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Towards a circular economy – Development, characterisation, techno-economic analysis and applications of activated carbons from industrial rest streams

Boek - Dissertatie

In order to cope with the increasing global population, increasing environmental pressure and depletion of natural resources, a rapid and radically change to a circular bioeconomy will be key to secure growth and jobs. A circular economy is designed to keep added value in products for as long as possible. Transition to a circular economy will require changes throughout the entire value chain. One part in the transition to a more circular economy is turning today’s waste into resources. Development of new recycling and reengineering methods will thus be key for future waste stream valorisation keeping value in the products. Interesting renewable resources for further valorisation are industrial organic waste streams. Despite their potential (high volume, known composition, …) as valuable and renewable resources for industrial exploitation, they have received little attention as a marketable product. Another problem arising from the production of goods and the increasing population that needs to be tackled is the contamination of water supplies e.g., groundwater, surface water, … As part of the transition to a more circular economy, addressing the remediation of water supplies, is the development of high value activated carbon from industrial organic waste streams replacing virgin resources. In this study, three industrial organic residues (brewer’s spent grain, particle board [glued with urea formaldehyde and glued with melamine urea formaldehyde] and melamine formaldehyde) are selected as precursors for the production of high value activated carbon for the remediation of contaminated water. The main objective is to answer the question whether industrial organic waste streams (i.e., brewer’s spent grain, melamine formaldehyde and particle board) are interesting renewable resources for the profitable production of activated carbons. In chapter 1, an introduction about the circular economy and the investigated industrial waste streams is presented. In addition, an overview of the production of activated carbon, its characteristics and the adsorption theory is discussed. The general framework for techno-economic assessment is provided. The research question and subquestions are formulated at the end of this chapter. The experimental approach and the methodology used for the characterisation of the waste streams and the production, characterisation and performance of activated carbons produced from the waste stream are described in Chapter 2. The development of a new laboratory pyrolysis/activation reactor which is suitable to produce sufficient amounts of activated carbon resembling industrial plants is discussed in Chapter 3. In Chapter 4, a preliminary techno-economic assessment is carried out for the production of activated carbon from particle board and melamine formaldehyde. First a process diagram of an activated carbon production technique (co-pyrolysis combined with physical activation) is developed and a discounted cash flow model is made. Based on this model, the net present value of the cash flows generated by an investment in co-pyrolysis and char activation is calculated. Because a number of values that have been assumed in the cash flow model are uncertain, Monte Carlo Sensitivity analysis is performed to identify the key variables for the profitability of the production of activated carbon from particle board and melamine formaldehyde waste. Before up scaling the research, the profitability of activated carbon production from blends of particle board and melamine waste is further evaluated based on preliminary research results and the discounted cash flow model (developed in Chapter 4) in Chapter 5. The valorisation of activated carbon from brewer’s spent grain and particle board for the remediation of phenol contaminated water is investigated in Chapter 6 and 7. First the characteristics of the waste materials are investigated followed by the effect of the temperature and time of steam activation on the yield and characteristics of the produced carbons. The performance of the activated carbons is evaluated by batch adsorption experiments in function of different parameters like time, temperature, ionic strength and pH using phenol as target compound. In Chapter 8 the performance of the produced carbons is evaluated for the remediation of water contaminated with pharmaceutical active compounds (ibuprofen, diclofenac an sulfamethoxazole) in three sequential types of assays e.g.,: Screening assay, Equilibrium assay and Kinetic assay.
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