20 The Israel Chemist and Chemical Engineer Issue 8 · November 2021 · Kislev 5782 History of Chemistry Articles stages, the commercialization of PRO technologies should emerge in the near future .” It is now about 50 years from the time that the idea for PRO started to take shape in Sid’s mind. The paper that I wrote in 2004 about the origins of PRO follows. The origins of PRO The research environment One of the primary purposes for the government-run Negev Institutes was to carry out applied research for the utilization of the arid climate to the benefit of both Israel and of other arid areas. The Institutes were to use local raw materials and natural resources. Located on the same site was a branch of the Israeli Bureau of Standards and the research division of the Dead Sea Works. From 1960 to 1970, Israel ’s energy consumption almost tripled, for which crude oil was the only primary source. Electricity output was based entirely on oil. Oil prices began to rise steeply in 1970. Construction of a canal connecting the Mediterranean Sea – Dead Sea - Red Sea was first proposed already in 1855 by William Allen as a cheaper alternative to the projected Suez Canal. Over the years, the proposal changed in form and intended goals, but at the heart of all of the proposals was always to make use of the 400 meter drop in altitude to the Dead Sea from the other bodies of water. Benefits to be derived from the proposed canal included transportation, hydroelectric power, elevation of the Dead-Sea level to meet the needs of industry and tourism, provision of cooling water for inland nuclear reactors and industry, creation of sea-water based inland industries – for example, fish ponds, inland lakes to promote tourism, and the production of fresh water by reverse osmosis. The idea Sidney Loeb was then in this environment where he was in touch with these ideas. The campus was active in research in three areas that all were to come together in Sidney Loeb’s mind in the form of PRO – energy, membranes, and the utilization of Israel ’s arid zone natural resources – in particular the Dead Sea. However, Loeb’s original patent (see last paragraph) mentions the combination of river water and sea water as a parallel possibility. Further to this, if one were tomake a movie of an operating RO plant and run the film backwards, we would have what looks like an operating PRO plant. In viewing the film running in the forward direction we would see an RO plant where one stream of salty water is entering the facility and two streams are leaving it – one fresh water for drinking and one more salty waste water. Energy is consumed in this osmotic process. If we were to view that same film in the reverse direction, we would now see two streams of water entering the facility, one of higher salt content than the other, and one stream leaving the plant. Energy is now being produced osmotically. Stated another way, as energy is required to desalinate water, then salination can be used to produce energy. As one can appreciate, Sidney Loeb, already in tune with RO, was ready and able to make the conceptual leap from RO to PRO. A colleague remembers Dr. Melvin Weintraub [no relation to author], a biochemist working with Sidney Loeb at around that time, recalls as follows: “I imagined that Sid thought of the process just by trying to see how membrane technology could fit in economically with power needs. This connection has always been the driving force for membrane technology, since you achieve the separation you want without a phase change, which saves a lot of energy and thereby, cost. With reverse osmosis, we are always concerned about fouling effects such as concentration polarization, and how to prevent or alleviate them. I imagine that while thinking about these things Sid may have been thinking if there was a way to use such effects to our advantage. That’s what a clever engineer would do. And, I suppose, he came up with pressure retarded osmosis out of that. It’s simple enough once you are smart enough to turn the problem around” (personal communication, Feb., 2004). Jordan River and the Dead Sea Loeb’s first thought was to use PRO to harness the power from the free energy of mixing of the Jordan River with the Dead Sea (see Figure 2). However, the Jordan River did not have a large enough flowrate to be useful for PRO. It is curious to note that among the other possibilities for application of PRO covered by the patent, Loeb also considered capturing the free energy of mixing for the production of power by “another” Jordan River as it runs into the Great Salt Lake of Utah. Prof. Loeb filed his first patent application on PRO in Israel on July 3, 1973, application number 42658 (This is shown as erroneously as July 3, 1974 on the front page of the US patent). The patent was issued on December 1, 1976. A United States patent application was filed on June 19, 1974, and the patent was granted as US 3,906,250 on September 16, 1975. The patents were assigned to the Ben-Gurion University of the Negev.