What phrase would be more appropriate in this context?

Oil derivates have to undergo additional processes in order to be suitable for commercial use or in order to be used as raw materials for other technological processes. In oil derivates, the compunds of sulphurus, oxygen and nitrogen are not welcome because they cause corrosion and instabilty of the derivate itself.
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Also, it should be derivatives.
62,000 hits on oil derivatives
much less for oil derivates
Thank you Marius. What about not welcome?
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rather than "are not welcome", i would use: "should be avoided"

and i agree with you on the use of "derivatives".
>What about not welcome?
Sounds OK.
'not welcome' is maybe not very technical though OK.

I would use 'not desirable'.

Also it's 'sulphur', not sulphurus
and 'instability'.
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for me best as:

"In oil derivatives, the compunds of sulphur, oxygen and nitrogen are undesirable impurities because they cause corrosion and instabilty of the derivatives themselves."

'Not welcome' and 'should be avoided' suggest that it's possible to keep out these trace elements as impurities during the processing treatments but that's not so. It depends on the original source of the petroleum as to whether they are there in the petroleum as it's taken out of the earth.

Some sources have low amounts of these elements and so have a higher price in world markets.
Thank you all.

Alan.es, how do you know so much about the topic? Are you an expert?
For my pains, I studied chemistry at University, spent ten years in the chemical industry, then taught at university and Secondary school level before beoming a Headteacher. After retirement I've spent fifteen years teaching English as a second language in Spain and some translating/interpreting.

i'm not an expert but have still got some grey matter left despite the advancing years. I hope that's not too colloquial for you ;-)
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