Granted Patent
Utility
US 4,902,321 · App. 07/324,444
Cryogenic rectification process for producing ultra high purity nitrogen
Inventor:
Harry Cheung
Patented Case
View Patent ↗
Granted: Feb 20, 1990
Filed: Mar 16, 1989
Inventor
Harry Cheung
Assignee (at issue)
Union Carbide Corporation
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.