Acid Regeneration - Methyl Methacrylate (MMA) Spent Acid
February 25, 2002

Introduction

Methyl methacrylate is an intermediate used in the manufacture of acrylic resin, plastics, and paints.  Most of the MMA produced in the world uses the acetone cyanohydrin (ACH) process which uses acetone as the feedstock.  ICI (UK) produces approximately 85% of the world’s supply in plants located in the UK, USA and Taiwan.

The process uses concentrated sulphuric acid as part of the catalysis system and as a carrier in the reactor train.  The MMA product is boiled of leaving an aqueous solution (spent acid) of ammonium sulphate, sulphuric acid and various organic compounds.  Approximately 3 tonnes of spent acid is produced for every tonne of MMA produced.

The relatively low sulphuric acid concentration of the spent acid makes the spent acid difficult recover economically without employing additional technology and process steps.  First the acid is preconcentrated which removes a larger portion of the water content.  This has the effect of reducing fuel consumption, furnace size and downstream plant size.  SO₂ concentration is increased resulting in a smaller sulphuric acid plant contact section.

The degree of preconcentration is a function of the solubility of ammonium sulphate in solution.  It is desirable to have the solution remain as a single phase.

Oxygen enrichment is also required to achieve satisfactory economics for the process.  Varying degrees of oxygen enrichment can be done all the way to 100% oxygen.

Typical Composition