The nitration of hydrocarbons generally produces a variety of products depending upon the reaction conditions and the feedstock structure.  For instance, the commercial vapor phase process for propane nitration results in a mixture of four nitroalkane products (nitromethane, 1-nitropropane, 2-nitropropane, and nitroethane) in essentially fixed relative concentrations.  Certain nitrated hydrocarbon products, however, may be more desirable than others and the desirability of particular products may change as commercial supply and demand conditions change.  It has been a long-time goal, therefore, to selectively produce the more desirable nitrated compounds at the expense of the less desirable compounds. 
In contrast to commercial vapor phase nitration, the mixed vapor-liquid phase or high pressure nitration of propane has been postulated in the past to be a technique by which 2-nitropropane, often a more desirable nitrated hydrocarbon, can be potentially produced without making other less desirable nitro compounds typically formed during vapor-phase nitration.  See e.g., U.S. Pat.  No.  2,489,320 (Nygaard et al.)  and Albright, L. F., “Nitration of Paraffins”, Chem.  Engr., ( 1966) pp.  149-156. 
Despite the initial optimism, the prior art technology for nitrating propane in the mixed vapor-liquid phase was never practical for a number of reasons, including because the conversion of nitric acid is low, the nitric acid is not readily recoverable, problems with reactor corrosion by the nitric acid, and difficulty in controlling reaction exotherm. 
Obtaining a high yield of desirable nitrated hydrocarbon(s) is an important economic factor to be considered since low yields necessitate the use of more feed and therefore result in higher costs.  Furthermore, when nitric acid is used as the nitrating agent, the unreacted nitric acid becomes a waste product and costs are incurred to dispose of waste products properly.  High conversion of the reactant hydrocarbon (to nitrated hydrocarbons) is also economically important in order to minimize capital and energy expenses associated with the purification and recycling of unreacted reactants. 
It would be a significant advance in the field, therefore, to provide more economical, selective, and environmentally friendly processes for the manufacture of desirable nitrated hydrocarbons.