Jadhav Amarsinh L, Malkar Radhika S, Yadav Ganapati D
Departmental of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai 400019, India.
ACS Omega. 2020 Feb 3;5(5):2088-2096. doi: 10.1021/acsomega.9b02230. eCollection 2020 Feb 11.
The activity and selectivity of hydrotalcites (HTs) can be suitably enhanced by the addition of different metal oxides. Zinc and titanium are prospective candidates for such a modification. Transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) using basic catalysts is an industrially important process for the production of bis(2-hydroxyethyl)terephthalate (BHET). BHET is a precursor for polyethylene terephthalate (PET) which is used in production of films, fibers, and molding materials. As against use of polluting liquid bases, solid bases could be employed. In the current work, transesterification of DMT with EG was studied over modified HT base catalysts wherein the HT was activated with the addition of zinc and titanium. These catalysts were prepared by the combustion synthesis using different fuels. The modified HT using Zn and Ti were well characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, Brunauer-Emmett-Teller surface area analyzer, temperature-programmed desorption, and X-ray diffraction. Effects of several parameters on the rate of reaction and conversion of the limiting reagent were investigated. Zinc-modified HT using glycine as fuel (Zn-HT-glycine) was found to be the most selective, active, and reusable catalyst. The Langmuir-Hinshelwood-Hougen-Watson model was used to establish the reaction mechanism and kinetics. All species were weakly adsorbed leading to a second-order kinetics. Using a mole ratio of 1:2 of DMT to EG and 0.05 g/cm Zn-HT-glycine loading resulted in to 64.1% conversion of DMT and 96.1% selectivity to BHET in 4 h at 180 °C. The apparent activation energy was 9.64 kcal/mol. The catalyst was robust and reusable.
通过添加不同的金属氧化物可以适当地提高水滑石（HTs）的活性和选择性。锌和钛是进行这种改性的潜在候选物。使用碱性催化剂使对苯二甲酸二甲酯（DMT）与乙二醇（EG）进行酯交换反应是生产双（2-羟乙基）对苯二甲酸酯（BHET）的一个重要工业过程。BHET是聚对苯二甲酸乙二酯（PET）的前体，PET用于生产薄膜、纤维和模塑材料。与使用污染性液体碱不同，可以使用固体碱。在当前工作中，研究了在改性HT碱催化剂上DMT与EG的酯交换反应，其中HT通过添加锌和钛进行活化。这些催化剂通过使用不同燃料的燃烧合成法制备。使用扫描电子显微镜、能量色散X射线光谱仪、布鲁诺尔-埃米特-泰勒表面积分析仪、程序升温脱附和X射线衍射对用锌和钛改性的HT进行了很好的表征。研究了几个参数对反应速率和限量试剂转化率的影响。发现以甘氨酸为燃料的锌改性HT（Zn-HT-甘氨酸）是最具选择性、活性和可重复使用的催化剂。使用朗缪尔-欣谢尔伍德-霍根-沃森模型建立了反应机理和动力学。所有物种的吸附都很弱，导致二级动力学。在180℃下，使用DMT与EG的摩尔比为1:2以及0.05 g/cm的Zn-HT-甘氨酸负载量，在4小时内DMT的转化率为64.1%，对BHET的选择性为96.1%。表观活化能为9.64 kcal/mol。该催化剂性能稳定且可重复使用。
