May-2020

The primrose path

To all our refining readers, especially those with mariners as customers, we send wishes for a successful IMO 2020.

Chris Cunningham
PTQ Editor

Article Summary

Yet more sulphur extraction for the refining industry. But if you regard those primrose coloured lumps falling into the bin at the last stage of the sulphur plant as waste product and a drain on capex, spare a moment to reflect on its values and history.

Until petroleum gradually assumed its current role, following the Second World War, as the world’s dominant traded raw material, sulphur was king. It was and remains a keystone raw material of the global chemical industry. Moreover, per capita consumption of sulphur was an economist’s index to a nation’s standard of living.

In its raw state, sulphur is a fairly innocuous material. To make good use of it, you first have to burn it to generate sulphur dioxide. This seems counter- intuitive; the whole reason for producing low-sulphur fuels is surely to prevent production of sulphur dioxide. However, keep the gas under control, run it over a catalyst, and you have sulphur trioxide. Dissolve the trioxide in water and you are in business.

Sulphur has thus become sulphuric acid, about the handiest simple reagent you could dream up. Thinned down from its full-on oily state with a little more water, it becomes a strong acid, strong enough to eat rock.

(A side note here: refiners can go directly to sulphuric acid with an extra process operation, WSA for instance, which is handy if you have chemical processing sites for neighbours.)

Now, if you look around your workplace – the walls, the furniture, your clothes too – sulphuric acid will have played some part in the production of virtually every manufactured or finished material. Its leading charm is that it will consume other raw materials without risk of emitting clouds of noxious gases.

Modern furnishings aside, sulphuric acid’s starriest role is less visible but a benefit to most. Dissolving phosphate rock in the acid is the start of a process chain that delivers complex chemical fertilizers. These may be anathema to the organic farming movement but, in the second half of the 20th century, they transformed crop production and ended mass famines arising from poor methods of cultivation in regions of Asia. 

So important has sulphur been, for so long, that during the earliest days of oil refining the chemical industry relied on natural (or ‘native’) sulphur for its supplies. Chief centres of production last century were Sicily and latterly West Texas. This is where the fortunes of sulphur and petroleum began to coincide. Sulphur was extracted from deep dome structures in Texas by the Frasch process, involving injection of superheated steam to melt the element so that it could be pumped to the surface. Meanwhile, commercial supplies of crude oil were emerging in the neighbourhood. West Texas Intermediate is now well established as, almost ironically, the sweetest of leading benchmark crudes.

The precursor rules leading to IMO 2020, Euro VI and future sulphur limits began to make their mark on oil processing worldwide, and on supplies of the yellow element, to the point where sulphur mining became an irregular source to balance supplies dominated by Claus production. The industry’s last rites were at the turn of the current century.

This short article was the editorial forward in the Q1 2020 issue of PTQ.

You can view the issue HERE