Half Order reactions and Scale determine economics:
1. The order of a reaction, like the hydroformylation of a double bond with a Rhodium triphenyl phosphine catalyst is half order, meaning that reaction rate is proportional to the square root of the catalyst concentration.
2. The investment in the reactor containing the catalyst/reaction is proportional to the cube root of the volume of the reactor. Annual costs for that reactor are proportional to it’s investment.
3. The price of Rh is relatively high ($2000/oz. in July, 2011) and if the proposed concentration in the reactor is 400 ppm, then for each carbonyl group added (H2=C=O or 30 lbs) the cost per pound of added product weight for once through use of Rh would be 2000*400*10^-6*14/30= 37.3 cents per lb.
4. An acceptable cost per pound of added product weight might be 5.0 cents per lb for catalyst cost, or nearly 10 fold lower than proposed. Rh recovery for recycle would normally be proposed.
5. Because of the reaction order and scale effect on reactor cost a preferred alternative would be to drop the Rh concentration by 100 fold while increasing the reactor volume by 10 fold.
6. Assuming a reactor investment of $1,000,000 for the 400 ppm case for 30*10^6 lbs of carbonyl with annual costs for maintainence, depreciation, taxes , insurance and other of $200,000/yr. the annual reactor cost would be 200,000*100/30,000,000=0.667 cents/lb of carbonyl. The larger reactor case would be 1.44 cents/lb of carbonyl cost.
Summary:
Case 400ppm 4ppm
Catalyst cost $/lb carbonyl 0.37 0.037
Reactor cost $/lb carbonyl 0.0067 0.0014
Sub total 0.377 0.0384
Conclusion:
The effect of scale and order combine to make an otherwise uneconomic proposal economic.
