1 SUMITOMO KAGAKU 2009 -IIIntroduction Polypropylene (PP) has the physical characteristics of a low specific gravity, rigidity, heat resistance… [619604]

1 SUMITOMO KAGAKU 2009 -IIIntroduction
Polypropylene (PP) has the physical characteristics
of a low specific gravity, rigidity, heat resistance andsuperior workability. In addition, since it is compara-tively low in cost, it is used in a variety of applications,such as films, industrial components for automobiles,furniture, etc., and miscellaneous goods. It has beenmore than 50 years since 1954, when G. Natta et al. ofItaly were successful in synthesizing high molecularweight, highly crystalline PP,
1)and the total worldwide
demand for PP has currently reached an amount ofapproximately 47 million tons (prediction for 2008).However, replacement of other materials and resins isprogressing even more, and moving forward, the fore-cast is for the highest growth rate among general pur-pose resins at an average of about 6% per year.
2)
This flourishing of the PP market has been support-
ed by the large improvements and simplification in themanufacturing process that had been accomplishedwith the leaps in catalyst performance. Furthermore, inaddition to the characteristics of PP itself describedabove, the fact that there have been large improve-ments in the transparency and impact resistance at lowtemperatures through copolymerization with ethyleneand other alpha olefins has probably been an importantfactor. With the increase in the level of requirementsfor quality in recent years, a variety of ideas and con-
trivances have been integrated into the manufacturingprocess for PP. In this paper, we will give a summary ofthe changes and the current state of the PP manufac-turing process based on information in the importantpatents and literature along with technologies devel-oped by Sumitomo Chemical.
Changes in the PP Manufacturing Process
The PP manufacturing process is mainly made up of a
raw material refining process, polymerization process,aftertreatment process and granulation process. The rawmaterial refining process is the furthest upstreamprocess and is a process for eliminating minute amountsof impurities that affect the process, such as water, oxy-gen, carbon monoxide, carbon dioxide, carbonyl sulfideand the like, from the propylene and other monomers aswell as the solvents and other raw materials and auxil-iary materials used. Moreover, this process may be setup at a raw material manufacturing plant positionedupstream of the PP manufacturing plant, but in eithercase, it is a fundamentally necessary process for stabi-lization of the overall process. The polymerizationprocess is a process for polymerization that brings thepropylene and, if necessary, ethylene and othermonomers into contact with a catalyst having polymer-Review on Development of
Polypropylene ManufacturingProcessSumitomo Chemical Co., Ltd.
Process & Production Technology Center
Hideki S ATO
Hiroyuki O GAWA
Polypropylene (PP) is a typical commodity plastic and has been widely used in many application fields
including packaging films, industrial components and miscellaneous goods, due to its excellence in propertiessuch as stiffness, heat resistance and processability in addition to light weight material density and also arelatively low price. The continued demands from the market for higher performances have stimulated,particularly in recent time, the improvement of PP manufacturing processes with newly created ideas. Thisreview describes, mainly based on the information published in literature and patents, an outline of thedevelopment history of PP manufacturing processes and an introduction to recent progress, including our owntechnologies.
This paper is translated from R&D Report, “SUMITOMO KAGAKU”, vol. 2009-I I.

2 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
ization activity. Most of the main industrial catalysts are
in a granular shape. The main catalysts are mostly in theform of secondary or tertiary particles of several tens ofµm that are aggregations of primary molecules havingdiameters of several hundred angstroms. The polymer-ization reaction occurs at the active points of the catalystparticles, and the PP that is formed precipitates out, andthe catalyst splits into primary particles. However, thereare few deviations in the shape of the catalyst, and thisforms PP particles that resemble the original aggregatedcatalyst shape.
3)The aftertreatment process is a process
for eliminating catalyst residue, the solvent and atacticpolymers (AP: noncrystalline polymers where themethyl groups of propylene units are arranged irregular-ly on the chain), which are components that are unnec-essary, from the PP particles obtained in thepolymerization process. Of these, the operation for elimi-nating the catalyst is known as deashing.
In addition, when a solvent is used in the polymeriza-
tion process, a process for recovering and purifying itis included. The granulation process is the furthestdownstream process, and it is a process for meltingand kneading additives and fillers into the PP particlesthat have undergone the after-processing and formingpellets.
In recent years, there are cases where large diameter
PP particles are shipped directly without granulationthrough improvements in the catalyst performance,methods of stabilizer distribution, etc. However, this islimited to a few examples still, and it has not come tothe point of completely eliminating the granulationprocess.
4)Moreover, storage, packaging and shipping,
etc., are indispensable further downstream in commer-cial plants, but since they are not unique to PP manu-facturing processes, we will not touch on them in thispaper.
Of these processes, there have been particularly
large improvements in simplifications for theaftertreatment process, such that they can be cited asa representative example of advances in chemical man-ufacturing processes. The PP manufacturing processcan be divided into three generations, the first genera-tion (deashing and AP removal), second-generation(non-deashing or non-solvent) and third-generation(non-deashing and non-AP removal) according to theseadvances in technology. In addition, classification canbe done according to the polymerization method intosolvent processes, bulk polymerization processes andvapor phase polymerization processes. Fig. 1 showsthe changes in the PP manufacturing processes
arranged according to the processes required for therepresentative polymerization process for each genera-tion. Moreover, the furthest upstream raw materialrefining process and the downstream granulationprocess, which are fundamentally required in all ofthese processes, are omitted in Fig. 1 .
We will give a summary of these changes in PP man-
ufacturing processes, using representative polymeriza-tion processes that Sumitomo Chemical has developedfor each generation.
1. Solvent polymerization process
Since the PP particles are dispersed in the form of a
slurry in the solvent with the solvent polymerizationprocess, this is also called the slurry polymerizationprocess, and it was a representative manufacturingprocess that was the main current in the first genera-tion. Fig. 2 shows the first-generation solvent polymer-
ization process developed by Sumitomo Chemical.
5)
The Sumitomo Chemical solvent polymerizationFig. 1 Polypropylene manufacturing process1st Generation
Solvent polymerization process
2nd Generation
a) Solvent polymerization process (Non-deashing)
3rd Generation
Vaper phase polymerization process (Non-deashing, Non-AP)Drying PP Degassing DeashingMonomer Recovery
Solvent Recovery
b) Bulk polymerization process (Non-solvent)AP, Ash
AP
AP, AshPolymerization
Drying PP DegassingMonomer Recovery
Solvent RecoveryPolymerization
PP ExtractionMonomer Recovery
Polymerization
PP Polymerization

3 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
process was one that initially introduced technology
from the Italian company Montecatini, which was thefirst in the world to industrialize PP, but subsequentlySumitomo Chemical made a large number of technicalimprovements of its own and licensed them to a num-ber of companies.
Solvent polymerization used an autoclave provided
with an agitator for the reactor, and the conditions area temperature of 50 to 80 °C and pressure of approxi-
mately 1 MPa. It is carried out in the presence of hexa-ne, heptane or another inert hydrocarbon solventwhere polymerization inhibitors have been eliminated.
In the first generation, PP particles were obtained
after going through separation and recovery of unreact-ed propylene, deashing (decomposition and elimina-tion of the catalyst using alcohol), washing in water,centrifugal separation and drying for the aftertreatmentprocesses. In addition, a process for separating the AP,which was produced as a secondary product at 10% ofthe amount polymerized was necessary at one time,and therefore, the AP was separated using its solubilityin the polymerization solvent. Not only was thisprocess complicated, but also the cost burden waslarge because of the separation and purification of theparticularly large amount of alcohol and water used indeashing from the solvent that was recovered. Subse-quently, in the second generation, the deashingprocess was omitted because of improvements in cata-lyst activity, and the large amounts of alcohol and waterbecame unnecessary.While the process was simplified in this manner, the
omission of the process for eliminating secondary APhad to wait for the advent of superior catalysts thatgave a high level of stereoregularity that made possiblea reduction in the proportion of secondary AP generat-ed in addition to increasing the polymerization activity.
2. Bulk polymerization process
The bulk polymerization process is also called the
mass polymerization process, and solvents such ashexane and heptane are not used. It carries out poly-merization in liquefied propylene. It aims at simplifyingthe process by also using the propylene monomer,which is the raw material, as the solvent.
Since no solvent other than the liquefied propylene
is used, the energy costs for the steam, electricity, etc.,required for recovering the solvent may be greatlyreduced. The bulk polymerization process is a processthat is representative of the second generation, but itcoexisted with the first generation, and even now whenthe third generation is the main current, there aretimes when it is advantageous for the manufacture ofpropylene homopolymers. It plays a part in a variety ofcommercial process groups Fig. 3 shows the second
generation bulk polymerization process developed bySumitomo Chemical, but if it is compared with the firstgeneration solvent polymerization process ( Fig. 2 ), we
can see that it has been made much simpler. This Sum-itomo Chemical process has been licensed to severalcompanies, and has been evaluated highly.
Fig. 2 Schematic flow diagram of Sumitomo ’s solvent polymerization processCompressor
Drainage AP Heavy
Fraction
Solvent RecoveryAlcoholReactorDeashing
TankDryerSolvent
Recovery
PPN2
DegasserCentrifugeWater
Slurry
TankSolventCatalyst
Propylene
Propylene
Recovery

4 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
It is characterized by the use of a continuous extrac-
tion tower that was developed by Sumitomo Chemicaland has a special internal structure.
5)Furthermore, in
addition to using a high performance catalyst that Sum-itomo Chemical developed itself, we were successful inbeing the first in the world to greatly simplify deashingand the secondary AP elimination process by providinga countercurrent washing system that uses refined liq-uefied propylene.
The typical operating conditions for the bulk polymer-
ization process are a temperature of 50 to 80 °C and a
pressure that is roughly the vapor pressure of propy-lene. It changes according to the temperature, but is in arange of 2 to 4 MPa. Since liquefied propylene, which isa monomer, is used for the solvent, the polymerizationreaction is rapid, and the retention time is shortened.Since the volumetric efficiency is greatly improved, thereactor size for obtaining the same production capacitycan be smaller than it was conventionally. However,even though there is high productivity, the heat elimina-tion surface area is insufficient for removing the poly-merization heat if the size of the device is reduced.Therefore, in the case of a stirred tank reactor, a specialexternal heat exchanger that implements measures forpreventing adherence of the polymer is used. On theother hand, loop reactors where the surface area forheat elimination can be increased relative to the reac-tion volume have become practical.
The bulk polymerization process is a process with
many advantages like these, but it is not suitable for themanufacture of the polymers known as impact copoly-mers. Impact copolymers are a mixture of a propylenehomopolymer component with a comparatively low mol-ecular weight and a rubber component, which is an eth-ylene-propylene copolymer with a comparatively highmolecular weight. This has improved impact strength at
low temperatures while at the same time maintainingthe rigidity, which is one of the superior original charac-teristics of PP, as much as possible. It is mainly used ininjection molding applications starting with automobilecomponents. Industrially, it is obtained by polymeriz-ing the latter following the polymerization of the for-mer, and during continuous production, individualreactors are required for polymerization of each of thecomponents. To polymerize the rubber component, thereaction composition must have a high ethylene con-centration, but if ethylene is dissolved in the liquefiedpropylene to the point of obtaining the required ethyl-ene concentration with bulk polymerization, the overallreaction pressure increases, so there have been almostno practical implementations. In addition, since therubber component is dissolved in the liquefied propy-lene, there is a problem with the limitations for poly-merization of the rubber component.
3. Vapor phase polymerization process
The vapor phase polymerization process falls under
the category of bulk (mass) polymerization processescarried out only with monomers in the broad sense, butsince polymerization is carried out in propylene gasrather than in liquefied propylene, it is handled as aprocess different from conventional bulk polymerization.It is positioned as a third-generation process, but the his-tory is longer than expected, and the technology alreadyexisted when first generation processes were the maincurrent. The vapor phase polymerization at that timewas inferior in terms of quality because there was noprocess for separating the very many AP secondaryproducts, and products were limited to special applica-tions. However, with the subsequent complete elimina-tion of deashing and AP removal operations because ofthe rapid improvement in catalyst performance, furthersimplifications were achieved in the process, and itachieved a position as the third generation process capa-ble of manufacturing high performance products withdiverse levels of quality. Fig. 4 shows the initial third-
generation vapor phase polymerization process devel-oped by Sumitomo Chemical for manufacturing impactcopolymers.
6)Manufacturing impact copolymers
requires at least two reactors, and a supply line for ethyl-ene, which is a comonomer, is installed for the secondstage reactor so that the rubber component can be poly-merized. Moreover, manufacturing is fundamentallypossible with one reactor for polymers other than impactFig. 3 Schematic flow diagram of Sumitomo ’s
bulk polymerization processAPPP
PowderCatalystRecycle Monomer
Propylene
Heavy
Fraction
Polymerization AP
SeparationPowder
SeparationExtraction Monomer
PurificationCompressor

5 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
narrow retention time distribution.
In the following, we will focus on the vapor phase
polymerization process and review the patent and refer-ence literature as well as the technology developed inrecent years, inclusive of technology developed bySumitomo Chemical, while focusing on the differencesin reactor types and configurations aimed at improvingthe uniformity of polymer granular structures accord-ing to required performance.
1. Improvement in uniformity in particles using
circulation type reactors
Improvement on the uniformity in the polymer parti-
cles produced is mainly aimed at controlling molecularweight distribution in many ways. In other words, sincethe physical characteristics such as the impact strengthof molded products can be improved, a high molecularweight for the PP is desirable, but on the other hand,processing is difficult. Therefore, it is necessary toinclude a suitable amount of low molecular weightcomponents for such improvements, and as a result,PP with a broad molecular weight distribution is desir-able. This concept itself is not original, but to obtain PPwith a broad molecular weight distribution, the molecu-lar weight has been varied during a series of reactionsin batch polymerization in the conventional process.Alternatively, a continuous polymerization methodwhere multiple complete mixing reactors are set upwith conditions that give different molecular weightsare simply connected has been used. However, sincethe productivity of batch polymerization is very inferi-or, its use is limited to special applications, and it hasnot been widely disseminated. Since there is also aretention time distribution in the polymer particles pro-duced with continuous polymerization, the molecularweight distribution varies with each particle. In addi-tion, it is difficult to avoid uneven distribution of com-ponents with different molecular weights within singleparticles. Fig. 5 shows conceptual diagrams of the poly-
mer particle structures produced in these processes.As is shown in Fig. 5 (a), the uneven distribution of the
various components in the polymer particles producedis an important problem where defects (causing reduc-tions in strength and problems with appearance) frompoor melting and mixing called fisheyes arise in theforming process particularly when there is a large dif-ference in the molecular weight between high molecu-lar weight components and the low molecular weightcomponents. To solve this problem, it is desirable tocopolymers. The typical operating conditions are a tem-
perature of 50 to 80 °C and a pressure in the range of 1 to
2 MPa. Various types of reactors, such as stirred tanksand fluidized beds, have been developed by various com-panies, but while there are small differences in construc-tion costs and variable costs, these are not determinersof the differences in the final product costs. The compe-tition between makers can be said to be mainly in thearea of product quality.
7)Along with the further improve-
ments to the process, Sumitomo Chemical has madegreat strides on the quality front by commercializing avariety of polymer designs based on our own high per-formance catalyst technology.
Current Status of PP Manufacturing Processes
With the increase in the level of performance
required for PP quality in recent years, a variety ofideas and contrivances have been integrated into themanufacturing process for PP. If we take a bird ’s eye
view of the trends in process development that focuson these improvements in quality, all of them are point-ing in one direction. In other words, while the configu-ration and conditions of the of the polymerizationreaction are varied to diversify the molecular weightdistribution and compositional distribution, attemptsare being made to hold heterogeneousness of the poly-mer particle structure produced that tends to occurwith this to a minimum.
There are roughly two directions for the specific
methods. One is improvement of uniformity of the poly-mer particles produced using a circulation type reactor,and the other is improvement in the uniformity amongpolymer particles produced by using a reactor with aFig. 4 Schematic flow diagram of Sumitomo ’s
vaper phase polymerization processCatalystRecycle Monomer
PP PowderPropylene
Ethylene
Powder Separation Polymerization

6 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
produce a polymer particle structure where the unifor-
mity in the particles is improved as shown in Fig. 5 (b),
and several measures for improvement have alreadybeen achieved.
In the following, we will introduce an example of the
development of a circulation type reactor as one exam-ple of this. The reactor (called external circulation flu-idized bed type reactor (1) in this paper) showing thisconcept in Fig. 6 can be thought of as an application of
an external circulation fluidized bed connected to a fastfluid bed (riser part) and a moving bed (downcomerpart) that are used in combustion furnaces and flu-idized catalytic cracking (FCC) devices in a PP manu-facturing reactor.
8), 9)
Since the gas flow rate in the riser part is high (0.8 to
5 m/s, particle terminal speed or greater), the coeffi-cient of heat transfer is large (a 30% increase over anon-circulating fluidized bed). It is said that as a resultthere is a large improvement in the energy consump-tion.
10)
However, the results on the quality of uniformity in
the particles may be thought of as meriting more atten-tion than these reductions in running costs. With thisreactor, the PP particles and gas that are dischargedfrom the riser part at high speeds are separated in thebuilt-in cyclone separator. Liquefied propylene is sup-plied from the top part, and the PP particles can beforced down into the downcomer part after the concen-tration of hydrogen, which is the chain transfer agentfor adjusting the molecular weight, is reduced by form-ing a gas barrier. Therefore, the low molecular weightcomponents are polymerized in the riser part with ahigh hydrogen concentration and the high molecularweight components in the downcomer part with a low
hydrogen concentration. The retention times in theriser part and downcomer part are short, and it is possi-ble to make the content of components with differentmolecular weights uniform in the particles by carryingout circulation polymerization repeatedly withoutreverse mixing.
10), 11)Moreover, this process was origi-
nally configured to have a reactor where the riser partand downcomer part were independent,
12)but subse-
quently, this was improved to an integrated type withthe loop shape described above. In addition, the exter-nal circulation fluidized bed type reactor (2) where anFig. 5 Schematic structure of polymer particle produced by two polymerization zone type reactor(a) Perfect mixing type reactorDistribution of
Composition/Molecluar Weight
wide wide
(b) Circulation type reactor (excluding impact co-polymer manufacturing)
wide nallow
nallow nallowDistribution of Residence Time Model Structure of Particle
(Red-color portion indicates schematically a part polymerized in the second stage.)
(c) Nallow residence time distribution type reactor (including batch type reactor)
Fig. 6 “External circulation fluidized bed type
reactor (1) ”Gas InletCatalyst InletProduct DischargeGas Outlet
Gas InletLiq. Monomer InletPowder Separator Zone
Downcomer ZoneRiser ZoneGas Barrier

7 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
external circulation function is configured for a conven-
tional fluidized bed reactor as shown conceptually inFig. 7 has been proposed.
13)
We have discussed examples of applications of exter-
nal circulation fluidized beds above, but several exam-ples of internal circulation fluidized beds have beenreported.
14)For example, as is shown conceptually in
Fig. 8 , an internal circulation fluidized bed type reactor
that is given an internal circulation function with a mov-ing bed provided in a conventional fluidized bed reac-tor has been proposed.
15)The fundamental thinking for
improvements can be assumed to be the same as forthe external circulation fluidized bed described above.It is possible to control uneven distribution of compo-nents with different molecular weights in the particlesby supplying liquefied propylene to the uppermost part
of the moving bed, forming a gas barrier and forminginternal circulation. In particular, since it is possible tofreely control the proportion of the retention time forthe moving bed, which polymerizes the high molecularweight components, and the fluidized bed, which poly-merizes the low molecular weight components, byindependently controlling the amount of PP particlesdischarged by the moving bed, polymer designs witheven more variety than with loop type external circula-tion reactors become possible.
These circulation type reactors can control the mole-
cular weight distribution variously, but it is also possi-ble to make various designs for the comonomercomposition distribution by also controlling thecomonomer concentration in each polymerizationstage in the same manner. However, when impactcopolymers are manufactured, the comonomers mustbe almost completely separated in the comonomerpolymerization stage, and it is difficult to use a circula-tion type reactor by itself. Therefore, while improve-ments in the uneven distribution in the polymerparticles produced are not achieved, the processes thatwill be discussed in the following aimed at producingpolymer particle structures with improved uniformityamong the particles like those shown in Fig. 5 (c) are
being developed.
2. Improvements in uniformity among particles
using narrow retention time distribution typereactors
For improvements in the uniformity among the poly-
mer particles produced, we can expect greatlyimproved results in quality when both a propylenehomopolymerization stage where the comonomers arealmost completely separated, mainly as in the impactcopolymers described above, and a polymerizationstage where the composition differs greatly when thecopolymerization stage has a high comonomer concen-tration are required. In the following, we will explainthe reasons why a narrow retention time distributiontype reactor is necessary, using the manufacture ofimpact copolymers as an example.
We have already discussed how continuous polymer-
ization of impact copolymers requires polymerizationof the comparatively low molecular weight propylenehomopolymer component and rubber component,which is a comparatively high molecular weight ethyl-ene-propylene copolymer, in separate reactors.
Fig. 7 “External circulation fluidized bed type
reactor (2) ”Gas InletGas Outlet
Catalyst InletProduct
DischargeLiq. Monomer InletGas Barrier
Product
DischargeGas InletLiq. or Gas
Monomer Inlet
Fig. 8 “Internal circulation fluidized bed type
reactor ”Gas InletGas Outlet
Catalyst
Inlet
Product dischargeLiq. Monomer Inlet
ValveGas Barrier

8 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
While ones with different configurations, such as
mixing tank types and fluidized bed types are used forcommercial production processes, the polymer parti-cles are normally mixed into a state close to completemixing in the reactors.
16)Therefore, in the two tank
continuous process, which is the most simple for pro-ducing impact copolymers, the polymers produced inthe end have a low mass ratio for the homopolymercomponent and the rubber component because of theretention time in each of the tanks, so they are mixeduntil it is high. If polymer particles with a high rubbercomponent content are included, it invites dispersionproblems during melting and mixing, and we havealready said that it causes a lowering of quality wherethe appearance deteriorates and the impact resistanceis lowered. The process has been improved with thegoal of narrowing the retention time distribution partic-ularly in the first stage to prevent a lowering of qualitybased on this mechanism.
A multi-tank device that increases the number of
continuous reaction devices connected in series hasbeen used to narrow the retention time distribution formanufacturing polymers with high quality from theconcept above.
However, at the same time, there is an increasing
demand for lowering costs along with increasing thePP performance, and there are limitations to the con-ventional method of just increasing the number of reac-tors. From this point of view, polymerization processesthat can narrow the retention time distribution for thepolymer particles with a smaller number of reactors arebeing developed. For example, a horizontal, mechani-cally stirred type reactor (1) like the one that showsthis conceptually in Fig. 9 (a) has been developed.
17)
This is one where the inside of the device is formed
into multiple partitions by dividers, and reverse mixingof the particles cannot be completely controlled. Whilethere is a range because of the retention time, it cannarrow the retention time distribution to the sameextent as one where 3 to 5 complete mixing reactorsare arranged in series with only one reactor.
18)
The horizontal, mechanically stirred type reactor (2)
for which the concept is shown in Fig. 9 (b) can be said
to be an improvement on the reactor described abovewith Fig. 9 (a). The dividers are installed at the top
rather than at the bottom, so mixing of the gas in thegas phase part above is controlled, and the controllabil-ity of the molecular weight distribution and composi-tional distribution can be improved.
19)However, thishorizontal, mechanically stirred type reactor has a
problem with deflection because of gravitational forceof the mixing shaft, so it is difficult to increase thescale. However, there has been success with increas-ing the size in recent years.
20)
On the other hand, there have been reports of form-
ing multiple chambers vertically with fluidized beds,for which the scale can be increased comparativelyeasily.
21)–24)In particular, along with increasing the
volume toward the bottom, which is the polymeriza-tion area, to make the retention time distribution atthe various stages uniform, the multi-stage fluidizedbed type reactor shown conceptually in Fig. 10 con-
trols reverse mixing by forming a multi-stage devicewith dividers at each stage.
24)These dividers are flat
heat exchangers, and the polymerization heat isremoved and the temperature made uniform at thevarious stages by providing a cooling jacket. Eventhough this device structure is extremely interesting,it is complicated, so we can assume that there will bedifficulties. In addition, since the gas flow pathbecomes smaller as we go up the stages, the gas col-umn velocity will be extremely fast at the upper stage,so we can assume that an individual gas discharge out-let must be provided for each stage.
In addition, since the particle diameter for the poly-
mer particles produced differs according to the degreeof particle growth, there have been reports of narrow-Fig. 9 “Horizontal, mechanically stirred type
reactor (1)(2) ”Liq. Monomer
Inlet
Gas InletGas OutletCatalyst
Inlet
Product dischargeHorizontal
Shaft AgitatorWeir Weir Weir
Liq. Monomer
Inlet
Gas InletGas Outlet Gas Outlet
Catalyst
Inlet
Product dischargeHorizontal
Shaft AgitatorWeir(a)
(b)Weir Weir
Gas InletLiq. Monomer
Inlet

9 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
ing the retention time distribution using particle classi-
fication.25)–29)
Among these, the example (called fluidized bed type
reactor with particle segregation zone in this paper)29)
developed by Sumitomo Chemical shown in Fig. 11 ,
sets up one integrated into a conventional fluidized bedtype reactor and forms drum-like stages with different
gas column velocities within the device. This is basedon a unique concept where short paths for polymer par-ticles that have not grown can be controlled by bendingthe particles using the differences in the gas columnvelocities. It has the important merit of making themodifications easy even with a conventional fluidizedbed reactor that has already been built.
Besides ones that are modifications based on con-
ventional devices such as the mixing tank types and flu-idized bed types above, the tubular type reactor shownconceptually in Fig. 12 , for example, has also been
reported.
30)This is a tubular type device where the
ratio of the length of the device to the diameter is 100or more, and even though there is solid-gas separationusing a cyclone at fixed distances and a circulation gasFig. 11 “Fluidized bed type reactor with particle
segregation zone ”Gas InletGas Outlet
Catalyst Inlet
Product DischargeInternalParticle Segregation Zone
Fig. 12 “Tubular type reactor ”Gas
Inlet
Catalyst
InletGas
Distributor
Fresh (co) monomer
Inlet
(Optional)Cyclone Separator Gas
Circulation
Fresh (co) monomer
Inlet
(Optional)Product
DischargeFig. 10 “Multi-stage fluidized bed type reactor ”Gas
InletProduct
DischargeN2 Gas
InletGas Outlet
Catalyst Inlet
Downcomer
Cooling Fluid
InletCooling Fluid
Outlet
Cooling
JacketSupplemental
Gaseous MonomerInlet
Surge VesselPlate Coil
Heat Exchanger
Gas Distribution PlateBlower

10 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
compressor, there is almost no reverse mixing, so the
retention time distribution is extremely narrow. How-ever, the fact that sufficient retention time cannot beassured with gas phase polymerization, which typicallyrequires several hours, because the retention time isabout 15 minutes even with a device length of 200 m isan important problem.
In addition, for example, we can also mention meth-
ods that use a moving bed type reactor developed bySumitomo Chemical.
31), 32)This is a process that uses a
non-circulating moving bed type reactor in the secondor later stages after growing polymer particles to anextent that does not melt and clump because of prob-lems with heat elimination. With this process configu-ration, it is thought that most of the retention timedistribution arises in the second or later stages and suf-ficient retention time can be assured.
Conclusion
In this paper, we have given a review of the changes
and current state of PP manufacturing processes,including technology developed by Sumitomo Chemi-cal, based on information in patents and the literature.We mainly focused on the trends in process develop-ment aiming at improving quality in particular, butbesides this, a variety of processes, such as many tech-nical improvements aiming at stable operation andprocesses
33)making high temperature polymerization
possible by improving the polymer particle andmonomer separation efficiency through operation inthe supercritical range for propylene, have been devel-oped. Even though a giant market has been formed forPP already, perfection of the manufacturing processesfor it has not been completed. Further progress isdesirable moving forward along with developing basictechnology starting with catalysts and various types ofperipheral technology to answer the demands from amarket that will not fail.
At Sumitomo Chemical, we are thinking in terms of
further polishing our own technology, which has beenbuilt up to this point and developing processes that pro-vide products that are attractive to the market.
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11 SUMITOMO KAGAKU 2009 -IIReview on Development of Polypropylene Manufacturing Process
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PROFILE
Hideki S ATO
Sumitomo Chemical Co., Ltd.
Process & Production Technology Center
Research Associate
Hiroyuki O GAWA
Sumitomo Chemical Co., Ltd.
Process & Production Technology Center
Senior Research Associate
(Present Post: Temporary Researcher)