Coal gasification produces synthesis gas (syngas), a mixture primarily of carbon monoxide and hydrogen. Syngas is a versatile feedstock. Hydrogenation of carbon monoxide can produce methanol, a precursor for ethanol. Nitroglycerine production can involve nitric acid, which can be indirectly linked to nitrogen compounds derived from syngas or other coal-derived processes. Urea is synthesized from ammonia and carbon dioxide; ammonia production often relies on hydrogen derived from syngas, and carbon dioxide is a byproduct of gasification.