DE19516362A1 - Monomer removal from butadiene-styrene copolymer synthesis latex - Google Patents

Abstract

Removal of monomer from a synthesis latex based on butadiene-styrene copolymer in a total vol. of latex sub-divided into several parts involves introducing the latex into a first part and discharging it from a second part and providing a common gas space over both parts. The monomer gas stream is discharged from the gas space and steam is passed into the latex before it enters each part. The novel features are that (a) satd. steam is added in amts. w.r.t stream in kg/hr., of (a-1) 0.01-0.03 times (w.r.t. wet stream in the first part) before the froth-retarding inlet, (a-2) 0.01-0.06 times in the first part and (a-3) 0.025-0.09 times in the second part; (b) the first part holds 30-50% of the total vol. of latex; and (c) the common gas space is at 1.1-1.4 bar.

Description

The process is used to remove butadiene from that prepared by polymerization in aqueous phase Butadiene-styrene copolymers.

Different demonomers are used in the literature procedure described. So it is common knowledge to mediate Passing water vapor or inert gases through the polymer rid the dispersion of monomers. This will be significant Amounts of steam or gas are used, especially with polymer dispersions that tend to foam cause difficulties to lead. The addition of defoamers makes the process more expensive, is not always effective and can affect the dispersion properties adversely affect.

In other known methods (DD 2 20 031, DD 1 44 922) the dispersion with steam or hot inert gases in one Tube mixed and the three-phase mixture formed shortly afterwards separated again into the dispersion and the gas phase. Doing it it turns out to be disadvantageous that due to the short Kon cycle times only a low degree of demonomerization with one comparatively high excess of water vapor is achieved. The short and therefore uneconomical contact times must also be complied with because it is with the steam / latex local overheating can occur. For the However, it is necessary to achieve low residual monomer contents derlich to achieve such treatment times that with the Transport of the monomer in the polymer phase by diffusion go compliant. At the same time, special equipment is available Steam / latex contacting necessary. There is always the risk that due to the susceptibility to coagulation of the Latex excretions occur which lead to deterioration or lead to failure of the procedure.

In other procedures, the expulsion of solutions middle residues from polymer dispersions by steam distillation in a lying, with vertical weirs provided container.  

The method described in DE-AS 25 20 591 is in one completely subdivided by vertical dividing walls Carried out in which the polymer to be treated latex the individual container sections through openings in the Partitions flowed through. The gas space is also divided and only has connection openings in the partitions each other on. The dispersion is at a container end fed and gets into the by overflowing the weirs successive container parts. Every part of the container contains a multi-stage impulse counterflow stirrer and on the bottom a steam entry. The steam flows through the dispersion and together with the expelled solvent deducted common gas space in the upper part of the container. The Dispersion is removed from the container after all weirs have passed dissipated.

Furthermore, foaming occurs when the steam is blown through Difficulties due to foaming are a problem for dispersions. To as far as possible the volatile components remove are longer dwell times and a relatively long one Steam consumption required. The recovery of such Components that are not released into the atmosphere is made difficult by the high amount of carrier gas.

Another disadvantage of this device is that in each Chamber a stirrer is used, which changes the technical Effort for multi-chamber containers increased significantly. The for the Monomer separation required by the Multiple division of the container volume only marginally influenced, the technical-technological effort increases but considerable. It also does not take into account that the residual monomer content decreases exponentially, so that the Residence time and the demonomerization parameters on this Behavior must be adjusted.

DE-PS 24 40 957 describes a method for removing Monomer components from aqueous dispersions of polymer Saten of the vinyl chloride described, in which the Dispersion mixed with saturated water vapor and in one  evacuated container with outgassing of the monomer components is relaxed. In such a process, the Demonomerization of butadiene-styrene copolymers with a very strong foam formation.

The invention has for its object that according to the Polymerization in the butadiene-styrene copolymer latex still contained monomers butadiene with an inexpensive simple procedure by treating the latex with water steam in a latex v divided into several partial volumes separate lumens. A strong foaming is said to occur be avoided.

The object is achieved by the claim illustrated method solved.

The method according to the invention is carried out in a container led, the interior of which is through a common gas space release partition in two partial volumes for synthesis latex is divided.

In a known manner, the latex to be treated comes out of the first partial volume over the top edge of the partition into the second Partial volume and from this for further processing.

The demonomerization process can then be special be advantageously carried out when the supply of the Latex flow in the gas space over a curved container surface like this takes place that the latex with a strongly suppressed foam bil strikes the surface in the first partial volume.

The advantage of the method is that the for Monomer expulsion required amount of steam in sections is added. This makes it possible to do the usual Minimize excess steam because of the steam used much closer to the equilibrium load that is possible under the specified process parameters. At the same time, it has a beneficial effect on coagulation behave of the latex when the steam is in multiple aliquots  is added as it does not cause local overheating and critical flow conditions can occur. Through the selected amount of steam and volume is achieved that only a certain amount of monomer is released in the sub-stages can be, so that the otherwise critical foam formation the demonomerization is minimized, which is an essential one Cause of the deterioration in demonomerization represents. Because this process increases with increasing temperature Increasing importance, it is beneficial the intensity of the Reduce fumigation while increasing the duration of treatment the rate of diffusion of the monomer in the polymer adapt. In addition, it is advantageous that the Demonomerization process above a pressure of 1 bar is carried out, whereby an expelled monomer is obtained, which is low in oxygen, so that the Reuse effort significantly reduced and at the same time the quality of the polymer is improved.

The invention is illustrated by the following examples:

example 1

One made by the emulsion polymerization process SBR latex is relaxed with a volume flow of 21,000 kg / h Supply container supplied in which a pressure of 1.4 bar is posed. The latex contains the unreacted monomers Styrene with 5.4% by mass and butadiene with 7.5% by mass. Just before the introduction into the container is at a mixing point Steam introduced, the steam 0.015 times the Latex current is.

Then the latex is placed over a curved tube sprayed on the curved container wall. The one running on the wall Latex gets into the 1st without additional foaming. Partial volume of the container that from the second partial volume by a Partition is separated, the upper edge of which is washed over by latex becomes. In this 1st container part, the 50% of the latex filling volume contains the container, water vapor is introduced, the  Water vapor is 0.05 times the latex flow. The up warmed latex is transported further into the 2nd partial volume, which contains 50% of the latex filling volume of the container. In this partial volume is also introduced water vapor, the water vapor being 0.03 times the latex flow. After this treatment, the latex still contains 1.6 Na% butadiene and 4.2 mass% styrene.

Example 2

One made by the emulsion polymerization process SBR latex with a volume flow of 21,000 kg / h Relaxation tank supplied in a pressure of 1.2 bar is set. The latex contains the unreacted Monomers styrene with 5.4 Na% and butadiene with 7.5 Ma%. Immediately before being introduced into the container is on a Mixing point water vapor introduced, the steam the Is 0.02 times the latex flow.

Then the latex is placed over a curved tube sprayed on the curved container wall. The one running on the wall Latex gets into the 1st without additional foaming. Partial volume of the container that from the second partial volume by a Partition is separated, the upper edge of which is washed over by latex becomes. In this 1st container part, the 30% of the latex filling volume contains the container, water vapor is introduced, the Water vapor is 0.035 times the latex flow. The up warmed latex is transported further into the second partial volume, that contains 70% of the latex filling volume of the container. In this partial volume is also introduced water vapor, the water vapor being 0.06 times the latex flow. After this treatment, the latex still contains 0.9% by mass of butadiene and 3.8 mass% styrene.

Claims (1)

Process for demonomerization of synthetic latex based on butadiene-styrene copolymers in a total volume of synthetic latex divided into several partial volumes, the synthetic latex entering in a first partial volume and emerging from a second partial volume and a common gas space being arranged above the partial volumes, from which the monomer gas stream escapes and water vapor is introduced into the synthetic latex before entering the first partial volume and the second partial volume, characterized in that

• - 0.01 to 0.03 times (based on the wet flow kg / h) of saturated water vapor is added to the synthetic latex stream before the foam-restricted entry into the first partial volume,
• - In the first partial volume, 0.01 to 0.06 times (based on the mass flow kg / h) of saturated steam is added to the synthetic latex stream
• and in the second partial volume 0.025 to 0.09 times (based on the mass flow kg / h) of saturated steam is added to the synthetic latex,
• - The first partial volume contains 30-50% of the total latex filling volume and the common gas space has a pressure between 1.1 and 1.4 bar.