The subject is whether the mass of a proton can vary, and if so, how much.
One can determine the mass of a particular atom or molecule in a chemical laboratory by measuring a gram-mole of the substance. This mass can be determined with high precision but it is only an average for a billion trillion trillion atoms or molecules. It does not determine if there is a variance in mass.
However, processes in industry do depend on the assumption that the proton does not vary in mass, and they would fail if it did.
An example is the separation of propane and propylene in the petrochemical plants. Propane has little use as anything but a fuel. However, propylene is a starting point for the creation of many useful chemical products, the most obvious being polypropylene.
Propylene is derived from propane by passing the propane through a furnace at very high temperature, elevated pressure and with the aid of steam and caustic soda. The propane undergoes "thermal cracking" where two hydrogen atoms are removed from each propane molecule. The process does not go to absolute completion, so the propylene must be separated from the remaining propane. These two compounds are very similar chemically and are completely soluable with one another.
The method of separation is by distillation, which utulizes their difference in vapor pressures. This particular distillation is the most difficult in the industry. It requires two distillation colums, each three hundred feet tall. Each column contains about 200 trays, which adds up to 400 separation stages. Liquid flows down each column from tray to tray and vapor flows up each column from tray to tray. The flow of the two phases is countercurrent. That is, a liquid and a vapor come into intimate contact on each tray and the resulting liquid and vapor that leave the tray are presumably in phase equilibrium. The more volatile compound, propylene, slowly migrates from the liquid into the vapor, and the less volatile compound, propane, migrates from vapor to liquid. At the top of the second column, all the rising vapor is condensed in a "reflux condenser". Almost all of this liquid is returned to the top tray in the column. A small fraction of the liquid is drawn off as high purity propylene. At the bottom of the first column, almost all of the descending liquid is vaporized in a "reboiler" and returned to the column. A very small amount of liquid is not vaporized and is drawn off as high purity propane.
The difference in vapor pressure between the compounds is primarily determined by their molecular weights: propane is 44.09721 and propylene is 42.08127. The vapor pressure of propylene is about 19% higher than propane at the same conditions.
There is a further complication. Because two hydrogen atoms (protons) have been removed from propane to create propylene, the propylene has less of a "Coulomb repulsion". This means that propylene molecules can reside closer to another than can propane molecules. Thus, liquid propylene is 7 percent denser than propane. In turn, it takes more energy to separate out propylene molecules and vaporize them.
If the mass of a proton varied by more than about 10 percent, it would be impossible to separate propane and propylene by distillation. This separation is already quite difficult. But there are hundreds of C3 distillation columns throughout the world. They are designed and operated with great precision and achieve high purity.
This is a Reality test of how much the mass of a proton can vary. My next posting will provide evidence that the vatiance in proton mass must be less than 10 percent.
Gregg Wilson
