Chemical Engineering April 2020 - 17

into the steam cracker at BASF's site in
Ludwigshafen in October 2018.
Recenso operates an industrialscale
pilot facility that uses its catalytic
tribochemical conversion (CTC)
process to convert municipal waste
into a liquid oil. In the process, metals,
stone and wet materials are first
separated from the waste. The resulting
material, predominantly plastic
films, foils, paper and some biomass,
is then fed to a slurry reactor, where it
is heated by friction to around 350°C,
and catalytically cracked into a pyrolysis
gas. The vapor is condensed
into a liquid oil that can be used as
a fuel, or as a feedstock to a steam
cracker, as is being done at BASF.
In a related project, Dow last August
reached an agreement with
Fuenix Ecogy Group (Weert, the
Netherlands; https://fuenix.com), for
the supply of pyrolysis oil feedstock,
which is made from plastic waste
(Chem. Eng., November 2019, pp.
12-14). The feedstock is being used
to produce new polymers at Dow's
production
facilities
at Terneuzen,
the Netherlands. The polymers produced
from this pyrolysis oil will be
identical to products produced from
traditional feedstocks, and as such,
they can be used in the same applications,
including food packaging.
Meanwhile, a process that directly
converts waste plastic into gaseous
building blocks is being developed by
a research group at Chalmers University
of Technology (Gothenburg, Sweden;
www.chalmers.se). This gasification
process avoids the need to first
convert plastic waste to a pyrolysis oil
that can be fed to an existing steam
cracker, and instead, directly cracks
the plastic waste into gaseous building
blocks that can operate in parallel
with existing crackers to make
new plastics. The new process could
transform today's plastic factories into
recycling refineries, within the framework
of their existing infrastructure,
according to the researchers.
The process is essentially a type of
steam cracking of the waste plastics.
Using experience gained from a firstof-its
kind plant that gasified biomass
into biomethane, the group has been
working to apply this technology - a
dual fluidized-bed (DFB) system -
for steam cracking of waste plastics.
" Through finding the right temperature
- which is around 850°C - and
the right heating rate and residence
time, we have been able to demonstrate
the proposed method at a
scale where we turn 200 kg of plastic
waste an hour into a useful gas mixture,
which can then be recycled at
the molecular level to become new
plastic materials of virgin quality, "
says Henrik Thunman, professor of
Energy Technology.
The experiments - reported in a
recent issue of Sustainable Materials
and Technologies - were carried
out at the Chalmers Power Central
facility in Gothenburg, using a DFB
system. The first commercial use
of a DFB-type system has been the
fluid catalytic cracking (FCC) reactor
in the petroleum-refining industry,
which uses gaseous feedstocks and
consists of two interconnected circulating
fluidized beds, explains Teresa
Berdugo Vilches, a postdoctoral researcher
in the Dept. of Space, Earth
and Environmental Energy Technology,
at Chalmers. " The DFB system
developed at Chalmers consists instead
of a bubbling bed connected
to a circulating fluidized bed, and it is
designed to handle solid feedstocks.
It differs from a conventional circulating
fluidized bed in the fact that it
has two reaction environments: the
bubbling bed that serves as a cracking
reactor of solid plastic particles,
and the circulating fluidized bed that
serves as a combustor, she explains.
" It was developed for gasification of
woody biomass and it has now been
applied for the cracking of plastics. "
" We are now moving on from the
initial trials, which aimed to demonstrate
the feasibility of the process, to
focusing on developing more detailed
understanding, " says Thunman. This
knowledge is needed to scale up the
process from a few metric tons of
plastic a day, to hundreds of metric
tons. That is when it becomes commercially
interesting, " says Thunman.
The process is said to be applicable
to all types of plastic that result
from our waste system, including
those that have historically been disposed
in landfills or at sea.
n
Gerald Ondrey
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Chemical Engineering April 2020

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