John Prausnitz

John Michael Prausnitz was born in Berlin, Germany, on 7 January 1928. His father and his mother's stepfather were both Jewish doctors. After the Nazi government stripped Jewish doctors of their licences in 1933, they were at first allowed to keep working because they had served at the front in the First World War.

In 1937, aged nine, he emigrated to the United States with his parents and sister. An uncle lived in Lynbrook, New York, and because New York State recognised his father's German medical licence, his father was able to practise medicine. The family lived in Lynbrook, then Manhattan and Forest Hills, Queens, and he attended Public School 101.

He earned a five-year Bachelor of Chemical Engineering at Cornell University in 1950 and a master's degree at the University of Rochester in 1951. He then went to Princeton University as a student of Richard H. Wilhelm, spending two summers at Brookhaven National Laboratory, and received his PhD in 1955 with a dissertation on liquid-phase turbulent mixing.

Prausnitz joined the College of Chemistry at the University of California, Berkeley, in 1955. He was attracted by Joel Hildebrand's research on mixtures and by Berkeley's unusual arrangement of chemical engineering within a college of chemistry.

He created the field of molecular thermodynamics, which uses the properties of molecules and their functional groups to predict the phase equilibria that underlie industrial separation processes. He initiated or helped develop the NRTL, UNIQUAC and UNIFAC models, which are built into the process simulation software used to design refineries and chemical plants. His research later extended to polymers, colloids, ionic liquids, crude oils, natural gas and protein solutions.

His books included Computer Calculations of Vapor-Liquid Equilibria (1967), the graduate textbook Molecular Thermodynamics of Fluid-Phase Equilibria (1969, 1986, 1999), and later editions of Regular and Related Solutions and The Properties of Gases and Liquids. A 2011 Festschrift in the Journal of Chemical and Engineering Data counted more than 760 articles in 134 journals with 421 co-authors.

He officially retired from teaching in 2004 but remained a Professor of the Graduate School and a Faculty Senior Scientist at Lawrence Berkeley National Laboratory. From 2008 to 2018 he was the founding editor of the Annual Review of Chemical and Biomolecular Engineering.

Prausnitz had two children, Stephanie Prausnitz and Mark Prausnitz, a professor of chemical and biomolecular engineering at the Georgia Institute of Technology. Born in Berlin, he remained fluent in German and kept close ties with Europe, returning often for conferences and for longer stays at universities in several European countries. He supported the Leonardo Project, inspired by Jacob Bronowski's The Ascent of Man, which created case studies linking science with society, art and philosophy for undergraduate teaching.

John Prausnitz died on 5 November 2026, aged 98. The cause of death was not made public. His death was recorded by Rolling Hills Memorial Park in Richmond, California, which listed the park as his final resting place. A full obituary had not been published at the time of writing.

Prausnitz is regarded as one of the most influential chemical engineers of the twentieth century. His activity coefficient models remain in everyday industrial use, and his textbook trained generations of engineers. The American Institute of Chemical Engineers renamed its Institute Lecturer Award the John M. Prausnitz AIChE Institute Lecturer Award in 2016. His academic family tree, which he kept on his office wall in Gilman Hall, ran to hundreds of academic grandchildren and great-grandchildren, and in 2026 the European Symposium on Applied Thermodynamics devoted a session to his work.