Showing papers by "Adam Harvey published in 2019"

Highly selective, sustainable synthesis of limonene cyclic carbonate from bio-based limonene oxide and CO2: A kinetic study

Abstract: Bio-derived cyclic carbonates are of significant research interest as building blocks for non-isocyanate polyurethanes (NIPUs). Cyclic carbonates from limonene are bio-renewable monomers for the production of fully bio-based polymers from citrus waste; however, there are currently very few reports on their synthesis. This work reports the synthesis of five-membered cyclic carbonates from bio-based limonene oxide (LO) and CO2 catalysed by commercially available inexpensive, tetrabutylammonium halides (TBAX). The cycloaddition of CO2 with commercial LO mixture of cis/trans-isomers (40:60) is highly stereoselective and the trans-isomer exhibits considerably higher conversion than the cis-isomer. Therefore, a stereoselective method of (R)-(+)-limonene epoxidation was performed to achieve a significantly higher yield of the trans-isomer (87 ± 2%) than cis-isomer, which leads to high conversion and yield to the corresponding cyclic carbonates. The catalytic effect of halide anions (X¯) and the influence of operational reaction parameters such as temperature, pressure, and catalyst amount were studied. High conversion (87%) was obtained after 20 h at 120 °C, 40 bar CO2 using 6 mol% tetrabutylammonium chloride (TBAC) catalyst. A detailed study of the reaction kinetics revealed the reaction to be first-order in epoxide (LO), CO2 and catalyst (TBAC) concentrations. Moreover, the temperature dependence of the reaction was studied using Arrhenius and Eyring equations. The activation energy (Ea) of the reaction was calculated to be 64 kJ mol–1. The high positive value of Gibbs free energy (ΔG‡ = 102.6 kJ mol–1) and negative value of activation entropy (ΔS‡ = –103.6 J mol–1) obtained as result of the thermodynamic study, indicate that the reaction was endergonic and kinetically controlled in nature.

Methane conversion to H2 and higher hydrocarbons using non-thermal plasma dielectric barrier discharge reactor

Abstract: The use of Non-Thermal Plasma (NTP) reactors has been proposed as an alternative solution to the World’s stranded gas challenge due to their ability to perform reactions, such as direct conversion of methane to H 2 and higher hydrocarbons (>C 1 ), at room temperature. An optimisation study varying plasma power (10–50 W) and residence time (3.82–19.08 s) was performed using a DBD reactor with no catalyst. The effects of additives including water vapour, nitrogen, and hydrogen were also explored. The optimum conditions for methane conversion (36.5%) without additives at ambient temperature (20 °C) were found to be maximum at 50 W and 19.08 s, resulting in a H 2 yield of 13.9%. The key finding from the additive study was that the addition of 10% N 2 resulted in an increase in conversion (37.6%) and an increase in H 2 yield (14.5%), at 50 W and 19.08 s.

Scale‐up and Sustainability Evaluation of Biopolymer Production from Citrus Waste Offering Carbon Capture and Utilisation Pathway

Abstract: Poly(limonene carbonate) (PLC) has been highlighted as an attractive substitute to petroleum derived plastics, due to its utilisation of CO2 and bio-based limonene as feedstocks, offering an effective carbon capture and utilisation pathway. Our study investigates the techno-economic viability and environmental sustainability of a novel process to produce PLC from citrus waste derived limonene, coupled with an anaerobic digestion process to enable energy cogeneration and waste recovery maximisation. Computational process design was integrated with a life cycle assessment to identify the sustainability improvement opportunities. PLC production was found to be economically viable, assuming sufficient citrus waste is supplied to the process, and environmentally preferable to polystyrene (PS) in various impact categories including climate change. However, it exhibited greater environmental burdens than PS across other impact categories, although the environmental performance could be improved with a waste recovery system, at the cost of a process design shift towards energy generation. Finally, our study quantified the potential contribution of PLC to mitigating the escape of atmospheric CO2 concentration from the planetary boundary. We emphasise the importance of a holistic approach to process design and highlight the potential impacts of biopolymers, which is instrumental in solving environmental problems facing the plastic industry and building a sustainable circular economy.

A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate

Abstract: Abstract Synthesis of styrene carbonate (SC) via the fixation of CO2 with styrene oxide (SO) has been investigated using a combination of zinc bromide (ZnBr2) and tetrabutylammonium halides (TBAX) as acid-base binary homogeneous catalysts. The combination of ZnBr2 and TBAB had a synergistic effect, which led to about 6-fold enhancement in the rate of SC formation as compared to using TBAB alone as a catalyst. Propylene carbonate (PC) was chosen as a green solvent for a comprehensive study of reaction kinetics. The reaction followed a first-order kinetics with respect to SO, CO2, and TBAB, whereas a fractional order was observed for the ZnBr2 when used in combination with the TBAB. Arrhenius and Eyring’s expressions were applied to determine the kinetic and thermodynamic activation parameters, where activation energy (Ea) of 23.3 kJ mol−1 was obtained for the SC formation over the temperature range of 90-120°C. The thermodynamic analysis showed that positive values for enthalpy (ΔH‡ = 18.53 kJ mol−1), Gibbs free energy (ΔG‡ = 79.74 kJ mol−1), whereas a negative entropy (ΔS‡ = –162.88 J mol−1 K−1) was obtained. These thermodynamic parameters suggest that endergonic and kinetically controlled reactions were involved in the formation of SC from SO and CO2.

Removal of Toluene as a Tar Analogue in a N 2 Carrier Gas Using a Non-thermal Plasma Dielectric Barrier Discharge Reactor

Abstract: The role of N2 carrier gas toward the conversion of tar analogue (toluene) was studied in a non-thermal plasma dielectric barrier discharge reactor. The parameters investigated were power (5–40 W), residence time (1.43–4.23 s), toluene concentration (20–82 g/Nm3), and wall temperature (from ambient to 400 °C). Almost complete removal (99%) of toluene was observed at 40 W and 4.23 s. The main gaseous product was H2, with a maximum selectivity of 40%. The other gaseous products were lighter hydrocarbons (LHCs, C1–C6, 5.5%). The selectivity to these LHCs could be increased to 10% by increasing the temperature to 400 °C. Introducing H2 to the N2 carrier gas at elevated temperatures opened up new reaction routes to enhance the selectivity to LHCs. The selectivity to methane reached 44% at 35% H2 at 400 °C, and the total selectivity to LHCs reached 57%.

Scale-Up of Gas-Liquid Mass Transfer in Oscillatory Multiorifice Baffled Reactors (OMBRs)

Abstract: The effect of scale-up on air–water mass transfer in oscillatory multiorifice baffled reactors (OMBRs) was investigated. Reactors of 10, 50, and 100 mm diameter were studied. The reactors had the s...

The development of helical vortex pairs in oscillatory flows – A numerical and experimental study

Abstract: When a liquid is oscillated in a tube containing a helical coil, there are two key flow phenomena: vortex-shedding and “swirl”. Together, they cause plug flow to be achievable over a wide range of conditions in this design. When an additional small cylindrical rod is placed in the centre of the helical coil, a new dual vortex regime is realised. This new flow regime was studied via CFD and PIV. It was demonstrated that a significant swirling velocity was generated by the helical coils, inducing an outward centrifugal force and inward pressure gradient, creating an instability resulting in the formation of a pair of counter-rotating vortices. The oscillatory amplitudes and frequencies necessary for the formation of these dual vortices at this scale (5 mm diameter) were centre-to-peak amplitude of 2–4 mm and frequency ≥ 3 Hz. The vortex pairs were also visualised in 3D, and exhibited a double-helix shape. Additionally, the transition of this flow to a more turbulent-like state was investigated. It was found to occur in the range R e o = 600–630. Through analysis of the swirl and radial numbers, it is clear that swirling dominates the flow structures at amplitudes of x o ≥ 4 mm.

Direct Conversion of Benzene as a Tar Analogue to Methane Using Non-thermal Plasma

Abstract: Direct conversion of benzene to methane (>90%) was achieved in a hydrogen atmosphere in a non-thermal plasma dielectric barrier discharge reactor at atmospheric pressure. The distribution of products was a function of both plasma input power and temperature. At ambient temperature, the selectivity to lower hydrocarbons increased from 20 to 56% as the power was increased from 50 to 85 W. However, at a wall temperature of 200 °C, the selectivity to lower hydrocarbons increased to 80% at 50 W and 97% at 75 W. The major product was methane, reaching a selectivity to 90% at 85 W and 200 °C. Increasing input power and temperature both promoted the formation of methane. However, the selectivity to >C1 started to increase when increasing the concentration at a constant power (85 W) and temperature (200 °C).

Coil-in-Coil Reactor: Augmenting Plug Flow Performance by Combining Different Geometric Features Using 3D Printing

Abstract: Additive manufacturing enables the fabrication of geometries previously unavailable via conventional means. Here, a helically coiled channel containing a secondary helical coil insert was 3D-printed and operated in a net flow with superimposed oscillation. This “coil-in-coil” geometry exhibited exceptional plug flow quality at low Reynolds numbers (Re = 10–50). High levels of plug flow were observed at oscillation amplitudes of 2–8 mm. The greatest degree of plug flow occurred with Reo/Ren = 2–7 and Sr = 1–2. Surprisingly, the coil-in-coil geometry demonstrated excellent plug flow behavior (N = 40–100) at very low oscillation frequencies (f = 0.25–0.5 Hz). Compared to various benchmark designs (“plain” coiled tube, straight tube containing a helical coil insert, and plain straight tube), the coil-in-coil geometry demonstrated enhanced plug flow quality at low frequencies (≤1 Hz) at all amplitudes and low amplitudes (1–2 mm) at all frequencies.

A reactive coupling process for co-production of solketal and biodiesel

Abstract: Abstract A “reactive coupling” process for one-pot transesterification of rapeseed oil into fatty acid methyl esters (FAME) for biodiesel, and in situ acetalisation of the glycerol by-product to solketal was investigated by both an experimental and a kinetic modelling approach. The aim was to develop a process with a more valuable co-products than glycerol, and to minimise glycerol production. The results showed that a one-stage reactive coupling achieved a solketal yield of 39.5 ± 5.1% and FAME yield of 99% after 8 h at 10:7:1 of methanol: acetone: oil molar ratio. However, based on these results and the predictions of the kinetic model developed, a “two-stage” reactive coupling process was investigated, in which some of the acetone was added later in the process. The two-stage process was demonstrated to achieve up to 98 ± 0.5% FAME and 82 ± 4% solketal yields under the same operating conditions.