9. "Quo vadis polyester catalyst?"

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162 CHEMICAL FIBERS INTERNATIONALVolume 54, June 2004RAW MATERIALSTable 1 Quality, process and handling problems of currently used antimony catalystsPropertyEffect or current situationA: catalyst puritywide range of Sb2O3sources with a broad span of impurity levels and impurity compositions, main impurities are As, Pb, Se, Bi, Fe, Ni,Cu, SO42-, Cl-, Sb2O5, Sb-metal, inconsistent levels not seldomB: chemical uniformity Sb2O3Sb2O5and Sbmetalby disproportion, amount depending on production route and purificationlow, good and excellent qualities in the marketSb(CH3-COO)3good - excellent qualitySb[O(CH2)2OH]3good - excellent qualityC: catalytic efficiencypolycondensation melt phase150-300 ppm Sb necessary to increase IV during polycondensation by 0.15-0.25 dl/g and hourSSP150-300 ppm Sb necessary to increase IV by 0.012-0.025 dl/g and hourD: precipitationdepending on the process stage and other additives main antimony precipitation is antimony metal, antimony phosphate and antimony poly-oxid-hydrates ?all precipitated matter acts as crystal nuclei and is causing haze ?fine Sb precipitations can act as flocculation accelerator to TiO2E: volatilityall EG condense circuits during melt phase production containing substantial amounts of antimony, antimony losses in a range of 10%, in closed loop EG recycling reuse of the catalyst and zero lossesF: discolorationespecially at high Sb-concentrations > 250 ppm Sb metal polymer gets the typically greenish to greyish-green hueG: deposits black shells and layers at all inner walls of melt guiding tubes, vessels, valves, dies and others ?black spots in products / filter plugging H: Sb-oligomersspinning smoke contains high content of Sb-oligomers?deposits around spinnerets, egg shells containing high amounts of antimonyI: leaching out during wastewater of wet dyeing processes might contain higher amounts of processing and usageantimonyBUT: water stored in PET bottles will contain 1 ppb or less Sb,EEC limit/Japanese recommendation is < 20 ppb Sb in drinking water,many natural water sources contain more than 1 ppb SbJ: incineration off-gas contains Sb-oxide residues and needs to be purifiedIt is nearly a decade ago now since Ak-zo researchers introduced new antimonyfree titanium based catalyst called "C94"to the public. Especially large polyesterproducers feared too much attention onan imaginary environmental problem at-tributed to the old and docile antimonycatalyst. At that time, the impact of polit-ically green ideas was still on the as-cending star and many people, especial-ly from the food container industry, wereworried about a possible sudden scan-dal caused by a "may be" impact of anti-mony to public health. For the polyesterchemists this signal came at the timewhere most of the important secrets ofthe polyester synthesis where unveiledand research money flowed to life sci-ence and e-business developments. In-terestingly, these unfounded environ-mental and health fears of the publicstarted a significant research movementtowards of antimony free catalystsaround the world, and polyesterchemists received the last chance for thetime being to step down to the mysteriesof metal complexes and ?-systems.The disenchantment came to all whostarted under the flag of earning lots ofmoney immediately with a new catalystand today still more than 90 % of theworld polyester production is made byadding 150-300 ppm antimony whetheras antimony oxide, antimony acetate orantimony glycolate. All the same, themove is to finally establish a new cata-lyst. The emphasis is on a better catalystwhich means firstly a more economicalone and secondly a catalyst, whichsmooths out the smaller and larger in-conveniences of antimony, which the in-dustry has become accustomed to overthe last half century of industrial poly-ester production.It should be taken into account that ourindustrial environment has drasticallychanged and only most easy handling instant or "plug and play" catalysts willmake the race. Plant management doesnot like to buy a whole new productiontechnology which might cause moreheadaches than cure them, even in lightof the fact that continuous plants up to800 tons/day capacity and a completelyclosed loop of internal glycol recyclingare running nowadays, and the changeover to a new catalyst is bearing highcapital risks. The new catalyst shouldprovide generic advantages over thestate of the art antimony catalysis.In Table 1 the most important and knownquality and process problems caused byantimony are shown.These points will enable us to define themain requirements for an acceptablenew polyester catalyst, which are as fol-lows:• less or at least same catalyst cost perton of polyester compared to antimony•easy to handle, instant application,plug and play•no FDA and EU hurdles, no poisons,no heavy metals •all registrations such as Einecs andTosca available•same or better polymer color and clarity•chemically defined, pure substance,consistent composition•no precipitation in the polymer•no shells, deposits or black spots onreactor walls or melt tubes•no remarkable volatility or losses dur-ing polymer production•no negative impact to the closed loopEG recovery in CPU•no sublimation during processing likespinning, performing and bottle blowing•same or better behavior in all down-stream operations.Quo vadis polyester catalyst?U.K. Thiele, Dr. Thiele Polyester Technology, Bruchköbel/GermanyAll together these needs are a real chal-lenge for all work in this field, and also asubstantial driving force to improve poly-ester technology.Publications, conference papers andpatents together with the knowledge andnetworking around the polyester indus-try are the sources for the following sta-tus analysis about important and devel-oped new polycondensation catalysts. Afirst summary was made in 2001 [1]where most of the new developmentswhere premature and Japanese compa-nies had not published their major offen-sive on the catalyst topic. Meanwhile,there are a variety of companies whichalready offer the new catalysts as com-mercial products to the industry. There isanother handful of companies which areactive in this field but which do not offertheir new catalyst to the public, whereassome of them are cooperating with se-lected customers based on licenseagreements. In Table 2 the commercial-ized catalysts are summarized.In Table 3 catalysts are listed which areknown to be under internal development.Chemical base and the status of devel-opment are extracted from publicly ac-cessable literature and patent informa-