Falling film evaporator

A method for evaporating an aqueous solution comprising the steps of

• feeding an aqueous solution through an inlet for the aqueous solution at top of a tube pass of a falling film evaporator,
• passing the aqueous solution at the top of the tube pass of the falling film evaporator through a distributing assembly that is placed below the top of the tube pass,
• forming a film of the aqueous solution along inner wall of the tube pass,
• flowing the film of the aqueous solution from the top to bottom on the inner wall of the tube pass vertically,
• accelerating flow rate of the aqueous solution in the tube pass in the same direction,
• evaporating the aqueous solution while reducing residence time of the aqueous solution in the tube pass, and
• obtaining a concentrated aqueous solution through an outlet for the aqueous solution at the bottom of the tube pass of the falling film evaporator.

A method for concentrating an aqueous solution comprising tetramethyl ammonium hydroxide comprising the steps of

• feeding an aqueous solution comprising tetramethyl ammonium hydroxide through an aqueous phase inlet at top of a tube pass of a falling film evaporator,
• passing the aqueous solution to the top of the tube pass of the falling film evaporator through a distributing assembly that is placed below the top of the tube pass,
• forming a film of the aqueous solution along inner wall of the tube pass through the distributing assembly,
• flowing the film of the aqueous solution from the top to bottom on the inner wall of the tube pass,
• accelerating flow rate of the aqueous solution in the tube pass in the same direction,
• evaporating water from the aqueous solution while reducing residence time of the aqueous solution in the tube pass, and
• obtaining a concentrated aqueous solution through an aqueous phase outlet at the bottom of the tube pass of the falling film evaporator,
• wherein the residence time the aqueous solution in the tube pass is in a range of about 2 to 60 seconds.