Density at Flow Conditions

For ideal gases, P₁V₁/T₁ = P₂V₂/T₂. But if the gas is close to condensing temperature (i.e., saturation), it gets more complicated.

D₂ = D₁(T₁/T₂)(P₂/P₁)

P & T are in absolute units e.g. T in Kelvin and P in bar a. D₁, T₁ and P₁ refer to STP conditions.

STP, more or less room temp and pressure has the gas molecules far enough apart that they act like billiard balls, collide, rebound etc., with long free paths between the molecules (relative to their sizes) between collisions. The pressure of 236 bar and associated temperature place the gas molecules a lot closer together, so there is less free space and the mean free path is far lower.

This means you can not use the formulas mentioned without a correction factor. There are purely mathematical correction factors in the literature, and there is also a mass of collected data on the gas you speak of at various pressures and temperatures that are close enough (or exactly there?) to allow to to determine the degree to which the gas will "depart from ideality" at your 236 bar and 74C. The best match is for the exact gas as close to your T & P as possible. Failing that, gasses of the same molecular weight and number of atoms composing each molecule have the highest chance of providing the correct correction factor for the formula.

Perry - the Chemical Engineer's Handbook, is a collection of a wide range of date on all manner of topis, including gasses at various T and P. It also has references for further search. A library at a major university will have the greatest chance of having some of the references. They may not be on line because no one may have placed them on line. Gas drilling companies have a lot of literature on gasses from oil and gas wells in various mixes etc., and some of these may be in their safety filing