A New Process For Cumene Hydroperoxide Hydrogenation To α-cumyl Alcohol

Dicumyl peroxide (DCP) is widely applied as a cross-linking agent for polyethylene (PE), ethylene vinyl acetate (EVA) copolymer, ethylene propylene terpolymer (EPT), and as a curing agent for unsaturated polystyrene (PS). Preparation ofα-cumyl alcohol (CA) from cumene hydroperoxide (CHP) is the key reaction in producing DCP. As current technology, sufide sodium (Na2S) or sufite sodium (Na2SO3) was adopted to reduce CHP to CA. It is a simple process with high conversion for CHP and selectivity to CA. However, it is a stoichiometric reaction with low atom-efficiency and generates large amounts of sulfide-containing water. Increasingly stringent legislation on environmental protection has restricted the development of this process. More economical as regards costs and environmental protection is the reduction of CHP by means of hydrogen with the aid of a catalyst.A series of supported Pd catalysts for CHP liquid phase hydrogenation to CA have been designed and prepared by impregnation, using various supports (Al2O3, Activated Carbon, MgO), precursors (K2PdCl4, Pd(NO3)2, (NH4)2PdCl4), reducing agents (formaldehyde, hydrogen), Pd content, calcination and reduction temperatures. All the catalysts were characterized by BET, inductively coupled plasma atomic emission spectrometry (ICP-AES), thermogravimetric analysis (TGA), X-ray diffraction (XRD), CO chemisorption, UV-visible spectroscopy, transmission electron microscory (TEM), temperature-programmed reduction (TPR) to correlate the physico-chemical properties with catalytic performance. The results showed that the 0.5wt%Pd/Al2O3 catalyst prepared by impregnation of AlOOH with K2PdCl4, calcinated at 600℃in air and reduced in hydrogen at 300℃exhibited the best catalytic activity and stability. Moreover, it was found that CHP hydrogenation was a structure-sensitive reaction, its activity can increase with Pd particle size.Kinetics of CHP hydrogenation to CA over Pd/Al2O3 catalyst in a trickle bed reactor was inverstigated. A mechanism was proposed for the hydrogenation of CHP. According to this mechanism, the step of hydrogen activated depends on the redox properties of the catalyst surface. High CHP concentration (LHSV) and low H2 pressure resulted in oxidized surface of Pd, leading to a zero-order with respect to CHP concentration in CHP hydrogenation. Low CHP concentration (LHSV) and high H2 pressure resulted in reduced surface of Pd, leading to a first-order with respect to CHP concentration in CHP hydrogenation. Based on the mechanism, the kinetics model has been established and the related parameters have been estimated. The activated energies were calculated to be 12.4 kJ/mol and 10.0 kJ/mol for zero-order and first-order reactions, respectively.Deactivation of Pd/Al2O3 catalyst in CHP hydrogenation in a trickle bed reactor was studied as well. It was found that the oxidation of Pd surface was the key factor for catalyst deactivation by means of ICP-AES, XRD, TEM and TGA. Moreover, the effect of composition of raw gas, reaction temperature, H2 pressure on the catalyst deactivation was also investigated. The results showed that CO in raw gas could result in catalyst deactication quickly. Luckily, the catalytic activity can be recovered by sweeping the catalyst with high pure hydrogen. Besides, a residual activity can be obtained in CHP hydrogenation, indicating deactivation of Pd/Al2O3 catalyst was reversible. Thus, the catalytic activity can be recovered by treating the spent catalyst in flowing pure hydrogen with relatively high temperature (300℃). Compared with temperature, H2 pressure has a more significant impact on the catalyst deactivation and residual activity. Higher residual activity can be obtained under higher H2 pressure. Kinetics of catalyst deactivation was established and the related parameters have also been evaluated.Based on the kinetics of CHP hydrogenation and catalyst deactivation, the optimized reaction conditions were obtained as follows:volume ratio of hydrogen to CHP solution=240, LHSV=5h-1, reaction temperature=65℃, H2 pressure=1.5MPa. Under the optimized reaction conditions, a similar product distribution was found when comparing hydrogenation and sufide reduction of CHP. Moreover, the catalyst showed a lifetime with 1000h and can be regenerated easily in flowing hydrogen gas. Finally, a one-pipe reactor suitable for industrial production was designed.