Method for recovering ethylene during the process for producing VAC and a device thereof

Abstract

The present invention discloses a method and a device for recovering ethylene during the process for producing vinyl acetate, wherein a double solvent absorption method composed of an absorbent solution and deionized water is adopted. The method is as follows: introducing an outlet stream as an absorbent solution from the upper section of the feeding plate in an acetic acid tower during the rectification stage of vinyl acetate production; delivering same to the top of the lower section of the ethylene recovery tower by a delivery pump; charging refined gas from the tower bottom of the ethylene recovery tower for contacting with the absorbent solution in a counter-current; delivering the absorption bottom solution to the rectification stage for treatment; the gas continuing to rise to the upper section of the ethylene recovery tower and contacting with the deionized water introduced from the top of the tower in a counter-current; absorbing and removing the acetic acid therein; and discharging the residual inert gas, such as N2, from the top of the ethylene recovery tower. The absorbent solution is a mixture of acetic acid, vinyl acetate and water, and comprises by weight percentage of 50-85% acetic acid, 5-30% vinyl acetate and 5-20% water.

Claims

1. A method for recovering ethylene during a process for producing vinyl acetate, comprising the following steps: (a) introducing a stream of absorbent solution from an acetic acid tower during a rectification stage of vinyl acetate production; (b) delivering said stream of absorbent solution to an ethylene recovery tower which comprises a top, a bottom, a top section, and a lower section having a top location to which said stream of absorbent solution is delivered by a delivery pump to allow said stream of absorbent solution to precipitate towards said bottom of said ethylene recovery tower; (c) charging said ethylene recovery tower with a refined gas flow from said bottom of said ethylene recovery tower to bring said refined gas flow in contact with said stream of absorbent solution which is precipitating in a counter-current; (d) delivering said stream of absorbent solution precipitated in said bottom of said ethylene recovery tower to a rectification unit; (e) allowing said refined gas flow to continue to rise to said upper section of said ethylene recovery tower where said refined gas flow contacts with deionized water introduced from said top of said ethylene recovery tower in a counter-current so that acetic acid is absorbed and removed from said refined gas flow and so that said refined gas flow then contains residual insert gases; and discharging said refined gas flow containing residual insert gases from said top of said ethylene recovery tower.

2. The method for recovering ethylene of claim 1, wherein said stream of absorbent solution is a mixture of acetic acid, vinyl acetate and water, accounting for 50-85%, 5-30%, and 5-20% by weight, respectively.

3. A device for recovering ethylene during a process for producing vinyl acetate, comprising a buffer tank with an inlet and an outlet, a delivery pump and an ethylene recovery tower with a top, a bottom, a top section, and a lower section, said lower section having a top location which is connected to said delivery pump for receiving a stream of absorbent solution delivered by said pump from said outlet of said buffer tank and said buffer tank in turn receives said stream via said inlet from an acetic acid tower in a rectification unit during vinyl acetate production; said upper section is for water washing and said lower section is for absorbent solution washing of a refined gas flow which enters said ethylene recovery tower from a lower location of said lower section.

4. The device of claim 3, wherein said ethylene recovery tower has an absolute operating pressure between 0.5-1.2 MPa and an operating temperature between 25-80 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The FIGURE shows a schematic diagram of the method for recovering ethylene during the process for producing VAC

DETAILED DESCRIPTION OF THE INVENTION

(2) The present invention is described in further details with reference to the FIGURE and embodiments. The present invention provides a device for recovering ethylene during the process for producing VAC, wherein the upper section of the feeding plate in an acetic acid tower for the rectification stage of VAC production is connected with the inlet of the buffer tank for the absorbent solution, the outlet of the buffer tank for the absorbent solution is connected with the inlet of the delivery pump for the absorbent solution; the outlet of the delivery pump for the absorbent solution is connected with the lower section of the ethylene recovery tower. Said ethylene recovery tower is a compound tower composed of the upper section and the lower section, wherein said upper section is for water washing and said lower section is for the absorbent solution washing. The operation pressure of the ethylene recovery tower is under 0.5-1.2 MPa by absolute pressure and the operation temperature is under 25-80 C.

Embodiment 1

(3) Introducing the outlet stream as absorbent solution from the upper section of the feeding plate in an acetic acid tower 4 during the rectification; delivering the same to the buffer tank 1, then to the top of the lower section of the ethylene recovery tower 3 by the delivery pump 2 for the absorbent solution; charging refined gas from the tower bottom of the ethylene recovery tower 3 for contacting with the absorbent solution in a counter-current, thus achieving selectively recover ethylene gas according to the solubility characteristics of the refined gas in the absorbent solution. Further, delivering the bottom solution to the rectification stage for degassing treatment. The rising unabsorbed gas includes inert gas such as N.sub.2 and a small amount of acetic acid. The gas continuing to rise to the upper section of the ethylene recovery tower and then contacting with the deionized water introduced from the top of the tower in a counter-current; absorbing and removing the acetic acid therein. The residual inert gas, such as N.sub.2 is discharged from the top of the ethylene recovery tower to prevent the accumulation of inert gas. The absorbent solution is a mixture of 78% acetic acid (wt %), 8% (wt %) VAC and 14% (wt %) water. The selectivity of the ethylene recovering is up to 90%.

Embodiment 2

(4) The method is same as Embodiment 1 except that the absorbent solution is a mixture of 85% acetic acid (wt %), 5% (wt %) vinyl acetate and 10% (wt %) water. And the selectivity of the ethylene recovery is 95%.

Embodiment 3

(5) The method is same as Embodiment 1 except that the absorbent solution is a mixture of 50% acetic acid (wt %), 30% (wt %) vinyl acetate and 20% (wt %) water. And the selectivity of the ethylene recovery is 60%.

Embodiment 4

(6) The method is same as Embodiment 1 except that the absorbent solution is a mixture of 65% acetic acid (wt %), 30% (wt %) vinyl acetate and 5% (wt %) water. And the selectivity of the ethylene recovery is 70%.

(7) The present invention discloses and provides a method and a device for recovering ethylene during the process for producing VAC. The technicians in this field can achieve the present invention by appropriately modifying the raw materials, the process parameters, the structure design and other aspects by referring to the content of the present invention. The method and technique of the present invention is described by better mode, and obviously can be carried out by technician in the field without deviating from the content, spirit and scope of the present invention by changing, appropriately modifying and combining the method and technology of the present invention. In particular, any similar replacement and change is obvious to the technician in the field and should be deemed to be included in the spirit, scope and content of the present invention.