Reducing total annual cost and CO2 emissions in batch distillation for separating ternary wide boiling mixtures using vapor recompression heat pump

This paper presents cost-effective heat pump assisted vapor recompression (VRC) design algorithms for the separation of ternary wide boiling mixture in batch distillation in order to reduce total annual cost (TAC) and carbon dioxide (CO2) emissions. A minimum TAC and CO2 is required by the batch distillation process industry for any investments in heat integrated systems, such as VRC. Consequently, the design conditions for implementing VRC should be chosen such that the energetic performance is maximum at minimum TAC. The model system selected in this paper is an application involving high temperature lift, that is, hexanol–octanol–decanol ternary wide boiling mixture. First, a systematic simulation algorithm was developed for conventional multicomponent batch distillation (CMBD) and single-stage vapor recompressed multicomponent batch distillation (SiVRMBD) to determine the optimal number of stages based on the maximum TAC savings. The SiVRMBD saves more energy and TAC than CMBD. However, SiVRMBD has a high compression ratio (CR) throughout the operation, which is not practically feasible for the batch distillation processing. Second, in order to increase the performance and minimize the SiVRMBD weakness, a novel optimal multi-stage vapor recompression algorithm was proposed to operate at the lowest possible CR (<3.5) throughout the batch operation while also conserving the most TAC. Overall, the findings suggest that the proposed optimal multi-stage VRC reduces TAC and CO2 emissions significantly when compared to CMBD. Finally, the influence of the different feed compositions on VRC performance is also studied.

Experimental study on essential anise star oil purification in vacuum batch distillation

Vietnam is one of the world’s largest annual anise harvest countries. However, products from anise are mainly in the form of dried anise fruit and crude star anise essential oil with low economic value. The main component of the star anise essential oil is trans-anethole which needs to be purified to produce higher-value products. This study focused on building an experimental system for purifying star anise essential oil by a batch distillation column working at vacuum pressure. The products obtained during the purification process were analysed by gas chromatography-mass spectrometry (GC-MS). Analytical results were used to evaluate the ability to separate volatile impurities in the crude star anise essential oil. Results showed that the bottom temperature of the tower below 150oC, corresponding to a vacuum pressure of less than 0.1 bar, can reduce the thermal decomposition of essential oils. The volatile components, such as α-pinene, β-phellandrene, limonene, and linalool, were thoroughly separated at the top of the tower. The purified star anise essential oil was from the bottom of the distillation and had the anethole composition of over 88% of mass fraction (wt.%). Anethole recovery efficiency was 98.5 and 88.8% at a pressure of 0.1 and 0.08 bar, respectively. The bottom product can have a higher anethole composition if increasing the column height, the reflux ratio, and decreasing the pressure and the quality of impurities removed at the top is increased.The experimental results are helpful for the calculation, design, manufacture, and operation of an industrial-scale essential oil purification system.

Separation of carvone by batch distillation from the mixture obtained from limonene oxidation

Limonene is the main constituent of citrus oils whose oxidation produces a set of fine chemical compounds such as carvone, carveol, and limonene 1,2-epoxide. This contribution reports the results of the experimental evaluation and computational simulation of carvone separation by fractional distillation from the reaction mixture. Carvone was obtained from limonene oxidation over a perchlorinated iron phthalocyanine supported on modified silica catalyst (FePcCl16-NH2-SiO2) and t-butyl hydroperoxide (TBHP) as oxidant. Both experimental and simulation results support that fractional distillation (in batch and continuous) is a suitable technique for concentrating carvone. However, in the presence of water, the formation of immiscible L-L phases makes the experimental separation of carvone more difficult. Simulation results of the batch distillation incorporating the NRTL-RK thermodynamic model indicate that if water, acetone, and t-butanol are previously removed from the reaction mixture, carvone composition can be enriched in the reboiler from 4% up to 50%, or around 86.5% if the removal is in a third distillate cut under vacuum conditions.

A survey on fractionation: the optimal control of distilling in batch and semibatch configurations

Since the middle of the last century, discussion about the operation of discontinuous fractionation to meet multifarious goals, such as product purity and recovery rate, by monitoring process variables including reflux or/and heat duty, is been on. The engineering practice showed intolerable events to occur; hereof the operation must be supervised, which makes it difficult to be in agreement with the batch distillation objectives. Hence, to uphold the effectuation of new operating policies into the industrial “know-how” techniques, different optimal control strategies can be conceived. The objective of this work is to offer a literature survey on the investigations of optimal control functioning for selected simple distillation column configurations employed in batch/semibatch distillation of homogeneous/reactive mixtures, as well as the approaches used in this regard. Available optimal control schemes have been reviewed in detail, emphasizing its major assets.