Scale-up and control of a multi-component emulsion polymerization system

Theron, Jacobus Petrus (2000-03)

Thesis (MScEng)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: ABSTRACT: A new emulsion (code name: NW 120) has been developed by Plascon on laboratory scale, for application in the paint industry. It is an environmentally friendly emulsion in which no coalescent solvent is used. It also has a core-shell morphology. Research was undertaken to scale-up (industrialize) the emulsion polymerization of NW 120. The use of a suitable pilot plant was investigated. An available bench-scale pilot plant (RCl, Mettler Toledo) was found to be very expensive. The reactors were very small (R:1.8 l) and the reactor set-ups (reactor, baffies and stirrer configuration) were not similar to the industrial size reactors used by Plascon. A fully computer controlled bench-scale pilot plant was subsequently designed and built at a fraction of the cost of the commercially available set-up. The reactor (5 I) was a scale-down replica (geometrically similar) of the industrial size reactors used by Plascon. The reactor was designed to also serve as a calorimeter. Very good control was achieved over the reaction temperature and addition rates of the monomers and catalyst. Heat loss and heat capacity models were derived for a variation in the reaction temperature between 82.5 - 87.5 °c in order to perform accurate energy balances (calorimeter) around the reactor. The accuracy of the calorimeter was verified at a reaction temperature of 85°C, by measuring the heat that evolved when a sodium hydroxide solution was diluted with water. The accuracy of the calorimeter was found to be extremely good. The pilot plant was commissioned with an industrially manufactured emulsion (code name: AE 446), well known to Plascon. The results obtained in the pilot plant reactor were very similar to those obtained for the full-scale manufacturing of AE 446. It was determined that if geometrical similarity between the pilot plant reactor and the industrial size reactor is preserved and if the correct process conditions (stirring speed, reaction temperature and addition rates of the monomers/catalyst) are maintained, then the direct scale-up of the production ofNW 120, from bench-scale to full-scale, would be possible. The reaction conditions were varied over a wide range, in order to find the optimum process conditions. The stirring speed was varied between 150 - 550 rpm. Shear sensitivity was observed at stirring speeds of 450 rpm and higher. The measured physical properties at 550 rpm were found to be unacceptable. The optimum stirring speed for the desired particle size and viscosity was found to lie between 150 rpm and 250 rpm. The reaction temperature was varied between 70 and 90 DC. The optimum reaction temperature was found to lie between 80 and 90 De. It was possible to successfully reduce the monomer addition time, and hence the reaction times, by increasing the addition rate of the monomers/catalyst, from 4 h to 2 ~ h. The method developed by Klein et al. (1996), for the scale-up of the stirring speed of emulsion polymerization reactions was used to determine the equivalent fullscale stirring speed. The scale-up of NW 120 was subsequently conducted at 85 DC, at a stirring speed of 35 rpm and the monomers/catalyst were added over a period of 4 h. The use of reduced reaction times were not considered in the first scale-up run since at that stage it was not clear whether the heat removal capability of the industrial size reactor would be adequate to cope with the increase in the evolved heat, associated with an increase in the addition rates of the monomers/catalyst. Very good results were obtained. The measured physical properties of NW 120 produced in the industrial size reactor were found to be almost exactly the same as in the pilot plant reactor.

AFRIKAANSE OPSOMMING: 'n Nuwe emulsie (kode naam NW 120) is deur Plascon op laboratorium skaal ontwikkel, vir die gebruik in die verfbedryf. Dit is 'n omgewingsvriendelike produk en geen oplosmiddels word gebruik vir die filmvormingsproses nie. Hierdie projek handeloor die opskalering (industrialisering) van die produksie van NW 120. Die gebruik van 'n geskikte loodsaanleg is eers ondersoek. Daar is gevind dat die beskikbare laboratorium skaalloodsaanleg (RCl, Mettler Toledo) baie duur was. Die reaktore is baie klein (:::::1.81). Die reaktoropstellings (reaktor, keerplate en roerder-konfigurasie) is ook nie in ooreenstemming met die industriële grootte reaktore wat deur Plascon gebruik word nie. 'n Ten volle rekenaarbeheerde loodsaanleg is ontwerp en gebou teen 'n breuk van die koste van soortgelyke kommersieel beskikbare opstellings. Die reaktor (5 I) is 'n skaalmodel (geometries gelykvormig) van die industriële grootte reaktore wat deur Plascon gebruik word. Die reaktor word ook aangewend as 'n kalorimeter. Baie goeie beheer oor die reaktortemperatuur, sowel as die toevoertempo's van die monomere en die katalis is verkry. Hitteverlies en hittekapasiteits modelle is afgelei vir variasies in die reaktortemperatuur tussen 82.5 - 87.5 °c om dit moontlik te maak om akkurate energiebalanse te kan opstel (kalorimeter). Die akkuraatheid van die kalorimeter is getoets by 85°C, deur die verdunningswarmte van 'n natriumhidroksiedoplossing te meet. Daar is gevind dat die kalorimeter baie akkuraat is. 'n Industrieel vervaardigde (plaseon) emulsie (kode naam: AB 446) is gebruik om die loodsaanleg in bedryf te stel. Die resultate wat in die loodsaanleg verkry is, was ongeveer dieselfde as die resultate wat in die industriële reaktore verkry word. Hierdie resultate toon dat indien die reaktore geometries gelykvormig is en indien die regte prosestoestande (roerspoed, reaksietemperatuur en toevoertempo's van die monomere/katalis) gebruik word, dit moontlik sou wees om NW 120 direk op te skaal van loodsaanleg tot volskaal. Die reaksietoestande is gevaneer oor 'n wye bereik om die optimum prosestoestande te probeer verkry. Die roerspoed is gevarieer tussen 150 - 550 opm. Daar is gevind dat die emulsie sleur sensitief is bokant 'n roerspoed van 450 opm. Die gemete fisiese eienskappe by 'n roerspoed van 550 opm was onaanvaarbaar. Die optimum roerspoed in terme van partikelgrootte en viskositeit lê tussen 150 en 250 opm. Die reaksietemperatuur is gevarieer tussen 90 - 70°C. Die optimum temperatuur lê tussen 90 - 80 °C. Dit was moontlik om die monomeer-toevoertyd, m.a.w die reaksietyd, te verminder deur die toevoertempo van die monomere/katalis te verhoog, van 4 tot 2 ~ uur. Die metode wat deur Klein et al. (1996) ontwikkel is vir die opskalering van die roerspoed van 'n emulsiepolimerisasie reaksie is gebruik om die ekwivalente roerspoed vir die opskalering te verkry. Die opskalering van NW 120 is uitgevoer by 'n reaksietemperatuur van 85°C en 'n roerspoed van 35 opm. Die monomere/katalis is toegevoer oor 'n tydperk van 4 uur. Die verkorte reaksietyd is nie oorweeg vir die opskaleringslopie nie omdat dit nog nie seker was of die hitteverwydering van die industriële reaktor effektief genoeg sou wees om die verhoging in die reaksiewarmte-ontwikkeling, wat geassosieer word met 'n verhoging in die toevoertempo van die monomere/katalis, te kan verwyder nie. Baie goeie resultate is verkry. Die gemete fisiese eienskappe van NW 120 wat verkry is in die industriële reaktor was ongeveer dieselfde as dié wat verkry is op die loodsaanleg.

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