As already noted, more information would result in more specific answers. Following thoughts (subject to criticism) could be useful in the general case.
1. The compressed gas (1200 psig) will be throttled. Enthalpy will remain same, but temperature will decrease. Final point of CO2 will be on the gas-liquid or gas solid curve (passing from critical and triple point) of temperature-pressure diagram, <http://en.wikipedia....ase_diagram.svg>. Liquid CO2 will be separated from gas easier than solid CO2 (clogging etc). One can investigate whether vapor pressure of CO2 liquid close to its triple point (i.e. close to 5.2 bara, -56 oC) could satisfy extent of CO2 recovery (required 95%). Liquid CO2 will be recovered, its overhead vapor will be taken away with rest gases, e.g. in a flash drum downstream throttling.
Note: <http://www.cheresour...4-co2-pipeline/> can be useful, but does not contain throttling.
2. It is convenient for engineering calculations to use enthalpies rather than Joule Thomson coefficients. For this you can start from NIST database, <http://webbook.nist....hemistry/fluid/>
3. It is not easy to find specific references, familiarity with flash calculation (thermo, unit operations) and CO2 properties (thermo, even books on physics) could help. Simulation would help, preferably after manual tries. Critical point may be to clarify "process procedure" first, including conditions.
4. A local feasibility study (2002) concerned exploitation of NG deposit containing 22% CO2 (mol/mol). Resulting water condensate was considered corrosive to carbon steel pipe, so the gas was dried (*) in TEG (triethylene glycol) package units, before being introduced to NG pipelines.
(*) to - 8 oC water dew point, preliminarily for the feasibility study.