Final answer:
The process that is NOT involved in the conversion of organic nitrogen to nitrogen gas is acidizing.
Step-by-step explanation:
The process that is NOT involved in the conversion of organic nitrogen to nitrogen gas is acidizing. Acidizing is a method used in the oil and gas industry to improve the productivity of a well by dissolving materials that obstruct the flow of oil or gas. It is not directly related to the conversion of organic nitrogen to nitrogen gas. The other processes mentioned, such as expansion valve, mechanical refrigeration, and turboexpander, are commonly used in NGL separation.