Method to minimize the transition time from one polymer grade to another polymer grade in a polymerization plant

Patent metadata

Field	Value
Publication number	US-10669374-B2
Application number	US-201515510046-A
Country	US
Kind code	B2
Filing date	Sep 1, 2015
Priority date	Sep 11, 2014
Publication date	Jun 2, 2020
Grant date	Jun 2, 2020

Abstract

A method is provided which reduces the transition time and/or the polymer waste in a continuous polymerization plant and/or process having a back-mixing reactor when polymer grades are changed from a first polymer grade to a second polymer grade. A monomer(s) and processing agent(s) are introduced to the reactor. The concentration of the processing agent(s) in a feed stream to the reactor is varied as a function of time from a first value associated with the first polymer grade to a final value associated with the second polymer grade. During the concentration variation one or more intermediate values of processing agent concentration are adjusted between at a first value, an intermediate value(s), and a final value. The intermediate values may be maintained for a time which is calculated on the basis of only residence time and steady-state correlations between input and output of the reactor and/or of the polymerization plant. The method is performed without performing dynamic modelling.

First claim

The invention claimed is:

1. A method for reducing transition time and/or polymer waste being out of specification during a change from a polymer having a first polymer grade to a polymer having a second polymer grade in a continuous polymerization process conducted in a polymerization plant having a back-mixing reactor, the method comprising the steps of adding into the back-mixing reactor a monomer and a processing agent comprising a catalyst, a co-catalyst, a polymerization initiator, a co-monomer, a chain-transfer agent, a branching agent, a solvent, or any combination thereof before and/or during the polymerization process, wherein the concentration of the processing agent introduced into the back-mixing reactor is varied as a function of time from a first value associated with the polymer having the first polymer grade to a final value associated with the polymer having the second polymer grade, wherein:
the polymer having the first polymer grade and the polymer having the second polymer grade have different polymer parameters, wherein the different polymer parameters are molecular weight of the polymer, composition of the polymer, structure of the polymer, amount of the polymer, or any combination thereof,
during the variation of the concentration of the processing agent from the first value to the final value the concentration is adjusted to an intermediate value, wherein the intermediate value is closer to the final value than to the first value, wherein the absolute difference between the intermediate value from the first value is greater than the absolute difference between the final and the first value, wherein the intermediate value is maintained for a time which is calculated on the basis of only residence time in the back-mixing reactor and steady-state correlations between input and output of the back-mixing reactor and/or of the polymerization plant,
the monomer is a cyclic ester,
the method is performed without performing dynamic modelling, and
during the variation of the concentration of the processing agent, the concentration of the processing agent is either:
(a) decreased from the first value c 1 to the intermediate value α·c 2 and then increased from the intermediate value α·c 2 to the final value c 2 , wherein the intermediate value α·c 2 is lower than the final value so that α<1, and wherein the intermediate value is maintained for a time

Δ
⁢

⁢
t

≤

τ
⁢

⁢

ln
⁡

(

1
-

α
⁢

⁢

c
2

⁢

/

⁢

c
1

(

1
+
ɛ
-
α

)

⁢

c
2

⁢

/

⁢

c
1

)

wherein:
c 1 is the first concentration of the processing agent,
c 2 is the final concentration of the processing agent,
α is the minimum factor, by which the minimum intermediate value is lower than the final concentration c 2 ,
τ is a time period being at least the average residence time of the reaction mixture in the back-mixing reactor and
ε is the relative tolerance on the final concentration of the processing agent, or
(b) increased from the first value c 1 to the intermediate value α·c 2 and then decreased from the intermediate value α·c 2 to the final value c 2 , wherein the intermediate value α·c 2 is higher than the final value so that α>1, and wherein the intermediate value is maintained for a time

Δ
⁢

⁢
t

≤

τ
⁢

⁢

ln
⁡

(

1
-

α
⁢

⁢

c
2

⁢

/

⁢

c
1

(

1
-
ɛ
-
α

)

⁢

c
2

⁢

/

⁢

c
1

)

wherein:
c 1 is the first concentration of the processing agent,
c 2 is the final concentration of the processing agent,
α is the maximum factor, by which the maximum intermediate value is higher than the final concentration c 2 ,
τ is a time period being at least the average residence time of the reaction mixture in the back-mixing reactor and
ε is the relative tolerance on the final concentration of the processing agent.

2. Th

Assignees

• Sulzer Chemtech Ag

Inventors

• Costa Liborio Ivano
• Codari Fabio

Classifications

• C08G63/08 Primary

  Lactones or lactides · CPC title

• C08G63/785 Primary

  characterised by the apparatus used · CPC title

• C08G63/82

  characterised by the catalyst used · CPC title

• G05D27/00

  Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00 · CPC title

• G05D11/08

  by sensing concentration of mixture, e.g. measuring pH value · CPC title