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  • Open Access English
    Authors: 
    Marina Šekutor; Kata Mlinarić-Majerski;
    Country: Croatia

    Biološka aktivnost različitih adamantanskih derivata i njihova primjena opisane su u brojnim preglednim člancima. Isto tako, mnogi revijalni članci opisuju biološku aktivnost i primjenu gvanidinskih spojeva. Međutim, do sada nije načinjen pregled koji bi se bavio gvanidinskim derivatima adamantana i drugih policikla, tj. spojevima koji sadrže obje navedene podjedinice u istoj molekuli. U ovom radu bit će stoga dan pregled policikličkih derivata gvanidina, i to s naglaskom na njihovu primjenu kao potencijalnih farmakofora.

  • Publication . Article . 2019
    Open Access English
    Authors: 
    Nenad Raos;
    Publisher: Croatian Society of Chemical Engineers

    Rad se bavi razvojem pojma elementa od antičkih vremena (Empedoklo, Aristotel) preko razdoblja alkemije i rane kemije (Paracelsus, Petar Bono, Boyle) te početaka moderne kemije (Lavoisier, Mendeljejev) do suvremenih shvaćanja utemeljenih na atomskoj teoriji. Pokazuje se da pojam elementa ima dva značenja, elementarne (jednostavne) tvari i elementa u užem smislu; dok se prvi pojam razvijao prateći napredak metoda kemijske analize, za razumijevanje drugog pojma, pojma elementa, bilo je nužno steći dublji uvid u narav kemijskih promjena.

  • Publication . Article . Other literature type . 2017
    Open Access English
    Authors: 
    Molčanov, Krešimir; Institut Ruđer Bošković, Bijenička 54, HR-10 000 Zagreb;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Radikale, kemijske vrste s nesparenim elektronima, obično se smatra vrlo nestablinima, tako da ih se može pri - praviti samo pod posebnim uvjetima i proučavati samo pomoću posebnih, vrlo skupih, instrumenata. Također ih se smatra štetnima te neprimjerenima za pokuse u školi. Ipak, radikali imaju ključnu ulogu u biološkim susta - vima. Zahvaljujući nesparenim elektronima, obično su živo obojani, tako da se njihovo nastajanje često može opaziti golim okom. Ovdje je opisano nekoliko jednostavnih reakcijâ s biološki najvažnijim radikalom, semikinonom. Lako ih je izvesti u školskom laboratoriju uporabom male količine jeftinih i bezopasnih tvari. Jednostavnim promatranjem tih reakcijâ dade se naučiti mnogo toga o kemiji (slob odnih) radikala

  • Open Access English
    Authors: 
    Valdrin Beluli;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Gjilan (42˚28’08” V, 21˚27’48” L) is one of the seven largest cities in Kosovo. Throughout the city flow three rivers: Mirusha and Stanishor which mix and discharge into the largest river called Morava. The reason for the research of these rivers is the extreme pollution resulting from the discharge of industrial waters. Analysis of these rivers shows that they are extremely polluted and some physicochemical parameters are not in accordance with the regulations of the European Union (EU) and the World Health Organization (WHO). Parameters analysed are: pH, CW, NTU, DO, COD, BOD5, A-HCl, HCO3, GH, CS, Cl–, Cl2, Ca2+, Mg2+, NO2–, NO3–, PO43–, and NH3–. This work is licensed under a Creative Commons Attribution 4.0 International License. Grad Gjilan (42˚28’08”, V 21˚27’48” L) jedan je od sedam najvećih gradova na Kosovu. Kroz njega prolaze tri rijeke: Mirusha i Stanishor koje se miješaju i ulijevaju u najveću rijeku Moravu. Razlog za istraživanje tih rijeka je njihovo onečišćenje nastalo ispuštanjem industrijskih voda. Analiza tih rijeka pokazuje izrazito onečišćenje te neusklađenost nekih fizikalno-kemijskih parametara s propisima Europske unije (EU) i Svjetske zdravstvene organizacije (SZO). Analizirani su sljedeći parametri: pH, CW, NTU, DO, COD, BOD5, A-HCl, HCO3, GH, CS, Cl–, Cl2, Ca2+, Mg2+, NO2–, NO3–, PO43– i NH3–. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

  • Open Access English
    Authors: 
    Shulan Yu; Jialin Peng; Xinwen Zhang; Guoguang Wang;
    Publisher: Croatian Society of Chemical Engineers

    It is of great challenge and significance to recycle activated carbon (AC), yet still with various problems in operation. Here, we have performed a simulation on the regeneration of AC by using an indirect heating method with an unsteady cylindrical heat transfer model. The result has shown that the optimal parameters for a regeneration tube of outer diameter Φ = 108 with wall thickness 4 mm were: heating in the tube for 30 min at a surrounding temperature of 550 °C. In these conditions, a temperature of 417.5 °C could be obtained at the centre of the cylindrical tube, reaching the temperature required for AC regeneration. The experimental values obtained in our laboratory were consistent with the simulation, providing significant references for scaling up pilot plant of AC regeneration.

  • Open Access English
    Authors: 
    Hichem Tahraoui; Abd Elmouneïm Belhadj; Adh’ya-eddine Hamitouche;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    The region of Médéa (Algeria) located in an agricultural site requires a large amount of drinking water. For this purpose, the water analyses in question are imperative. To examine the evolution of the drinking water quality in this region, firstly, an experimental protocol was done in order to obtain a dataset by taking into account several physicochemical parameters. Secondly, the obtained data set was divided into two parts to form the artificial neural network, where 70 % of the data set was used for training, and the remaining 30 % was also divided into two equal parts: one for testing and the other for validation of the model. The intelligent model obtained was evaluated as a function of the correlation coefficient nearest to 1 and lowest mean square error (RMSE). A set of 84 data points were used in this study. Eighteen parameters in the input layer, five neurons in the hidden layer, and one parameter in the output layer were used for the ANN modelling. Levenberg Marquardt learning (LM) algorithm, logarithmic sigmoid, and linear transfer function were used, respectively, for the hidden and the output layers. The results obtained during the present study showed a correlation coefficient of R = 0.99276 with root mean square error RMSE = 11.52613 mg dm–3. These results show that obtained ANN model gave far better and more significant results. It is obviously more accurate since its relative error is small with a correlation coefficient close to unity. Finally, it can be concluded that obtained model can effectively predict the rate of soluble bicarbonate in drinking water in the Médéa region. This work is licensed under a Creative Commons Attribution 4.0 International License. Regija Médéa (Alžir) smještena na poljoprivrednom zemljištu zahtijeva veliku količinu pitke vode te je stoga analiza vode od iznimne važnosti. Da bi se ispitao razvoj kvalitete pitke vode u toj regiji, najprije je napravljen eksperimentalni protokol za dobivanje skupa podataka uzimajući u obzir nekoliko fizikalno-kemijskih parametara. Zatim je dobiveni skup podataka podijeljen na dva dijela za stvaranje umjetne neuronske mreže, gdje je 70 % skupova podataka upotrijebljeno za trening, a preostalih 30 % dodatno je podijeljeno na dva jednaka dijela: jedan za testiranje, a drugi za validaciju modela. Dobiveni inteligentni model procijenjen je kao funkcija koeficijenta korelacije najbližeg 1 i najnižeg korijena srednje kvadratne pogreške (RMSE). U ovom istraživanju upotrijebljen je skup od 84 podatkovnih točaka. Za modeliranje ANN-a upotrijebljeno je osamnaest parametara u ulaznom sloju, pet neurona u skrivenom sloju i jedan parametar u izlaznom sloju. Za skriveni i izlazni sloj upotrijebljeni su algoritam učenja Levenberg Marquardt (LM), logaritamski sigmoid i funkcija linearnog prijenosa. Rezultati dobiveni tijekom ovog istraživanja pokazali su koeficijent korelacije R = 0,99276 s korijenom srednje kvadratne pogreške RMSE = 11,52613 mg dm–3. Ti rezultati pokazuju da je dobiveni model neuronske mreže dao daleko bolje rezultate, jer je točniji a njegova relativna pogreška je mala s koeficijentom korelacije blizu 1. Konačno, zaključeno je da taj model može učinkovito predvidjeti brzinu topljivosti bikarbonata u vodi za piće u regiji Médéa. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

  • Open Access English
    Authors: 
    F. Bikić; M. Rizvanović; M. Cacan;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    The influence of portland cement class on the corrosion rate of steel reinforcement in cement mortar caused by penetrating chloride or sulfate from the environment in already hardened cement mortar is investigated in this paper. Three classes of portland cement have been used for the tests, PC 35, PC 45 and PC 55. Cylindrical samples of cement mortar with steel reinfor- cement in the middle were treated 6 months at room temperature in the following solutions: w(SO42-) = 2.1 % and w(Cl-) = 5 %. Two techniques have been used for testing corrosion rate of steel reinforcement in cement mortar: Tafel extrapolation technique and potentiodynamic polarization technique. Investigations were conducted by potentiostat/galvanostat Princeton Applied Research 263A-2 with the software PowerCORR®. The results of both techniques indi-cate the most active corrosion of steel reinforcement in the samples prepared from cement PC 35 in both treated solutions, while the lowest corrosion of the steel reinforcement was observed in cement samples prepared from cement PC 55. This conclusion was drawn by analyzing the results shown in Figs. 1–4. Comparing corrosion current density of samples, working electrodes, Figs. 1 and 2, Table 2, the results show the most stable corrosion of steel reinforcement in samples prepared from cement PC 55, and the most active corrosion in samples prepared from ce- ment PC 35. The most active corrosion in samples prepared from cement PC 35 is evident from the positions of the open circuit potentials whose values are less for samples prepared from cement PC 35 in both the treated solution, Figs. 1 and 2, Table 2. Comparison of the anodic polarization curves of the working electrodes in both the treated solutions, Figs. 3 and 4, also shows that the intensity of corrosion is the largest for the working electrodes prepared from cement PC 35 and the smallest for the working electrodes prepared from cement PC 55. Investigation results should be considered as preliminary. To make the recommendations for the construction of reinforced concrete structures in the maritime environment the impact of sulphates on concrete and steel bars should be investigated. U ovom je radu ispitivan utjecaj klase portland-cementa na brzinu korozije čelične armature u cementnom mortu, uzrokovane prodiranjem klorida ili sulfata iz okoliša u već očvrsli cementni mort. Za ispitivanja su upotrijebljene tri klase portland-cementa, PC 35, PC 45 i PC 55. Radi navedenih ispitivanja cilindrični uzorci od cementnog morta s čeličnom armaturom u sredini tretirani su šest mjeseci na sobnoj temperaturi u sljedećim otopinama: w(SO42-) = 2,1 % i w(Cl-) = 5 %. Za ispitivanje brzine korozije čelične armature u cementnom mortu primijenjene su elektrokemijske tehnike potenciostatske polarizacije, i to tehnika ekstrapolacije Tafelovih krivulja i tehnika potenciodinamičke polarizacije. Ispitivanje je provedeno na potenciostatu/ galvanostatu Princeton Applied Research 263A-2, programskim paketom PowerCORR®. Rezultati obje primijenjene tehnike pokazuju da su korozijski najaktivnije čelične armature u uzorcima pripremanim od cementa klase PC 35 u obje tretirane otopine, dok su korozijski najstabilnije čelične armature u uzorcima pripremanim od cementa klase PC 55. Rezultate provedenih istra?ivanja treba smatrati preliminarnima. Radi davanja preporuka za gradnju armiranobetonskih konstrukcija u morskom okolišu, potrebno je provesti ispitivanja utjecaja sulfata na beton i armaturu, na betonskim i armiranobetonskim uzorcima.

  • Open Access English
    Authors: 
    Petračić, Ana; Sander, Aleksandra; Ćurić, Marija; Furač, Dora; Šimičević, Albina; Parlov Vuković, Jelena;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Given the fact that biodiesel produced from oil used in the food industry is not competitive with fossil-based diesel, it is necessary to use cheaper raw materials for its production. Thereby, waste edible oil, by-products of the manufacturing process of edible oils, inedible oils, and waste animal fat are considered the economically acceptable raw materials. The goal of this work was to investigate the applicability of deep eutectic solvents for extractive deacidification of waste animal fats and removal of glycerol and glycerides from crude biodiesel. Extractive deacidification of waste animal fat was conducted using deep eutectic solvent potassium carbonate – ethylene glycol (1 : 10, mol.), and it was used in mass ratio 1 : 4 (solvent : fat), at 60 °C for 30 min. Total acid number was reduced from 26.63 to 1.1 mg KOH/g fat. After purification of the feedstock, biodiesel was synthesised with different catalysts (KOH and NaOH), and KOH exhibited better conversion; therefore it was chosen for further experiments. In order to define the optimal reaction conditions, the influence of mass ratio catalyst : methanol : fat on the conversion of triglycerides into fatty acid methyl esters was investigated. At all reaction conditions, high quality biodiesel was obtained, i.e., the ester content was above the EN 14214 limit (96.5 %). The influence of catalyst load was greater than of methanol. At the highest concentration of catalyst, neutralisation of free fatty acids occurred. Biodiesel synthesised at 1 : 40 : 100 (KOH : methanol : fat) was chosen as the best, and was used for further experiments – extraction of glycerol and glycerides from crude biodiesel. For that purpose, deep eutectic solvent choline chloride – ethylene glycol (1 : 2.5, mol.) was used. The influence of mass ratio solvent : biodiesel and extraction duration was investigated. Increase in mass ratio and extraction duration resulted in a slight increase in ester content. To confirm the removal of glycerol and unreacted glycerides, samples of biodiesel before and after extraction were analysed by gas chromatography. Three samples after extraction were chosen – one at the lowest and one at the highest mass ratio of solvent to biodiesel, and one at the highest duration of extraction. Crude biodiesel contained too high concentrations of free and total glycerol. After extraction for 90 min, a significant reduction was observed – the extraction efficiencies for free glycerol, diglycerides, triglycerides, and total glycerol were: 90.77 %, 13.19 %, 10.43 %, and 21.59 %, respectively. The content of glycerol and glycerides after extraction was well below the EN 14214 limit. Density and viscosity of biodiesel were within the range defined by the European standard EN 14214. U ovom je radu istražena mogućnost primjene niskotemperaturnih eutektičkih otapala za ekstrakcijsku deacidifikaciju otpadnih životinjskih masti te uklanjanje glicerola i glicerida iz sirovog biodizela. Istraživanje je uključilo odabir povoljnog katalizatora te masenog omjera katalizatora, metanola i masti koji bi rezultirali najvećom konverzijom triglicerida u metilne estere masnih kiselina. Definirano je potrebno vrijeme pročišćavanja sirovog biodizela te optimalan maseni omjer otapala i sirovog biodizela. Ekstrakcijskom deacidifikacijom pomoću niskotemperaturnog eutektičkog otapala na bazi kalijeva karbonata uspješno je reducirana kiselost sirovine uz relativno mali utrošak otapala (maseni omjer otapala i masti: 0,25 : 1,00) i kratko vrijeme trajanja procesa (30 min). Kalijev hidroksid pokazao se kao učinkovitiji katalizator. Udio katalizatora u reakcijskoj smjesi utječe više na konverziju masti od udjela metanola. Udio glicerola i glicerida reduciran je ekstrakcijom pomoću niskotemperaturnog eutektičkog otapala na bazi kolin klorida na vrijednosti manje od standardom propisane vrijednosti (EN 14214:2019). Odabrano se otapalo pokazalo selektivnim zbog toga što nije došlo do redukcije udjela metilnih estera. Pri masenom omjeru otapala i biodizela 1 : 1 i 90 min trajanja ekstrakcije postignuti su najbolji rezultati. Pročišćeni biodizel također zadovoljava standard kvalitete s obzirom na udio estera, gustoću i viskoznost.

  • Publication . Other literature type . Article . 2016
    Open Access English
    Authors: 
    Jelena Parlov Vuković;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    U ovome preglednom radu opisane su najznačajnije i najčešće primjenjivane jednodimenzijske i dvodimenzijske tehnike NMR u analizi biodizela. Biodizel je ekološki prihvatljivo alternativno gorivo koje se sastoji od zasićenih i nezasićenih metilnih estera masnih kiselina. Budući da analiza kemijskog sastava i proučavanje svojstava biodizela i ostalih biogoriva analitičarima predstavlja izazov, sve više se razvijaju nove i učinkovitije analitičke metode. Spektroskopija NMR jedna je od takvih metoda koja može dati niz informacija o sastavu i strukturi biodizela. Nadalje, analiza spektara NMR pruža vrijedne podatke i o sirovinama iz kojih nastaje biodizel te o procesu esterifikacije. Isto tako primjenom tehnika 1H i 13C NMR može se odrediti sastav aditiva koji se dodaju za sprječavanje rasta mikroorganizama i sastav smjese acetilglicerola i sličnih nusproizvoda sinteze biodizela. U tu svrhu se osim spektara 1H i 13C analiziraju i spektri 31P. U radu su dani karakteristični spektri biodizela, dizela, biljnog ulja tretiranog vodikom te reprezentativan spektar jednog od uzoraka biocida snimljeni u Laboratoriju za spektroskopiju NMR u INA d. d.

  • Open Access English
    Authors: 
    H. Shao; X.-G. Liu; J.-G. Li; D.-W. Wang; Z.-F. Zhang;
    Publisher: Croatian Society of Chemical Engineers

    A series of sodium bentonite and thiamine were used as raw materials to prepare a new adsorbent – thiamine-modified bentonite. The adsorbent was applied in the pretreatment of pharmaceutical wastewater. The optimum preparation conditions of thiamine-modified bentonite were studied. The experiments showed that the removals of COD (chemical oxygen demand) reached 47.98 % under optimal condition. The FTIR results indicated that bentonite has been modified by thiamine. The X-ray diffraction result showed that the inter planar distance of modified bentonite was increased by intercalating thiamine. From the analyses of the SEM photographs, it can be clearly observed that the bentonite, after thiamine insertion reaction, loses its foliated structure and exhibits a rougher surface. Among several isotherm equations, Langmuir and Freundlich adsorption isotherms were investigated. They were widely used to describe equilibrium data for water and wastewater treatment applications. Adsorption isotherms correlate well with the Langmuir isotherm model. Detailed isothermal and kinetic studies show that the modified bentonite removes organic pollutants from pharmaceutical wastewa ter by physical adsorption processes.

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207 Research products, page 1 of 21
  • Open Access English
    Authors: 
    Marina Šekutor; Kata Mlinarić-Majerski;
    Country: Croatia

    Biološka aktivnost različitih adamantanskih derivata i njihova primjena opisane su u brojnim preglednim člancima. Isto tako, mnogi revijalni članci opisuju biološku aktivnost i primjenu gvanidinskih spojeva. Međutim, do sada nije načinjen pregled koji bi se bavio gvanidinskim derivatima adamantana i drugih policikla, tj. spojevima koji sadrže obje navedene podjedinice u istoj molekuli. U ovom radu bit će stoga dan pregled policikličkih derivata gvanidina, i to s naglaskom na njihovu primjenu kao potencijalnih farmakofora.

  • Publication . Article . 2019
    Open Access English
    Authors: 
    Nenad Raos;
    Publisher: Croatian Society of Chemical Engineers

    Rad se bavi razvojem pojma elementa od antičkih vremena (Empedoklo, Aristotel) preko razdoblja alkemije i rane kemije (Paracelsus, Petar Bono, Boyle) te početaka moderne kemije (Lavoisier, Mendeljejev) do suvremenih shvaćanja utemeljenih na atomskoj teoriji. Pokazuje se da pojam elementa ima dva značenja, elementarne (jednostavne) tvari i elementa u užem smislu; dok se prvi pojam razvijao prateći napredak metoda kemijske analize, za razumijevanje drugog pojma, pojma elementa, bilo je nužno steći dublji uvid u narav kemijskih promjena.

  • Publication . Article . Other literature type . 2017
    Open Access English
    Authors: 
    Molčanov, Krešimir; Institut Ruđer Bošković, Bijenička 54, HR-10 000 Zagreb;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Radikale, kemijske vrste s nesparenim elektronima, obično se smatra vrlo nestablinima, tako da ih se može pri - praviti samo pod posebnim uvjetima i proučavati samo pomoću posebnih, vrlo skupih, instrumenata. Također ih se smatra štetnima te neprimjerenima za pokuse u školi. Ipak, radikali imaju ključnu ulogu u biološkim susta - vima. Zahvaljujući nesparenim elektronima, obično su živo obojani, tako da se njihovo nastajanje često može opaziti golim okom. Ovdje je opisano nekoliko jednostavnih reakcijâ s biološki najvažnijim radikalom, semikinonom. Lako ih je izvesti u školskom laboratoriju uporabom male količine jeftinih i bezopasnih tvari. Jednostavnim promatranjem tih reakcijâ dade se naučiti mnogo toga o kemiji (slob odnih) radikala

  • Open Access English
    Authors: 
    Valdrin Beluli;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Gjilan (42˚28’08” V, 21˚27’48” L) is one of the seven largest cities in Kosovo. Throughout the city flow three rivers: Mirusha and Stanishor which mix and discharge into the largest river called Morava. The reason for the research of these rivers is the extreme pollution resulting from the discharge of industrial waters. Analysis of these rivers shows that they are extremely polluted and some physicochemical parameters are not in accordance with the regulations of the European Union (EU) and the World Health Organization (WHO). Parameters analysed are: pH, CW, NTU, DO, COD, BOD5, A-HCl, HCO3, GH, CS, Cl–, Cl2, Ca2+, Mg2+, NO2–, NO3–, PO43–, and NH3–. This work is licensed under a Creative Commons Attribution 4.0 International License. Grad Gjilan (42˚28’08”, V 21˚27’48” L) jedan je od sedam najvećih gradova na Kosovu. Kroz njega prolaze tri rijeke: Mirusha i Stanishor koje se miješaju i ulijevaju u najveću rijeku Moravu. Razlog za istraživanje tih rijeka je njihovo onečišćenje nastalo ispuštanjem industrijskih voda. Analiza tih rijeka pokazuje izrazito onečišćenje te neusklađenost nekih fizikalno-kemijskih parametara s propisima Europske unije (EU) i Svjetske zdravstvene organizacije (SZO). Analizirani su sljedeći parametri: pH, CW, NTU, DO, COD, BOD5, A-HCl, HCO3, GH, CS, Cl–, Cl2, Ca2+, Mg2+, NO2–, NO3–, PO43– i NH3–. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

  • Open Access English
    Authors: 
    Shulan Yu; Jialin Peng; Xinwen Zhang; Guoguang Wang;
    Publisher: Croatian Society of Chemical Engineers

    It is of great challenge and significance to recycle activated carbon (AC), yet still with various problems in operation. Here, we have performed a simulation on the regeneration of AC by using an indirect heating method with an unsteady cylindrical heat transfer model. The result has shown that the optimal parameters for a regeneration tube of outer diameter Φ = 108 with wall thickness 4 mm were: heating in the tube for 30 min at a surrounding temperature of 550 °C. In these conditions, a temperature of 417.5 °C could be obtained at the centre of the cylindrical tube, reaching the temperature required for AC regeneration. The experimental values obtained in our laboratory were consistent with the simulation, providing significant references for scaling up pilot plant of AC regeneration.

  • Open Access English
    Authors: 
    Hichem Tahraoui; Abd Elmouneïm Belhadj; Adh’ya-eddine Hamitouche;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    The region of Médéa (Algeria) located in an agricultural site requires a large amount of drinking water. For this purpose, the water analyses in question are imperative. To examine the evolution of the drinking water quality in this region, firstly, an experimental protocol was done in order to obtain a dataset by taking into account several physicochemical parameters. Secondly, the obtained data set was divided into two parts to form the artificial neural network, where 70 % of the data set was used for training, and the remaining 30 % was also divided into two equal parts: one for testing and the other for validation of the model. The intelligent model obtained was evaluated as a function of the correlation coefficient nearest to 1 and lowest mean square error (RMSE). A set of 84 data points were used in this study. Eighteen parameters in the input layer, five neurons in the hidden layer, and one parameter in the output layer were used for the ANN modelling. Levenberg Marquardt learning (LM) algorithm, logarithmic sigmoid, and linear transfer function were used, respectively, for the hidden and the output layers. The results obtained during the present study showed a correlation coefficient of R = 0.99276 with root mean square error RMSE = 11.52613 mg dm–3. These results show that obtained ANN model gave far better and more significant results. It is obviously more accurate since its relative error is small with a correlation coefficient close to unity. Finally, it can be concluded that obtained model can effectively predict the rate of soluble bicarbonate in drinking water in the Médéa region. This work is licensed under a Creative Commons Attribution 4.0 International License. Regija Médéa (Alžir) smještena na poljoprivrednom zemljištu zahtijeva veliku količinu pitke vode te je stoga analiza vode od iznimne važnosti. Da bi se ispitao razvoj kvalitete pitke vode u toj regiji, najprije je napravljen eksperimentalni protokol za dobivanje skupa podataka uzimajući u obzir nekoliko fizikalno-kemijskih parametara. Zatim je dobiveni skup podataka podijeljen na dva dijela za stvaranje umjetne neuronske mreže, gdje je 70 % skupova podataka upotrijebljeno za trening, a preostalih 30 % dodatno je podijeljeno na dva jednaka dijela: jedan za testiranje, a drugi za validaciju modela. Dobiveni inteligentni model procijenjen je kao funkcija koeficijenta korelacije najbližeg 1 i najnižeg korijena srednje kvadratne pogreške (RMSE). U ovom istraživanju upotrijebljen je skup od 84 podatkovnih točaka. Za modeliranje ANN-a upotrijebljeno je osamnaest parametara u ulaznom sloju, pet neurona u skrivenom sloju i jedan parametar u izlaznom sloju. Za skriveni i izlazni sloj upotrijebljeni su algoritam učenja Levenberg Marquardt (LM), logaritamski sigmoid i funkcija linearnog prijenosa. Rezultati dobiveni tijekom ovog istraživanja pokazali su koeficijent korelacije R = 0,99276 s korijenom srednje kvadratne pogreške RMSE = 11,52613 mg dm–3. Ti rezultati pokazuju da je dobiveni model neuronske mreže dao daleko bolje rezultate, jer je točniji a njegova relativna pogreška je mala s koeficijentom korelacije blizu 1. Konačno, zaključeno je da taj model može učinkovito predvidjeti brzinu topljivosti bikarbonata u vodi za piće u regiji Médéa. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

  • Open Access English
    Authors: 
    F. Bikić; M. Rizvanović; M. Cacan;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    The influence of portland cement class on the corrosion rate of steel reinforcement in cement mortar caused by penetrating chloride or sulfate from the environment in already hardened cement mortar is investigated in this paper. Three classes of portland cement have been used for the tests, PC 35, PC 45 and PC 55. Cylindrical samples of cement mortar with steel reinfor- cement in the middle were treated 6 months at room temperature in the following solutions: w(SO42-) = 2.1 % and w(Cl-) = 5 %. Two techniques have been used for testing corrosion rate of steel reinforcement in cement mortar: Tafel extrapolation technique and potentiodynamic polarization technique. Investigations were conducted by potentiostat/galvanostat Princeton Applied Research 263A-2 with the software PowerCORR®. The results of both techniques indi-cate the most active corrosion of steel reinforcement in the samples prepared from cement PC 35 in both treated solutions, while the lowest corrosion of the steel reinforcement was observed in cement samples prepared from cement PC 55. This conclusion was drawn by analyzing the results shown in Figs. 1–4. Comparing corrosion current density of samples, working electrodes, Figs. 1 and 2, Table 2, the results show the most stable corrosion of steel reinforcement in samples prepared from cement PC 55, and the most active corrosion in samples prepared from ce- ment PC 35. The most active corrosion in samples prepared from cement PC 35 is evident from the positions of the open circuit potentials whose values are less for samples prepared from cement PC 35 in both the treated solution, Figs. 1 and 2, Table 2. Comparison of the anodic polarization curves of the working electrodes in both the treated solutions, Figs. 3 and 4, also shows that the intensity of corrosion is the largest for the working electrodes prepared from cement PC 35 and the smallest for the working electrodes prepared from cement PC 55. Investigation results should be considered as preliminary. To make the recommendations for the construction of reinforced concrete structures in the maritime environment the impact of sulphates on concrete and steel bars should be investigated. U ovom je radu ispitivan utjecaj klase portland-cementa na brzinu korozije čelične armature u cementnom mortu, uzrokovane prodiranjem klorida ili sulfata iz okoliša u već očvrsli cementni mort. Za ispitivanja su upotrijebljene tri klase portland-cementa, PC 35, PC 45 i PC 55. Radi navedenih ispitivanja cilindrični uzorci od cementnog morta s čeličnom armaturom u sredini tretirani su šest mjeseci na sobnoj temperaturi u sljedećim otopinama: w(SO42-) = 2,1 % i w(Cl-) = 5 %. Za ispitivanje brzine korozije čelične armature u cementnom mortu primijenjene su elektrokemijske tehnike potenciostatske polarizacije, i to tehnika ekstrapolacije Tafelovih krivulja i tehnika potenciodinamičke polarizacije. Ispitivanje je provedeno na potenciostatu/ galvanostatu Princeton Applied Research 263A-2, programskim paketom PowerCORR®. Rezultati obje primijenjene tehnike pokazuju da su korozijski najaktivnije čelične armature u uzorcima pripremanim od cementa klase PC 35 u obje tretirane otopine, dok su korozijski najstabilnije čelične armature u uzorcima pripremanim od cementa klase PC 55. Rezultate provedenih istra?ivanja treba smatrati preliminarnima. Radi davanja preporuka za gradnju armiranobetonskih konstrukcija u morskom okolišu, potrebno je provesti ispitivanja utjecaja sulfata na beton i armaturu, na betonskim i armiranobetonskim uzorcima.

  • Open Access English
    Authors: 
    Petračić, Ana; Sander, Aleksandra; Ćurić, Marija; Furač, Dora; Šimičević, Albina; Parlov Vuković, Jelena;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    Given the fact that biodiesel produced from oil used in the food industry is not competitive with fossil-based diesel, it is necessary to use cheaper raw materials for its production. Thereby, waste edible oil, by-products of the manufacturing process of edible oils, inedible oils, and waste animal fat are considered the economically acceptable raw materials. The goal of this work was to investigate the applicability of deep eutectic solvents for extractive deacidification of waste animal fats and removal of glycerol and glycerides from crude biodiesel. Extractive deacidification of waste animal fat was conducted using deep eutectic solvent potassium carbonate – ethylene glycol (1 : 10, mol.), and it was used in mass ratio 1 : 4 (solvent : fat), at 60 °C for 30 min. Total acid number was reduced from 26.63 to 1.1 mg KOH/g fat. After purification of the feedstock, biodiesel was synthesised with different catalysts (KOH and NaOH), and KOH exhibited better conversion; therefore it was chosen for further experiments. In order to define the optimal reaction conditions, the influence of mass ratio catalyst : methanol : fat on the conversion of triglycerides into fatty acid methyl esters was investigated. At all reaction conditions, high quality biodiesel was obtained, i.e., the ester content was above the EN 14214 limit (96.5 %). The influence of catalyst load was greater than of methanol. At the highest concentration of catalyst, neutralisation of free fatty acids occurred. Biodiesel synthesised at 1 : 40 : 100 (KOH : methanol : fat) was chosen as the best, and was used for further experiments – extraction of glycerol and glycerides from crude biodiesel. For that purpose, deep eutectic solvent choline chloride – ethylene glycol (1 : 2.5, mol.) was used. The influence of mass ratio solvent : biodiesel and extraction duration was investigated. Increase in mass ratio and extraction duration resulted in a slight increase in ester content. To confirm the removal of glycerol and unreacted glycerides, samples of biodiesel before and after extraction were analysed by gas chromatography. Three samples after extraction were chosen – one at the lowest and one at the highest mass ratio of solvent to biodiesel, and one at the highest duration of extraction. Crude biodiesel contained too high concentrations of free and total glycerol. After extraction for 90 min, a significant reduction was observed – the extraction efficiencies for free glycerol, diglycerides, triglycerides, and total glycerol were: 90.77 %, 13.19 %, 10.43 %, and 21.59 %, respectively. The content of glycerol and glycerides after extraction was well below the EN 14214 limit. Density and viscosity of biodiesel were within the range defined by the European standard EN 14214. U ovom je radu istražena mogućnost primjene niskotemperaturnih eutektičkih otapala za ekstrakcijsku deacidifikaciju otpadnih životinjskih masti te uklanjanje glicerola i glicerida iz sirovog biodizela. Istraživanje je uključilo odabir povoljnog katalizatora te masenog omjera katalizatora, metanola i masti koji bi rezultirali najvećom konverzijom triglicerida u metilne estere masnih kiselina. Definirano je potrebno vrijeme pročišćavanja sirovog biodizela te optimalan maseni omjer otapala i sirovog biodizela. Ekstrakcijskom deacidifikacijom pomoću niskotemperaturnog eutektičkog otapala na bazi kalijeva karbonata uspješno je reducirana kiselost sirovine uz relativno mali utrošak otapala (maseni omjer otapala i masti: 0,25 : 1,00) i kratko vrijeme trajanja procesa (30 min). Kalijev hidroksid pokazao se kao učinkovitiji katalizator. Udio katalizatora u reakcijskoj smjesi utječe više na konverziju masti od udjela metanola. Udio glicerola i glicerida reduciran je ekstrakcijom pomoću niskotemperaturnog eutektičkog otapala na bazi kolin klorida na vrijednosti manje od standardom propisane vrijednosti (EN 14214:2019). Odabrano se otapalo pokazalo selektivnim zbog toga što nije došlo do redukcije udjela metilnih estera. Pri masenom omjeru otapala i biodizela 1 : 1 i 90 min trajanja ekstrakcije postignuti su najbolji rezultati. Pročišćeni biodizel također zadovoljava standard kvalitete s obzirom na udio estera, gustoću i viskoznost.

  • Publication . Other literature type . Article . 2016
    Open Access English
    Authors: 
    Jelena Parlov Vuković;
    Publisher: Croatian Society of Chemical Engineers
    Country: Croatia

    U ovome preglednom radu opisane su najznačajnije i najčešće primjenjivane jednodimenzijske i dvodimenzijske tehnike NMR u analizi biodizela. Biodizel je ekološki prihvatljivo alternativno gorivo koje se sastoji od zasićenih i nezasićenih metilnih estera masnih kiselina. Budući da analiza kemijskog sastava i proučavanje svojstava biodizela i ostalih biogoriva analitičarima predstavlja izazov, sve više se razvijaju nove i učinkovitije analitičke metode. Spektroskopija NMR jedna je od takvih metoda koja može dati niz informacija o sastavu i strukturi biodizela. Nadalje, analiza spektara NMR pruža vrijedne podatke i o sirovinama iz kojih nastaje biodizel te o procesu esterifikacije. Isto tako primjenom tehnika 1H i 13C NMR može se odrediti sastav aditiva koji se dodaju za sprječavanje rasta mikroorganizama i sastav smjese acetilglicerola i sličnih nusproizvoda sinteze biodizela. U tu svrhu se osim spektara 1H i 13C analiziraju i spektri 31P. U radu su dani karakteristični spektri biodizela, dizela, biljnog ulja tretiranog vodikom te reprezentativan spektar jednog od uzoraka biocida snimljeni u Laboratoriju za spektroskopiju NMR u INA d. d.

  • Open Access English
    Authors: 
    H. Shao; X.-G. Liu; J.-G. Li; D.-W. Wang; Z.-F. Zhang;
    Publisher: Croatian Society of Chemical Engineers

    A series of sodium bentonite and thiamine were used as raw materials to prepare a new adsorbent – thiamine-modified bentonite. The adsorbent was applied in the pretreatment of pharmaceutical wastewater. The optimum preparation conditions of thiamine-modified bentonite were studied. The experiments showed that the removals of COD (chemical oxygen demand) reached 47.98 % under optimal condition. The FTIR results indicated that bentonite has been modified by thiamine. The X-ray diffraction result showed that the inter planar distance of modified bentonite was increased by intercalating thiamine. From the analyses of the SEM photographs, it can be clearly observed that the bentonite, after thiamine insertion reaction, loses its foliated structure and exhibits a rougher surface. Among several isotherm equations, Langmuir and Freundlich adsorption isotherms were investigated. They were widely used to describe equilibrium data for water and wastewater treatment applications. Adsorption isotherms correlate well with the Langmuir isotherm model. Detailed isothermal and kinetic studies show that the modified bentonite removes organic pollutants from pharmaceutical wastewa ter by physical adsorption processes.

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