DT275

Module 1 Assignment

Aspirin Process

Lecturer paul.ashall@dit.ie, hassan.ali@dit.ie

A process for the production of aspirin

PA Pharmaceuticals have developed a process for the production 1 million kg of aspirin (acetyl salicylic acid) per year. The process is based on the reaction between salicylic acid and 20% stoichiometric excess of acetic anhydride and 10% by wt concentrated sulphuric acid (based on the mass of salicylic acid).

This reaction is exothermic (heat of reaction is – 84 kJ/mol) and is carried out in a batch reactor operating in semi-batch mode. The plant runs 24 hours a day and is available for operation 8000 hours per year.

The reaction is carried out at a temperature of 90 °C. Assume the reaction yield to be 95 %. i.e. 95% of the limiting reactant salicylic acid is converted to product in the reactor. Batch reaction cycle is 5 hours.

At the end of the reaction cycle the reactor contents are discharged to a crystalliser where the contents are cooled to 0 deg. cent. at a rate of 0.1 deg. cent. per min. To avoid a delay before the next batch is started, a number of crystallisers are required.

Other separation and purification processes required are: centrifugation (or filtration), including a washing cycle, and drying. These processes are assumed to take a total of 5 hours.

The mother liquor from the centrifugation (or filtration) step is separated by distillation. Acetic anhydride is reused in the process and the acetic acid is recovered for resale.

Waste waters are treated in a waste water treatment plant.

Refer to the notes page for a number of assumptions and directions to assist with the assignment.

The assignment is broken down into consecutive sections. Prepare a report on the following using a standard referenced report format.

Item	Requirements
1	Prepare a PFD flowsheet showing steps/ operations, main items of equipment and streams (use MS Visio) Carry out an annual and batch mass balance on each process step/operation and tabulate mass balance data	Draft submission deadline Nov 3
2	Carry out an annual heat (enthalpy) balance on each unit operation and tabulate data. Comment critically on assumptions made in this exercise.	Draft submission deadline Dec5

Note : A defence of your work at interview may be requested to assist in assessment.

Deadline for submission is Dec 19

Draft submissions for review and feedback can be made up to Dec 5

References

Assignment and Thesis Writing, J. Anderson and M. Poole, 4^th ed., Wiley, 2001

Perry’s Chemical Engineers Handbook

The Properties of Gases and Liquids, R. Reid et al, 4^th ed., McGraw-Hill, 1987

Chemical Engineering, Coulson and Richardson, vol. 6, 3^rd ed.

US Patent 2987539, 1961

Ullmans Encyclopedia of Industrial Chemistry, 6^th ed.

Kirk-Othmer Encyclopedia of Chemical Technology

CRC Handbook of Chemistry and Physics

Elementary Principles of Chemical Processes, R. M. Felder and R. W. Rousseau, John Wiley, 3^rd ed., 2000

Chemical Process Technology, J.A.Moulijn et al pp314/315

Introduction to Industrial Chemistry, H.L.White, pp181 – 183

US Pharmacopeia

European Pharmacopeia

et al

Notes

1. Check final aspirin specification required in the Pharmacopoeia.

2. Assume all the aspirin is recovered at crystallisation.

3. Assume after initial centrifugation (or filtration) ‘solid’ is 98% aspirin and 2% mother liquor by weight.

4. Assume after washing cycle in centrifugation (or filtration) operation, ‘solid’ is 98% aspirin and 2% water by weight, i.e. traces of mother liquor in ‘solid’ are removed into a waste water stream.

5. Assume mother liquor from initial centrifugation is recycled in process after removal of acetic acid by distillation.

6. Assume all materials entering the reactor are at room temperature.

7. Assume one reactor only is used.

8. Assume mixture for distillation is binary and consists of acetic acid and acetic anhydride only. Ignore other components in distillation analysis.