Studies on mass transport in HZSM-5 zeolite :: CO2 adsorption in Packed-bed adsorber

INDRAJATI, Ihda Novia, Ir. Panut Mulyono, M.Eng.D.Eng

2006 | Tesis | S2 Teknik Kimia

Kombinasi antara pemodelan dan eksperimen telah dilakukan untuk mempelajari dan meneritukan parameter difusi untuk studi kasus adsorpsi CO2 dalam sebuah unggun adsorber. Studi ini bertujuan untuk menghasilkan data difusi untuk aplikasi pada studi kelayakan VGS (water gus shi/1) zeoiile-me,nbrane reactor. Eksperimen terdiri dan dua macam, yaitu eksperimen untuk tracer dan adsorpsi. Kedua eksperimen ini dilakukan dalarn sebuah unggun yang tersusun atas serbuk zeolit HZSM-5 dan dilakukan dengan metode transient step change. Secara umum kedua eksperimen ini rnempunyai prosedur operasional yang sarna. Perbedaannya hanya terletak pada komposisi umpan gas. Pada eksperimen tracer digunakan campuran gas Ar/He (Ar==20% volum), sedangkan pada eksperimen adsorpsi digunakan campuran gas C02/He dengan variasi konsentrasi CO2 40% dan 80%. Eksperimen-eksperimen ini dilakukan pada temperatur 373, 423 dan 473 K dan tekanan I atm. Sebuah model disusun untuk adsorpsi CO2 pada HZSM-5 dalam sebuah unggun adsorber dengan asumsi: aliran plug flow, isotermal dan isobarik, single site Langmuir physisorption, tahanan perpindahan massa di lapisan film gas diabaikan dan digunakan teori Maxwell-Stefan untuk difusi di mikropori. Data eksperimen dicocokkan dengan model. Data ini dioptimasi untuk mendapatkan nilai jIlted parameter termodifikasi, Dm (faktor pre-exponensial pada persamaan Arrhenius-ívpe) dan (energi aktivasi difusi). Hasil dan pemodelan dan eksperimen menunjukkan bahwa model cocok dengan data eksperimen. Nilai fitted parameter termodifikasi, D1=(1.5519±0.003l)xl08 m2.s1 dan E5.0907±0.0024 kJ.moF1. Difusivitas pada berbagai temperatur dapat ditentukan

Zeolite is an inorganic porous material having a highly regular structure of pores and chambers that allows some molecules to pass through and causes others to be either excluded or broken down. This property allows zeolite to be described as molecular sieve. Zeolites are well known as potential candidates for gas separation processes in the form of powder or membranes. Experimental and modeling have been done to study and to determine the diffusion parameters for a case study of CO2 adsorption in a packed-bed adsorber. This study has been done in order to provide diffusion data for application to in WGS membrane reactor feasibility study. Experiment works consisted of tracer and adsorption experiments. Basically both of them were the same. The difference was just on the composition of the feed gas. Tracer experiments used the mixture of Ar/He gases with the concentration 20/80 (% volume) within the temperature of 373, 423 and 473 K. These experiments were conducted to measure dispersion and time lag effect of the bed and reactor system. The residence time distributions (RTD) were analyzed in order to determine the number of tank in series (n) which represented the convective flow in the bed. The feed gas of adsorption experiments were consisted of the mixture of CO2/He gases with concentration of 40/60 (%volume) and 80/20(%volume) within various temperatures of 373, 423 and 473 K. The experiments were conducted by using transient step change adsorption. A model of CO2 adsorption on HZSM-5 had been set up for transient packed-bed adsorber by assuming plug flow, isothermal and isobaric, single site Langmuir physisorption, no gas film mass transport resistance and Maxwell-Stefan mass transport in micropore applied. All the data were then optimized to get the best value of modified fitted parameter, Dom and EDm by using MATLAB 6.5. Tracer experiments resulted in the mean residence time tm was 8.7493 s and the number of tank in series n was 5. The results indicated that at higher temperature, the quantities of gas adsorbed were decrease. This was due to lower adsorption capacity which occurs at higher temperature. The model was in a good agreement with the experiment data, with Dom=(1.5519±0.0031)x10-8 m2.s-1 and EDm=5.0907±0.0024 kJ.mol- 1as fitted parameter. The fitted diffusivity were 7.0678x10-10 m2.s-1 at 373 K, 8.5814x10-10 m2.s-1 at 423 K and 10.0000x10-10 m2.s-1 at 473 K. Diffusivity tended to increase by increasing temperatures. The sensitivity of the model was tested by simulating the crystal size (diameter) within various value (10, 12, 16, 20, 24, 60, 80 and 100 μm). This simulation was used to see the effect of increasing or decreasing the crystal diameter (from the estimated value) on the fitted diffusivity.

Kata Kunci : Perpindahan Massa,Zeolit HZSM,5,Adsorpsi CO2,HZSM-5 zeolite, CO2 adsorption, packed-bed adsorber modeling