Unit and process for purification of crude methyl methacrylate

Process fir purifying crude methyl methacrylate (MMA), said crude methyl methacrylate (MMA) being prewashed with water before the purification said process comprises the following steps:

• introducing pre-washed crude methyl methacrylate (MMA) in a median part of a first distillation column (210), in order to separate said first column into a lower (212) and an upper (213) part, at least 90% of the introduced MMA and heavy impurities flowing downward of said first column (210) with liquid phase, and at least 98% of introduced light impurities flowing upward with the gas phase, liquid phase being further laterally extracted, at an extraction liquid outlet located in the upper part of said first distillation column, in order to be cooled and washed with water and to obtain a phase separation between an aqueous phase containing water and methanol, and an organic phase containing MMA which is recycled into said upper part (213) of said first distillation column (210), below said extraction liquid outlet;
• introducing liquid phase issued from the bottom of first distillation column (210) into a median part of a second distillation column (250) in order to separate said second column into a lower (252) and an upper (253) part, at least 98% of introduced heavy impurities flowing downward of said second distillation column (250) with liquid phase, while at least 90% of introduced purified MMA flows upward with gas phase.