Batch and continuous processes

Chemicals may be manufactured using batch processes.

These are the main features of a batch process.

Chemicals may also be manufactured using continuous processes.

These are the main features of a continuous process.

Ethanol can be produced industrially by the fermentation of sugar.

The sugar may come from sources such as molasses (a by-product of the sugar industry) and maize starch.

Fermentation needs yeast, single-celled fungi containing enzymes that catalyse the conversion of sugar to ethanol.

The yeast are maintained at around 40 °C.

Fermentation produces up to 15% ethanol by volume, which kills the yeast and stops the process.

Fermentation also produces carbon dioxide, which may be compressed and sold to fizzy drinks manufacturers.

Ethanol can be produced industrially by the hydration of ethene with steam.

A high temperature of about 300 °C is needed.

A high pressure of about 60 atmospheres, 6000 kPa, is also needed.

Concentrated phosphoric acid on a silica support is used as a catalyst.

The two main processes for the industrial production of ethanol, fermentation and hydration of ethene, have different characteristics.

They have different rates of reaction.

They produce different percentage yields of ethanol.

The purities of the initial products are different.

They have different energy needs and use different types of resources.

These are the advantages of producing ethanol by hydration of ethene.

These are the advantages of producing ethanol by fermentation.

Fermentation has economic and environmental advantages that mean it is often the process of choice, despite the advantages of the direct hydration of ethene.

These are some typical batch processes.

These are some typical continuous processes.