Browsing by Author "Naron, David Rangnaan"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Catalytic pyrolysis conversion of lignin from different sources to phenols
    (Stellenbosch : Stellenbosch University, 2019-04) Naron, David Rangnaan; Gorgens, Johann F.; Tyhoda, Luvuyo; Collard, Francois-Xavier
    ENGLISH ABSTRACT: Lignin is a by-product of the paper and pulp industry and the emerging cellulosic ethanol production technologies. Both industries only considered lignin a source of energy to complement the energy needs of their processes. However, the phenolic nature of lignin makes it a valuable renewable resource for sustainable production of chemical products. In the current study, prior to lignin conversion to phenolic chemical products, physico-chemical characterisation of several lignins were conducted using conventional methods namely, wet chemical, gel permeation chromatography (GPC), and Fourier transform infra-red spectroscopy (FTIR). In addition to these methods, a novel analytical pyrolysis method was developed combining thermogravimetric analysis (TGA), thermal desorption (TD), and gas chromatography coupled to mass spectrometry (GC-MS), named as TGA-TD-GC-MS. It was used to analyse and estimate the monomeric phenolic products namely, syringol (S), guaiacol (G) and phenol (H) from lignins. The phenolic monomeric proportions (S/G/H), obtained using the TGA-TD-GC-MS was compared with the ones obtained by thioacidolysis (wet chemical method). The lignin monomeric products obtained by pyrolysis, based on internal calibration, was in the range of 5.5-12.9 wt.%. The ability of the TGA-TD-GC-MS to break several types of bonds gave it the advantage over thioacidolysis, resulting in the production of monomeric phenolic compositions that were more representative of the lignin. A comparison of phenols production from catalytic pyrolysis of lignins of different biomass origin, namely eucalyptus (hardwood) lignin, pine (softwood) lignin, and sugarcane bagasse (herbaceous) lignin was studied using the TGA-TD-GC-MS. The lignins were impregnated with two hydroxides (NaOH and KOH) and two metal oxides (ZnO, and Al2O3), with amounts equivalent to 1 wt.% of the lignin mass, and pyrolysed at the temperature of 600 °C using a heating rate of 10 °C/min. KOH produced the most catalytic effect on the yield of total phenols from sugarcane bagasse (S-S) lignin, leading to the highest increase of +26%, and likewise NaOH for eucalyptus (E-K) lignin (+40%). Syringol yield being the major syringol-type (S-type) phenols reached a record high of 1.8 wt.%, equivalent to 90% increase from E-K lignin, catalysed by NaOH. Additionally, NaOH increased the yield of 4-vinylguaicol-the guaiacol-type (G-type) phenol from E-K lignin up to 2.8 wt.%, equivalent to 39% increase, as compared to the non-catalytic yield. A catalyst screening study was conducted in which twelve catalysts, namely Al2O3, Fe2O3, MoO3, TiO2, Ni/Al2O3-SiO2, CaO, ZnO, MgO, NaOH, CuO, KOH and NiO were each impregnated on three different types of sugarcane bagasse lignins with amounts equivalent to 1 wt.% of the lignin mass. KOH, CaO, and Fe2O3 recorded the highest effects on the total yield of phenols from soda (SD), soda-anthraquinone (SAQ), and steam explosion combined with enzymatic hydrolysis lignins respectively. The increases were 11.2 wt.%, 8.2 wt.%, and 8.6 wt.%, equivalent to + 26%, + 60% and + 43% respectively. Syringol, guaiacol, and 4-vinylguaiacol were the most improved with yield increases ranging from 0.6 to 2.8 wt.%, equivalent to 32-121% from the lignins. Optimisation of phenols was investigated. Pyrolysis was first conducted at analytical scale and then applied in the second stage at bench scale. The results at analytical scale showed that the amounts of KOH required to maximise the yield of phenols (15.3-16.0 wt.%) were in the range of 5-7 wt.%. Analysis of the bio-oil showed that the yields of syringol and guaiacol had their maximum values at 450 °C and 4.5 wt.% KOH content with yield increases of 0.70 wt.% and 0.6 wt.%, which represent 106% and 83% respectively, compared with that of pyrolysis without catalyst. Phenol (the P-type phenol) achieved a maximum at 450 °C and 8.5 wt.% KOH content, with a yield of 0.96 wt.%, corresponding to 141% increase.