Kesetimbangan fase padat-cair polistiren dalam pelarut toluen-etanol

BUDI, M. Sri Prasetyo, Ir. Rochmadi, SU.,PhD

2002 | Tesis | S2 Teknik Kimia

Kesetimbangan fase padat-cair berperan dalam perancangan suatu proses pembuatan polimer. Pengetahuan perilaku fase dari larutan poliiner/solven adalah penting untuk operasi pemurnian dan produksi polimer. Tetapi kemampuan inemperkirakan model teknik cainpuran suatu larutan sangat terbatas. Beberapa model koefisien ahifitas dicoba untuk ineinperkirakan kesetimbangan fase padat-cair polistiren dalam pelarut toluen-etanol yaitu model Unifac, nzodIJied-Unifac dan Unifac-Free Volum. Penelitian ini bertujuan untuk menentukan model yang paling cocok diantara ke tiga model tersebut. Percobaan dilakukan dalam labu leher tiga yang dilengkapi pendingin balik, pengaduk merkuri dan water bath. Campuran toluen dan etanol sebanyak 30 mL dengan perbandingan tertentu, dipanaskan sambil diaduk. Setelah suhu tertentu yang diinginkan tercapai, 4 gram polistiren dimasukkan. Suhu dijaga tetap konstan. Setelah keadaan setimbang tercapai pengadukan dihentikan. Sebanyak 3 mL larutan diambil, ditimbang dalam gelas arloji dan kemudian diuapkan dalam eksikator hampa. Padatan yang tertinggal ditimbang kembali untuk dihitung fraksi mol polistiren dalam larutan. Untuk mengetahui berat molekul polistiren digunakan viscometer Ostwald. Variabel yang diteliti adalah pengaruh suhu dan komposisi campuran pelarut. Hasil penelitian menunjukkan bahwa model Flory I1 tnemberikan hasil lebih baik dibanding model rnodlfied-Unifac dan model Unifac-Free Volume dengan penyimpangan 6,2 1 %. Model mod$ed-Unifac memberikan penyimpangan sebesar 16,24% dan model Unifac-Free Volume memberikan penyimpangan sebesar 62,99%. Model mod$ed-Unifac mampu memperbaiki model Unifac dengan memasukkan satu udlustuhle parurneter yaitu nilai eksponen P sebesar 0,7674.

Solid-liquid phase equilibria played a crucial role in the design of polymer manufacturing processes. The phase behavior of polymer/solvent solution is important for polymer production and purification operations. However, the predictive ability of engineering models describing such mixtures were still rather limited. Several activity coefficient models were used to predict the solid-liquid equilibrium for polystyrene in toluene-ethanol system. The models are Unifac, modified Unifac and Unifac-Free Volume. The aim of this research is to find the most appropriate model for this system. Experiment was carried out in a three-necked boiling flask, with a reflux condenser, mercury stirrer and water bath. Around 30 mL of toluen and ethanol mixture with certain ratio was heated and stirred at the desired temperature. After the temperature achieved, 4 gram of polystyrene was added. Liquid sample ( f 3 mL ) was taken after the equilibrium condition reached and then vaporized in a vaccum exicator. Solid in the sample was weighed to determine the mole fraction of polystyrene in solution. The molecular weight of polystyrene was measured by viscometer Ostwald. Variables studied were temperature and composition of mixed solvent. The results showed that Flory I1 model with 6.21% of error was better than modified-Unifac model and Unifac-Free Volume model. Modified-Unifac model gave 16.21% of error and Unifac-Free Volume model gave 62.99%. Modified-Unifac model can improve Unifac model with one ad;ustable parameter with the exponent P= 0.7674.

Kata Kunci : Perpindahan Massa, Kesetimbangan Fase