Načrtovanje visokotlačnih procesov za predelavo polimerov in izboljšave prenosa top

The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions. In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles. In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured. Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied. In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2. V doktorski disertaciji je predstavljeno načrtovanje visokotlačnih procesov, ki izkoriščajo »zelena topila« t.i. nadkritične fluide. Z njihovo uporabo lahko pridobivamo nove produkte z višjo dodano vrednostjo pri nizki porabi energije. Doktorska dizertacija je razdeljena na tri osrednja poglavja: procesiranje polimerov in formulacija aktivnih zdravilnih učinkovin, merjenje transportnih lastnosti iz geometrije viseče kaplje in študij prenosa toplote pri nadkritičnih pogojih. V prvem delu smo se osredotočili na uporabo biorazgradljivih polimernih materialov z namenom pridobivanja praškastih delcev in struktur za formulacijo aktivnih farmacevtskih učinkovin. Biorazgradljivi polimerni materiali so pomembni v številnih farmacevtskih aplikacijah pri nadzorovanem sproščanju zdravil. Uporabili smo patentiran visokotlačni PGSSTM postopek za formulacijo netopnih aktivnih zdravilnih učinkovin nimodipina, fenofibrata, o-vanilina in esomeprazola z namenom izboljšanja njihove biološke uporabnosti in hitrosti raztapljanja. Kot nosilni material smo uporabili biorazgradljive polimere polioksietilen stearil eter (Brij 100 in Brij 50) in polietilen glikol (PEG 4000). Preliminarno smo določili transportno-termodinamske parametre polimernima nosilcema polietilen glikolu (PEG) in polioksietilen stearil eteru (Brij S) v sistemih z nadkritičnimi fluidi. Izmerjene parametre smo uporabili za optimalno formulacijo aktivnih učinkovin. Kombinacija zmanjšanja velikosti delcev in medsebojni vpliv med aktivno zdravilno učinkovino in hidrofilnimi nosilci sta pripomogla k povečanju hitrosti raztapljanja dobljenih praškastih delcev. V drugem delu smo razvili novo visokotlačno merilno tehniko in izpeljali matematični model za določitev difuzijskih koeficientov in površinskih napetosti iz geometrije viseče kaplje. Nastanek asimetrične kapljice fluida smo preučevali z uporabo računalniškega algoritma, ki vključuje iterativno uporabo Young-Laplace-ove enačbe za opis razmerja med gravitacijsko deformacijo kapljice in površinsko napetostjo. Metodo smo umerili z meritvami površinske napetosti in difuzijskih koeficientov v sistemu voda/superkritični CO2. Določili smo površinsko napetost in difuzijske koeficiente še neraziskanemu sistemu propilen glikola/CO2 pri temperaturah 120 °C in 150 °C v tlačnem razponu od 5 MPa do 17.5 MPa. Novo metodo smo nadalje uporabili za preučitev sistemov pomembnih pri geološkem zajemanju CO2. Z namenom zmanjšanja izpustov toplogrednega CO2 v ozračje smo preučili in izmerili gostote in površinske napetosti sistemom slanica/CO2 in preučili vpliv nečistoče Ar na skladiščenje CO2 v geološke formacije. V tretjem delu doktorske naloge smo preučevali učinkovitosti prenosa toplote v bližini kritične točke CO2, etana in njune azeotropne mešanice. Izdelali smo dvocevni prenosnik toplote, ki je omogočil meritve pri povišanih temperaturah (25 °C do 90 °C) in tlakih (5 MPa do 30 MPa). Prenos toplote v sistemu z nadkritičnim fluidom smo merili v smeri iz notranje visokotlačne cevi protitočno na zunanjo cev po kateri se je pretakala voda. Izmerili smo koeficiente prenosa toplote nadkritičnemu CO2, etanu in njuni mešanici. Preučili smo učinek masnega pretoka, toplotnega toka, vzgona, tlaka in temperature na vrednosti koeficientov prenosa toplote. Za pravilno oceno potenciala in učinkovitosti azeotropne mešanice CO2 in etana smo izračunali koeficiente zmogljivosti (COP) za cikel toplotne črpalke in jih primerjali s sistemi, ki delujejo izključno na CO2.