Juncheng Zhou

Safe Direct Synthesis of High Purity H2O2 through a H2/O2 Plasma Reaction

Extensive studies have been done on direct H2O2 synthesis from a H2/O2 mixture. To achieve high efficiency, direct H2O2 synthesis is generally performed in acidified solvent over supported noble-metal catalysts (Au, Pd, Au–Pd, and Pd– Pt). However, the direct synthesis of H2O2 from a H2/O2 mixture catalyzed by metals is quite hazardous, and it is very difficult to directly obtain high-purity and high-concentration H2O2. Research 13] published in the 1960s has demonstrated that H2O2 can be generated in H2/O2 non-equilibrium plasma through free-radical reactions in the absence of any catalyst or chemical. However, this plasma method has not yet drawn much attention, owing to low H2O2 yield (less than ca. 5%) and safety concerns about the discharge-triggered H2/O2 reaction. The content of O2 must be strictly controlled below 4 mol % in order to prevent explosion and ignition. Our previous research showed that the structure of the plasma reactor played an important role in the direct synthesis of H2O2. A H2/O2 mixture containing 3 mol% of O2 reaches 100% O2 conversion, but the H2O2 selectivity is only 3.5% (based on O2) in a single dielectric barrier discharge (SDBD) plasma reactor with a naked metal highvoltage (HV) electrode and an aqueous grounding electrode. On the other hand, 57.8% O2 conversion and 56.3 % H2O2 selectivity (based on O2) can be obtained by using a double dielectric barrier discharge (DDBD) plasma reactor with a pyrex-covered metal HV electrode (the pyrex cover acts as an additional dielectric barrier) and an aqueous grounding electrode. Although the selectivity has been greatly improved, the safety concerns and low efficiency, owing to low O2 content, are still big challenges. Herein, we report an experimental realization of controllable H2/O2 combustion processes by an optimized plasma reactor. High purity (Grade 1 electronic grade H2O2 according to the SEMI standard) and highly concentrated H2O2 solution (ca. 60 wt %) can be directly produced from a H2/O2 mixture without explosion. These results suggest a different mechanism from conventional H2/O2 combustion processes in the H2/O2 plasma reaction. As shown in Scheme 1, the electron activation of H2 into H is responsible for H2O2

Gas Phase Epoxidation of Propylene with TS-1 and in Situ H2O2 Produced by a H2/O2 Plasma

Gas phase epoxidation of propylene was performed by directly contacting propylene and gaseous H2O2 on the surface of TS-1 catalyst in an integrated reactor. The gaseous H2O2 was produced in situ by a H2/O2 plasma. The H2O2 formation rate can be enhanced by increasing the power density of the H2/O2 plasma reactor. The yield and selectivity for propylene oxide (PO) can be increased by optimizing the reaction conditions and using suitable TS-1 catalysts. With a power injection of 3.5 W, flow rates of H2, O2, and propylene of 170, 8, and 18 ml/min, respectively, catalyst loading of 0.8 g, and epoxidation temperature of 110 °C, the yield and selectivity for PO and the utilization rate of H2O2 were 246.9 g/(kg·h), 95.4%, and 36.1%, respectively. During the gas phase reaction, no decline of TS-1 activity was observed.

Direct and continuous synthesis of concentrated hydrogen peroxide by the gaseous reaction of H2/O2 non-equilibrium plasma

Under ambient conditions, H2O2 has been synthesized with 32.51% yield and 56.25% selectivity via the gas-phase reaction of H2/O2 non-equilibrium plasma.

Direct Oxidation of Methane to Hydrogen Peroxide and Organic Oxygenates in a Double Dielectric Plasma Reactor

Hydrogen peroxide is an important green oxidizing agent. The conventional process for hydrogen peroxide production is the indirect anthraquinone process, which employs multiple unit operations, generates considerable waste, and requires significant energy input. Hence, the development of a simple and highly efficient process for the synthesis of hydrogen peroxide 3] is of great scientific and practical importance. The direct synthesis of H2O2 from H2 and O2 is a much greener route, and supported Pd and Au–Pd alloy catalysts are known to be effective. However, an inherent hazard of this direct route are the very wide flammability limits of H2/O2 mixtures (4– 94 mol %). Hence, safe working practices stipulate a H2 concentration below 4 mol %, and this limit greatly reduces the H2O2 formation rate. Natural gas, of which CH4 is the main component, is an inexpensive and abundant resource with a low environmental impact. Considerable efforts to develop processes for converting CH4 into more valuable products have been made. The most extensively studied processes are oxidative coupling of CH4 ; [11, 12] partial oxidation of CH4 to synthesis gas; [13] and the formation of oxygenated compounds, including methanol, formaldehyde, and formic acid. 20] To the best of our knowledge, H2O2 has not been effectively produced by oxidation of CH4, although H2 can be manufactured from CH4 and H2O2 can be produced by oxidation of H2. Spectroscopic evidence of the formation of H2O2 in a microwave discharge plasma of CH4/ O2 has been reported. [21] We have shown that the structure of the discharge reactor plays an important role in the direct synthesis of H2O2 with the plasma method. With a specially designed plasma reactor, an O2 conversion of 57.8 % with a H2O2 selectivity of 56.2 % can be obtained in the gaseous plasma of a H2/O2 mixture. Taking all these observations into account, the effective formation of H2O2 might be achieved by CH4/O2 discharge with a proper plasma reactor. Herein, we report that in a double dielectric (DD) plasma reactor a satisfactory yield of H2O2 can be achieved under ambient temperature and atmospheric pressure from a stoichiometric (1:1) feed of CH4 and O2 by using the plasma method. The oxidation of CH4 to H2O2 offers considerable advantages over the oxidation of H2 to H2O2 because valuable organic oxygenates (methanol, formaldehyde, and formic acid) can be effectively produced at the same time. Furthermore, a wide range of CH4 concentrations can be used without any explosion hazards. The DD plasma reactor was prepared according to our previous work; one modification is the use of a nonmetal composite high-voltage electrode. We call this reactor a DD plasma reactor because it uses two dielectrics. As shown in Table 1, when a CH4/O2 mixture containing 50 mol % O2 is fed into the DD plasma reactor at a total flow rate of 50 mL min 1 (CH4+O2), the reactor converts 90.8 % of the O2 and generates