  We report a numerical simulation for the phase diagram of a simple two
dimensional model, similar to one proposed by Noro and Frenkel [J. Chem. Phys.
\textbf{114}, 2477 (2001)] for membrane proteins, but one that includes the
role of the solvent. We first use Gibbs ensemble Monte Caro simulations to
determine the phase behavior of particles interacting via a square-well
potential in two dimensions for various values of the interaction range. A
phenomenological model for the solute-solvent interactions is then studied to
understand how the fluid-fluid coexistence curve is modified by solute-solvent
interactions. It is shown that such a model can yield systems with
liquid-liquid phase separation curves that have both upper and lower critical
points, as well as closed loop phase diagrams, as is the case with the
corresponding three dimensional model.
