b) The Reppe process for the manufacture of acrylic esters uses acetylene and ca
ID: 635364 • Letter: B
Question
b) The Reppe process for the manufacture of acrylic esters uses acetylene and carbon monoxide, with nickel carbonyl catalyst having high acute and chronic toxicity, to react with an alcohol to make the corresponding acrylic ester. The stoichiometry is as follows; Ni(CO) CH-CH + CO + ROH HO CH2-CHCOR Anhydrous HCI is very toxic by inhalation and is also highly corrosive. The acrylic ester product is self-reactive and must be stabilized using polymerization inhibitors before being sent to storage (it will polymerize, which is why it is useful, however if the polymerization occurs in an uncontrolled manner, it can cause a storage vessel to explode). An alternative route is propylene oxidation which proceeds according to the following stoichiometry; 3 Catalyst CH2 CHCH3 02CH2 CHCO2H H20 Propylene is oxidised to acrylic acid which is then esterified with the appropriate alcohol (for example, ethanol to make ethyl acrylate) in the presence of a strong acid catalyst to make the desired ester Compare and comment on the hazards of the two processes from an inherent safety viewpoint. [8 marks]Explanation / Answer
Firstly looking at the disadvantages of Reppe process, which has many (almost every unit used) hazardous elements.
1. Acetylene - Highly reactive and flammable too.
2. Carbonmonoxide - Toxic and flammable.
3. Nickel carbonyl - Toxic, being a heavy metal it is environmentally hazardous and also a carcinogen (cancer causing metal).
4. HCl - very corrosive and Toxic too.
We know that, inorder to maintain inherent safety we have to look into 4 important aspects namely : Minimise, Moderate, Substitute and Simplify.
As this process contains many hazardous materials and likely to exployed we opt for a process which is less hazardous and more safe.
So, by substituting Reppe process with Propylene oxidation to acrylic acids thereby converting these acrylic acids to acrylic ester. By doing so, this process eliminates the major headaches of Acetylene, Nickel carbonyl, Carbon monoxide and HCl which ultimately reduces hazards and toxic material upto some reasonable extent. But, this process too has some other disadvantages (which are less hectic than the previous one) which need to be taken care of to avoid explosion.
1. Propylene oxidation is a gas phase reaction i.e., gaseuos hydrocarbon reaction which indicates that there is a possibility of explosion. So, care mjst be taken on every stream so that temperature donot exceed flammable limit of propylene.(Upper flammable Limit).
2. As the first step of process is highly exothermic, care must be taken to avoid explosion. Proper check must be done to avoid temperatures go beyond auto-ignition temperatures of propylene and propane. Also every stream should be sealed well to avoid leakage as the expense of leakage would be very distractive and results in explosion.
3. Arcylic acid is non-toxic but readily miscible with water, so organic content in water increases as a results waste water treament should be implimented.
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