Communicationspropylene > 45 % leads to losses in the selectivity of 1,2-propandiol. The best space-time yield of 1,2-propandiol gained is with 36 mol h ±1 L ±1 in the range of the industrial production (hydrolysis of propylene oxide) [10,11].
Activation Energy and VolumeIn the temperature range 300 to 475 C the activation energy is not constant. A positive value (approx. +20 kJ mol ±1 ) is found below the critical temperature of water, a negative above (approx. ±30 kJ mol ±1 ). Above 425 C a normal Arrhenius behavior is obtained. The values of the activation energies calculated for the separate intervals are very low. The broken partial reaction orders for propylene (a = 0.2) and oxygen (b = 0.3) indicate a complex reaction mechanism [12].The absolute amount of the activation volume at incomplete oxygen conversion is considerably higher (±DV ¹ = 2540 cm 3 mol ±1 ) than at complete conversion (±DV ¹ = 687 cm 3 mol ±1 ). An acceleration of the reaction by increasing pressure is therefore primarily possible at a high oxygen feed concentration.
SummaryThe partial oxidation of propylene was investigated in suband supercritical water with the help of an especially developed continuous high-pressure plant. A differential loop reactor was used in the form of a jet loop reactor. The test parameters extended from 300 to 475 C, 20 to 35 MPa, propylene feed concentration from 0.5 to 4 % (mol mol ±1 ) and oxygen feed concentration from 0.2 to 2 % (mol mol ±1 ). Depending on the other parameters the residence time ranged between 0.8 and 7.2 s.Due to the high reactivity of propylene (double bond and three acidic hydrogen atoms) a multitude of products are formed. The dosed oxygen is mostly converted completely. The main products are 1,2-propandiol, acetaldehyde and CO. The most important by-products are formaldehyde, CO 2 , methanol as well as hydrocarbons. Also oligomerization products could be detected. The highest selectivity to the desired product 1,2-propandiol (45 % at approx. 40 % conversion of propylene) was found at the lowest temperature setting used (300 C).
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Abbildung.Beurteilung einer Batch-Reaktion mit dem HarsMeth-Tool.
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