Pretreatment of corn cobs for bioethanol production

Lignocelulozne sirovine su jeftine i obnovljive sirovine za proizvodnju biogoriva no, zbog svoje kompleksne strukture moraju biti podvrgnute predobradi, te daljnjoj hidrolizi polisaharida u fermentabilne ugljikohidrate. Kukuruzni oklasci, korišteni u ovom radu, usitnjeni su mljevenjem i provedena je predobrada u visokotlačnom reaktoru uz različite koncentracije sumporne kiseline (w = 0,5 % i 1,0 %) kao katalizatora. Postupak predobrade proveden je pri 210°C i tlaku pare od 20 bara pri različitim vremenima zadržavanja od 1 do 10 minuta. Nakon postupka predobrade kukuruznih oklasaka, dobiveni hidrolizat se sastoji od dvije faze, tekuće i čvrste faze. Svaka faza je zasebno analizirana te je određen sastav i koncentracija polimera, odnosno fermentabilnih ugljikohidrata, lignina topivog u kiselini, lignina netopivog u kiselini i nusproizvoda (octena kiselina, levulinska kiselina, mravlja kiselina, furani). Navedeni nusproizvodi mogu imati inhibitorni učinak na rast mikroorganizama. Tijekom postupak preodbrade kukuruznih oklaska pri temperaturi od 210 °C, tlaku pare od 20 bara i vremenu zadržavanja od 5 minuta uz 1,0% sumpornu kiselinu kao katalizator proizvedeno je najviše fermentabilnih ugljikohidrata u hidrolizatu kukuruznih oklasaka, dok je najmanje inhibirajućih spojeva proizvedeno tijekom postupka predobrade pri temperaturi od 210 °C, tlaku pare od 20 bara i vremenu zadržavanja od 5 minuta uz 0,5 % sumpornu kiselinu kao katalizator.Lignocellulose raw materials are low-cost and renewable materials for production of biofuels. Due to its complex structure, lignocellulose must be subjected to different pretreatment methods and subsequently to further hydrolysis of polysaccharides to fermentable monosaccharides. Corn cobs, used in this work, were milled and resulting material was pretreated in high pressure reactor with dilute sulphuric acid (w = 0,5 % and 1,0 %). Pretreatment was performed at 210°C, 20 bar vapor pressure at different holding times, from 1 to 10 minutes. After the pretreatment obtained hydrolysate consisted of two phases, liquid and solid phase. Each phase was analyzed separately, and composition of polymers, fermentable carbohydrates, acid soluble lignin, acid insoluble lignin and different byproducts (acetic acid, levulinic acid, formic acid and furans). These byproducts can have inhibitory effect on growth of microorganisms. Highest concentrations of fermentable carbohydrates in hydrolysates of corn cobs were achieved after pretreatment of corn cobs at 210 °C, vapor pressure of 20 bars, 5 minutes hold time and 1,0 % sulfuric acid. The lowest amount of inhibiting compounds was produced after pretreatment of corn cobs at 210 °C, vapor pressure 20 bars, 5 minutes hold time and 0,5 % sulfuric acid