Study On Gas Phase Oxidation Reaction Of Propylene With Molecular Oxygen Using Plasma Activation

Propylene oxide (PO), propionaldehyde, acrolein and acetone are one of the most important chemical feedstocks. Molecular oxygen is the best oxidant due to low cost and significant advantages for the environment. Because the allylic protons of propylene possess high acidity, propylene is easily oxidized to acrolein but is difficultly oxidized to propylene oxide or acetone by molecular oxygen. So, gas phase propylene oxidation to prepare C₃ partial oxidation products (especially PO) with molecular oxygen as the oxidant is the most desirable reaction and is one of the most challenging topics in catalysis.The pulse corona plasma and dielectric barrier discharge plasma are typical non-equilibrium cold plasma in a gas at atmospheric pressure. They are excellent source of energetic electrons with 1-10 eV and high density. Their unique advantages are to generate low excited atomic and molecular species, free radicals and excimers with several electron volt energy. The electron temperature is very high, yet the ionic or molecular temperature is rather low in non-equilibrium cold plasma.In this paper, C3 partial oxidation products (PO, propionaldehyde, acrolein and acetone) were obtained by oxidizing propylene directly using O₂ or air as oxidant at room temperature and atmospheric pressure, and the reaction was activated by pulse corona plasma and dielectric barrier discharge plasma. Active oxygen species were utilized by using molecular oxygen (O2 or air) as oxidant and organic oxygen carrier and catalyst were not needed in the process of reaction. This technique was one-step and low cost green-synthesis route of C3 partial oxidation products (PO, propionaldehyde, acrolein and acetone), which was due to cheap raw material, simple operatione process and without equipment corrosion or environmental pollution.The following results were obtained:1. The reaction of direct gas phase oxidation to C3 partial oxidation products (PO, propionaldehyde, acrolein and acetone) of propylene can be driven using O₂ as oxidant by means of pulse corona plasma without catalyst at room temperature and atmosphere pressure. When total flow rate was 200ml/min, space between electrodes was 4mm, pulse discharge voltage was 18kV and discharge frequency was 120Hz, the conversion of propylene, the total selectivity and total yield of C3 partial oxidation products were 19.2%, 52.5% and 10.1%, respectively. The discharge parameters, structure of reactor, space between electrodes, ratio of V(C₃H₆) to V(O₂) and total flow rate were main factors that affected the reaction under pulse corona plasma.2. C3 partial oxidation products (PO, propionaldehyde, acrolein and acetone) were successfully prepared from propylene and Ot directly by method of dielectric barrier discharge plasma at room temperature and atmosphere pressure. When electrode was made of stainless steel, the total flow rate was 160.8ml/min, discharge frequency was 1.38kHz, ratio of F(C3H6) to V(O2) was 1:200, and dielectric barrier discharge voltage was 21kV, the conversion of propylene, the total selectivity and total yield of C3 partial oxidation products were 81.6%, 43.0% and 35.1%, respectively. The ratio of V(Ct,H() to F(C>2) caused a great effect on products distribution. The dielectric barrier discharge voltage has an effect on the conversion of propylene, total selectivity and yield of C3 partial oxidation products, composition and distribution of products. It is very advantageous for the conversion of propylene and disadvantageous for the total yield of C3 partial oxidation products and other organic oxides under intermediate frequency, but, C3 total yield increases under low frequency. The total flow rate affects the conversion of propylene, the selectivities of C3 and other products at a certain extent.3, The reaction of direct gas phase oxidation of propylene to prepare C3 partial oxidation products (PO, propionaldehyde, acrolein and acetone) can be driven using air as oxidant by means of dielectric barrier discharge plasma with water electrode at room temperature and atmosphere pressure. When total flow rate was 40.4ml/min, dielectric barrier discharge voltage was 21.5kV, dielectric barrier discharge frequency was 1.38kHz and ratio of F(C3H6) to F(air) was 1:99, the conversion of propylene, the total selectivity and total yield of C3 partial oxidation products were 63.5%, 52.4% and 33.3%, respectively. The dielectric barrier discharge voltage has a crucial effect on propylene conversion and selectivity of products. The composition of glass reactors has a great effect on propylene epoxidation reaction under dielectric barrier discharge plasma. The glass composition of more SiC>2 and less B2O3 is effective for conversion of propylene and PO yield, moreover, this composition inhibits also further oxidated reaction of products at a certain extent. Other condations is same, With the increase of the length of reactor and the inside diameter of water electrode, the conversion of propylene increases, the selectivities of C3 partial oxidation products decrease, the selectivities of other products increase. The proportion and the total flow rate of reaction gas have effect on the conversion of propylene, the total yield of C3 partial oxidation products and other products distribution at a certain extent.