过氧化氢预处理对褐煤物化性质及生物产气的影响

Effects of hydrogen peroxide pretreatment on physicochemical properties and biogas production of lignite

摘要:

【目的】研究过氧化氢预处理对褐煤物化性质及生物产气的影响。【方法】以胜利5号褐煤为研究对象，利用正交试验对过氧化氢预处理褐煤条件进行优化，在最优条件下处理褐煤得到处理后的残煤和处理液，通过X射线衍射分析(X-ray diffraction, XRD)、扫描电镜分析(scanning electron microscopy, SEM)、比表面积分析及孔隙分析(brunauer-emmett-teller, BET)、气相色谱-质谱分析(GC-MS)、高效液相色谱分析(HPLC)等方法对原煤、残煤和处理液的物化性质进行比较分析。【结果】经过氧化氢预处理，褐煤的最优条件为过氧化氢浓度5.0%、预处理时间20 d、液固比30:1，处理液中总有机碳含量为105 mg/L。在最优条件下，过氧化氢处理后残煤表面裂痕、凹陷增多，表面结构变得松散；煤的芳香面网间距增加，芳环结构更加疏松，晶核结构变小；孔隙度和比表面积均增大。处理后残煤中的固定碳、C元素和镜质组的相对含量降低，而灰分、挥发分、O和H元素及惰质组含量增加，残煤中O=C-O、C=C、C=O官能团含量增加，而N-H、C-H官能团含量则减少。生物产气结果表明反应液和残煤产气量均低于原煤，分别减少了39.13%和94.46%。过氧化氢预处理主要作用于煤中镜质组，使其有机碳溶解，煤中大分子结构的官能团发生变化，改变煤的芳环结构，在氧化作用下煤结构中的小分子溶解进入处理液。处理液中有机物以短链脂肪酸为主。经生物产气后，反应液中小分子酸以及有机物种类减少，被微生物利用产气。而各产气试验组中优势菌门及优势菌属的菌群丰度呈现出显著差异，古菌中原煤产气组盐杆菌门(Halobacteriota)为优势菌门，甲烷八叠球菌属(Methanosarcina)为优势菌属；反应液产气组热变形菌(Thermoprotei)为优势菌门，深古菌属(Bathyarchaeia)为优势菌属；细菌中原煤产气组放线菌门(Actinomycetota)为优势菌门，Gaiellales为优势菌属；反应液产气试验组假单胞菌门(Pseudomonadota)为优势菌门，代尔夫特菌属(Delftia)为优势菌属。【结论】煤溶解有机碳可以被微生物利用产气，但是煤中有机组分的过氧化脱除导致生物产气量减少。

关键词:褐煤;生物产气;化学预处理;过氧化氢

Abstract:

[Objective] To investigate the effects of hydrogen peroxide treatment on the physicochemical properties and biogas production of lignite. [Methods] We carried out orthogonal experiments to optimize the conditions of hydrogen peroxide pretreatment for Shenli No.5 lignite. Lignite was treated under the optimal conditions to obtain coal residues and treatment solutions. The physicochemical properties, including elemental and maceral composition, mineral components, microcrystalline structure, porosity, permeability, surface morphology, organic functional groups, and organic composition in the treatment solution were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), brunauer-emmett-teller (BET), gas chromatography-mass spectrometry (GC-MS), and high-performance liquid chromatography (HPLC). The physicochemical properties were then compared among the raw coal, treated residue, and treatment solution. [Results] The optimal pretreatment conditions of lignite were treatment with 5.0% hydrogen peroxide at a liquid-to-solid ratio of 30:1 for 20 days, under which the total organic carbon yield in the treatment solution was 105 mg/L. After treatment under these optimal conditions, the treated residue exhibited increased cracks and dents on the surface and loosened surface structures. In addition, the interlayer spacing of the aromatic plains of the coal increased while the aromatic ring structure became more open with smaller crystal nucleus structures. Both porosity and specific surface area increased after the treatment. Compared with that before treatment, the treated residue showcased decreased fixed carbon, carbon, and vitrinite and increased ash, volatile matter, oxygen and hydrogen, and inertinite. The content of functional groups such as O=C-O, C=C, and C=O increased in the treated residue, while that of N-H and C-H reduced. The biogas production of the treatment solution and the treated residue was 39.13% and 94.46%, respectively, lower than that of raw coal. Hydrogen peroxide pretreatment primarily acted on vitrinite, dissolving organic carbon and altering the functional groups of large molecular structures in coal. This altered the aromatic ring structure of coal, causing small molecules to dissolve into the treatment solution under oxidative conditions. The organic compounds in the treatment solution mainly consisted of short-chain fatty acids. After biogas production, the number of low-molecule-weight acids and organic compounds decreased in the treatment solution. The relative abundance of dominant microbial phyla and genera varied significantly among different microcosms. Regarding the archaea for biogas production, the dominant phylum and genus were Halobacteriota and Methanosarcina in the raw coal and Thermoproteota and Bathyarchaeia in the treatment solution, respectively. In terms of the bacteria for biogas production, the dominant phylum and genus were Actinomycetota and Gaiellales in the raw coal and Pseudomonadota and Delftia in the treatment solution, respectively. [Conclusion] The organic carbon dissolved from coal can be utilized by microorganisms for biogas production. However, the removal of organic components by over-oxidation may decrease the biogas production.

Key words:lignite;biogas production;chemical pretreatment;hydrogen peroxide