Kinetic analyisis of copper ions sorption on zeolite NaX in a batch reactor under different hydrodynamic conditions : doctoral thesis

Abstract

Sažetak Zeoliti su mikroporozni kristalni alumosilikati koji su svojom primjenom kao katalizatori i sorbensi promijenili petrokemijsku i kemijsku industriju. Katalitička svojstva zeolita mogu se prilagoditi „umetanjem” iona teških metala u zeolit, a jedna od metoda koja se može koristiti za pripremu katalizatora je sorpcija. Sorpcija na zeolitima koristi se i za uklanjanje metala iz kontaminiranih voda. Ako se proces sorpcije vodi u kotlastom (šaržnom) reaktoru njegova učinkovitost ovisi o različitim procesnim parametrima, uključujući i parametre miješanja, a čiji utjecaj na samu sorpciju još uvijek nije dovoljno istražen. Hidrodinamički uvjeti u određenom sustavu posljedica su geometrijskih karakteristika reaktora i korištenog miješala te brzine vrtnje miješala. Stoga je u ovom radu ispitan utjecaj hidrodinamičkih uvjeta u reaktoru na učinkovitost i kinetiku sorpcije bakrovih iona na sintetskom zeolitu NaX u otvorenom šaržnom reaktoru s razbijalima virova. Miješanje se provodilo upotrebom triju različitih tipova miješala: aksijalnog propelerskog miješala, radijalno-aksijalnog turbinskog miješala s ravnim lopaticama nagnutim pod kutom (PBT) i radijalnog turbinskog miješala s ravnim lopaticama (SBT). Za sve tipove miješala sagledan je utjecaj tipa miješala te masene koncentracije zeolita NaX u otopini na kritičnu brzinu vrtnje miješala za postizanje stanja potpune suspenzije, N JS , kao i na kinetiku i na učinkovitost sorpcije bakrovih iona na zeolitu NaX. Pri najnižoj ispitivanoj masenoj koncentraciji suspenzije zeolita NaX u otopini, za sve tipove miješala, ispitan je utjecaj brzine vrtnje miješala, N/N JS , na provedbu ispitivanog procesa. Za PBT tip miješala je ispitan i utjecaj pozicije i promjera miješala na kinetiku i na učinkovitost ispitivanog procesa pri najnižoj ispitivanoj masenoj koncentraciji zeolita NaX u otopini. Procjena kinetičkih parametara provedena je nelinearnom i linearnom regresijskom analizom za tri kinetička modela: Ritchiejev model, Miješani kinetički model adsorpcije kontrolirane površinskom reakcijom i difuzijom (Miješani model) te Weber-Morrisov model. Kinetičkom analizom dobivenih eksperimentalnih podataka odabranim kinetičkim modelima utvrđeno je koji kinetički model najprikladnije opisuje kinetiku sorpcije bakrovih iona na zeolitu NaX te su izračunati kinetički parametri. Budući da je sorpcija heterogeni proces određen je i najsporiji korak procesa za ispitivane uvjete. Analizom eksperimentalnih kinetičkih podataka utvrđeno je da sorpciju bakrovih iona na zeolitu NaX najpotpunije opisuje Ritchiejev model. Međutim, pri brzinama vrtnje propelerskog i SBT miješala N/N JS od 0,60 i 0,80, Miješani model se bolje slaže s eksperimentalnim kinetičkim podatcima, sugerirajući da je reakcija drugog reda ograničena difuzijom. Da bi se dobio potpuniji uvid u hidrodinamička zbivanja u ispitivanom sustavu, uporabom programskog paketa ANSYS Fluent v17.2 simulirani su tokovi fluida. S obzirom na kinetiku i količinu sorbiranih bakrovih iona predložena je najpovoljnija geometrija reaktora.Abstract Zeolites are microporous crystalline aluminosilicates that have transformed the petrochemical and chemical industries through their use as catalysts and sorbents. The catalytic properties of zeolites can be altered by introducing heavy metal ions into the zeolite, and one of the methods used to prepare catalysts is sorption. Sorption on zeolites can also be used to remove metals from contaminated water. If the sorption process is carried out in a batch reactor, its efficiency depends on various process parameters, including the mixing parameters, the influence of which on sorption itself has not been sufficiently studied. The hydrodynamic conditions in a given system result from the geometrical characteristics of the reactor and the impeller used, as well as from the impeller rotation speed. For this reason, the influence of hydrodynamic conditions on the efficiency and kinetics of copper ions sorption on synthetic zeolite NaX in an uncovered batch reactor with baffles was studied in this work. Mixing was performed using three different impeller types: an axial propeller impeller, a radial-axial pitched blade turbine impeller (PBT), and a radial straight blade turbine impeller (SBT). For all impeller types, the effect of impeller type and zeolite NaX mass concentration in a solution on the critical impeller speed required to achieve a state of complete suspension, N JS , was investigated. The effect of impeller type on the kinetics of copper ions sorption on zeolite NaX and removal efficiency was studied. At the lowest mass concentration of NaX zeolite in the solution investigated, the effect of the impeller rotation speed, N/N JS , on the performance of the studied process was also investigated for all impeller types. For the PBT impeller, the effect of the impellers' position and its diameter on the kinetics of the copper ion sorption process on zeolite NaX and the removal efficiency at the lowest mass concentration of NaX zeolite in the solution investigated, were studied too. Kinetic parameter estimation was performed using nonlinear and linear regression analysis for three kinetic models: Ritchie’s model, Mixed kinetic model of adsorption controlled by surface reaction and diffusion (Mixed model), and Weber-Morris model. By kinetic analysis of the obtained experimental data using the selected kinetic models, a kinetic model that describes the kinetics of sorption of copper ions onto zeolite NaX, and the kinetic parameters were calculated. Since sorption is a heterogeneous process, the slowest step of the process was defined for the conditions studied. By analysing the experimental kinetic data, it was found that the sorption of copper ions onto zeolite NaX is well described by the Ritchie’s model. However, at impeller speeds of N/N JS 0.60 and 0.80, the Mixed model agrees better with the experimental kinetic data, suggesting that the second order reaction is suppressed by diffusion. To obtain a more complete insight into the hydrodynamic processes in the studied system, the fluid flows were simulated using the ANSYS Fluent v17.2 software package. Taking into account the obtained results, i.e. the kinetics and the amount of sorbed copper ions, the most favourable reactor geometry was proposed