Ethyl alcohol produced from fermentation processing of biomass can be used to produce acetaldehyde by oxidation mechanism. Removing a water molecule from the ethanol with help of oxygen on a catalyst like silver generate one acetaldehyde molecule. This can also be named as dehydration of ethanol. The reaction is exothermic and generates 242 KJ of energy per mole of acetaldehyde formation.
Preliminary acetaldehyde process description:
Ethanol is vaporized and heated to 280-300 oC. It is mixed with air, which is preheated with product effluent stream of the multitubular reactor. The tubes are packed with silver pellets randomly which act as catalyst for the reaction to enhance forward. The mixed stream is feed to the reactor through the preheater to obtained 460-480oC. The catalytic reaction converts 75-80 percent of ethanol in a single pass. Unreacted ethanol is separated by a purification column and recycled to the main streams after separation of water by a separator. Acetaldehyde obtained is about 99% pure is pumped to storage tanks.
Operating pressure in reactor is above atmosphere around 2 to 5 atm. High pressure operations do not favor acetaldehyde formation and purification systems consumes more energy.
C2H5OH + 0.5O2→ C2H4O + H2O
Acetaldehyde process operations flow diagram:
Drawback in the acetaldehyde oxidation reaction due to presence of water:
Mostly catalyst used in ethyl alcohol oxidation process is Pt- and Rh-based multimetallic electrocatalysts. Its tendency to adsorption on the catalyst surface is affected by the water molecules. This leads to partial oxidation of produced acetaldehyde at high temperature zone. Due to this reaction, formation of impurities like methyl acetate and acetic acid takes place.
- Acetaldehyde is used to produce acetals. With help of acidic ion exchange resin they can be formed by using glycerol and acetaldehyde. It most commonly used for oxygenated diesel additives. The reaction is simple first order and a batch reactor is used for the manufacturing process.
- Used for direct ethanol fuel cell along with the ethanol.
Other production methods: