【作者】 翟豪；

【导师】 张爱清；

【作者基本信息】 中南民族大学 ， 高分子化学与物理， 2011， 硕士

【摘要】 环己烯具有活泼的双键,是一种重要的有机化工原料,在制药工业和石油工业中都有广泛的用途。尤其是在高聚物领域,以环己烯为原料生产尼龙6和尼龙66,具有工艺简单,生产成本低的特点。环己烯为苯加氢反应的中间产物,由于最终产物环己烷的热力学稳定性比环己烯要高得多,所以苯加氢反应很难被控制在环己烯阶段,而是倾向于生成最终加氢产物环己烷。因此,苯部分加氢制备环己烯反应的催化剂研究,具有十分重要的理论和现实意义。Pt、Pd、Ru、Ni等金属均可以作为苯加氢催化剂,其中Pt的加氢活性最高,其储量相对较大,且铂类催化剂工业使用寿命大于5年。在铂催化苯加氢反应中,进行适当的催化剂改性可以提高中间产物环己烯的选择性。P. Dini等提出铂/尼龙类的复合催化剂用于苯加氢反应时有环己烯产物生成,在其研究中,当环己烯的选择性达到48%时,苯的转化率为0.4%,而当苯的转化率达到25.9%时,环己烯的选择性仅为0.1%。另外,D. Francisco等用0.5%铂负载在硅土/氧化铝上催化苯加氢反应,只能得到唯一产物环己烷。本课题组先前研究了用聚酰亚胺包裹铂纳米簇制备杂化膜,及其催化苯加氢反应性能,其中环己烯选择性可达到72.4%。由此可见,利用液态反应物苯以溶胀的方式与杂化膜中的催化活性中心相接触,通过控制膜的溶胀程度以及膜的化学组成来控制液态反应物和生成物在膜中的停留时间,从而可达到控制苯加氢的程度、选择性生成环己烯的目的。但是,由于聚酰亚胺膜的制备过程较为复杂、成本较高,因此,本文选用价廉易得的天然高分子壳聚糖作为包覆材料,其具有良好的成膜性能和生物可降解性等特点,且主链上含有大量氨基和羟基,对金属离子具有较强的螯合能力。具体包括以下几个方面的内容:1.以聚乙烯基吡咯烷酮为保护剂、乙二醇为还原剂和溶剂,在微波加热条件下,通过化学还原方法还原氯铂酸,制备了铂金属簇。用壳聚糖为包裹材料,制备了铂纳米簇/壳聚糖杂化膜,用IR、TEM、XRD、XPS和TG对空白膜以及杂化膜进了表征。TEM和XRD显示铂纳米簇能在壳聚糖膜中均匀分散的同时,依然保存完整晶型;XPS和TG显示杂化膜中氮氧原子与铂纳米簇存在螯合作用的同时,杂化膜的热学性能良好。催化苯部分加氢实验显示,当Pt负载量为10%反应2h时,环己烯的选择性最大,达到68%。2.在壳聚糖酸溶液中用不同质量的丙醛、己醛、十二碳醛反应生成西弗碱,再用硼氢化钠还原,从而得到烷基化壳聚糖,IR、NMR结果显示不同取代度并且不同碳链长度的烷基成功的接枝到了壳聚糖上。制备了铂纳米簇/烷基化壳聚糖杂化膜,并用XPS、XRD对其进行了表征。支链的引入改变了壳聚糖薄膜的结晶程度以及苯等非极性溶剂在其中的溶胀度。丙基化壳聚糖负载铂纳米簇催化苯加氢反应显示,随着丙基化壳聚糖取代度的增加,苯的转化率逐渐升高,而环己烯的选择性则出现先增大后减小的趋势,当取代度为28.9%时,环己烯的选择性达到最大值—85.2%。己基化壳聚糖负载铂纳米簇催化苯加氢反应显示,随着己基化壳聚糖取代度的增加,苯的转化率逐渐升高,而环己烯的选择性也出现先增大后减小的趋势,当取代度为32%时,环己烯的选择性可达60.3%。十二碳基化壳聚糖负载铂纳米簇催化苯加氢反应显示,随着十二碳基化壳聚糖取代度的增加,苯的转化率逐渐升高,而环己烯的选择性出现减小的趋势。3.在壳聚糖分子链上引入疏水性基团GMA,并对其进行了IR、NMR、XRD和XPS表征。疏水性基团GMA的引入改变了CS-g-GMA薄膜的结晶程度的同时使得非极性溶剂,如苯、环己烯和环己烷等,在其中的溶胀度明显增加。苯分子在Pt/CS-g-GMA杂化膜中流动速度的增加,直接使得苯加氢反应的转化率明显增加,而环己烯选择性还基本维持在55%左右。更多还原

【Abstract】 Cyclohexene is an important chemical raw material with active double bond, which has widespread use in the pharmaceutical and petroleum industry. Especially in polymer field, the production route of Nylon 6 or 66 with cyclohexene as the raw material is simple and low-cost. Although cyclohexene is an intermediate product of benzene hydrogenation, cyclohexane is always produced because of the kinetically favored hydrogenation of cyclohexene to cyclohexane. Thus, investigation of catalyst for the partial hydrogenation of benzene to cyclohexene is the key.Several metals can be used as hydrogenation catalysts, such as Pt, Pd, Ru, and Ni, in which Pt has the highest catalytic activity for benzene hydrogenation. Dini et al found that cyclohexene was a reaction product of benzene hydrogenation when the Pt/polyamide was used as catalysts. In their studies, the highest selectivity to cyclohexene was 48.0%, but the conversion of benzene was 0.4%, while the conversion of benzene got to 25.9%, but then the selectivity to cyclohexene was only 0.1%. In addition, Domínguez et al reported that when catalysts of 0.5% Pt supported on gallia/alumina were used in benzene hydrogenation, the only product was cyclohexane. Nagahara reported a particularly efficient catalyst composed of Ru-black promoted with ZnO. In their studies, the yield of 56% and the selectivity of 80% were believed to be high enough to develop an industrial process. Recently, William et al have studied the activities for low-temperature hydrogenation of benzene by Pt/Ni bimetallic catalysts supported onγ-Al2O3. It was observed that the bimetallic catalysts were more active than either parent metal catalyst, but in this paper cyclohexane was the only observed reaction product.In our previous studies, we have investigated the fabrication of Pt nano-cluster/polyimide hybrid membrane and its catalytic activity to the partial hydrogenation of benzene, in which the selectivity to cyclohexene reached to 72.4%. Thus it can be supposed that benzene may contact the active center of catalyst in the hybrid membrane through swelling method, and the controlling of the hydrogenation to obtain higher selectivity of cyclohexene can be realized by controlling the swelling degree of membrane. However, the preparation process of polyimide is complex and costly, so in this research the cheap and abundant natural polymer chitosan (CS) was chosen. Chitosan is the N-deacetylated derivative of chitin, which is suitable functional material because of its biocompatibility, biodegradability, non-toxicity, adsorption properties, etc. In addition, the large number of -NH2 and -OH in CS has good chelating ability to metal. There are three parts to be included in this paper: 1. Monodispersed Pt nano-clusters were prepared by the reduction of H2PtCl6 with eth ylene glycol under microwave conditions. IR、TEM、XRD、XPS and TG were used to characterize the structure of platinum nano-particles and Pt/CS. TEM and XRD sho wed that Pt nanoclusters can be dispersed in the chitosan membrane, while keep intact crystal; XPS and TG data indicated that Pt was coordinated with N and O in CS to some extend, while hybrid membrane has good thermal properties. Experimental results showed that Pt/CS catalyst gave a high selectivity for cyclohexene of 68% in the liquid phase hydrogenation of benzene, while there was no cyclohexene in the product when the catalyst was only Pt nano-particles without chitosan hybrid membrane.2. N-arylation of chitosan was performed via a Schiff bases formed by the reaction between the 2-amino group of glucosamine residue of chitosan with different quality of propionaldehyde, hexanal, twelve carbon aldehyde under acidic condition followed by reduction of the Schiff base intermediate with sodium borohydride.IR and NMR di fferent degrees of substitution and different length of alkyl chain has been grafted on to chitosan.Pt/ N-aryl chitosans were characterized by XRD,XPS and TG. With the in creasing of extent of substitution of N-n-propyl, the swelling degrees of PCS membr anes in benzene, cyclohexene, and cyclohexane were all increased. Experimental of hydrogenation of benzene catalyzed by Pt/C3H5-CS showed that with the increasing of the extent of substitution of N-n-propyl, the conversion of benzene was gradually increased, while the selectivity of cyclohexene increased at first and then decreased. With 28.9 % of ES, the selectivity of cyclohexene was as high as 85.2 %. Experimental of hydrogenation of benzene catalyzed by Pt/C6H13-CS showed that with the increasing of the extent of substitution of N-n- C6H13, the conversion of benzene was gradually increased, while the selectivity of cyclohexene increased at first and then decreased. With 32 % of ES, the selectivity of cyclohexene was as high as 60.3 %. Experimental of hydrogenation of benzene catalyzed by Pt/C12H25-CS showed that with the increasing of the extent of substitution of N-n- C12H25, the conversion of benzene was gradually increased, while the selectivity of cyclohexene decreased.3. Chitosan grafted hydrophobic groups GMA were characterized by IR, NMR, XRD and XPS. The introduction of hydrophobic groups GMA changed the degree of crystallinity of CS-g-GMA , also made the swelling ratio of non-polar solvents such as benzene, cyclohexene and cyclohexane, in CS-g-GMA increase significantly. With the increasing of flow velocity of benzene molecules in the Pt / CS-g-GMA hybrid membrane made conversion of benzene hydrogenation reaction significantly increase, while the selectivity of cyclohexene is also essential to maintain the 55%.更多还原