Study On Concentration Of Mixed Acid In Side Stream Of Absorption Column In Acrylic Acid Production By Membrane Process

Acrylic acid is an important monomers in the synthesis of acrylate.The polymer synthesized by acrylate has advantages of stability and durability which is widely used in coating,adhesive,textile,rubber,etc.The absorption tower is used to absorb the hot vapor contained acrylic acid in the production of acrylic acid.The concentration of acrylic acid in the bottom of the absorption tower is low,which increases the cost of acrylic acid distillation in the later process.Besides,large amount of acidic wastewater will be generated.In this work,a new method was proposed to concentrate the solution of the absorption column for the intensification of absorption process.Part of absorption solution was taken from a certain position in the absorption column,of which the acetic acid and acrylic acid were concentrated outside by lower energy consumption technology.Then the concentrated solution was returned to the tray with the same acid concentration.The dilution water from the concentration system can be reused for absorption.At the same time,the amount of fresh wastewater was also decreased.The mixed acid solution contained acrylic acid and acetic acid was conducted concentration test by electrodialysis and reverse osmosis.The electrodialysis was used to concentrate the solution contained acrylic acid and acetic acid.The influence of operating conditions including voltage,flow velocity,temperature,initial acid concentration on concentration rate and specific energy consumption were investigated by a laboratory-scale device.The concentration rate of acrylic acid and acetic acid was increased with the increasing of operating voltage,flow velocity or operating temperature.But the specific energy consumption was increased with the increasing of operating voltage.When the operating voltage was 10V,volumn rate of dilute and concentration was 3,and the initial solution contained 2.5%acrylic acid and 2.5%acetic acid,the concentration rates of acrylic acid and acetic acid could be 203.3%and 156.6%.The absorption process combined with ED was simulated by Aspen.The results shown that the flow rate of spray water was decreased by 37.1%,and the acrylic acid concentration at the bottom of the tower was increased by 4.56%.The changes of ions exchange membranes performance after using in the acid solution were characterized.After using 1,200 hours,the transport number and ion exchange capacity of anion exchange membrane and cation exchange membrane were reduced by 1.03%,18.39%and 1.09%,14.4%.And the membrane area resistance of anion exchange membrane and cation exchange membrane was 2.5Ω·cm^-2and 3.5Ω·cm^-2.The reverse osmosis was used to concentrate the solution contained acrylic acid and acetic acid.The effects of operating conditions including pressure,temperature,and feed concentration on permeate flux and acid retention for two kinds membranes（SWC5 and SWC6）were examined.And immersion experiment was also carried out to test the stability in different concentration of acid solution.The increases in pressure and temperature could promote water through the membranes,while higher pressure and lower temperature favored the retention of acids.With the increasing of concentration of initial acid solution,the permeate flux was decreased and the acid retention was nearly unchanged.For both membranes,around 78%of total acid retention was achieved at 3.5 MPa.With the increasing of acid concentration and exposure time in immersion test,the variation of membrane performance was large.After 6 months immersion in the acid solution containing 2.5%acrylic acid and 2.5%acetic acid,the acid retentions for both membranes were still above 75%.The performance of SWC6 was relatively stable than SWC5 after exposure to acid solution.