Acid waste, minimisation

Throughout this chapter, and indeed in much of this book, we have seen an insight into a cleaner brighter future for the chemical industry. Catalysis is a key player in the chemistry of waste minimisation. We have seen just a few examples of how the application of new catalysts to existing processes can help to reduce waste at source, by increasing conversions, improving selectivities and by eliminating undesirable waste byproducts, such as heavy metals and acid waste, which are inherent problems in conventional systems. 

The extract is vacuum-distilled ia the solvent recovery column, which is operated at low bottom temperatures to minimise the formation of polymer and dimer and is designed to provide acryUc acid-free overheads for recycle as the extraction solvent. A small aqueous phase in the overheads is mixed with the raffinate from the extraction step. This aqueous material is stripped before disposal both to recover extraction solvent values and minimise waste organic disposal loads. 

Hydrolysis. The hydrolysis of dialkyl and monoalkyl sulfates is a process of considerable iaterest commercially. Successful alkylation ia water requires that the fast reaction of the first alkyl group with water and base be minimised. The very slow reaction of the second alkyl group results ia poor utilisation of the alkyl group and gives an iacreased organic load to a waste-disposal system. Data have accumulated siace 1907 on hydrolysis ia water under acid, neutral, and alkaline conditions, and best conditions and good values for rates have been reported and the subject reviewed (41—50). 

Modified polyacrylic acid size for continuous filament nylon. Prevents the build-up of electrostatic charge during rebeaming on warper/sizer systems. Minimises contamination due to fly waste when weaving staple yarn weft into filament wraps. 

Wastes also arise from the product separation or work up parts of a process. Solvents may be used to extract or wash the product, acid or base to neutralise reaction products, catalysts, particularly homogeneous ones may escape, or be unsuitable for reuse. Careful selection and operation of plant, from reactors to filtration equipment can help to minimise the amounts of wastes which are produced. 

Category 1 effluents may be separately collected in ponds and can be used as process water after neutralisation of any acidity. The total proportion of effluents in this category should be maximised so as to minimise the requirements for effluent processing and generation of associated solid wastes. 

---