The Catalyst Review July 2024 - 9

SPECIAL FEATURE
new donor, activator and catalyst formulations
provides a very versatile PO production platform.
CPChem has responded with a similar design using
a multi-zone patented loop reactor, to produce
multimodel resins comprising HDPE, MDPE, LDPE,
LLDPE or any combinations as a homopolymer or
copolymer, particularly suitable where lower amounts
of gels are required such as in the use for pipe. This
patent although quite detailed in its engineering
design provides less useful information for a lack
of production examples. Borealis's patent takes a
slightly different but more comprehensive approach
presenting a double cone gas phase reactor design,
with production examples, which provide more details.
The advantage of this new process is to produce
resins with a much narrower particle size distribution
(using a system of three cyclones connected to the
reactor zones) which provides a more consistent and
homogeneous resin product (see Figure 4). There are
several intrinsic advantages in that because it contains
Figure 4 Borealis Double cone Reactor Schematic.
Source: TCGR 2020
no mixing devices, no disengagement zone and in the gas
phase area no distribution plate, allowing for higher space time
yields and small reactor volumes compared to conventional
gas phase fluid bed reactor designs. Borealis states that
the gas-solids flowdynamic pattern follows fast fluidization
conditions, which improves the gas-solids mixing capabilities,
the polymer production and reduces the segregation
phenomena in the gas phase reactor along the three different
reactor zones.
● Super-Condensed Mode in Gas Phase Reactors for LLDPE
ExxonMobil described in the mid-1990s the so-called
Super-Condensed Mode of operation in a gas phase fluid
bed PE process in which an inert condensing agent (ICA)
such as isopentane is added to the reactor. The isopentane
is condensed in the cooling circuit and is fed back to the
reactor as a liquid, increasing heat removal potential through
the latent heat of evaporation. This has a drawback in production of low-density grades in that, at high levels of condensate,
the isopentane swells the polymer particles, making them sticky and increasing the risk of sheeting and lump formation. Many
HFCs (hydrofluorocarbon) are anti-solvents for polyolefins so that the polymer is not swelled and cannot become sticky, thus
increasing the safe level of condensate in the reactor and increasing plant output potential. ExxonMobil describes in a patent
an advance of using two or more ICAs that increase production rate and increase grade flexibility, controlled by the vapor
pressure (See Figure 5).
Figure 5 ExxonMobil Increased Production Rate with Mixed ICA.
Source: TCGR 2020
● Very Large-scale Bulk Slurry PP Process
Large loop-reactors for PP bulk slurry process with single-line capacities of 600,000 to 800,000 tons/yr are now feasible.
The process line comprises two loop reactors connected in series, with each reactor including 6 to 8 legs, for a productivity
of about 100,000 tons/yr per leg. The process can produce bimodal grades as might be required for high crystallinity and
stiffness, or for an easier and faster processing. Production at this scale would obviously lead to lower production costs
but would require great attention to plant reliability and on-stream time, as lost production would have a large impact on
profitability. As such, the industry trend has reverted to compact designs, giving higher versatility using reactor's-controlled
zones.
The Catalyst Review
July 2024
9

The Catalyst Review July 2024

Table of Contents for the Digital Edition of The Catalyst Review July 2024