Valorisation of bio-aromatics from pulp mill residues and commercial forest species in South Africa

Van Zyl, Madelein (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANS OPSOMMING: Die ontwerp van industriële prosesse wat fokus op die vervaardiging van bio-gebaseerde poliëtileen-tereftalaat (PET) het populariteit verwerf tydens die bekendstelling van die PlantBottle®. Motivering vir laasgenoemde is versterk deur die volhoubaarheids eienskappe daarvan, die groei van die PET mark asook die winste geassosieer met die kommersialisering van die ontwerpte proses. PET bestaan eerstens uit monoëtileenglikool (MEG), wat op hede op ‘n bio-basis gekommersialiseer is. Daarenteen is ‘n bio-basis proses vir die tweede komponent, gesuiwerde tereftalsuur (TPA), nog nie ontwikkel nie. In hierdie projek het die ondersoek op huidige literatuur (eksperimentele data) gelei tot die ontwikkeling van nuwe prosesskemas wat deur tegniese en ekonomiese metodes geanaliseer is, om ten einde individuele lewensvatbaarhede te bepaal. Verskeie maatskappye, insluitende The Coca-Cola Company, Virent en Anellotech, het in hierdie navorsing belê. Ongelukkig is die tegniese en ekonomiese data van hierdie prosesse nie beskikbaar aan die publiek nie en daarom was alternatiewe metodes van vergelyking van gebruik gemaak. Die eerste doel van hierdie prosesskemas is om gebruik te maak van tweede generasie roumateriale as bronne vir die ekstraksie van TPA voorlopers (senario een). Literatuur was oorweeg met die fokus dat hierdie projek die Suid-Afrikaanse kapasiteit van die roumateriaal in ag neem. Fokus was geplaas op die vervaardiging van terftalsuur vanuit terpeen-voorlopers wat in salignabloekom blare en basden naalde (bosbou-afval bronne) asook pre-hidrolisaat verligtingsgas (PHR) (papierfabriek afvalstroombron) gevind word. Die industriële toepassing van die ontwikkelde prosesskemas is in Aspen Plus® gesimuleer, waarna die produksiekapasiteit en energieverbruik deur ‘n vloeiskema analise van elke proseskema. Energie verbruikingsoptimalisering is gedoen deur gebruik te maak van energie-integrasie (“pinch-point”) analise in Aspen Plus®. Die kostes geassosieer met elke proses was bereken deur gebruik te maak van ASPEN Process Economic Analyser asook koste-formules. Die berekening van die ekonomiese indikator, DCFROR, het getoon dat hierdie prosesse nie ekonomies lewensvatbaar is nie. Bydraende faktore sluit in; ‘n lae konsentrasie van die hoof terpene wat in die roumateriaal voorkom, die gebruik van suiwer suurstof in twee belangrike afdelings van elke proses, suiweringsmetodes wat vermoeilik is deur ander terpene en byprodukte asook die kleinskaalse produksie wat gelei het tot ‘n hoë gemiddelde produksiekoste. Die tweede doel (senario twee) ondersoek die ekonomiese lewensvatbaarheid van eerste en tweede generasie prosesse op ‘n 10% PET markskaal (‘n redelike aandeel tot die mark vir nuwe produk in die korttermyn). Dieselfde stappe, soos in senario een, was gebruik om die eerste generasie proses te ontwikkel. Die ‘discounted cash flow analyses’ van elke proses het ‘n struikel-persentasie van 16% gebruik (omdat nominale terme gebruik was) om elke minimum TPA verkoopsprys te bepaal: Proses Minimum verkoopsprys ‘Green premium’ Pine $5 227/tonne 647% Eucalyptus $22 443/tonne 3106% PHR $38 114/tonne 5345% Stysel basis $1953/tonne 179% FDCA $2130/tonne 204% Deur die analise van elke verkoopsprys, tesame met elke ooreenkomstige ‘green premium’, is die tweede generasie prosesse as nie ekonomies lewensvatbaar verklaar. Deur die vergelyking met die TPA ekwivalent, FDCA (ook vervaardig vanaf styselbronne), was dit bevestig dat die eerste generasie wel die potensiaal het om ekonomies lewensvatbaar te word deur verdere navorsing en optimalisering. Dit is ook bevestig dat dit die potensiaal het om die realistiese ‘green premium’ van 125% te haal deur minder prosesseringstappe, meer effektiewe suiweringsmetodes, geoptimaliseerde en goedkoper kataliste asook addisionele byprodukwinste. Uiteindelik, bied hierdie proses die begin van vele geleenthede wat poog om volledige bio-gebasseerde PET te vervaardig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102991
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