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

Abstract

Hydrogen peroxide (H 2 O 2 ), the most desired green oxidant, [1] is almost exclusively produced by an anthraquinone (AQ) process. [2] Direct oxidation of H 2 with O 2 has long been considered an ideal alternative for H 2 O 2 production. [3] Extensive studies have been done on direct H 2 O 2 synthesis from a H 2 /O 2 mixture. To achieve high efficiency, direct H 2 O 2 synthesis is generally performed in acidified solvent over supported noble-metal catalysts (Au, Pd, Au-Pd, and Pd-Pt). [4][5][6][7][8][9][10][11] However, the direct synthesis of H 2 O 2 from a H 2 /O 2 mixture catalyzed by metals is quite hazardous, and it is very difficult to directly obtain high-purity and high-concentration H 2 O 2 .Research [12,13] published in the 1960s has demonstrated that H 2 O 2 can be generated in H 2 /O 2 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 H 2 O 2 yield (less than ca. 5 %) and safety concerns about the discharge-triggered H 2 /O 2 reaction. [12,14] The content of O 2 must be strictly controlled below 4 mol % in order to prevent explosion and ignition. [15] Our previous research [16] showed that the structure of the plasma reactor played an important role in the direct synthesis of H 2 O 2 . A H 2 /O 2 mixture containing 3 mol % of O 2 reaches 100 % O 2 conversion, but the H 2 O 2 selectivity is only 3.5 % (based on O 2 ) 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 % O 2 conversion and 56.3 % H 2 O 2 selectivity (based on O 2 ) 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 O 2 content, are still big challenges.Herein, we report an experimental realization of controllable H 2 /O 2 combustion processes by an optimized plasma reactor. High purity (Grade 1 electronic grade H 2 O 2 according to the SEMI standard) and highly concentrated H 2 O 2 solution (ca. 60 wt %) can be directly produced from a H 2 /O 2 mixture without explosion. These results suggest a different mechanism from conventional H 2 /O 2 combustion processes in the H 2 /O 2 plasma reaction. As shown in Scheme 1, the electron activation of H 2 into H is responsible for H 2 O 2 formation. However, the electron activation of O 2 into O and O 2 * (vibrational and electronic excited states) leads to H 2 O formation and explosion of the H 2 /O 2 mixture. Moreover, low-electron-density H 2 /O 2 plasma leads to a low degree of H 2 and O 2 activation, which plays quite a significant role in producing H 2 O 2 and controlling H 2 /O 2 combustion.The plasma reactor used in our experiments is a double aqueous electrode DDBD reactor (Support...

Gas-Phase Epoxidation of Propylene with Hydrogen Peroxide Vapor: Effect of Modification with NaOH on TS-1 Titanosilicate Catalyst in the Presence of Tetra-propylammonium Bromide

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“…In past decades, we have been working on the direct synthesis of H 2 O 2 vapor with H 2 /O 2 nonequilibrium plasma method. 4,5 The first attempt of propylene gas-phase epoxidation with plasma-derived H 2 O 2 vapor was accomplished by Zhou by 2007. 6 With a specially designed two-stage integrated reactor consisted of a hollow dielectric-barrier discharge (DBD) tube (first stage) and a fixedTS-1 catalyst bed (second stage), approximately 7% propene conversion, 93% PO selectivity, and 0.24 kg PO kg TS-1 −1 h −1 productivity were obtained.…”

Atmospheric Pressure and Room Temperature Synthesis of Methanol through Plasma-Catalytic Hydrogenation of CO2

“…Nonthermal plasma (NTP) technology provides an attractive and promising alternative to thermal catalysis to tackle these challenges facing CO 2 activation. NTP shows a significant superiority in activating thermodynamically stable molecules (e.g., CO 2 ) over a catalytic process at atmospheric pressure and low temperatures. − NTP can generate numerous highly energetic electrons with a typical electron energy of 1–10 eV. This has created growing interest in the use of energetic electrons as an alternative “catalyst” to activate reactants (e.g., CO 2 and H 2 ) into a range of chemically reactive species (e.g., radicals and excited atoms, ions and molecules) for the initiation and propagation of chemical reactions.…”