Title of Invention

PROCESS FOR POLYMERISATION OF OLEFINS AND LOOP REACTOR THEREFOR

Abstract The inventions discloses a process for Polymerisation of olefins comprising : (a) polymerising olefins in a liquid diluent to produce a liquid slurry containing particles of normally solid polymer within a loop reactor; (b )allowing the polymer to settle in a settling leg; and (c) periodically opening a 180° rotating product take-off valve located at the end of the settling leg to allow a charge of particles to flow out of the settling leg, the product take-off valve being operated by a pneumatically driven double-acting actuator, the pneumatic system being regulated by a system comprising pneumatic control valves characterised in that the control valves are V-ball valves. The invention is also for a loop reactor for carrying out said polymerisation.
Full Text

This invention relates to the withdrawal of solid polyolefin from a slurry of such solids. In
a particular aspect, it relates to a method and apparatus for controlling the recovery of
particulate polyolefin from a slurry thereof, for example from a stream of polymerisation
mixture continuously flowing in a loop reactor.
US-A-3,242,150 disclosed an improvement to loop reactors consisting in adding to the
bottom part of a loop reactor a receiving zone, since known as settling leg, wherein the
solids settle by gravitation, and withdrawing a traction concentrated in solids from said
receiving zone.
US-A-3,293,000 disclosed a loop reactor with several settling legs. Control of the valve is
described at column 3, lines 2 to 22.
US-A-3,374,211 disclosed a modified process for removing polymer.
More recently, US-A-5,183,866 related to the employment of a flash line heater in
conjunction with the periodic operation of a settling leg of a loop reactor. The process is
characterised by the fact that the elongated zone is constructed such that the flow time of
the charge of slurry in an elongated confined zone including the flash line heater is equal to
at least about 25% of the time between the closing of the settling leg valve and the next
opening of the settling leg valve.
US-A-5,455,314 discloses a method for controlling in a continuous manner me withdrawal
of a reaction slurry containing a polymer product from a polymerization reactor by
manipulating continuously a V-notch ball valve in a primary effluent line and by
automatically open a control valve in a redundant line as a backup for the primary control
valve in the event the primary line becomes plugged
The invention relates to a polymerisation process comprising polymerising olefins in a
liquid diluent to produce a liquid slurry containing particles of normally solid polymer
within a loop reactor, allowing the polymer to settle in a settling leg, periodically opening a
180° rotating product take-off valve located at the end of the settling leg to allow a charge

of particles to flow out of the settling leg, the product take-off valve being operated by a
pneumatically driven double-acting actuator, the pneumatic system being regulated by a
system comprising pneumatic control valves characterised in that the control valves are V-
ball valves.
The invention relates also to the use of V-ball control valves to regulate the pneumatically
driven double-acting actuator operating a 180° rotating product take-off valve of the
settling leg of a loop reactor.
Finally, the invention relates to a loop reactor comprising a settling leg, a 180° rotating
product take-off valve located at the end of the settling leg, the 180° rotating product take-
off valve being operated by a pneumatically driven double-acting actuator, the pneumatic
system being regulated by a system comprising pneumatic control valves, characterised in
that the control valves are V-ball valves.
Preferably, the control valves are automatic control valves.
Brief Description of the Accompanying Drawings:
Figure 1 is a schematic diagram of a loop reactor with two settling legs and their control
system.
Figure 2 is a schematic diagram of the control system.
Figure 3 is a schematic diagram of the bottom part of a settling leg, showing the product
take-off valve and its actuating mechanism.
Figure 4 is a schematic diagram of the pneumatic system.
Figure 5 is a schematic diagram of the electronic control system.
The invention will now be described with reference to the drawings.
In the embodiment illustrated in Figure 1, polymerisation is carried out in a loop reactor
10. The monomer and the diluent are introduced respectively through lines 14 and 16
merging into line 13, and the catalyst is introduced through line 17. A propeller 11 linked
to a motor M circulates the mixture. As polymer particles are produced, they accumulate in

settling legs 22. The settling legs are each provided with a product take-off valve (PTO
valve or PTO) 23 connected to a conduit 20.
Referring now to Figure 2, there is shown a loop reactor 10 provided with two settling legs
22a and 22b, each provided with a PTO valve (respectively 23a and 23b) controlled by a
control unit 28.
Figure 3 shows the bottom of a settling leg 22, with a PTO valve 23 connecting it to
conduit 20. The PTO valve is a rotating valve, the rotation being controlled by a
mechanism M.
The PTO valve 23 of the settling leg 22 is only periodically opened, whereby the polymer
particles present in the settling leg 22 can pass into conduit 20. The opening time of the
PTO valve 23 should be closely controlled, in order that substantially all particles present
in the settling leg 22 pass into conduit 20, whilst substantially no monomer and diluent
leave the reactor 10.
Two types of PTO valves are in use. The most common relies on a 180° rotation of the
moving part of the valve, whereby the valve turns from closed (0°) to open (90°) then
closed (180°); during the next cycle, the valve rotates backwards. Valves with a 90°
rotation are also in use, whereby the moving part turns fronm closed (0°) to open (90°) then
backwards to closed (0°). The present invention provides an improved control system for
the first type of PTO valves.
PTO valves are generally pneumatically actuated. Figure 4a shows that each PTO valve 23
is provided with a double acting pneumatic actuator 40, which controls the speed at which
it turns. In the case of a 180° rotation, the speed at which the PTO turns is particularly
important in the sense that it directly controls the time it remains open.
The air flow sent to the double acting pneumatic actuator 40 is directed by a two-way
system 45 driven by a solenoid. Figure 4b shows one position of the system 45, wherein air
coming from conduit 50 is sent via conduit 42 into the actuator 40, returns via conduit 41
and exits through conduit 51. Figure 4c shows the other position of the system 45, wherein
air coming from conduit 50 is sent via conduit 41 into the actuator 40, returns via conduit
42 and exits through conduit 52.

Pneumatically actuated PTO valves were always controlled by manually adjusting the
outlet flow of air using control valves 61 and 62. There is provided a separate control for
each valve 61 and 62, in case the ball in the PTO valve 23 would turn at different speed in
each direction.
It has now been surprisingly found that control of a PTO valve 23 is improved by using
automatic control valves 61 and 62. In a preferred embodiment, V-ball control valves are
used. Such valves throttle using the rotation of a notched ball segment whose shape is such
that it allows at the same time to have a very precise control of the flow air for small
openings while having a full bore opening when needed. As an example of V-ball valve,
there can be cited a Worcester V-fiow control valve type V44-66UMPTN90.
It was not obvious to find appropriate control valves 61 and 62, because all control valves
tested up to now did not provide a precise control of the flow of air, taking into account
that the amount of air in the actuator 40 is relatively small. More importantly, it was not
obvious that operation of the reactor 10 would be more stable.
The use of automatic control valves provides several advantages with regard to a better
reliability of the PTO valves. Indeed, the frequent operation of the PTO valves, such as
every 15 to 90 seconds, leads to the wear of said valves which then operate slower. This
effect is immediately compensated by an automatic increasing of the amount of air needed
by the actuators. An automatic control of the amount of air needed by the actuators avoids
that the PTO valves get stuck in an open position. The use of automatic control valves
allows also a more precise control of the amount of air entering into the actuators than the
manual control valves do. When using manual control valves, there is always a risk that
when reducing the amount of air entering into the actuators, the PTO valves finally get
blocked in an open position leading to the depressurisation of the reactor. This may occur
with die first reactor of a double loop system when long opening times of the PTO valve of
said reactor are needed.
The use of automatic control valves and of 180° rotating PTO valves allows a good control
opening time of said PTO valves. This could not be achieved in the same way by using 90°
rotating PTO valves.

It has also been found that the inner volume of conduits S1 and 52 had to be reduced to the
maximum possible without creating a restriction to airflow. Conduits 51 and 52 have a
diameter ranging from 1.27 cm (1/2 inch) to 2.54 cm (1 inch), preferably said conduits
have a diameter of about 1.9 cm (3/4 inch). Conduits 51 and 52 have a length of less man
150 cm, preferably less than 100 cm. In a most preferred embodiment, conduits 51 and 52
have a diameter of about 1.9 cm (3/4 inch) and a length of about 20 cm between the system
45 to the automatic control valves 61 and 62.
Referring now to Figure 5, there is shown a preferred embodiment of the control
mechanism. The PTO valve 23 is provided with sensors 71 and 72, located in the double
actuating actuator, which indicate the position of the valve 23. Information from the
sensors 71 and 72 is sent respectively via transmitter 73 and cables 74 and 75 to a
computer 76 to determine the rotation time of the PTO valve. The rotation time of the PTO
valve is sent to a rotation controller 79, which also receives a set point for rotation time 81
of the PTO valve from the operator. Depending on the difference between the rotation time
of the working PTO valve and of the desired rotation time introduced by the operator, a
signal 82 is sent to the control V-ball valves, the opening of the V-ball valve either
increases by 1% at every cycle when the rotation time is slower than the operator set point
or decreases by 1% when the rotation time is faster than the operator set time.
The set point of the rotation time of the PTO valve may be adjusted manually by the
operator or controlled by the system as a function of the reactor pressure drop at each
opening of the reactor.
EXAMPLE AND COMPARATIVE EXAMPLE
A loop reactor was fitted with a system according to the invention. The loop reactor had
the following characteristics:
- nominal capacity: 5.5 tons/hr.
- volume: 19 m3
- number of settling legs: 4
- size of the settling legs: 20.3 cm

- size of the flash lines: 7.6 cm
- size of the PTO valves: 5 cm
The double acting actuators 40 of the PTO valves 23 were each provided with a control
system according to Figure 4. The conduits 41 and 42 had a 1.27 cm (1/2 inch) diameter
and a 3 m length. The automatic control valves 61 and 62 were Worcester V-flow control
valves type V44-66UMPTN90 with a Cv of 8, connected to the system 45 by conduits of
1.9 cm (3/4 inch) diameter and 20 cm length.
The stability of the operation of the reactor was measured in regard of the variations of the
pressure measured in the reactor. The reactor operation was very stable. Indeed, said
variations were lower by 25% when compared to those of a comparative reactor equipped
with control valves 61 and 62 of the manually controlled type, the other characteristics of
the comparative reactor being the same as those of the example. In addition, in 1he
comparative reactor, the capacity of each settling leg was lower by 10 %.

WE CLAIM:
1. A process for polymerisation of olefins comprising :
(a) polymerising olefins in a liquid diluent to produce a liquid slurry containing
particles of normally solid polymer within a loop reactor;
(b )allowing the polymer to settle in a settling leg; and
(c) periodically opening a 180° rotating product take-off valve located at the end of
the settling leg to allow a charge of particles to flow out of the settling leg, the product
take-off valve being operated by a pneumatically driven double-acting actuator, the
pneumatic system being regulated by a system comprising pneumatic control valves
characterised in that the control valves are V-ball valves.
2. The process of claim 1, wherein the control valves are automatic control valves.
3. Loop reactor (10) comprising a settling leg (22), a 180° rotating product take-off
valve (23) located at the end of the settling leg, the 180° rotating product take-off valve
being operated by a pneumatically driven double-acting actuator, the pneumatic system
being regulated by a system comprising pneumatic control valves, characterised in that the
control valves are V-ball valves.
4. Loop reactor according to claim 3, wherein the control valves are automatic control
valves.



The inventions discloses a process for Polymerisation of olefins comprising : (a)
polymerising olefins in a liquid diluent to produce a liquid slurry containing particles of
normally solid polymer within a loop reactor; (b )allowing the polymer to settle in a
settling leg; and (c) periodically opening a 180° rotating product take-off valve located at
the end of the settling leg to allow a charge of particles to flow out of the settling leg, the
product take-off valve being operated by a pneumatically driven double-acting actuator,
the pneumatic system being regulated by a system comprising pneumatic control valves
characterised in that the control valves are V-ball valves.
The invention is also for a loop reactor for carrying out said polymerisation.

Documents:


Patent Number 246134
Indian Patent Application Number 2044/KOLNP/2006
PG Journal Number 07/2011
Publication Date 18-Feb-2011
Grant Date 15-Feb-2011
Date of Filing 20-Jul-2006
Name of Patentee TOTAL PETROCHEMICALS RESERCH FELUY
Applicant Address ZONE INDUSTRIELLE C, B-7181 SENEFFE (FELUY)
Inventors:
# Inventor's Name Inventor's Address
1 VERLEYSEN MARK KARDELAAN 92, B-2180 EKEREN
PCT International Classification Number B01J 19/24
PCT International Application Number PCT/EP2005/050566
PCT International Filing date 2005-02-09
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 04100577.8 2004-02-13 EUROPEAN UNION