Process for preparing and purifying acrylic acid from propylene having improved capacity

A process comprising the steps of:

• (A) feeding a reactant composition comprising:
• (i) greater that 7 percent by volume propylene, (ii) oxygen, (iii) water vapor, and (iv) the remainder including a major amount of at least one inert gas, into a reactor;
• the reactor including a plurality of contact tubes, containing at least one catalyst, disposed in a shell, wherein the inside of the reactor shell contains at least one heat transfer zone through which heat transfer medium passes and each contact tube comprises at least one reaction zone capable of effecting the preparation of acrolein from propylene,
• (B) contacting the reactant composition with the at least one reaction zone to form a mixed product gas comprising actolein,
• (C) cooling the mixed product gas comprising acrolein in a heat exchanger,
• (D) feeding the cooled mixed product gas comprising acrolein to a second reactor;
• the second reactor including a plurality of contact tubes, containing at least one catalyst, disposed in a shell, wherein the inside of the reactor shell contains at least one heat transfer zone through which a heat transfer medium passes and each contact tube comprises at least one reaction zone capable of effecting the preparation of acrylic acid from acrolein, and
• (E) contacting the mixed product gas comprising acrolein with the at least one reaction zone to form a mixed product gas comprising acrylic acid;
• wherein the mixed product gas comprising acrylic acid is absorbed in an absorption tower with water and at least one polymerization inhibitor to form an aqueous acrylic acid stream containing from 32% to 55% by weight acrylic acid;
• said process further comprising purifying the acrylic acid wherein the purification comprises:
• feeding the aqueous acrylic acid stream to a fight ends stripper to remove light ends from the aqueous acrylic acid stream,
• contacting the aqueous acrylic acid stream from the light ends stripper with an organic stream selected from toluene, isopropyl acetate and combinations thereof in at least one extractor to generate an extract stream and a raffinate stream,
• feeding the extract stream to an extract stripper comprising a reboiler and a column having a top and lower trays, wherein a vapor phase polymerization inhibitor is added to the reboiler and lower trays of the column, and a liquid phase polymerization inhibitor is added to the top of the column, and wherein a water and toluene/isopropyl acetate stream and an extract stripper stream are generated,
• feeding the raffinate stream to a raffinate stripper to generate a waste water stream and a toluene/isopropyl acetate recycle stream,
• feeding the extract stripper stream to at least one crude acrylic acid distillation column to generate an acetic acid stream from the top of the column and a crude acrylic acid stream,
• separating the water and toluene/isopropyl acetate stream into a toluene/isopropyl acetate steam, which optionally is recycled to the extract stripper, and an aqueous steam, which optionally is recycled to the raffinate stripper.