Figure 3: WO 03046045 Method and Device for Production Highly Condensed Polyesters in the Solid Phase

By assembling fluid bed pre-crystallizer and second crystallizer in parallel to the SSP tube and conveying the hot crystallized chips to the top of the SSP tube the building height might be also possible to be reduced.

2. High viscosity resin without SSP and its further treatment

• Technology status of different vendor companies

Within the last two years we are observing conflicting statements regarding the best way to produce polyester resin of high IV and low AA for packaging. As seen in the first chapter there is significant cost saving potential in some new SSP technology. At the same time there is increasing advertisement about the direct conversion of the melt to the desired processing viscosity for bottles which is between 0, 75 0, 85 dl/g.

The knowledge to polymerize polyester in the melt phase up to an IV of 1, 00 dl/g is more than 30 years old. For instance published Zimmer-AG several high IV-reactor process principles which are executed as well in high IV PBT production as in tire cord direct spinning [4]. With further development of finisher technology meanwhile high viscosity melt phase processes of high capacity are offered from the leading engineering companies. Two technical problems for high IV melt phase processes are still left. First problem to be solved is to compete with the meanwhile huge melt phase plant capacity which is at normal IV of 0,60 dl/g safely between 800 and 1200 t/d. And the second problem to be solved is how to get rid of the acetaldehyde.

The solution of the first problem is on a good way because Uhde-Inventa-Fischer announced on July 14, 2005 - that its Melt-To-Resin-technology in a capacity of 200 000 t/y will in part be utilized in the recently announced expansion of the DAK Americas' Cape Fear Manufacturing Site near Wilmington, N.C. (USA) [5]

• Direct crystallization and AA removal

For the second problem to remove the AA are different methods of resolution in process. When transferring the polymer melt to chips one is receiving under normal strand cutter conditions amorphous granulate which is for the processing in preform machines to crystallize anyhow. It is self evident to combine now the cutting and the crystallization step to gain the heat of the polyester melt to trigger the crystallization process and to remove at the same thermal treatment the main portion of AA. This idea was base of several patents in the past like direct crystallization by stretching in USP 5,292,865 [6] or in connection to a standard cutter in EP 0822214A3 [1] where the melt is only cooled to a temperature between 160 and 220C where the crystallization is taking place. Similar approaches are described in PCT-WO-EP 00/06691 [1] and WO 94125239 [1]. The usage of this principle and its adaptation to under water die face pelletizing is described in WO 2005044901A1 [1]. It will be interesting to see which of the patented ideas will finally be outlived as granted.

Independent on technical lay out the high viscosity polycondensation has to be combined to the direct crystallization because there is at one side the need to reduce the acetaldehyde content which is possible only at elevated temperature and at the other side the PET resin granulate must be dealt crystallized to enable the simple drying prior preform production. So the removal of acetaldehyde is possible during cutting and crystallization and during predrying prior preforming. Knowing the strong demand regarding low acetaldehyde for water packaging it would be advisable to remove it as much as possible prior trading which means on needs residence time and gas treatment where we are back to a tube reactor, a gas circuit and respective equipment which is similar to simple drying. To avoid or minimize this equipment another way out is the addition of AA-scavenger which includes drawbacks like running scavenger cost and the possible diffusion of scavenger traces to the packed liquid. Another way to reduce AA is described in USP-Appl. 20050014929 [6] and USP-Appl. 20050049391 [6] by adding a catalyst during the melt phase which destroys acetaldehyde and reduces in this way the overall AA- content.

Melt to resin process is of advantage from downstream processing quality aspect especially because of the relatively low degree of crystallization of this polyester resin granulate which provides gentle melting and