尼龙66是一种用途广泛的聚酰胺化合物，然而其主要生产原料己二腈一直被外国公司垄断。丁二烯氢氰化法是最先进的己二腈生产工艺，该工艺包括丁二烯氢氰化、2-甲基-3-丁烯腈(2M3BN)异构化和3-戊烯腈(3PN)氢氰化三步反应。本课题组在己二腈工艺研发过程中发现催化剂(NiL4)存在稳定性差和选择性低的缺点，此外，配体的构效关系也未见报道。因此，明确催化剂失活的原因、探索配体的构效关系和设计高效稳定的催化剂具有重要的学术意义和应用价值。在2M3BN异构化反应中，实验表明：2-甲基-2-丁烯腈(2M2BN)和2-戊烯腈(2PN)明显降低催化剂的活性，相比纯度90%2M3BN，72.8%2M3BN的转化率由74%降低到35%。DFT计算表明：2M2BN或2PN与NiL4生成了热力学上稳定的中间物[(2M2BN)NiL2和(2PN)NiL2]，使催化剂脱离反应体系，从而表现为催化活性低；进一步，提出了包括直接抑制、取代2M3BN和取代3PN三种途径的催化剂失活机理。为了抑制催化剂失活，基于催化活性中心周围空间拥挤度参数，设计出一种新型催化剂(DPPP5)NiL2 (DPPP5：1, 5-双二苯基磷戊烷)。通过动力学分析和工艺优化，新型催化剂将催化活性由35%提高到65%，3PN选择性由90%提高到95%，且可以重复使用，满足了工艺需求，真正实现了己二腈技术的国有化。为了提高3PN选择性，通过实验和DFT计算相结合的方法考察了2M3BN异构化反应中的构效关系。对于单齿磷配体，锥顶角在139.68°时，3PN选择性最高(90%)。对于双齿膦配体，以12种双齿膦配体为研究对象，转移电荷为纽带，采用4个配体参数和多元回归方法建立配体的构效关系模型；采用8种双齿膦配体验证该模型的准确性和普适性，从而实现定量预测催化选择性和配体的快速筛选。最后基于该构效关系模型，筛选出高效配体1, 4-双二苯基磷丁烷(DPPB)，相应的3PN选择性大于99%。将DPPB配体应用于丁二烯氢氰化反应中，3PN选择性大于97%，从而实现两步法制己二腈。基于DFT计算提出了DPPB参与催化丁二烯氢氰化反应机理，包括HCN加成、丁二烯插入、氰基迁移和甲基烯丙基重排形成3PN以及甲基烯丙基旋转和氰基还原消除生成2M3BN，填补了DPPB参与丁二烯氢氰化反应的机理空白，为己二腈工艺上使用DPPB从而改进整个工艺提供理论支撑。
Nylon 66 is a versatile polyamide compound, but its main raw material adiponitrile has been monopolized by foreign companies. The hydrocyanation of butadiene is the most advanced adiponitrile production process, which includes the hydrocyanation of butadiene, the isomerization of 2-methyl-3-butenenitrile (2M3BN) and the hydrocyanation of 3-pentenenitrile (3PN). During the process development, our research team discovered that the catalyst (NiL4) has the disadvantages of poor stability and low selectivity. In addition, the structure-performance relationship of the ligand has not been reported. Therefore, clarifying the reasons of catalyst deactivation, exploring the structure-performance relationship of ligands, and designing efficient and stable catalysts have important academic significance and application value.In the isomerization of 2M3BN, the experiments showed 2-methyl-2-butenenitrile (2M2BN) and 2-pentenenitrile (2PN) significantly reduced the catalystic activity. Compared with the purity of 90% 2M3BN, the conversion of 72.8% 2M3BN was reduced from 74% to 35%. DFT calculations showed 2M2BN or 2PN and NiL4 generated thermodynamically stable intermediates [(2M2BN)NiL2 or (2PN)NiL2], which made the catalyst separate from the reaction system, thereby showing low catalytic activity. Further, the catalyst deactivation mechanism was proposed including three ways: direct inhibition, replacing 2M3BN and replacing 3PN. In order to suppress these deactivation, a new catalyst (DPPP5)NiL2 (DPPP5:1, 5-bis-diphenylphosphopentane) was designed based on the parameter of the congestion of the space around the catalytic active center. Through kinetic analysis and process optimization, the new catalyst exhibited higher catalytic activity (>65%) and 3PN selectivity (>95%), and could be reused, which satisfied the process requirements and truly realized the nationalization of adiponitrile technology.The structure-performance relationship in the isomerization has been investigated by combining experiments and DFT calculations to improve the selectivity to 3PN. For monodentate phosphorous ligands, when the cone angle is 139.68°, the 3PN selectivity is the highest (90%). For bidentate phosphine ligands, 12 bidentate phosphine ligands were used as the research object, charge transferred was used as the link, and the structure-performance relationship model of the ligand was established by using 4 key parameters and multiple regression methods. 8 bidentate phosphine ligands were used to verify the accuracy and universality of the model, so as to realize quantitative prediction of catalytic selectivity and rapid screening of ligands. Finally, based on this structure-performance relationship model, the effective ligand 1, 4-bis-diphenylphosphobutane (DPPB) was selected, and the 3PN selectivity was greater than 99%. The DPPB ligand has been used in the hydrocyanation of butadiene, and the selectivity to 3PN is greater than 97%, realizing the two-step production of adiponitrile. Based on DFT calculations, the mechanism of the catalytic hydrocyanation of butadiene with the participation of DPPB was proposed, including the addition of HCN, the insertion of butadiene, the migration of CN and the rearrangement of methallyl to form 3PN, the rotation of methallyl and the reductive elimination of CN to produce 2M3BN, which filled the gap in the mechanism of DPPB participating in the hydrocyanation, and provided the support for the use of DPPB in the adiponitrile process to improve the entire process.
