What is the mass of 1 Liter of ethylene at 2000 bar pressure?
If we treat it as an ideal gas, then
\begin{aligned}
  PV &amp;= n\mathcal{R}T \\ \mathcal{R} &amp;=0.08314~\mathrm{L~bar~K^{-1}~mol^{-1}}\\
  n &amp;=\frac{PV}{\mathcal{R}T}=\frac{2000\cdot1}{0.08314\cdot310}=77.6~\mathrm{mol}\\
  M(\ce{ethylene}) &amp;=28~\mathrm{g~mol^{-1}}\\
  \text{mass of ethylene} &amp;= (28\cdot77.6) = 2.17~\mathrm{kg}
\end{aligned}

Edit:
 Using the link[a] in the comment I find that the density of ethylene at $310~\mathrm{K}$ and $1800~\mathrm{bar}$ is $\varrho = 20.385~\mathrm{mol/L}$, and $\varrho = 21.065~\mathrm{mol/L}$ at $2200~\mathrm{bar}$.  Averaging these two numbers gives an estimated density of $\varrho = 20.725~\mathrm{mol/L}$ at $310~\mathrm{K}$ and $2000~\mathrm{bar}$.  So 1 liter of ethylene under these conditions would contain 
\begin{aligned}
  \varrho\cdot M_{\ce{C2H4}}\cdot V &amp; ~= m_{\ce{C2H4}}\\
  20.725~\mathrm{\frac{mol}{L}} \cdot 28~\mathrm{\frac{g}{mol}}\cdot 1~\mathrm{L} &amp; ~\approx 580~\mathrm{g}.\\
\end{aligned}
  Is that more in line with your expectations?

[a] Majid Jahangiri, Richard T Jacobsen, Richard B. Stewart and Robert D. McCarty: Thermodynamic Properties of Ethylene from the Freezing Line to 450 K at Pressures to 260 MPa. J. Phys. Chem. Ref. Data 1986, 15 (2), 593. (DOI:10.1063/1.555753) (mirror at www.nist.gov)