Browsing by Author "Van Zyl, Madelein"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Valorisation of bio-aromatics from pulp mill residues and commercial forest species in South Africa
    (Stellenbosch : Stellenbosch University, 2017-12) Van Zyl, Madelein; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: The design of industrial processes towards the production of bio-based polyethylene terephthalate (PET) gained much attention after the introduction of the PlantBottle®. This is further motivated through sustainability appeal, a continuous increase in the PET market growth as well as economic gains (most importantly revenue generation) through commercialisation of the designed process. The first component of PET, monoethylene glycol, is currently commercially produced from a bio-based source, while there is a need for a production scheme for the second component, purified terephthalic acid (TPA), which has not yet been developed. In this project, investigation of reported experimental data lead to the development of a number of novel processing schemes, which were subsequently subjected to technical and economic analyses to determine feasibilities. Multiple companies, including The Coca-Cola Company, Virent and Anellotech, have invested in this research. However technical and economic data from these sources are not publicly released, therefore alternative methods of comparison where selected. The developed processing schemes firstly aimed to utilise second-generation feedstocks for the extraction of TPA precursors, based on feedstock availability in South Africa (scenario one). Focus was placed on terephthalic acid production from terpene precursors found in Eucalyptus grandis leaves and Pinus elliottii needles (forestry waste sources) as well as pre-hydrolysate relief gas from the pulping processes (pulp mill residue source). The industrial application of the proposed schemes was simulated in Aspen Plus®, where flow-sheet analysis revealed the production capabilities and utility demands of each scheme. Energy efficiency optimisation was performed through pinch point analysis applied through Aspen Plus®. Costing of these processes (through ASPEN Process Economic Analyser and costing formulae) as well as the calculation of the economic indicator, DCFROR, revealed that the second-generation processes are economically unviable. Contributing factors include low concentration of major terpenes (TPA precursors) within feedstocks, necessity for pure oxygen for two major section of each process, complex purifications (due to similar boiling points between major terpenes and by-products/multiple other terpenes) and small scale production that lead to a high average production cost. The second aim (scenario two) involved determining the economic viability of first and second generation processes at a 10% PET market share (reasonable share for novel processes in the short-term). The same approach was used to derive the first generation processes as for scenario one. The discounted cash flow analyses of each process considered a 16% hurdle rate (for nominal terms used) to determine the minimum TPA selling price: Process Minimum selling price Green premium Pine $5 227/tonne 647% Eucalyptus $22 443/tonne 3106% PHR $38 114/tonne 5345% Starch-based $1953/tonne 179% FDCA $2130/tonne 204% Through the evaluation of these selling prices together with their accompanying green premiums, the second generation processes were deemed economically unviable. Through the selling price comparison of the TPA equivalent, FDCA (also from a starch-based feedstock), which was deemed worthwhile for further research and optimisation, it was concluded that the first generation process has the potential to become economically viable. Therefore, it has the potential to reach the realistic premium of 125% through fewer processing steps, more effective purification methods, optimised and less expensive catalysts and additional by-product revenue. Ultimately, this process initialises the opportunities towards fully bio-based PET.