Intensified processes for FAME production from waste cooking oil: a technological review

This article reviews the intensification of fatty acid methyl esters (FAME) production from waste cooking oil (WCO) using innovative process equipment. In particular, it addresses the intensification of WCO feedstock transformation by transesterification, esterification and hydrolysis reactions. It also discusses catalyst choice and product separation. FAME production can be intensified via the use of a number of process equipment types, including as cavitational reactors, oscillatory baffled reactors, microwave reactors, reactive distillation, static mixers and microstructured reactors. Furthermore, continuous flow equipment that integrate both reaction and separation steps appear to be the best means for intensifying FAME production. Heterogeneous catalysts have also shown to provide attractive results in terms of reaction performance in certain equipment, such as microwave reactors and reactive distillation

Reactive distillation for cosmetic ingredients : an alternative for the production of isopropyl myristate?

This thesis starts with a brief overview of the current production processes for fatty acid esters. Because these processes have several drawbacks, a new technology is proposed: Entrainer-based Reactive Distillation. In Entrainer-based Reactive Distillation, in situ separation is used to improve the yield of reaction, whereas an entrainer feed is added to overcome the alcohol-water azeotrope, by selectively increasing the relative volatility of water. The objective of this research is the development of a multi-product Entrainer-based Reactive Distillation process for the synthesis of fatty acid esters using a heterogeneous catalyst, and evaluate its attractiveness compared to the current technologies. In Chapter 2 it is demonstrated that, due to the similarities between Entrainer-based Reactive Distillation and azeotropic distillation, the same selection rules can be applied to select a suitable entrainer. From a list of suitable entrainers for the azeotropic distillation of isopropanol and water, cyclohexane and isopropyl acetate are chosen. Residue curve maps, simulations of the distillation section of the column, and simulations of the total Entrainer-based Reactive Distillation concept show that both can be used as an entrainer in Entrainer-based Reactive Distillation. Whether Entrainer-based Reactive Distillation will be feasible, strongly depends on the kinetics of the reaction. For this reason Chapter 3 discusses the reaction kinetics of the esterification of myristic acid with isopropanol and with n-propanol, using sulphated zirconia (SZ) and ( p)-toluene sulphonic acid (pTSA) as catalysts, for a temperature range of 343-403K. SZ appeared to be an unsuitable catalyst for the esterification of myristic acid with isopropanol since it did not increase the reaction rate of the uncatalysed reaction. For the reactions with pTSA the reaction rates are determined. The reactions follow first order kinetics in all components. The kinetic model corresponds with the results for the esterification of myristic acid with isopropanol and the results for the esterification of palmitic acid from literature. As expected, the reaction rate increases with increasing amount of catalyst and with increasing temperature. The reaction rate and equilibrium conversion increases with an increasing alcohol to myristic acid feed ratio. The reaction with n-propanol is considerably faster (at 373K about 3.8 times) than the reaction with isopropanol. On the basis of the entrainer selection and kinetics studies Chapter 4 will discuss the gains that can be obtained using Entrainer-based Reactive Distillation with regard to conventional Reactive Distillation. Five process configurations for the esterification of myristic acid with isopropanol and ( n)-propanol using a homogeneous catalyst, are compared, by simulation in Aspen Plus. In the esterification with isopropanol at 1 bar, the addition of the entrainer has no positive influence on the conversion, because the amount required for water removal causes temperature decrease in the column. This temperature decrease has a negative in°uence on the conversion, because the high activation energy of the reaction cannot be overcome. However, in the esterification with iso-propanol at 5 and 10 bar and in the esterification with n-propanol (either 1, 5 or 10 bar), the addition of the entrainer has a positive influence on the conversion. More entrainer leads to a higher conversion. Surprising is the observation that the conventional Reactive Distillation configuration (RD1) reaches the desired purity and conversion. Because of its polarity, water is pressed out of the liquid phase, in which the reaction takes place, so the reaction can reach nearly complete conversion. Because the decrease of the reaction volume due to the addition of the entrainer is rather small and the energy consumption is comparable, conventional Reactive Distillation (RD1) is the preferable configuration for the esterification of myristic acid with either isopropanol or n-propanol. Subsequently, the Aspen Plus process for the reactive distillation is validated through pilot plant experiments in Chapter 5. A detailed model of the pilot plant is created for different operating conditions. Experiments with a pilot column are performed to verify the model. The conducted experiments correspond well with the predicted values; the model can be used in the construction of a conceptual design. However, not all the intended validation experiments could be performed, because of the practical difficulties that arise when negligible liquid level in the column has to be ensured. Also the break down of the pumps due to clogging appeared a limiting factor in the experiments.Finally, the process model from Chapter 5 is used to construct a conceptual design for the esterification of myristic acid with isopropanol through reactive distillation (packed, tray and bubble column). A parameter optimisation study is performed to investigate the influence of the different process parameters. Finally all results are integrated in conceptual designs for the industrial scale processes, which are evaluated against the batch process based on required reaction volumes. The required reaction volume can be decreased with 27 or 79%, allowing a maximum temperature of respectively 170 and 220ºC, using a packed reactive distillation column. Using a tray reactive distillation column and a maximum temperature of 220ºC, the required reaction volume can be decreased with 93%. Due to the less favourable mass transfer characteristics, in the bubble column the required reaction volume can only be decreased with 78%. It is further noted that, at a temperature of 220ºC, the tray reactive distillation is the preferable process for the esterification of myristic acid isopropanol, based on the required reaction volumes. The influence of the maximum column temperature and the influence of a larger liquid hold-up per stage as a result of a different column configuration are of equal importance for the required reaction volume. This thesis shows that reactive distillation can be used for the production of isopropyl myristate, which results in an enormous decrease in reaction volume compared to the batch process. Therefore, it can be concluded that reactive distillation has the potential to become an economically attractive alternative, not only for fatty acid esters based on methanol and primary alcohol which is already known, but also for the production of isopropyl myristate

Recent advances and future perspectives on more sustainable and energy efficient distillation processes

Distillation has held a very strong position in the chemical process industries for well over a century, and has, as a separation method, been around for millennia. The process can be designed directly without the need for experimentation unlike other novel separation processes, and distillation is a standard part of any undergraduate curriculum. So why the ongoing interest in this separation dinosaur? Due to distillation’s significant importance in industry, and its associated high energy requirements and thereby contribution to global warming, considerable effort is still needed to make the process more energy efficient, as well as to consider other heating sources beyond traditional fossil fuels. In this work, we will outline the most significant methods currently considered for energy efficiency of distillation, and provide an overview of where we may be heading as a discipline in our quest for a more sustainable chemical engineering future. We will argue that significant improvements have already been made, but more is still required by both industry and legislators. We need to consider a future without the use of fossil fuel-based feedstock or energy sources and switch towards renewable sources, and our future graduates need to be adequately prepared for such a future

An investigation of the interactions between system characteristics and controllability for reactive distillation systems

Reactive distillation is an emerging process intensification technology, although its operation and control are complex due to the interactions between reaction and separation within the column. In this work, the impact of reaction and separation, as well as design parameters, on the controllability of reactive distillation processes is investigated, using a systematic methodology developed. Case studies of industrial interest are considered, varying in the key (reaction, separation and design) parameters, in order to investigate the relative impact of the latter on the controllability of the reactive distillation systems. It is shown that the system with slower kinetics demonstrates an increased difficulty in rejecting feed disturbances for both one point (V-only) and two-point (LV) control configurations. Even when linear model predictive control (MPC) is considered based on a state-space representation of the model, the system with slower reaction kinetics is still more difficult to control, for both set point change and load disturbance. It is also shown that revision of the optimal steady state design variables, such as the total number of stages, may be beneficial for the controllability of the process. The importance of maintaining feed ratio in stoichiometric processes is identified and discussed, as failure to do so may result in failure to maintain both product purities when two point control is considered

Economic recovery of biobutanol-a platform chemical for the sugarcane biorefinery.

Master of Science in Chemical Engineering. University of KwaZulu-Natal. Durban, 2017.In recent years, the South African sugar industry has faced challenges, such as drought, low prices and labour issues that have impacted negatively on the perceived sustainability. The adoption of the sugarcane biorefinery concept by the sugar industry is a possible solution to improving the sustainability of the industry amid these challenges. In this envisioned biorefinery, multiple products are created within an integrated system that maximises sustainability, as opposed to relying on producing one or very few products. In this study, the potential economic viability of the recovery of biobutanol was explored with the ultimate intention of using this biobutanol as a platform chemical for the production of higher value products to include in the biorefinery’s product portfolio. Biobutanol is produced from biomass via the ABE (acetone, butanol, and ethanol) fermentation process. Biobutanol production is characterised by very low butanol concentrations in the fermentation broth (around 2 wt. %) due to high inhibition, resulting in a very high cost of recovery (distillation) and the need for several downstream purification steps. Following a literature search on technologies that have been proposed and previously implemented for biobutanol production, processes integrating gas stripping and extraction were simulated on Aspen Plus® and techno economic analyses performed to determine the profitability based on cash flows over a 25 year period. Gas stripping and liquid-liquid extraction experiments were first carried out in order to have a way of validating simulation results. Gas stripping experiments created scenario-based results of the expected butanol concentration in the gas phase once a steady state butanol concentration can be maintained in the fermenter. The extraction experiments were conducted to establish a quick way of evaluating the extractive properties of a solvent based on the distribution coefficients and selectivities with respect to butanol. Five solvents were evaluated including hexyl acetate and diethyl carbonate, which have not been reported on but have been previously applied in biomass processing. Distribution coefficients of 3.57 and 6.15 and selectivities of 367.09 and 396.00, with respect to butanol, were obtained for hexyl acetate and diethyl carbonate, respectively. Four processes were then simulated on Aspen Plus® and they all assumed a fermentation process that make use of 281.67 t/h clear juice from a South African generic sugar mill iv model. A study estimate type economic evaluation, accurate within ±30% error, was performed with profitability being assessed in terms of the Net Present Value (NPV) and the Internal Rate of Return (IRR) over the 25 year period. Process Scheme 1 was the benchmarking case and consists of the conventional series of five distillation columns. For this process a Total Capital Investment (TCI) of US$124.85 million was obtained and based on the sales and production costs a negative NPV of US$3.80 million was obtained. This indicates a non-viable process under the current economic conditions. Process Scheme 2 included in situ recovery by gas stripping and final purification using distillation. Five distillation columns were still required to purify the condensate from the stripper due to a large amount of water that is carried in. The increased productivity in the fermenter and the reduction the downstream column sizes in this process, compared to the benchmarking case, resulted in a reduced capital cost of US$67.43 million. This recovery process also yielded a potential to be profitable with a positive NPV of US$505.88 million and an IRR of 31%. This was attributed to the reduced TCI as well as the ability of the process to yield all the three ABE solvents to sellable purities. Process Scheme 3 that included gas stripping and liquid-liquid extraction had almost the same TCI as Process Scheme 2 (US$68.94 million) but could only yield butanol to sellable quality due to the selective property of the solvent used (2-ethyl-hexanol). This reduction in sales led to an IRR of 6NPV of US$82.38 million resulted. Process Scheme 4, making use of a two-stage gas stripping and distillation, was the most profitable process and it was concluded it would be the process to attach to the sugar mill model and also to be considered for the higher value chemical production. An NPV of US$524.09 and an IRR of 32% were realised for this process. Sensitivity analyses on these four processes showed that the cost of the substrate (clear juice) and the butanol selling price have the major effects on the profitability. It was, therefore, recommended that other streams from the sugar mill be considered as substrates for higher value chemical products which can attract higher prices than butanol which is regulated by the petro based butanol. Finally, a structure of a functionalised ionic liquid was suggested based on group contribution methods to be a potential reactive extraction reactant for converting butanol to a higher value ester product

Modeling and Simulation of Ethyl Acetate Reactive Distillation Column

Reactive distillation (RD) is an attractive way of improving process economics by combining distillation and reaction, especially for equilibrium limited reactions such as esterification. Two of the most studied esterification reactions via RD in the literature are methyl acetate synthesis and ethyl acetate synthesis. The ideal performance of the RD column would be to achieve almost complete conversion of both reactants while at the same time producing pure esters as distillate. From literature it was found that unlike other RD systems such as MTBE and ETBE, it is impossible to achieve ideal performance with normal double feed configuration, though the achieve conversion and purity of these systems are higher than the conventional method of reaction followed by separation. This is du,e to the formation of azeotropes between reaction products and reactant, which in tuin hinders the achievement of complete conversion and producing pure esters as di~tillate. Researchers had successfully exploit the mixture properties of methyl acetate system and device a RD configuration known as reactive-extractive distillation (RED) column that ultimately overcomes the azeotropic conditions in a single column and hence able to achieve ideal performance for this system. However, the conditions in ethyl acetate RD column do not allow us to exploit the mixture properties and furthermore the presence of four azeotropes as compared to two azeotropes in methyl acetate system complicates the separation process in ethyl acetate RD column. Thus in this study attention were given to improve the ethyl acetate RD column performance. Initially, simulation model for esterification of acetic acid by ethanol in a RD column was developed and verified against equivalent experimental work and published simulation results. Upon confirming the applicability of the simulation model, the effects of changing various operating and design parameters on the column performance were studied in order to explore the possibility of improving the column performance. Through this analysis it is evident that the column performance could not be enhanced significantly due to formation of azeotropes between reaction products and reactant for nearly equal product split at both end of the column. Finally a new configuration that involves the introduction of extractive zones below ethanol feed point and above acetic acid feed point with extraneous component as an extractive agent in the system in order to break one of the azeotropes between product and reactant, thus allowing the attainment of higher conversion and purity was proposed. With this configuration the column performance was significantly improved