TABLE OF CONTENTS Probably the most fundamental problem facing the development of greener products and processes is the measurement of progress and the development of appropriate methods for comparison of alternatives. In many instances it will be obvious that improvements have been made, for example when a toxic material is replaced by a non-toxic alternative, keeping all other process conditions essentially the same, or when the energy requirement of a process is reduced.
Consider the example of dimethyl carbonate production. The traditional way of preparing dimethyl carbonate involved the reaction of highly toxic phosgene with methanol (Equation 3.1). As well as using phosgene the process produced two moles of unwanted HCl per mole of product, which requires disposal, further increasing the environmental burden. In addition the product was also contaminated with trace amounts of toxic chlorinated by-products, resulting in dimethyl carbonate being classed as a harmful material.
| (3.1) |  |
Today most dimethyl carbonate is made by methanol carbonylation (Equation 3.2) using a copper chloride catalyst with a very long life. This process produces pure dimethyl carbonate, which is not now classified as harmful, and water as a by-product.
| (3.2) |  |
Despite the toxicity of CO, and the high pressure required for the process it would be generally accepted that the carbonylation process is a significant step in the right direction.
In other instances the 'green' improvements will be more controversial, for example replacement of a material used in a relatively large volume, producing large amounts of benign waste, by a...
