reduced AA regeneration. Because today the first melt to
resin project is still under execution one has to wait until this plant will be
started up and the first results from the field are available. Besides all skepticism
this technology will be one of the further polyester process developments which
will become of significant impact to the polyester industry.
3. Direct converting of melt to preform or yarn
- Advertised direct performing processes of
Uhde-Inventa-Fischer and Zimmer-AG
The advertisement of the direct preforming or melt to preform process was actively performed by the leading engineering companies during the last
year. On the occasion of 9th World Congress Polyester PET Chain in
Zurichin 2004 Uhde-Inventa-Fischer gave the public the possibility to observe
the melt to preform pilot facility in Domat/Ems. Zimmer-AG demonstrated its
direct performing to selected customers. Several companies are possessing
respective process patents like USP 5,656,221 [6] and DE 10356298 [1] from Zimmer-AG,
USP 5,656,719 [6] from Uhde-Inventa-Fischer or WO 97/31968 [1] from Eastman.
To transfer this innovative process to the industry two main
problems are still existent. First problem is the melt distribution and preform processing logistic. Different to direct spinning which is the paradigm process each high output preforming machine is consuming between 2000 and 5000 kg melt per hour.
This is a factor x 20 -250 compared to spinning where each spinning position is
processing between 20 and 100 kg/h. Each stop of one performing machine is
causing significant melt flow differences and process discomposure which are in
DE 10356298 [1] suggested to be compensated by a complicated side stream
cutting and melt recycling system. This could mean the continuous melt phase process connected to a direct preforming plant would be in general less stable and the preform producer becomes at the same time a resin producer with unpredicted amounts of
granulate. May be the solution might be another way around when in the future a
resin producer who is running a melt to resin process will connect one or two
high output preform machines to produce a certain amount of standard preforms.
- AA-scavenger - the still existing hurdle
The second and more severe problem is the removal of
acetaldehyde. For the time being most of the developments are focussing on the
addition of AA scavenger. But unfortunately these substances are mainly of
smaller molecule size which permits their diffusion from bottle wall to the
packed liquid. Other disadvantages of the scavenger technology are the running
additive costs and the tendency of those nitrogen-based additives to
discoloration in presence of air and at elevated temperature during recycling.
Because AA is a highly volatile substance one should not forget the physical
AA-removal via vacuum, surface renewing or gas stripping like described in USP
5,656,221 [6] and WO 97/31968 [1]. As an outlook about direct preforming technology one can sum up that all necessary technology parts are available today.
Missing is the entrepreneur who will locate the right combination of technologies
together with intelligent plant operation and available market potential.
- Direct spinning of tire cord
Another interesting field of high melt viscosity polyester
is direct spinning of tire cord. Here an Intrinsic Viscosity of 0, 90 1, 05
dl/g at the outlet of the finisher is desired. Also this technology is executed
in production units of about 40 60 t/d which are still running in the US and France. Problems here are the long time performance especially regarding reactor fouling,
increasing discoloration and creation of black spots and the desired low level
of carboxyl end-groups in the yarn. Reactor fouling could be terminated by
applying latest melt phase technology existing of whipped wall finisher. That
equipment is complicated and expensive compared to the common
SSP/extrusion-technology. The reduction of COOH groups is a hurdle similar to
acetaldehyde in bottle grade. Termination of COOH-groups applying additives
like imidazoles or oxazolines is possible but it makes the process more complicated and expensive. And similar to direct preforming there is a conflict
between tire cord production related plant size and economically feasible plant
size of polycondensation facilities. Economical short term calculations with
amortization periods of 4 5 years as they are often applied for new
installations are not applicable to exculpate the relatively high investment.
