About: http://webisa.webdatacommons.org/439758495

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	However, because nitrogen containing compounds in heavier fraction material are difficult to identify and, at best, are a complex mixture of compounds, removal has been illusive.
http://www.w3.org/ns/prov#wasQuotedFrom	google.co.uk