Browsing by Author "Gura, Liberty"

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    Development of pyrolysis process models for the production of lignin based phenols using Aspen Plus®
    (Stellenbosch : Stellenbosch University, 2017-03) Gura, Liberty; Gorgens, Johann F.; Mandegari, Mohsen A.; Collard, Francois-Xavier; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Lignin is an abundant organic solid waste presently produced in the form of black liquors from the paper and pulp industry, and is expected to be produced from lignocellulose biorefineries via chemical/biochemical processes for implementation in the sugar industry in fore sable future. Unlike various other organic wastes, lignin is made of chemical compounds called phenols, which have a relatively high market values (i.e. US$1500 – 12 000 per tonne), and can be produced from lignin residues by pyrolysis. In order to determine the techno economics of extracting phenols from lignin, this robust catalytic pyrolysis of lignin Aspen Plus® models were developed in this study.. Four scenarios were developed and results of the models were compared against each other to determine the most economically viable process of producing phenols from lignin. Scenarios 1 and 2 were about producing a crude phenolic mixture called creosote via catalytic pyrolysis of lignin, whilst scenarios 3 and 4 were about producing phenolic fractions from the lignin via catalytic pyrolysis and fractional distillation. Scenarios 1 and 3 used a relatively cheap catalyst sodium hydroxide, whilst scenarios 2 and 4 use relatively expensive catalyst zeolite. The technical performance analysis showed that scenarios 1 and 2 performed better, as they were found to be energy self-sufficient as the energy generated in combustion of char was able to meet the energy demands of the plants. Unlike scenarios 1 and 2, scenario 3 and 4 were found to need imported energy so as to meet the energy demands of the plants. The economic analysis showed that scenario 3 and 4 had the highest IRR values of 19.27% and 18.23% respectively. Production of crude phenolic solution (creosote) had generated the lowest IRR where scenarios 1 and 2 had IRR values of 1.10% and 2.07% respectively. Both scenario 3 and 4 showed it was more economically viable to produce phenolic fractions from lignin but is was found to be economically feasible to produce a phenolic mixture using a cheap catalyst as evidenced by the IRR of scenario 3. Production of phenolic fractions from pyrolysis of lignin using a catalyst of high market value (i.e. scenario 3) was economically viable but it was lower than scenario 3 which generated additional sales revenue through selling the by-product sodium oxide. The environmental impact analysis (CO2 emissions) showed that all four scenarios emitted less CO2 than fossil based phenols (4.5 kg CO2 per kg phenol). Comparison of the CO2 emissions of the four scenarios showed that scenario 4 emitted the highest CO2 emissions (2.72 kg CO2 per kg phenol) whilst scenario 1 was found to emit the least CO2 emissions (1.80 kg CO2 per kg phenol). Thus it can be concluded that production of phenolic fractions from lignin was preferred economically viable route but the yields of the phenolic compounds have to increase above the current 1wt % of lignin so as to increase the productivity of the phenolic fractions that will in turn increase the IRR thus attracting more investment.