Efficient conversion of wheat straw into furan compounds, bio-oils, and phosphate fertilizers by a combination of hydrolysis and catalytic pyrolysis

Abstract

The development of sustainable techniques to convert lignocellulosic materials into value-added chemicals remains a significant challenge. Herein, we report a novel technique to directly convert wheat straw to furan compounds, bio-oils, and phosphate fertilizers. Untreated wheat straw was initially converted into 5hydroxymethylfurfural (HMF) and furfural in a biphasic reaction system using FePO 4 and NaH 2 PO 4 as cocatalyst. The remaining FePO 4 in the solid residues was used as the catalyst to pyrolyze the solid residues, producing bio-oils and bio-char-based phosphate fertilizers. This combination of FePO 4 and NaH 2 PO 4 co-catalyst exhibited higher selectivity towards HMF and furfural production than using only FePO 4 as a catalyst in the conversion of wheat straw. The maximum HMF yield, 44%, was obtained when the reaction was carried out at 160 C for 60 min, while the highest furfural yield, 92%, was achieved when the reaction occurred at 150 C for 60 min. This reaction system is one of the most effective reaction systems to date for the conversion of wheat straw. Excessive Brønsted or Lewis acid sites (Fe ions) cannot give high yields of HMF and furfural due to the formation of by-products, indicating that a synergistic combination of Brønsted and Lewis acid sites is critical to obtain high yields of furan compounds. Interestingly, FePO 4 could effectively catalyze the pyrolysis of unconverted cellulose into new compounds, such as 5-methylfuran and 2,5-methylfuran, which is not observed in non-catalyzed pyrolysis.

Conversion of Sugars and Biomass to Furans Using Heterogeneous Catalysts in Biphasic Solvent Systems

“…THF has been employed as an organic solvent in several biphasic systems, and in order to achieve sufficient phase separation, the use of NaCl (or other solvents or salts) as a modifier was necessary at the temperatures used. Modifiers added to monophasic systems can induce phase separation to biphasic systems and can be used to initiate the salting‐out effect.…”

“…Despite this decrease in furfural yield, the NaCl modified THF/H 2 O biphasic system shows the potential for the simultaneous synthesis of furfural and HMF at reasonable yields. FePO 4 is soluble at the increased reaction temperatures and observed patterns of recrystallization suggested a possible contribution of a homogeneous reaction …”

“…to synthesize both furfural and HMF, biphasic THF/H 2 O systems modified with NaCl were used with FePO 4 and NaH 2 PO 4 as co‐catalysts. For reactions at 150 °C and 1 h, furfural and HMF yields of 92 % and 34 %, respectively, were achieved; HMF yields increased to 44 % at 160 °C and 1 h at the cost of decreasing furfural yields by 4 % . Despite this decrease in furfural yield, the NaCl modified THF/H 2 O biphasic system shows the potential for the simultaneous synthesis of furfural and HMF at reasonable yields.…”

High conversion of glucose to 5-hydroxymethylfurfural using hydrochloric acid as a catalyst and sodium chloride as a promoter in a water/γ-valerolactone system

“…Several groups have reported their explorations about glucose conversion to HMF. Some Lewis acids, such as CrCl 2 , SnCl 4 , AlCl 3 and FeCl 3 , 30,31 various liquid Brønsted acids such as HCl, H 2 SO 4 and H 3 PO 4 , 32 the combination of both Lewis acids and Brønsted acids, [33][34][35]46 and also solid acid catalysts such as Sn-Mont, 36 and CMK-3, 37 were tested in different systems with applying various organic solvents. However, in these studies, solid acids modied with Brønsted acid or Lewis acid sites usually tend to result in only moderate HMF yields.…”

Efficient conversion of 5-hydroxymethylfurfural to high-value chemicals by chemo- and bio-catalysis

“…18 Various substrates are used for the production of HMF: hexoses themselves, oligosaccharides as well as cellulose [19][20][21] and the raw biomass such as wheat straw (see in Scheme 2). 22 It is generally accepted that the production of HMF from biomass must include the acid-catalyzed hydrolysis of biomass to produce hexose in the rst step. In the second dehydration step, starts from ketohexose (e.g.…”