Projektiranje i uvećanje mjerila biokemijskih reaktora s višestrukim miješalima

Mechanically agitated gas-liquid contactors are frequently used in the chemical, food and biochemical industries as fermenters and as hydrogenation or chlorination reactors. However wide is the usage of such vessels, their design is not based on chemical engineering data, but is still rather empirical. Thus, it is highly desirable to have a tool for the rational design of agitated gas-liquid contactors that is based on fundamental chemical engineering parameters that are transferable to other systems and operating conditions. Focusing on liquid film-controlled processes and using the data from fermenters of different scales, we develop kLa correlations that are suitable for scale-up. First, we discuss how to determine the proper experimental kLa values, which are not distorted by other equipment parameters as is the gas residence time. We demonstrate the possible kLa distortion on the pilot-plant experimental data by comparing the results obtained by two different experimental techniques. Further, we present physically correct kLa data for fully non-coalescent (sodium sulphate solution) batch. The data are presented both for laboratory and pilot-plant fermenters. We identify the process parameters, the values of which are dependent on the vessel scale when operated under the same power input per volume, and, using these parameters, we develop common kLa correlations suitable to describe the data for various scales of the vessel. The correlations developed reduce the uncertainty in predicting the volume of industrial scale fermenters from almost 1/2 to 1/4 of their total volume, thereby enabling significant reductions in both the initial costs, and operating costs.Uređaji za mehaničko miješanje sustava kapljevina-plin često se upotrebljavaju u kemijskoj, prehrambenoj i biokemijskoj industriji kao fermentori i kao reaktori za hiodrogeniranje i kloriranje. No u širokoj primjeni takvih reaktora njihov se dizajn ne temelji na kemijsko-inženjerskim podatcima te je još uvijek prilično empirijski. Dakle, vrlo je poželjno imati alat za racionalno projektiranje/dizajn uređaja za mehaničko miješanje sustava kapljevina-plin koji se temelji na fundamentalnim kemijsko-inženjerskim parametrima koji su prenosivi i na druge sustave i druge radne uvjete. Usredotočivši se na procese kontrolirane tekućim filmom i primjenjujući podatke iz fermentera različitih mjerila, razvijene su korelacije kLa koje su pogodne za uvećanje mjerila. Najprije se govori o načinu kako utvrditi odgovarajuće eksperimentalne vrijednosti kLa koje nisu narušene drugim parametrima kao to je to vrijeme zadržavanja plina. Pokazuje se moguća distorzija eksperimentalnih podataka kLa poluindustrijskih postrojenja usporedbom rezultata koji su dobiveni dvjema različitim eksperimentalnim tehnikama. Nadalje, prikazuju se fizički ispravni podatci kLa za smjesu (otopinu natrijeva sulfata) u potpunosti bez koalescencije (spajanja). Podatci su prikazani i za laboratorij i za fermentore poluindustrijskih postrojenja. Utvrđuju se procesni parametri vrijednosti koje su ovisne o mjerilu reaktorske posude, kada djeluju pod istom ulaznom snagom po jedinici obujma i primjenom ovih parametara razvijaju se uobičajene korelacije kLa prikladne za opisivanje podataka za različita mjerila reaktorske posude. Razvijene korelacije smanjuju nesigurnost u predviđanju obujma fermentora industrijskih razmjera s gotovo 1/ 2 do 1 / 4 od svog ukupnog obujma i time omogućuju znatno smanjenje početnih operativnih trokova.</p

Self-assembly mechanism in colloids: perspectives from Statistical Physics

Motivated by recent experimental findings in chemical synthesis of colloidal particles, we draw an analogy between self-assembly processes occurring in biological systems (e.g. protein folding) and a new exciting possibility in the field of material science. We consider a self-assembly process whose elementary building blocks are decorated patchy colloids of various types, that spontaneously drive the system toward a unique and predetermined targeted macroscopic structure. To this aim, we discuss a simple theoretical model -- the Kern-Frenkel model -- describing a fluid of colloidal spherical particles with a pre-defined number and distribution of solvophobic and solvophilic regions on their surface. The solvophobic and solvophilic regions are described via a short-range square-well and a hard-sphere potentials, respectively. Integral equation and perturbation theories are presented to discuss structural and thermodynamical properties, with particular emphasis on the computation of the fluid-fluid (or gas-liquid) transition in the temperature-density plane. The model allows the description of both one and two attractive caps, as a function of the fraction of covered attractive surface, thus interpolating between a square-well and a hard-sphere fluid, upon changing the coverage. By comparison with Monte Carlo simulations, we assess the pros and the cons of both integral equation and perturbation theories in the present context of patchy colloids, where the computational effort for numerical simulations is rather demanding.Comment: 14 pages, 7 figures, Special issue for the SigmaPhi2011 conferenc

Ninth and Tenth Order Virial Coefficients for Hard Spheres in D Dimensions

We evaluate the virial coefficients B_k for k<=10 for hard spheres in dimensions D=2,...,8. Virial coefficients with k even are found to be negative when D>=5. This provides strong evidence that the leading singularity for the virial series lies away from the positive real axis when D>=5. Further analysis provides evidence that negative virial coefficients will be seen for some k>10 for D=4, and there is a distinct possibility that negative virial coefficients will also eventually occur for D=3.Comment: 33 pages, 12 figure

The Design and Scale-Up of Multiple-Impeller Fermenters for Liquid Film Controlled Processes

Mechanically agitated gas-liquid contactors are frequently used in the chemical, food and biochemical industries as fermenters and as hydrogenation or chlorination reactors. However wide is the usage of such vessels, their design is not based on chemical engineering data, but is still rather empirical. Thus, it is highly desirable to have a tool for the rational design of agitated gas-liquid contactors that is based on fundamental chemical engineering parameters that are transferable to other systems and operating conditions. Focusing on liquid film-controlled processes and using the data from fermenters of different scales, we develop kLa correlations that are suitable for scale-up. First, we discuss how to determine the proper experimental kLa values, which are not distorted by other equipment parameters as is the gas residence time. We demonstrate the possible kLa distortion on the pilot-plant experimental data by comparing the results obtained by two different experimental techniques. Further, we present physically correct kLa data for fully non-coalescent (sodium sulphate solution) batch. The data are presented both for laboratory and pilot-plant fermenters. We identify the process parameters, the values of which are dependent on the vessel scale when operated under the same power input per volume, and, using these parameters, we develop common kLa correlations suitable to describe the data for various scales of the vessel. The correlations developed reduce the uncertainty in predicting the volume of industrial scale fermenters from almost 1/2 to 1/4 of their total volume, thereby enabling significant reductions in both the initial costs, and operating costs.<br

Alternative Approaches to the Equilibrium Properties of Hard-Sphere Liquids

An overview of some analytical approaches to the computation of the structural and thermodynamic properties of single component and multicomponent hard-sphere fluids is provided. For the structural properties, they yield a thermodynamically consistent formulation, thus improving and extending the known analytical results of the Percus–Yevick theory. Approximate expressions for the contact values of the radial distribution functions and the corresponding analytical equations of state are also discussed. Extensions of this methodology to related systems, such as sticky hard spheres and squarewell fluids, as well as its use in connection with the perturbation theory of fluids are briefly addressed.