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  • Open Access English
    Authors: 
    Amina Lachenani‬; Mohamed Bentchikou; Mouloud Boumahdi; Salah Hanini; Maamar Laidi;
    Country: Croatia

    U ovom radu predloženo je i primijenjeno šest novih matematičkih modela temeljenih na poluempirijskom proračunu za karakterizaciju procesa sušenja u pećnici kompozita cementne žbuke ojačane celuloznim vlaknima (CMCRCF). Pokusi sušenja provedeni su pri četiri razine temperature sušenja u pećnici (70, 85, 105 i 120 °C) s četiri različita udjela celuloznih vlakana (0, 5, 10 i 20 %). Dobiveni rezultati uspoređeni su s onima dobivenim regresijskom analizom šest najčešće primjenjivanih matematičkih modela sušenja (Newton, Page, Page modified1, Page modified2, Handerson Pabis i Logarithmic) uz šest predloženih modela. Regresijska točnost procesa sušenja procijenjena je koeficijentom determinacije (R2), srednjom kvadratnom pogreškom (MSE), korijenom srednje kvadratne pogreške (RMSE) i srednjom apsolutnom pogreškom (MAE). Primijenjeni su i dodatni kriteriji da bi se osigurala veća valjanost odabranih modela. Dobivene vrijednosti pokazuju dobro slaganje predloženog modela MR9 s eksperimentalnim vrijednostima, što znači da predloženi model može jasno interpretirati eksperimentalne podatke o sušenju i predvidjeti suho stanje CMCRCF-a. In this paper, six novel mathematical models based on semi-empirical calculus are proposed and applied to characterise the oven-drying process of cement mortar composites reinforced with cellulosic fibres (CMCRCFs). The drying experiments were carried out on four levels of oven-drying temperatures (70, 85, 105, and 120 °C), with four different cellulosic fibres content (0, 5, 10, and 20 %). Obtained results were compared to those derived by regression analysis of six most typically used mathematical drying models (Newton, Page, Page modified1, Page modified2, Handerson Pabis, and Logarithmic) in addition to six proposed models. The regression accuracy of the drying process was evaluated by the coefficient of determination (R2), low mean square error (MSE), low root mean squared error (RMSE), and mean absolute error (MAE). Additional criteria were used to ensure more validity of the selected models. The obtained values indicate a highly accurate fit of the proposed model MR9, meaning that the proposed model can clearly interpret the experimental drying data and predict the dry state of CMCRCFs.

  • Publication . Other literature type . Article . 2022
    Open Access English
    Authors: 
    Dornjak, Luka; Ostojić, Karla; Klaser, Teodoro; Urlić, Inga; Rogina, Anamarija;
    Country: Croatia

    Kitozanski nosači su efektivni biološki aktivni materijali sa širokom primjenom u kemiji i medicini. Kitozan je linearni polisaharid, derivat hitina, koji posjeduje dobru biokompatibilnost koja se pripisuje prisustvu funkcionalnih skupina kao što su −OH i −NH2 koje pridonose biorazgradljivim i antibakterijskim svojstvima. U kiselim vodenim otopinama kitozan je polikationske strukturne prirode, koja ima veliku sposobnost stvaranja kompleksa s različitim metalnim ionima i važnim biomolekulama, kao što su DNA, proteini i lipidi. Jedinstvena struktura, kao i uvođenje specifičnih funkcionalnih skupina odgovorni su za antibakterijska svojstva, hemostatsku aktivnost i analgetska svojstva tog biopolimera. Za poboljšanje angiogenih i antimikrobnih svojstava, kitozan se može modificirati borom (boratnim ionima). Cilj ovog rada bio je pripremiti bornom kiselinom modificirane kitozanske nosače, upotrebljavajući bornu kiselinu kao prekursor bora, u svrhu priprave potencijalnih bioaktivnih okosnica za regeneraciju tkiva. Boratni ioni imaju sklonost stvaranja kompleksa s hidroksilnim skupinama, međutim, takve interakcije između funkcionalnih skupina kitozana i bora rezultiraju slabijom učinkovitosti njegove inkapsulacije. Da bi se osigurala bolja ugradnja bora, kitozanski nosači su umreženi genipinom, manje toksičnim umreživalom u odnosu na glutaraldehid koji se obično upotrebljava za pripremu stabilnih materijala čiji se sastav temelji na kitozanu. Stupanj deacetilacije (DD) i koncentracija otopine kitozana kao i koncentracija otapala važni su parametri koji utječu na proces umreživanja. Nadalje, dodatak borne kiseline mogao bi utjecati na proces umreživanja zauzimanjem funkcionalnih skupina kitozana. U ovom radu kitozanski nosači modificirani su bornom kiselinom različite koncentracije, dok su koncentracija otopine kitozana (1,2 w/v), koncentracija genipina (2 % w/w) i koncentracija octene kiseline (0,5 % v/v) bile konstantne. Dobiveni nosači okarakterizirani su pretražnom elektronskom mikroskopijom (SEM), energetski disperzivnom rendgenskom spektroskopijom (EDS), diferencijalnom pretražnom kalorimetrijom (DSC), infracrvenom spektroskopijom s Fourierovom transformacijom (FTIR), dok je citotoksičnost procijenjena kao funkcija koncentracije materijala i vremena izloženosti stanica materijalu. Rezultati su pokazali uspješnu ugradnju bora u umrežene kitozanske nosače, visoko poroznu strukturu i nisku citotoksičnost. Chitosan scaffolds are an effective biologically active material with versatile application in chemistry and medicine. Chitosan is a linear polysaccharide, a derivative of chitin, with great biocompatibility due to the possession of functional groups such as −OH and −NH2, which allow for biodegradability and antibacterial function. Chitosan has a polycation nature allowing complex formation with metal ions and many biomolecules such as DNA, proteins and lipids, while its specific structure and functional groups are responsible for antibacterial, hemostatic, and analgesic properties. To improve its angiogenic and antimicrobial potential, chitosan can be modified by boron (borate ions). The aim of this work was to prepare boric acid modified chitosan scaffolds, using boric acid as a boron precursor, as potential bioactive scaffolds for tissue regeneration. Borate ions tend to form complexes with hydroxyl groups, however, such physical interactions between boron and chitosan functional groups result in poor encapsulation efficiency. To ensure higher boron incorporation, chitosan scaffolds were cross-linked by genipin, a cross linker with lower cytotoxicity in contrast to glutaraldehyde commonly used to prepare stable chitosan-based materials. The degree of deacetylation (DD) and concentration of chitosan solution as well as the concentration of a solvent are important parameters that affect the crosslinking process. Moreover, the addition of boric acid could interfere with the crosslinking process by occupying chitosan functional groups. Here, chitosan scaffolds were modified with different concentrations of boric acid, while the concentrations of chitosan solution (1.2 w/v), genipin (2 % w/w), and acetic acid (0.5 % v/v) were kept constant. Obtained scaffolds were characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR), while cytotoxicity was evaluated as a function of materials concentration and exposure time. The results indicated successful incorporation of boron into cross-linked chitosan scaffolds with highly porous structure and low cytotoxicity.

  • Open Access English
    Authors: 
    Bensaber Bensebia; Fatma Zohra Chaouche; Soumia Kouadri Moustefaï;
    Country: Croatia

    Knowledge of gas holdup is important for the development of the three-phase fluidized bed reactors. This work concerns the study of the effect of different operating conditions on gas retention in a turbulent bed contactor type 2 (TBC), such as superficial gas and liquid velocities, liquid to gas mass flows ratio (L/G), particle diameter and density, static bed height and free-open area of the supporting grid. The influence of the free area of the packing support grid (φ) on gas holdup was demonstrated and proved. The gas holdup increased to 22.92 % when φ decreased from 0.82 to 0.32. The experimental data (1746) led to the development of two correlations to predict gas holdup, one of which incorporated the ratio (L/G) which is an important design factor for gas-liquid contactors. The predicted results of holdup gas were in good agreement with the experimental data. Poznavanje zadržavanja plina važno je za razvoj trofaznih reaktora s fluidiziranim slojem. Ovaj rad bavi se proučavanjem utjecaja različitih radnih uvjeta na zadržavanje plina u kontaktoru s turbulentnim slojem tipa 2 (TBC), kao što su površinske brzine plina i tekućine, omjer masenih protoka tekućine i plina (L/G), promjer čestica i gustoća, statička visina sloja i slobodna otvorena površina potporne rešetke. Dokazan je utjecaj slobodne površine potporne rešetke (φ) na zadržavanje plina. Zadržavanje plina povećalo se na 22,92 % kad se φ smanjio s 0,82 na 0,32. Iz dobivenih eksperimentalnih rezultata (1746) razvile su se dvije korelacije za predviđanje zadržavanja plina, od kojih je jedna uključivala omjer L/G, koji je važan faktor pri dizajnu plinsko-tekućinskih kontaktora. Predviđeni rezultati zadržavanja plina podudarali su se s eksperimentalnim podatcima.

  • Publication . Other literature type . 2022
    Open Access English
    Authors: 
    Čulo, Ivana; Grgić, Filip; Jurina, Tamara; Šalić, Anita; Benković, Maja; Valinger, Davor; Gajdoš Kljusurić, Jasenka; Jurinjak Tušek, Ana; Zelić, Bruno;
    Country: Croatia

    Emulsions are traditionally prepared with the application of high shear forces generated by the use of static mixers, homogenisers, or ultrasound. The resulting emulsions are sensitive to change of process conditions. The application of high forces and temperatures can significantly affect the constituents of the emulsions and their final stability. Microfluidic technology seems to be a very efficient alternative to classic emulsification methods. The dimensions of microdevices in combination with continuous processes offer a great advantage over classic batch emulsification processes carried out on a larger scale. The small dimensions of the microdevices allow easy transport of equipment, better control and safety of the process, and intensified mass and energy transfer. The mixing time in microdevices is reduced to a few milliseconds because the molecules in the microchannels have a short diffusion path. In this paper, an overview of emulsification processes, the advantages of use of microfluidics in emulsification, and future perspectives of microemulsification are presented. Tradicionalno se emulzije pripremaju primjenom jakih smičnih sila koje nastaju upotrebom statičkih miješala, homogenizatora ili primjenom ultrazvuka. Tako proizvedene emulzije osjetljive su na promjenu procesnih uvjeta. Primjena jakih sila i povišenih temperatura može značajno utjecati na komponente emulzija i njihovu konačnu stabilnost. Primjena protočnih mikrosustava pokazala se učinkovitom alternativnom tehnologijom klasičnim metodama emulgiranja. Male dimenzije mikrouređaja u kombinaciji s kontinuiranom provedbom procesa omogućuje brojne prednosti u odnosu na klasične šaržne procese emulsifikacije koji se provode u većem mjerilu. Male dimenzije mikrouređaja omogućuju lakši transport opreme, bolju kontrolu i sigurnost procesa te intenzivniji prijenos tvari i topline. Vrijeme miješanja u mikrouređajima smanjeno je na nekoliko milisekundi zbog kratkog difuzijskog puta molekula u mikrokanalima. U ovom radu dan je pregled procesa emulgiranja, prednosti primjene protočnih mikrosustava u provedbi procesa emulgiranja te potencijalnih novih područja primjene te tehnologije.

  • Open Access English
    Authors: 
    Mirha Pazalja; Mirsada Salihović; Alisa Smajović;
    Country: Croatia

    Ash is a by-product of wood biomass combustion that must be removed daily from stoves or fireplaces. Therefore, operators or owners are exposed to the potential impact of ash. The goal of this study was to determine whether heavy metal present in wood pellet ash posed a health concern to stove operators/owners. The risk assessment procedure was carried out in several steps, including exposure evaluation, toxicity evaluation, and risk categorisation. The hazard coefficient (HQ) and non-carcinogenic hazard index (HI) were calculated for Cd, Cr, Cu, Ni, Pb, and Zn. HQ had the highest value for the ingestion pathway (3.62 ∙ 10–6), and the value for non-carcinogenic HI was 3.70 ∙ 10–6. The value HI < 1 suggests that there is no risk to operator health related to heavy metals in analysed wood pellets ash. The carcinogenic risk (CR) was calculated for Ni, Pb, Cr, and Cd, and the values were within the permitted limits. The risk assessment based on HI and CR indicators proved that there was no significant health concern regarding exposure to the analysed ashes. Pepeo je nusproizvod izgaranja drvne biomase koji se svakodnevno mora uklanjati iz peći ili kamina. Stoga su operateri ili vlasnici izloženi potencijalnom utjecaju pepela. Ovo istraživanje ima cilj procijeniti zdravstveni rizik izloženosti operatera/vlasnika pepelu drvenih peleta zbog sadržaja teških metala. Postupak procjene rizika proveden je u nekoliko koraka uključujući procjenu izloženosti, procjenu toksičnosti i kategorizaciju rizika. Izračunati su koeficijent opasnosti (HQ) i indeks nekarcinogene opasnosti (HI) za Cd, Cr, Cu, Ni, Pb i Zn. HQ je imao najveću vrijednost za izloženost putem gutanja (3.62 ∙ 10–6), a vrijednost za nekarcinogeni HI bila je 3.70 ∙ 10–6. Vrijednost HI < 1 ukazuje na to da sadržaj teških metala u analiziranom pepelu ne predstavlja rizik za zdravlje operatera. Karcinogeni rizik (CR) izračunat je za Ni, Pb, Cr i Cd, a vrijednosti su bile unutar dopuštenih granica. Rizik procijenjen primjenom HI i CR pokazatelja potvrdio je da ne postoji značajna opasnost za zdravlje osoba koje dolaze u kontakt s analiziranim pepelom.

  • Open Access English
    Authors: 
    Malika Khelladi; Meriem Abaidia; Senouci Boulerial; Khalida Bekrentchir; Abdellah Benhamou; Abdelkader Debab;
    Country: Croatia

    As part of a comprehensive evaluation of post-treatment techniques for the removal of chemical and microbiological pollutants from lagoon effluents, an aerated biofilter was designed. The main objective of this study was to evaluate the performance of pozzolan and Luffa cylindrica as low-cost packing materials for the advanced treatment of Stidia natural lagoon effluent. The aerated biofilter operates in down-flow with HLRs of 11.37 to 28.43 m3 m–2 d–1 and an air/liquid flow ratio of 3 : 1. The different experiments performed on the pilot showed that the percentages of sCOD removal vary with the HLRs and the wastewater concentration at the biofilter inlet. In this study, sCOD removal efficiencies above 78.9 % were achieved depending on HLR, and a maximum removal efficiency of TSS of 71.5 % was obtained for 28.43 m3 m–2 d–1. At low HLR (11.37 m3 m–2 d–1), the treated effluent had the following average concentrations: sCOD of 29.5 mg l–1, BOD5 of 21.7 mg l–1 and TSS of 26.4 mg l–1. These experimental results were used with an empirical model to determine the media constant n and treatability factor K. The faecal coliforms and Escherichia coli detected in the treated effluent were less than 105 CFU/100 ml, which meet the national guidelines for wastewater reuse in irrigation. U sklopu sveobuhvatne procjene tehnika naknadnog uklanjanja kemijskih i mikrobioloških onečišćenja iz efluenta laguna, projektiran je aerirani biofiltar. Glavni cilj ovog istraživanja bio je procijeniti učinak pucolana i biljke Luffa cylindrica kao jeftinih punila za naprednu obradu efluenta prirodne lagune Stidia. Aerirani biofiltar radi s brzinom hidrauličkog opterećenja (HLR) od 11,37 do 28,43 m3 m–2 d–1 i omjerom protoka zrak/tekućina od 3 : 1. Eksperimenti provedeni na pilotu pokazuju da smanjenje KPK (izražene s obzirom na otopljene tvari) varira ovisno o HLR-u i koncentraciji otpadne vode na ulazu u biofiltar. U ovom istraživanju postignute su učinkovitost smanjenja KPK iznad 78,9 % ovisno o HLR-u, a maksimalna učinkovitost uklanjanja ukupnih suspendiranih čestica (TSS) od 71,5 % dobivena je pri 28,43 m3 m–2 d–1. Pri niskom HLR-u (11,37 m3 m–2 d–1), KPK, BPK5 i TSS obrađene otpadne vode iznosili su 29,5 mg l–1, 21,7 mg l–1 odnosno 26,4 mg l–1. Ti eksperimentalni rezultati korišteni su u empirijskom modelu da bi se odredila konstanta medija n i faktor obrade K. CFU vrijednosti fekalnih koliforma i bakterije Escherichia coli u obrađenoj otpadnoj vodi bile su ispod 105 CFU/100 ml što zadovoljava nacionalne smjernice za upotrebu tih voda u navodnjavanju zemljišta.

  • Open Access English
    Authors: 
    Wahiba Maouche; Mustapha Douani; Abdallah Labbaci; Ümran Tezcan Ün; Masoud Derakhshandeh;
    Country: Croatia

    For major thermal engines used in industrial sectors, the use of chillers has been growing steadily over the previous decades. Indeed, this is linked strongly to their large energy performance despite their investment costs, which are still high, in particular for low powers. Performance coefficients for absorption chillers are relatively low, and their profitability depends on the costs of the main equipment and more particularly on the price of the absorber. Several studies focusing on the development of mass contactors are underway with the principal objective of further improving their performance of mass and energy transfer. Relating to the mass and heat transfer, it is specified that the contact between the phases in circulation is ensured by different types of contactors. The transfer performance is correlated with the heat and mass transfer coefficient on the one hand, and the specific exchange area, i.e., the exchange area per unit volume of the contactor on the other hand. These contactors are distinguished by their mode of contact between phases (bubbling, spraying, falling film, etc.). While the exchange coefficient depends on the hydrodynamics regime in the contactor (flow regime and physicochemical properties of phases), the specific exchange area is dictated by its operating mode. Any limitation of its use for a specific application (physicochemical phenomena, such as crystallisation, deposited dust, etc.) requires research and development of better devices more adapted. Moreover, the most used contactors in chemical engineering are plate columns, packed columns, falling film columns, spray columns, etc. In order to intensify exchanges, a new absorber of the pulverised type is to be explored in relation with the physicochemical properties of the phases, and of their hydrodynamic flow conditions in the sprayed column. Therefore, an experimental study of the influence of operating variables (nozzle diameter, fluids flow rate, their concentrations, size of droplets, etc.) on the overall coefficient of mass transfer in gaseous phase in the absorber of the absorber chiller was conducted. After having fixed the pressure in the absorber, the first part of the study allowed developing new correlations linking the experimental results of the KG ∙ a to all operating variables (L, C, dd, etc.). The second part was devoted to the simulation of the absorption chiller functioning by introducing the concept of energy and exergy yields based on the mass transfer correlations. Posljednjih desetljeća vidljiv je stalan porast upotrebe rashladnih uređaja kod glavnih toplinskih motora koji se upotrebljavaju u industrijskim sektorima. Koeficijenti učinka apsorpcijskih rashladnih uređaja relativno su niski, a njihova isplativost ovisi o troškovima glavne opreme, točnije o cijeni apsorbera. U tijeku je nekoliko studija razvoja kontaktora masa usmjerenih na poboljšanje prijenosa tvari i energije u kontaktorima. Vezano uz prijenos tvari i topline, specificirano je da se kontakt između cirkulirajućih faza ostvaruje različitim tipovima kontaktora. Učinak prijenosa koreliran je s koeficijentom prijenosa tvari i topline s jedne strane te specifičnom površinom izmjene, tj. površinom izmjene po jedinici volumena kontaktora, s druge strane. Kontaktori se razlikuju po načinu kontakta faza (mjehurići, raspršenje, padajući film, itd.). Dok koeficijent izmjene ovisi o hidrodinamičkom režimu u kontaktoru (režim protoka i fizikalno-kemijska svojstva faza), specifična površina izmjene ovisi o njegovu načinu rada. Ograničenje njegove uporabe na neku određenu primjenu (fizikalno-kemijske pojave poput kristalizacije) zahtijeva istraživanje i razvoj uređaja koji bi više bili prilagođeni spomenutoj primjeni. Štoviše, najčešće upotrebljavani kontaktori u kemijskom inženjerstvu su kolone s pliticama, kolone s punilima, kolone s padajućim filmovima, kolone za raspršivanje, itd. S ciljem povećanja izmjena, istražit će se novi praškasti apsorber i to s obzirom na fizikalno-kemijska svojstva faza i njihove hidrodinamičke uvjete strujanja u koloni za raspršivanje. Stoga je provedeno istraživanje utjecaja radnih varijabli (promjera mlaznice, protoka fluida, koncentracije fluida, veličine kapljica, itd.) na ukupni koeficijent prijenosa tvari u plinovitoj fazi u apsorberu rashladnog uređaja. Nakon fiksiranja tlaka u apsorberu, prvi dio istraživanja omogućio je razvoj novih korelacija koje povezuju eksperimentalne KG ∙ a rezultate sa svim radnim varijablama (L, C, dd, itd.). Drugi dio bio je posvećen simulaciji rada apsorpcijskog rashladnog uređaja uvođenjem koncepta energetskih i eksergijskih prinosa temeljenih na izrazima za prijenos tvari.

  • Open Access English
    Authors: 
    Zahira Mohamed Seghir; M'hamed Djennad; Reinhard Schomäcker; Mouffok Rédouane Ghezzar;
    Country: Croatia

    The requirement for environmentally friendly catalysts for the isomerization of alkanes has prompted research on the tungstate-zirconia (WZ) system. The present work examines the activity and selectivity of lanthanum (La) promoted tungstate-zirconia (LWZ) and niobium (Nb) promoted tungstate-zirconia (NWZ) catalysts. In this study, 1 % La promoted WZ (1 % LWZ) and 1 % Nb promoted WZ (1 % NWZ) catalysts were investigated in isomerization of n-butane in the presence of hydrogen. The studied catalysts were characterized by different methods: nitrogen physisorption, temperature programmed desorption of NH3, thermogravimetric analysis, and X-ray diffraction. The catalytic activity and selectivity were significantly improved by the addition of 1 % Nb. The redox process in the Nb-containing catalyst (1 % NWZ) played a central role by providing the highest acidic sites (283.53 µmol g–1) with appropriate activation energies for the skeletal rearrangement of the reactant (n-butane). Furthermore, this study highlights the determining role of the transfer process of adsorbed species from ZrO2 to W as well as to the Nb environment. The conversion of n-butane (27.34 %) and the selectivity to i-butane (92.34 %) for NWZ were significantly higher than WZ and LWZ catalysts. The experimental results revealed that Nb was a more effective promoter than La. Potreba za ekološki prihvatljivim katalizatorima primjenjivim za izomerizaciju alkana potaknuo je istraživanje sustava volframat-cirkonij (WZ). Ovaj rad ispituje aktivnost i selektivnost lantanom i niobijem potaknutih WZ katalizatora. U studiji je ispitana primjena WZ katalizatora potaknutih dodatkom 1 % lantana (1 % LWZ), odnosno 1 % niobija (1 % NWZ), u izomerizaciji n-butana u prisutnosti vodika. Karakterizacija je provedena različitim metodama: fizisorpcijom dušika, temperaturno programiranom desorpcijom amonijaka, termogravimetrijskom analizom i rendgenskom difrakcijskom analizom. Katalitička aktivnost i selektivnost znatno su poboljšani dodatkom 1 % niobija. Redoks-proces u katalizatoru koji je sadržavao niobij odigrao je glavnu ulogu osiguravajući najviše kiselih mjesta (283,53 µmol g–1) s odgovarajućom energijom aktivacije za preslagivanje n-butana. Konverzija n-butana (27,34 %) i selektivnost prema i-butanu (92,34 %) kod NWZ katalizatora bili su znatno veći nego kod WZ i LWZ katalizatora. Eksperimentalna istraživanja ukazuju učinkovitije poticanje dodatkom niobija u usporedbi s lantanom.

  • Open Access English
    Authors: 
    Mirsada Salihović; Mirha Pazalja; Selma Špirtović-Halilović; Elma Veljović; Melita Huremović; Maida Srabović;
    Country: Croatia

    The content of micro- and macroelements in dry wild and edible Morchella esculenta and Lactarius piperatus mushrooms collected in Bosnia and Herzegovina was determined using the ICP-OES (inductively coupled plasma optical emission spectrometry) technique. The contents of microelements in M. esculenta and L. piperatus expressed in mg kg–1 DW (dry weight) were as follows: Co 0.08 and 0.28, Cu 37.35 and 27.66, Fe 174.29 and 28.11, Mn 21.26 and 19.31, Se 0.46 and 0.52, Zn 122.84 and 45.06, Al 27.80 and 24.80, Cr 0.83 and 1.06, Ni 0.99 and 0.96, As 0.32 and 0.09, Cd 0.48 and 0.13, and Pb 0.61 and 0.12, respectively, while the contents of macroelements were: K 26989.48 and 36117.20, Na 70.85 and 28.60, Ca 643.48 and 271.93, Mg 684.16 and 840.64, S 2329.33 and 610.42, and P 10339.35 and 5107.63, respectively. In this study, the potential health risks of heavy metals were assessed, and target hazard quotient (THQ) for As, Cd, Pb, Cu, Zn, Ni, and Cr in the tested mushrooms was lower than the safe level. Edible wild mushrooms M. esculenta and L. piperatus, according to this study, could be used in human nutrition due to their favourable characteristics. Based on the accumulations of heavy metals in the tested mushrooms, it was shown that the collection surfaces are environmentally acceptable. Mushrooms collected from this area are generally safe to eat and pose no health risks to humans. Sadržaj mikro i makroelemenata u sušenim divljim jestivim gljivama Morchella esculenta i Lactarius piperatus prikupljenim u Bosni i Hercegovini određen je tehnikom ICP-OES (induktivno spregnuta plazma s optičkom emisijskom spektrometrijom). Sadržaj mikroelemenata kod M. esculenta i L. piperatus izražen u mg kg–1 suhe težine bio je sljedeći: Co 0,08 i 0,28, Cu 37,35 i 27,66, Fe 174,29 i 28,11, Mn 21,26 i 19,31, Se 0,46 i 0,52, Zn 122,84 i 45,06, Al 27,80 i 24,80, Cr 0,83 i 1,06, Ni 0,99 i 0,96, As 0,32 i 0,09, Cd 0,48 i 0,13, te Pb 0,61 i 0,12, dok je sadržaj makroelemenata bio: K 26989,48 i 36117,20, Na 70,85 i 28,60, Ca 643,48 i 271,93, Mg 684,16 i 840,64, S 2329,33 i 610,42, te P 10339,35 i 5107,63. U ovom radu procijenjeni su potencijalni zdravstveni rizici teških metala, a kvocijent ciljane opasnosti (THQ) za As, Cd, Pb, Cu, Zn, Ni i Cr u ispitivanim gljivama bio je niži od sigurnosne razine. Prema rezultatima istraživanja, divlje jestive gljive M. esculenta i L. piperatus, zbog svojih povoljnih karakteristika, mogle bi se upotrebljavati u ljudskoj prehrani. Podatci o akumuliranosti teških metala u ispitivanim gljivama pokazali su da su sabirne površine ekološki prihvatljive, a gljive sigurne za jelo.

  • Open Access English
    Authors: 
    Safia Ali Haimoud; Nesrine Naas; Imane Kebaili;
    Country: Croatia

    Enrichment of food is a strategy to reduce the incidence of deficiencies in micronutrients in a population. Couscous is widely consumed in Algeria, thus the objective of this study was to obtain an enriched couscous with enhanced therapeutic potencies and with good physicochemical, technological, and microbiological characteristics. Three mass ratios of the traditional preparation Issoufer (10, 20, and 30 %) were added to wheat couscous, and then compared with a control couscous made 100 % of semolina. A significant (p < 0.05) increase was noticed in the ash, proteins, lipids, carbohydrates, phenolic compounds, flavonoids, and anti-radical activity values, for all the mass ratios of Issoufer powder. In contrast, the moisture and pH-value revealed a significant (p < 0.05) decrease in Issoufer powder. The acute toxicity study revealed no lethal effects and behavioural signs of toxicity at the tested doses (100, 250, 500, and 750 mg kg–1) of the extract of Issoufer during the 5 days of observation. The results of antibacterial activity showed diameters of inhibition zones had achieved 29.90±0.60 mm. Based on obtained results, Issoufer powder can be considered a good ingredient to develop functional couscous naturally enriched of secondary metabolites, and can be used in the prevention of several diseases, as well as used in the food industry. Obogaćivanje hrane je način da se smanji učestalost nedostataka mikronutrijenata u populaciji. Kus-kus je namirnica koja se u Alžiru konzumira u velikoj mjeri. Stoga je cilj ovog istraživanja bio dobiti obogaćeni kus-kus s poboljšanim terapeutskim potencijalom i dobrim fizikalno-kemijskim, tehnološkim i mikrobiološkim karakteristikama. Pšeničnom kus-kusu dodan je tradicionalni pripravak Issoufer (10, 20 i 30 %), te je smjesa uspoređena s kontrolnom čistom kus-kus krupicom. Znatno povećanje (p < 0,05) pepela, proteina, lipida, ugljikohidrata, fenolnih spojeva, flavonoida i anti-radikalne aktivnosti, zabilježeno je kod svih smjesa s dodanim Issoufer pripravkom. S druge strane, znatno (p < 0,05) su se smanjili udio vlage te pH-vrijednost. Studija akutne toksičnosti nije pokazala smrtonosne učinke i znakove toksičnosti pri ispitanim dozama ekstrakta Issoufera (100, 250, 500 i 750 mg kg–1) tijekom pet dana promatranja. Rezultati antibakterijske aktivnosti pokazali su da su promjeri zona inhibicije dosegli vrijednost od 29,90 ± 0,60 mm. Na temelju dobivenih rezultata, Issoufer prah može se smatrati dobrim sastojkom za razvoj funkcionalnog kus-kusa prirodno obogaćenog sekundarnim metabolitima te se može upotrebljavati za prevenciju više bolesti, ali i u prehrambenoj industriji.

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  • Open Access English
    Authors: 
    Amina Lachenani‬; Mohamed Bentchikou; Mouloud Boumahdi; Salah Hanini; Maamar Laidi;
    Country: Croatia

    U ovom radu predloženo je i primijenjeno šest novih matematičkih modela temeljenih na poluempirijskom proračunu za karakterizaciju procesa sušenja u pećnici kompozita cementne žbuke ojačane celuloznim vlaknima (CMCRCF). Pokusi sušenja provedeni su pri četiri razine temperature sušenja u pećnici (70, 85, 105 i 120 °C) s četiri različita udjela celuloznih vlakana (0, 5, 10 i 20 %). Dobiveni rezultati uspoređeni su s onima dobivenim regresijskom analizom šest najčešće primjenjivanih matematičkih modela sušenja (Newton, Page, Page modified1, Page modified2, Handerson Pabis i Logarithmic) uz šest predloženih modela. Regresijska točnost procesa sušenja procijenjena je koeficijentom determinacije (R2), srednjom kvadratnom pogreškom (MSE), korijenom srednje kvadratne pogreške (RMSE) i srednjom apsolutnom pogreškom (MAE). Primijenjeni su i dodatni kriteriji da bi se osigurala veća valjanost odabranih modela. Dobivene vrijednosti pokazuju dobro slaganje predloženog modela MR9 s eksperimentalnim vrijednostima, što znači da predloženi model može jasno interpretirati eksperimentalne podatke o sušenju i predvidjeti suho stanje CMCRCF-a. In this paper, six novel mathematical models based on semi-empirical calculus are proposed and applied to characterise the oven-drying process of cement mortar composites reinforced with cellulosic fibres (CMCRCFs). The drying experiments were carried out on four levels of oven-drying temperatures (70, 85, 105, and 120 °C), with four different cellulosic fibres content (0, 5, 10, and 20 %). Obtained results were compared to those derived by regression analysis of six most typically used mathematical drying models (Newton, Page, Page modified1, Page modified2, Handerson Pabis, and Logarithmic) in addition to six proposed models. The regression accuracy of the drying process was evaluated by the coefficient of determination (R2), low mean square error (MSE), low root mean squared error (RMSE), and mean absolute error (MAE). Additional criteria were used to ensure more validity of the selected models. The obtained values indicate a highly accurate fit of the proposed model MR9, meaning that the proposed model can clearly interpret the experimental drying data and predict the dry state of CMCRCFs.

  • Publication . Other literature type . Article . 2022
    Open Access English
    Authors: 
    Dornjak, Luka; Ostojić, Karla; Klaser, Teodoro; Urlić, Inga; Rogina, Anamarija;
    Country: Croatia

    Kitozanski nosači su efektivni biološki aktivni materijali sa širokom primjenom u kemiji i medicini. Kitozan je linearni polisaharid, derivat hitina, koji posjeduje dobru biokompatibilnost koja se pripisuje prisustvu funkcionalnih skupina kao što su −OH i −NH2 koje pridonose biorazgradljivim i antibakterijskim svojstvima. U kiselim vodenim otopinama kitozan je polikationske strukturne prirode, koja ima veliku sposobnost stvaranja kompleksa s različitim metalnim ionima i važnim biomolekulama, kao što su DNA, proteini i lipidi. Jedinstvena struktura, kao i uvođenje specifičnih funkcionalnih skupina odgovorni su za antibakterijska svojstva, hemostatsku aktivnost i analgetska svojstva tog biopolimera. Za poboljšanje angiogenih i antimikrobnih svojstava, kitozan se može modificirati borom (boratnim ionima). Cilj ovog rada bio je pripremiti bornom kiselinom modificirane kitozanske nosače, upotrebljavajući bornu kiselinu kao prekursor bora, u svrhu priprave potencijalnih bioaktivnih okosnica za regeneraciju tkiva. Boratni ioni imaju sklonost stvaranja kompleksa s hidroksilnim skupinama, međutim, takve interakcije između funkcionalnih skupina kitozana i bora rezultiraju slabijom učinkovitosti njegove inkapsulacije. Da bi se osigurala bolja ugradnja bora, kitozanski nosači su umreženi genipinom, manje toksičnim umreživalom u odnosu na glutaraldehid koji se obično upotrebljava za pripremu stabilnih materijala čiji se sastav temelji na kitozanu. Stupanj deacetilacije (DD) i koncentracija otopine kitozana kao i koncentracija otapala važni su parametri koji utječu na proces umreživanja. Nadalje, dodatak borne kiseline mogao bi utjecati na proces umreživanja zauzimanjem funkcionalnih skupina kitozana. U ovom radu kitozanski nosači modificirani su bornom kiselinom različite koncentracije, dok su koncentracija otopine kitozana (1,2 w/v), koncentracija genipina (2 % w/w) i koncentracija octene kiseline (0,5 % v/v) bile konstantne. Dobiveni nosači okarakterizirani su pretražnom elektronskom mikroskopijom (SEM), energetski disperzivnom rendgenskom spektroskopijom (EDS), diferencijalnom pretražnom kalorimetrijom (DSC), infracrvenom spektroskopijom s Fourierovom transformacijom (FTIR), dok je citotoksičnost procijenjena kao funkcija koncentracije materijala i vremena izloženosti stanica materijalu. Rezultati su pokazali uspješnu ugradnju bora u umrežene kitozanske nosače, visoko poroznu strukturu i nisku citotoksičnost. Chitosan scaffolds are an effective biologically active material with versatile application in chemistry and medicine. Chitosan is a linear polysaccharide, a derivative of chitin, with great biocompatibility due to the possession of functional groups such as −OH and −NH2, which allow for biodegradability and antibacterial function. Chitosan has a polycation nature allowing complex formation with metal ions and many biomolecules such as DNA, proteins and lipids, while its specific structure and functional groups are responsible for antibacterial, hemostatic, and analgesic properties. To improve its angiogenic and antimicrobial potential, chitosan can be modified by boron (borate ions). The aim of this work was to prepare boric acid modified chitosan scaffolds, using boric acid as a boron precursor, as potential bioactive scaffolds for tissue regeneration. Borate ions tend to form complexes with hydroxyl groups, however, such physical interactions between boron and chitosan functional groups result in poor encapsulation efficiency. To ensure higher boron incorporation, chitosan scaffolds were cross-linked by genipin, a cross linker with lower cytotoxicity in contrast to glutaraldehyde commonly used to prepare stable chitosan-based materials. The degree of deacetylation (DD) and concentration of chitosan solution as well as the concentration of a solvent are important parameters that affect the crosslinking process. Moreover, the addition of boric acid could interfere with the crosslinking process by occupying chitosan functional groups. Here, chitosan scaffolds were modified with different concentrations of boric acid, while the concentrations of chitosan solution (1.2 w/v), genipin (2 % w/w), and acetic acid (0.5 % v/v) were kept constant. Obtained scaffolds were characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR), while cytotoxicity was evaluated as a function of materials concentration and exposure time. The results indicated successful incorporation of boron into cross-linked chitosan scaffolds with highly porous structure and low cytotoxicity.

  • Open Access English
    Authors: 
    Bensaber Bensebia; Fatma Zohra Chaouche; Soumia Kouadri Moustefaï;
    Country: Croatia

    Knowledge of gas holdup is important for the development of the three-phase fluidized bed reactors. This work concerns the study of the effect of different operating conditions on gas retention in a turbulent bed contactor type 2 (TBC), such as superficial gas and liquid velocities, liquid to gas mass flows ratio (L/G), particle diameter and density, static bed height and free-open area of the supporting grid. The influence of the free area of the packing support grid (φ) on gas holdup was demonstrated and proved. The gas holdup increased to 22.92 % when φ decreased from 0.82 to 0.32. The experimental data (1746) led to the development of two correlations to predict gas holdup, one of which incorporated the ratio (L/G) which is an important design factor for gas-liquid contactors. The predicted results of holdup gas were in good agreement with the experimental data. Poznavanje zadržavanja plina važno je za razvoj trofaznih reaktora s fluidiziranim slojem. Ovaj rad bavi se proučavanjem utjecaja različitih radnih uvjeta na zadržavanje plina u kontaktoru s turbulentnim slojem tipa 2 (TBC), kao što su površinske brzine plina i tekućine, omjer masenih protoka tekućine i plina (L/G), promjer čestica i gustoća, statička visina sloja i slobodna otvorena površina potporne rešetke. Dokazan je utjecaj slobodne površine potporne rešetke (φ) na zadržavanje plina. Zadržavanje plina povećalo se na 22,92 % kad se φ smanjio s 0,82 na 0,32. Iz dobivenih eksperimentalnih rezultata (1746) razvile su se dvije korelacije za predviđanje zadržavanja plina, od kojih je jedna uključivala omjer L/G, koji je važan faktor pri dizajnu plinsko-tekućinskih kontaktora. Predviđeni rezultati zadržavanja plina podudarali su se s eksperimentalnim podatcima.

  • Publication . Other literature type . 2022
    Open Access English
    Authors: 
    Čulo, Ivana; Grgić, Filip; Jurina, Tamara; Šalić, Anita; Benković, Maja; Valinger, Davor; Gajdoš Kljusurić, Jasenka; Jurinjak Tušek, Ana; Zelić, Bruno;
    Country: Croatia

    Emulsions are traditionally prepared with the application of high shear forces generated by the use of static mixers, homogenisers, or ultrasound. The resulting emulsions are sensitive to change of process conditions. The application of high forces and temperatures can significantly affect the constituents of the emulsions and their final stability. Microfluidic technology seems to be a very efficient alternative to classic emulsification methods. The dimensions of microdevices in combination with continuous processes offer a great advantage over classic batch emulsification processes carried out on a larger scale. The small dimensions of the microdevices allow easy transport of equipment, better control and safety of the process, and intensified mass and energy transfer. The mixing time in microdevices is reduced to a few milliseconds because the molecules in the microchannels have a short diffusion path. In this paper, an overview of emulsification processes, the advantages of use of microfluidics in emulsification, and future perspectives of microemulsification are presented. Tradicionalno se emulzije pripremaju primjenom jakih smičnih sila koje nastaju upotrebom statičkih miješala, homogenizatora ili primjenom ultrazvuka. Tako proizvedene emulzije osjetljive su na promjenu procesnih uvjeta. Primjena jakih sila i povišenih temperatura može značajno utjecati na komponente emulzija i njihovu konačnu stabilnost. Primjena protočnih mikrosustava pokazala se učinkovitom alternativnom tehnologijom klasičnim metodama emulgiranja. Male dimenzije mikrouređaja u kombinaciji s kontinuiranom provedbom procesa omogućuje brojne prednosti u odnosu na klasične šaržne procese emulsifikacije koji se provode u većem mjerilu. Male dimenzije mikrouređaja omogućuju lakši transport opreme, bolju kontrolu i sigurnost procesa te intenzivniji prijenos tvari i topline. Vrijeme miješanja u mikrouređajima smanjeno je na nekoliko milisekundi zbog kratkog difuzijskog puta molekula u mikrokanalima. U ovom radu dan je pregled procesa emulgiranja, prednosti primjene protočnih mikrosustava u provedbi procesa emulgiranja te potencijalnih novih područja primjene te tehnologije.

  • Open Access English
    Authors: 
    Mirha Pazalja; Mirsada Salihović; Alisa Smajović;
    Country: Croatia

    Ash is a by-product of wood biomass combustion that must be removed daily from stoves or fireplaces. Therefore, operators or owners are exposed to the potential impact of ash. The goal of this study was to determine whether heavy metal present in wood pellet ash posed a health concern to stove operators/owners. The risk assessment procedure was carried out in several steps, including exposure evaluation, toxicity evaluation, and risk categorisation. The hazard coefficient (HQ) and non-carcinogenic hazard index (HI) were calculated for Cd, Cr, Cu, Ni, Pb, and Zn. HQ had the highest value for the ingestion pathway (3.62 ∙ 10–6), and the value for non-carcinogenic HI was 3.70 ∙ 10–6. The value HI < 1 suggests that there is no risk to operator health related to heavy metals in analysed wood pellets ash. The carcinogenic risk (CR) was calculated for Ni, Pb, Cr, and Cd, and the values were within the permitted limits. The risk assessment based on HI and CR indicators proved that there was no significant health concern regarding exposure to the analysed ashes. Pepeo je nusproizvod izgaranja drvne biomase koji se svakodnevno mora uklanjati iz peći ili kamina. Stoga su operateri ili vlasnici izloženi potencijalnom utjecaju pepela. Ovo istraživanje ima cilj procijeniti zdravstveni rizik izloženosti operatera/vlasnika pepelu drvenih peleta zbog sadržaja teških metala. Postupak procjene rizika proveden je u nekoliko koraka uključujući procjenu izloženosti, procjenu toksičnosti i kategorizaciju rizika. Izračunati su koeficijent opasnosti (HQ) i indeks nekarcinogene opasnosti (HI) za Cd, Cr, Cu, Ni, Pb i Zn. HQ je imao najveću vrijednost za izloženost putem gutanja (3.62 ∙ 10–6), a vrijednost za nekarcinogeni HI bila je 3.70 ∙ 10–6. Vrijednost HI < 1 ukazuje na to da sadržaj teških metala u analiziranom pepelu ne predstavlja rizik za zdravlje operatera. Karcinogeni rizik (CR) izračunat je za Ni, Pb, Cr i Cd, a vrijednosti su bile unutar dopuštenih granica. Rizik procijenjen primjenom HI i CR pokazatelja potvrdio je da ne postoji značajna opasnost za zdravlje osoba koje dolaze u kontakt s analiziranim pepelom.

  • Open Access English
    Authors: 
    Malika Khelladi; Meriem Abaidia; Senouci Boulerial; Khalida Bekrentchir; Abdellah Benhamou; Abdelkader Debab;
    Country: Croatia

    As part of a comprehensive evaluation of post-treatment techniques for the removal of chemical and microbiological pollutants from lagoon effluents, an aerated biofilter was designed. The main objective of this study was to evaluate the performance of pozzolan and Luffa cylindrica as low-cost packing materials for the advanced treatment of Stidia natural lagoon effluent. The aerated biofilter operates in down-flow with HLRs of 11.37 to 28.43 m3 m–2 d–1 and an air/liquid flow ratio of 3 : 1. The different experiments performed on the pilot showed that the percentages of sCOD removal vary with the HLRs and the wastewater concentration at the biofilter inlet. In this study, sCOD removal efficiencies above 78.9 % were achieved depending on HLR, and a maximum removal efficiency of TSS of 71.5 % was obtained for 28.43 m3 m–2 d–1. At low HLR (11.37 m3 m–2 d–1), the treated effluent had the following average concentrations: sCOD of 29.5 mg l–1, BOD5 of 21.7 mg l–1 and TSS of 26.4 mg l–1. These experimental results were used with an empirical model to determine the media constant n and treatability factor K. The faecal coliforms and Escherichia coli detected in the treated effluent were less than 105 CFU/100 ml, which meet the national guidelines for wastewater reuse in irrigation. U sklopu sveobuhvatne procjene tehnika naknadnog uklanjanja kemijskih i mikrobioloških onečišćenja iz efluenta laguna, projektiran je aerirani biofiltar. Glavni cilj ovog istraživanja bio je procijeniti učinak pucolana i biljke Luffa cylindrica kao jeftinih punila za naprednu obradu efluenta prirodne lagune Stidia. Aerirani biofiltar radi s brzinom hidrauličkog opterećenja (HLR) od 11,37 do 28,43 m3 m–2 d–1 i omjerom protoka zrak/tekućina od 3 : 1. Eksperimenti provedeni na pilotu pokazuju da smanjenje KPK (izražene s obzirom na otopljene tvari) varira ovisno o HLR-u i koncentraciji otpadne vode na ulazu u biofiltar. U ovom istraživanju postignute su učinkovitost smanjenja KPK iznad 78,9 % ovisno o HLR-u, a maksimalna učinkovitost uklanjanja ukupnih suspendiranih čestica (TSS) od 71,5 % dobivena je pri 28,43 m3 m–2 d–1. Pri niskom HLR-u (11,37 m3 m–2 d–1), KPK, BPK5 i TSS obrađene otpadne vode iznosili su 29,5 mg l–1, 21,7 mg l–1 odnosno 26,4 mg l–1. Ti eksperimentalni rezultati korišteni su u empirijskom modelu da bi se odredila konstanta medija n i faktor obrade K. CFU vrijednosti fekalnih koliforma i bakterije Escherichia coli u obrađenoj otpadnoj vodi bile su ispod 105 CFU/100 ml što zadovoljava nacionalne smjernice za upotrebu tih voda u navodnjavanju zemljišta.

  • Open Access English
    Authors: 
    Wahiba Maouche; Mustapha Douani; Abdallah Labbaci; Ümran Tezcan Ün; Masoud Derakhshandeh;
    Country: Croatia

    For major thermal engines used in industrial sectors, the use of chillers has been growing steadily over the previous decades. Indeed, this is linked strongly to their large energy performance despite their investment costs, which are still high, in particular for low powers. Performance coefficients for absorption chillers are relatively low, and their profitability depends on the costs of the main equipment and more particularly on the price of the absorber. Several studies focusing on the development of mass contactors are underway with the principal objective of further improving their performance of mass and energy transfer. Relating to the mass and heat transfer, it is specified that the contact between the phases in circulation is ensured by different types of contactors. The transfer performance is correlated with the heat and mass transfer coefficient on the one hand, and the specific exchange area, i.e., the exchange area per unit volume of the contactor on the other hand. These contactors are distinguished by their mode of contact between phases (bubbling, spraying, falling film, etc.). While the exchange coefficient depends on the hydrodynamics regime in the contactor (flow regime and physicochemical properties of phases), the specific exchange area is dictated by its operating mode. Any limitation of its use for a specific application (physicochemical phenomena, such as crystallisation, deposited dust, etc.) requires research and development of better devices more adapted. Moreover, the most used contactors in chemical engineering are plate columns, packed columns, falling film columns, spray columns, etc. In order to intensify exchanges, a new absorber of the pulverised type is to be explored in relation with the physicochemical properties of the phases, and of their hydrodynamic flow conditions in the sprayed column. Therefore, an experimental study of the influence of operating variables (nozzle diameter, fluids flow rate, their concentrations, size of droplets, etc.) on the overall coefficient of mass transfer in gaseous phase in the absorber of the absorber chiller was conducted. After having fixed the pressure in the absorber, the first part of the study allowed developing new correlations linking the experimental results of the KG ∙ a to all operating variables (L, C, dd, etc.). The second part was devoted to the simulation of the absorption chiller functioning by introducing the concept of energy and exergy yields based on the mass transfer correlations. Posljednjih desetljeća vidljiv je stalan porast upotrebe rashladnih uređaja kod glavnih toplinskih motora koji se upotrebljavaju u industrijskim sektorima. Koeficijenti učinka apsorpcijskih rashladnih uređaja relativno su niski, a njihova isplativost ovisi o troškovima glavne opreme, točnije o cijeni apsorbera. U tijeku je nekoliko studija razvoja kontaktora masa usmjerenih na poboljšanje prijenosa tvari i energije u kontaktorima. Vezano uz prijenos tvari i topline, specificirano je da se kontakt između cirkulirajućih faza ostvaruje različitim tipovima kontaktora. Učinak prijenosa koreliran je s koeficijentom prijenosa tvari i topline s jedne strane te specifičnom površinom izmjene, tj. površinom izmjene po jedinici volumena kontaktora, s druge strane. Kontaktori se razlikuju po načinu kontakta faza (mjehurići, raspršenje, padajući film, itd.). Dok koeficijent izmjene ovisi o hidrodinamičkom režimu u kontaktoru (režim protoka i fizikalno-kemijska svojstva faza), specifična površina izmjene ovisi o njegovu načinu rada. Ograničenje njegove uporabe na neku određenu primjenu (fizikalno-kemijske pojave poput kristalizacije) zahtijeva istraživanje i razvoj uređaja koji bi više bili prilagođeni spomenutoj primjeni. Štoviše, najčešće upotrebljavani kontaktori u kemijskom inženjerstvu su kolone s pliticama, kolone s punilima, kolone s padajućim filmovima, kolone za raspršivanje, itd. S ciljem povećanja izmjena, istražit će se novi praškasti apsorber i to s obzirom na fizikalno-kemijska svojstva faza i njihove hidrodinamičke uvjete strujanja u koloni za raspršivanje. Stoga je provedeno istraživanje utjecaja radnih varijabli (promjera mlaznice, protoka fluida, koncentracije fluida, veličine kapljica, itd.) na ukupni koeficijent prijenosa tvari u plinovitoj fazi u apsorberu rashladnog uređaja. Nakon fiksiranja tlaka u apsorberu, prvi dio istraživanja omogućio je razvoj novih korelacija koje povezuju eksperimentalne KG ∙ a rezultate sa svim radnim varijablama (L, C, dd, itd.). Drugi dio bio je posvećen simulaciji rada apsorpcijskog rashladnog uređaja uvođenjem koncepta energetskih i eksergijskih prinosa temeljenih na izrazima za prijenos tvari.

  • Open Access English
    Authors: 
    Zahira Mohamed Seghir; M'hamed Djennad; Reinhard Schomäcker; Mouffok Rédouane Ghezzar;
    Country: Croatia

    The requirement for environmentally friendly catalysts for the isomerization of alkanes has prompted research on the tungstate-zirconia (WZ) system. The present work examines the activity and selectivity of lanthanum (La) promoted tungstate-zirconia (LWZ) and niobium (Nb) promoted tungstate-zirconia (NWZ) catalysts. In this study, 1 % La promoted WZ (1 % LWZ) and 1 % Nb promoted WZ (1 % NWZ) catalysts were investigated in isomerization of n-butane in the presence of hydrogen. The studied catalysts were characterized by different methods: nitrogen physisorption, temperature programmed desorption of NH3, thermogravimetric analysis, and X-ray diffraction. The catalytic activity and selectivity were significantly improved by the addition of 1 % Nb. The redox process in the Nb-containing catalyst (1 % NWZ) played a central role by providing the highest acidic sites (283.53 µmol g–1) with appropriate activation energies for the skeletal rearrangement of the reactant (n-butane). Furthermore, this study highlights the determining role of the transfer process of adsorbed species from ZrO2 to W as well as to the Nb environment. The conversion of n-butane (27.34 %) and the selectivity to i-butane (92.34 %) for NWZ were significantly higher than WZ and LWZ catalysts. The experimental results revealed that Nb was a more effective promoter than La. Potreba za ekološki prihvatljivim katalizatorima primjenjivim za izomerizaciju alkana potaknuo je istraživanje sustava volframat-cirkonij (WZ). Ovaj rad ispituje aktivnost i selektivnost lantanom i niobijem potaknutih WZ katalizatora. U studiji je ispitana primjena WZ katalizatora potaknutih dodatkom 1 % lantana (1 % LWZ), odnosno 1 % niobija (1 % NWZ), u izomerizaciji n-butana u prisutnosti vodika. Karakterizacija je provedena različitim metodama: fizisorpcijom dušika, temperaturno programiranom desorpcijom amonijaka, termogravimetrijskom analizom i rendgenskom difrakcijskom analizom. Katalitička aktivnost i selektivnost znatno su poboljšani dodatkom 1 % niobija. Redoks-proces u katalizatoru koji je sadržavao niobij odigrao je glavnu ulogu osiguravajući najviše kiselih mjesta (283,53 µmol g–1) s odgovarajućom energijom aktivacije za preslagivanje n-butana. Konverzija n-butana (27,34 %) i selektivnost prema i-butanu (92,34 %) kod NWZ katalizatora bili su znatno veći nego kod WZ i LWZ katalizatora. Eksperimentalna istraživanja ukazuju učinkovitije poticanje dodatkom niobija u usporedbi s lantanom.

  • Open Access English
    Authors: 
    Mirsada Salihović; Mirha Pazalja; Selma Špirtović-Halilović; Elma Veljović; Melita Huremović; Maida Srabović;
    Country: Croatia

    The content of micro- and macroelements in dry wild and edible Morchella esculenta and Lactarius piperatus mushrooms collected in Bosnia and Herzegovina was determined using the ICP-OES (inductively coupled plasma optical emission spectrometry) technique. The contents of microelements in M. esculenta and L. piperatus expressed in mg kg–1 DW (dry weight) were as follows: Co 0.08 and 0.28, Cu 37.35 and 27.66, Fe 174.29 and 28.11, Mn 21.26 and 19.31, Se 0.46 and 0.52, Zn 122.84 and 45.06, Al 27.80 and 24.80, Cr 0.83 and 1.06, Ni 0.99 and 0.96, As 0.32 and 0.09, Cd 0.48 and 0.13, and Pb 0.61 and 0.12, respectively, while the contents of macroelements were: K 26989.48 and 36117.20, Na 70.85 and 28.60, Ca 643.48 and 271.93, Mg 684.16 and 840.64, S 2329.33 and 610.42, and P 10339.35 and 5107.63, respectively. In this study, the potential health risks of heavy metals were assessed, and target hazard quotient (THQ) for As, Cd, Pb, Cu, Zn, Ni, and Cr in the tested mushrooms was lower than the safe level. Edible wild mushrooms M. esculenta and L. piperatus, according to this study, could be used in human nutrition due to their favourable characteristics. Based on the accumulations of heavy metals in the tested mushrooms, it was shown that the collection surfaces are environmentally acceptable. Mushrooms collected from this area are generally safe to eat and pose no health risks to humans. Sadržaj mikro i makroelemenata u sušenim divljim jestivim gljivama Morchella esculenta i Lactarius piperatus prikupljenim u Bosni i Hercegovini određen je tehnikom ICP-OES (induktivno spregnuta plazma s optičkom emisijskom spektrometrijom). Sadržaj mikroelemenata kod M. esculenta i L. piperatus izražen u mg kg–1 suhe težine bio je sljedeći: Co 0,08 i 0,28, Cu 37,35 i 27,66, Fe 174,29 i 28,11, Mn 21,26 i 19,31, Se 0,46 i 0,52, Zn 122,84 i 45,06, Al 27,80 i 24,80, Cr 0,83 i 1,06, Ni 0,99 i 0,96, As 0,32 i 0,09, Cd 0,48 i 0,13, te Pb 0,61 i 0,12, dok je sadržaj makroelemenata bio: K 26989,48 i 36117,20, Na 70,85 i 28,60, Ca 643,48 i 271,93, Mg 684,16 i 840,64, S 2329,33 i 610,42, te P 10339,35 i 5107,63. U ovom radu procijenjeni su potencijalni zdravstveni rizici teških metala, a kvocijent ciljane opasnosti (THQ) za As, Cd, Pb, Cu, Zn, Ni i Cr u ispitivanim gljivama bio je niži od sigurnosne razine. Prema rezultatima istraživanja, divlje jestive gljive M. esculenta i L. piperatus, zbog svojih povoljnih karakteristika, mogle bi se upotrebljavati u ljudskoj prehrani. Podatci o akumuliranosti teških metala u ispitivanim gljivama pokazali su da su sabirne površine ekološki prihvatljive, a gljive sigurne za jelo.

  • Open Access English
    Authors: 
    Safia Ali Haimoud; Nesrine Naas; Imane Kebaili;
    Country: Croatia

    Enrichment of food is a strategy to reduce the incidence of deficiencies in micronutrients in a population. Couscous is widely consumed in Algeria, thus the objective of this study was to obtain an enriched couscous with enhanced therapeutic potencies and with good physicochemical, technological, and microbiological characteristics. Three mass ratios of the traditional preparation Issoufer (10, 20, and 30 %) were added to wheat couscous, and then compared with a control couscous made 100 % of semolina. A significant (p < 0.05) increase was noticed in the ash, proteins, lipids, carbohydrates, phenolic compounds, flavonoids, and anti-radical activity values, for all the mass ratios of Issoufer powder. In contrast, the moisture and pH-value revealed a significant (p < 0.05) decrease in Issoufer powder. The acute toxicity study revealed no lethal effects and behavioural signs of toxicity at the tested doses (100, 250, 500, and 750 mg kg–1) of the extract of Issoufer during the 5 days of observation. The results of antibacterial activity showed diameters of inhibition zones had achieved 29.90±0.60 mm. Based on obtained results, Issoufer powder can be considered a good ingredient to develop functional couscous naturally enriched of secondary metabolites, and can be used in the prevention of several diseases, as well as used in the food industry. Obogaćivanje hrane je način da se smanji učestalost nedostataka mikronutrijenata u populaciji. Kus-kus je namirnica koja se u Alžiru konzumira u velikoj mjeri. Stoga je cilj ovog istraživanja bio dobiti obogaćeni kus-kus s poboljšanim terapeutskim potencijalom i dobrim fizikalno-kemijskim, tehnološkim i mikrobiološkim karakteristikama. Pšeničnom kus-kusu dodan je tradicionalni pripravak Issoufer (10, 20 i 30 %), te je smjesa uspoređena s kontrolnom čistom kus-kus krupicom. Znatno povećanje (p < 0,05) pepela, proteina, lipida, ugljikohidrata, fenolnih spojeva, flavonoida i anti-radikalne aktivnosti, zabilježeno je kod svih smjesa s dodanim Issoufer pripravkom. S druge strane, znatno (p < 0,05) su se smanjili udio vlage te pH-vrijednost. Studija akutne toksičnosti nije pokazala smrtonosne učinke i znakove toksičnosti pri ispitanim dozama ekstrakta Issoufera (100, 250, 500 i 750 mg kg–1) tijekom pet dana promatranja. Rezultati antibakterijske aktivnosti pokazali su da su promjeri zona inhibicije dosegli vrijednost od 29,90 ± 0,60 mm. Na temelju dobivenih rezultata, Issoufer prah može se smatrati dobrim sastojkom za razvoj funkcionalnog kus-kusa prirodno obogaćenog sekundarnim metabolitima te se može upotrebljavati za prevenciju više bolesti, ali i u prehrambenoj industriji.

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