沥青基炭制品的碳结构高度依赖前驱体沥青的性质。采用化学交联的方法对沥青进行改性处理时,尽管化学交联的反应机理为亲电取代反应,但交联剂、催化剂的种类不同,沥青改性程度存在差异,进而影响炭制品结构。以中低温煤沥青为原料,探索3种交联剂(对苯二甲醇(PXG)、苯甲醛(BA)、对苯二甲酰氯(TPC))、5种催化剂(对甲苯磺酸、浓硫酸、浓硝酸、浓盐酸、硼酸)对沥青交联改性后炭制品结构的影响。通过TG-DTG、FT-IR研究交联改性后沥青热稳定性及沥青官能团的变化;借助XRD、Raman表征改性后沥青炭制品的微观结构差异。结果表明:交联剂和催化剂的存在促进了沥青分子的交联,有效阻止了热转化过程中轻组分挥发,提高了沥青的结焦值、软化点、热稳定等指标。以PXG为交联剂,沥青支链上亚甲基CH2的H不易被取代;而以硼酸为催化剂时,支链末端甲基上的H易被取代;以BA为交联剂,取代氢的位置明显发生在芳香环上;以TPC为交联剂、浓硫酸为催化剂时,交联产品的C==O官能团含量增加,说明在这种组合下,TPC参加反应较多。无论与哪种交联剂相结合,浓盐酸为催化剂时,交联反应更易促进苯环上和支链上的C—H键发生取代反应。经过交联改性后的沥青,炭化过程中分子间较强的π-π相互作用减弱,有效阻止碳有序结构的形成,碳无序结构含量ID/IG增大。同时碳微晶层间距d002明显增加,有序堆积平均堆积高度Lc减小,芳香层数降低,说明化学交联不仅影响有序碳结构排列,还可抑制碳微晶结构发育。其中硼酸作为催化剂时,催化效果更理想。获得的炭制品d002在同组产品中最大。PXG、硼酸组合与沥青发生交联时,所得碳材料的d002达0.377nm。本研究为进一步定向调控和构筑沥青基碳材料奠定基础。

The microstructure of pitch-based carbon products is highly dependent on the properties of precursor pitch. While using chemical cross-linking to modify asphalt, although all the reaction mechanism of chemical cross-linking operates via electrophilic substitutionreaction, the degree of such modification fluctuates based on the type of cross-linking agent and catalyst utilized, which in turn impactsthe structure of resulting carbon products. Using medium and low temperature coal tar pitch as raw materials, the effects of three crosslinking agents: terephthalyl alcohol(PXG), benzaldehyde (BA), p-phenylenediamine chloride (TPC), coupled with five catalysts: ptoluenesulfonic acid, concentrated sulfuric acid, concentrated nitric acid, concentrated hydrochloric acid, and boric acid on the structureof carbon products after asphalt crosslinking modification were explored. The thermal stability and functional group changes of cross-linking modified pitch through TG-DTG and FT-IR were studied. XRD and Raman were used to characterizethe microstructural differencesof modified pitch carbon products. The results show that the presence of cross-linking agents and catalysts facilitate occurrence of molecular crosslinking in pitch, effectively curbing the volatilization of light components during thermal conversion, and substantially enhancingpitch′s coking value, softening point, and thermal stability among other metrics. When PXG serves as a cross-linking agent, the methylene H on the branched chain within the cross-linked product is not easily replaced. Conversely, when boric acid functions as the catalyst,the methyl H at the branch chain′s end is more prone to replacement. Utilizing BA as cross-linking agent,the position of hydrogen substitution predominantly occurs on the aromatic ring. When TPC is used as the cross-linking agent and concentrated sulfuric acid is used asthe catalyst, the content of C==O functional groups in the cross-linked product increases, indicating that TPC participates more in the reaction under this combination. Irrespective of the cross-linking agent used, when concentrated hydrochloric acid is employed as a catalyst,the crosslinking reaction substantially promotes the substitution of C—H bonds on the benzene ring and branch chains. After cross-linking modification, the strong π - π interactions among molecules in pitch′s carbonization process are weakened, effectively hindering theformation of ordered carbon structures, thereby increasing ID / IG values. Simultaneously, the interlayer spacing d002 of carbon microcrystalssignificantly expands, while the Lc value demonstrates a declining trend and the number of aromatic layers reduces, indicating that chemical cross-linking not only disrupts the arrangement of ordered carbon structures, but also restrains the development of carbon microcrystals. When boric acid isused as a catalyst, the catalytic effect is more ideal. The resultant carbon product′s d002 exhibits the highest performance amongst its group. When PXG and boric acid collectively cross-link with pitch, the d002 of the achieved carbon material extendsto 0.377 nm. In conclusion, this study lays a robust practical basis for the further targeted regulation and construction of pitch-based carbon materials.

0 引言

1 试验

   1.1 试验原料

   1.2 样品制备

   1.3 分析测试

2 结果与讨论

   2.1 交联后样品基本性能

   2.2 交联后产品热重分析

   2.3 交联后产品FT-IR分析

   2.4 炭化产品碳结构

3 结论