、镜质组随机反射率以及高温热解和黏结倾向的影响。结果表明，不黏煤热处理后干燥无灰基挥发分脱除至21％-25％；煤样的含氧官能团中羧基脱除率最高可达90％以上；处理样的H／C变化不大，O／C降低50％左右。实验验证了预处理煤样替代配煤组分的可能性。     

低阶煤中氧的测定方法及对煤直接液化的影响

氧是煤中最丰富的杂原子,其含量和存在形式对煤的性质有很大影响,特别是对低阶煤的影响更为显著。低阶煤中的氧主要以酚羟基和醚键形式存在,此外还有羰基、羧基和呋喃等。介绍了低阶煤中含氧官能团的测定方法,结果发现:物理方法方便快捷,但XPS、IR等分析手段因一些峰值无法识别,降低了实用性;化学方法步骤繁琐,操作时间长且准确性较差。综述了含氧官能团对煤直接液化的影响,酚羟基在液化过程中因发生交联反应而产生负面影响;高级醚类具有高的液化特性;羧基的液化机理复杂,没有统一的意见。     

热改质对宁东羊场湾煤成浆性能影响研究

采用低温(200℃~450℃)加热的方法,对宁东地区羊场湾煤进行改质实验,并考察改质对煤成浆性能的影响。实验结果表明:250℃~300℃时,煤的内水含量减少到最小,煤样的表面含氧官能团特别是羧基和羟基含量是影响煤成浆的主要因素,低温改质可大大提高煤的成浆性能。最佳的低温改质条件是:改质温度为350℃,加热时间30 min。     

褐煤中含氧官能团的测定与研究

煤表面的官能团的种类和数目对煤的化学性质有很大的影响,最重要的表面基团是含氧官能团。含氧官能团对煤的性质,尤其是表面性质,如亲水性、疏水性、表面电性、表面作用及表面作用方式等的影响较大,从而也对煤的选别、煤炭改质、煤炭转化及其合理加工利用影响较大。干燥后的煤样与原煤相比,固定碳含量逐步提高,氧含量呈逐步降低的趋势,O/C比逐步降低,煤样的芳碳率和平均缩环数也是随着干燥工艺的不同而呈现出递增的趋势,说明干燥后煤样的芳构化程度加深,基本结构单元的缩合度增加,干燥工艺在一定程度上提高了内蒙古褐煤的"煤阶"。     

胜利褐煤超临界乙醇脱氧实验研究

为有效脱除褐煤中含氧官能团,采用超临界乙醇工艺处理胜利褐煤,研究温度、停留时间和醇煤质量比对胜利褐煤脱氧效果的影响,并利用FT-IR和GC/MS对固液相产物进行表征。结果表明,胜利褐煤超临界乙醇脱氧的最佳工艺条件为:温度270℃,停留时间90 min,醇煤质量比5∶1,此时煤样总氧含量为9.29%,脱氧率为61.40%,固相产率为89.62%。在220℃得到的液相产物中,80%左右为芳香族类化合物,酚类和酯类含氧化合物体积分数低于5%,其他含氧类化合物11.29%。270℃得到的液相产率中芳香族类化合物体积分数降低31.69%,含氧类化合物体积分数增加2.81%,酚类和酯类含氧化合物增至35%左右。褐煤经超临界醇解后,乙醇与煤分子作用发生了醚氧桥键的断裂反应,煤分子发生了脱羧反应,液相产物中含有大量酚类(主要为苯酚及其取代物)和酯类(主要为乙酯类)。     

胜利褐煤在液化预反应中氧脱除的初步研究

采用X光电子能谱法(XPS)研究了我国内蒙胜利褐煤中有机氧的赋存形态,将其分为碳氧单键类、羰基基团和羧基基团三种类型,与元素分析法结合得到不同形态含氧官能团在胜利褐煤中的绝对含量,与化学分析法测试煤中含氧官能团进行比较.在容积为0.5 L震荡式高压釜中对内蒙胜利褐煤在液化预反应阶段氧的脱除进行了研究,实验所选温度为330 ℃,360 ℃,400 ℃和430 ℃,分别考察三种催化剂(MnO2,Fe2O3和MoO3)的脱氧效果,并与无催化剂的脱氧效果进行比较,结果表明,氢压1 MPa无催化剂在360 ℃～400 ℃的液化预反应条件下,脱氧率较高.     

酸洗脱除矿物对煤化学组成及润湿性的影响

为探究酸洗处理对煤尘含氧官能团和矿物质变化及对煤尘结构和润湿性的影响,采用盐酸、磷酸、乙酸和盐酸-氢氟酸对榆林煤(YL)进行处理,并利用FTIR,XRD及XRF分析煤尘化学组成及结构变化,借助毛细管上向渗透法研究煤尘的吸湿量,考察煤的灰分、矿物质组成及官能团对润湿性的影响规律。结果表明:酸处理能够脱除煤中的大部分矿物质,对含Si的矿物质元素脱除效果较差,对Ca和K等碱金属矿物的脱除效果较好,盐酸-氢氟酸脱除率最高,为95.3%,盐酸、磷酸、乙酸的单独脱灰率分别为88.4%,84.0%和79.9%。由XRD谱可以看出,酸处理后灰样谱图上的矿物质杂峰数量明显减少,石英峰在处理后增强。通过对XRD参数拟合,发现酸处理破坏了煤中碳的微晶结构,使煤的结构发生了一定程度的解体。FTIR分析表明,酸处理后煤中的羟基官能团含量下降,羧酸和酚羟基C—O的吸收峰占比增加;对灰分含量、矿物质元素组成、官能团变化与润湿性的拟合关系进行分析,发现酸处理降低了灰分含量,降低了煤尘润湿性;无机矿物质元素中Si和Al元素的变化与润湿性的变化规律一致;对比原煤和脱灰煤的润湿性变化与含氧官能团的含量关系,发现在1 050cm-1～1 250cm~(-1)处的酚羟基C—O的峰面积与YL的润湿性变化趋势相反,3 400cm~(-1)～3 450cm~(-1)处羟基的峰面积与YL的润湿性变化趋势相同。     

不同变质程度煤的液化差异及其分子结构研究

对霍林河14煤、补连塔2-2煤和新疆41煤三个不同变质程度煤样,分别进行了加氢液化实验.结果表明,三种煤样的油产率和转化率高低顺序为霍林河14煤、新疆41煤、补连塔2-2煤,并采用红外光谱实验方法对三种煤样液化的差异进行了分析.分析认为,煤中芳香氢和脂氢强度的不同是导致不同煤液化转化率和油收率差异的重要原因;羟基和含氧官能团的丰度则对不同煤液化水产率的高低和气体产物中CO2和CO气体的多少具有较高的影响;此外,利用三个煤样的元素分析数据和红外光谱实验结果,采用Chem3D软件分别模拟建立了三种煤样的分子结构,通过与实验数据比较,认为所建立的煤分子结构比较合理.     

几种低阶煤的过氧化氢氧化解聚性能研究

在40℃利用5％H2 O2水溶液分别对神府次烟煤（ SF）、准东次烟煤（ ZD）、胜利褐煤（ SL）和先锋褐煤（ XF）四种低阶煤进行了氧解,计算其氧解转化率和CO2生成率,结合元素分析、红外光谱以及酸性官能团测定结果比较了四种低阶煤的氧解性能以及其结构特征对氧化解聚性能的影响。结果表明,煤的氧化解聚与变质程度密切相关,变质程度越高,氧化反应性降低。另外煤的氧含量越高,特别是羧基以及酚羟基含量较高时,氧化解聚程度增大。     

Dependence of the water wettability of the surfaces of fossil coals on their structure and properties

The dependence of the water wettability of coal surface on the structure and properties of coals of different stages of diagenesis and metamorphism was studied based on the evaluation of the angles of contact. It was found that the caking coals of Zh and K ranks exhibited maximum hydrophobic properties. Hydrophilic properties were most pronounced in brown coals and low-rank black coals with the highest concentrations of hydroxyl and carboxyl groups and a developed porous structure.     

Evolution of organic oxygen bonds during pyrolysis of coal

Five Czech coals of different rank (70.2, 71.5, 74.5, 75.0 and 83.3 wt% carbon) were heated at different temperatures in the range 250–850 °C and the contents of oxygen-containing functional groups (OH, COOH, CO, OCH₃) were determined in the coals and carbonization residues. The coals and residues were subjected to pyrolysis chromatography at 740 °C and the yields of phenol produced were measured. The dependence of the oxygen functions and the phenol yield on temperature and coal rank is discussed. In the coals studied, the most resistant oxygen groups appear to be hydroxyl and methoxyl; carboxyl and carbonyl oxygen are eliminated below 550 °C.     

The kinetics of oxidation of humic coals in dimethyl sulfoxide

The alkali-catalyzed oxidation of humic coals of different metamorphic ranks with molecular oxygen at 75°C was studied. As a result of analysis of the rate curves, an equation was derived to describe the oxygen uptake as a function of time. It was found that the initial reaction rate depends on the class and grade of coal. It was shown that the amount of carboxyl groups in oxidized sample increased by a factor of 9. On the basis of the experimental data and the summarized results of investigation of organic substances of various structures in highly basic media, it was concluded that low-rank coals could be oxidized at quite a high rate due to the presence of highly acidic C-H groups in them, yielding humic acids as the main oxidation products.     

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H₂O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO₂ from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H₂O.     

Studies of the effects of O-methylation on the pyrolysis behaviour of four coals

O-methylation of coal was found to exhibit a noticeable effect on the pyrolysis behaviour of the original coal. Significant increases in tar yields and a low-temperature fraction, 150–300 °C, were found for the low-rank O-methylated coals. It is proposed that methylation prevents formation of new ether cross linkages through water elimination reactions of hydroxyl functional groups thus allowing for the release of a low-temperature fraction as well as a higher temperature tar. KBr studies of CD₃ labelled O-methylated coals using CD₃I as the methylating agent have resulted in the identification of three distinct i.r. absorptions in the C-D stretching region which have been assigned to methylated phenolic, methylated carboxylic and methylated aliphatic hydroxyl groups. Pyrolysis studies of the O-methylated coals have resulted in better insight into the decomposition mechanisms of different methylated hydroxyl functional groups. Methanol or formaldehyde are seen to be the principle products from the pyrolysis of methylated carboxylic and aliphatic hydroxyls. Decomposition of methylated phenolic groups occurs at a slightly higher temperature and produces principally methane and carbon monoxide.     

Re-examination of the phenolic hydroxyl contents of coals

In connection with studies of the dependence of liquefaction behaviour on coal characteristics, parameters were needed that might effectively characterize the organic chemical structures. Accordingly, the phenolic hydroxyl contents of 37 coals from three geological provinces of the USA have been determined, by acetylation with ¹⁴C-labelled acetic anhydride. The results, when expressed as fractions of the total organic matter in the coals, showed a good inverse correlation with the carbon contents (dmmf). However, application of a stepwise multiple regression analysis to the data developed a linear equation relating hydroxyl content to the vitrinite reflectance, calorific value and vitrinite content, the fraction of variance explained being 92%. When the hydroxyl contents were expressed in the alternative manner, as fractions of the total oxygen content, no correlation could be seen with carbon content. However, in the wide scatter of points on the graph, the data are seen to fall into three reasonably distinct populations such that at the same level of rank, hydroxyl contents typically decrease for coals from the three provinces in the order Interior > Eastern > Rocky Mountain, implying that coals from these areas differ in structure as a result of differing antecedents. Statistical analyses showed that $\text{OH}\text{O}$ has some significance in determining liquefaction behaviour, but it is not among the coal properties found most significant.     

Effect of hydrothermal treatment on the extraction of coal in the CS2/NMP mixed solvent

The extraction of four Chinese different rank bituminous coals with the carbon disulfide/N-2-pyrrolidinone (CS₂/NMP) mixed solvent (1:1 by volume) was carried out in room temperature. It was found that one of middle bituminous raw coal of the four coals gave more than 74% (daf) extraction yield, suggesting an associative structural model for the coal. The four coals were hydrothermal treated under different conditions, and it was found that the extraction yields of the treated coals obviously increased. This will have great significance for coal liquefaction. FTIR measurements show the removal of minerals after the hydrothermal treatment of coals suggesting the dissociation of the coal aggregation structure due to ionic interactions and/or hydrogen bonds broken because of the removal of oxygen and hydroxyl oxygen proceeded through ionic pathways, resulting in the extraction yields of the treated coals increase. However, breaking of π-cation interactions by hydrothermal treatment may be one of possible mechanisms for the enhancement of extraction yield of higher rank of treated coal. The mechanism of hydrothermal treatment of coal was discussed in the paper.     

Reactivity of hydrolysed coals in liquefaction

A hvA bituminous, a subbituminous and a lignite coal have been hydrolysed by 20–30% aqueous caustic solution at 100–300 °C and total pressure from ambient to 8.3 MPa (1200 psi). Reactivity of these pretreated coals toward liquefaction has been examined. The conversion to benzene-soluble material (BS) and oil increases, and the preasphaltene and char residue decreases after pretreatment. Improvement in the conversion to the BS fraction is only marginal for the pretreated bituminous coal, but substantial for the low-rank coals. For the subbituminous coal, the liquefaction reactivity (conversion to BS) increases with the severity of hydrolysis pretreatment. Analyses of chemical compositions, ¹H n.m.r. nuclei distributions and hydroxyl concentrations of the acid-insoluble hydrolysis coal extracts indicate that both O and S are enriched in the extracts with half of the oxygen atoms being in hydroxyl forms. The hydroxyl concentrations of the extracts (acid-insoluble) are ≈2 to 3 times higher than their parent coals. Coal activation by this alkali pretreatment is explained by the hydrolytic attacks on ether C–O linkages, and the removal of some constituents rich in oxygen functional groups which are responsible for poor liquefaction behaviour.     

Determination of carboxyl groups in low-rank coals

The determination of carboxyl groups in low-rank coals by exchange with barium chloride-triethanolamine reagent is re-examined. The difference in carboxyl contents calculated from the barium content of the exchanged coal, and the amount of acid used to extract the barium, is discussed. Reliable carboxyl contents are obtained providing the latter procedure is used.