Synthesis of n-hexyl acetate in batch and chromatographic reactors

Petrochemical and fine chemical industries face a daunting problem in recovering acetic acid from its aqueous solutions. The recovery of acetic acid could be done through esterification reaction. However, esterification is an equilibrium limited reaction. Multi-functional reactors such as chromatographic reactor (CR) and reactive distillation column (RDC) are promising technologies mainly for equilibrium limited reactions wherein reaction and separation of products are carried out in a single equipment that tends to shift the equilibrium towards the desired direction which is not possible in a classical batch reactor. Physical and chemical characterisation of ion exchange resin catalysts such as scanning electron microscopy, Brunauer-Emmett-Teller (BET) surface area measurement, pore size distribution, elemental analysis, true density and particle size distribution were carried out to access the catalysts performance for n-hexyl acetate synthesis. Esterification of acetic acid with n-hexanol was studied with both dilute and concentrated acid in the presence of cation exchange resins (macroporous and gelular) in a jacketed stirred batch reactor to synthesise a value added ester, namely n-hexyl acetate and also to study the recovery of acetic acid from the waste aqueous streams. The effect of various parameters such as speed of agitation, catalyst particle size, feed mole ratio of n-hexanol to acetic acid, reaction temperature, catalyst loading and reusability of catalysts was studied for the optimisation of the reaction condition in a batch reactor. The non-ideality of each component in the reacting mixture was accounted for by using the activity coefficient via the use of the UNIFAC group contribution method. The kinetic data were correlated with both pseudo-homogeneous (PH) and adsorption based heterogeneous reaction rate models, e.g., Eley-Rideal (ER), Langmuir-Hinshelwood-Hougen-Watson (LHHW), and the modified LHHW (ML). Pseudo-homogeneous (PH) model gave the best representation of the kinetic data found experimentally. The feasibility of reactive distillation for the recovery of acetic acid using n-hexanol was evaluated through residue curve map (RCM) determination experiments. RCM provides information to a design engineer of the existence of separation boundaries imposed by the singular points corresponding to the reactive/non-reactive azeotropes, thus provides an insight into the feasibility of reactive distillation for this purpose. A laboratory scale batch chromatographic reactor was designed and constructed. Batch chromatographic reactor experiments were carried out using different parameters such as feed flow rate, feed mole ratio of n-hexanol to acetic acid, desorbent (n-hexanol) flow rate and reaction step to maximise the formation of n-hexyl acetate as well to achieve complete conversion of acetic acid. Continuous chromatographic reactor was designed, constructed and commissioned on the basis of the results obtained from the batch chromatographic reactor experiments. The experiments carried out in continuous chromatographic reactor correlated very well with the results from the batch chromatographic reactor for the optimised condition

Startup of a reactive distillation process with a decanter

The startup of a reactive distillation process for the production of propyl acetate including a decanter is studied. A simulation model is presented which describes the whole startup from a cold and empty state and takes into account the liquid phase split in the decanter. The simulation model is successfully validated with own dynamic experimental data. Different startup strategies are developed and analysed in simulation studies showing the high influence of the initial charging of decanter and reboiler on the startup time

Synthesis of The Stereoismomers of DEHP and MEHP from Kinetically Resolved 2-ethyl-1-hexanol

Di(2-ethylhexyl) phthalate (DEHP) is a known chiral persistent organic pollutant found in many different consumer products, and the toxicities of its stereoisomers and their metabolites are not well known. To determine their adverse health effects, each enantiomer has to be synthesized. Using lipase PS from Burkholderia cepacia in dichloromethane at 0˚C for 48 hours, 2-ethyl-1-hexyl acetate was obtained in 55% yield (75:25 e.r.), while (R)-2-ethyl-1-hexanol (1) was obtained in 29% yield (96:4 e.r.). The acetate was then hydrolyzed to recover the (S) enriched alcohol (82% yield). The enriched alcohol was acylated a second time to yield (S)-(1) in 39% yield (91:9 e.r.). R-(1) and phthalic anhydride were reacted in 1:3 pyridine/toluene at 100˚C for 2 hours to synthesize (R)-mono(2-ethylhexyl) phthalate ((R)-MEHP) in 50% yield. Difficulty was encountered in separating MEHP from (1) in the reaction mixture, with numerous solvent systems, vacuum distillation, and chemically active extraction attempted without success. The resulting impure (R)-MEHP was reacted with (R)-(1) in the presence of N,N\u27-diisopropylcarbodiimide and 4-dimethylaminopyridine in dichloromethane for 19 hours at room temperature to synthesize(R,R)- DEHP in 36% yield. Future work will synthesize the other isomers of DEHP, further purify (1), and successfully separate MEHP from (1)

From 3,3,4,4-Tetraethoxybut-1-yne to furan derivatives

The starting material for this project was the highly functionalized compound 3,3,4,4- tetraethoxybut-1-yne (TEB) and it can be prepared from ethyl vinyl ether by a 4-steps synthesis. The third and the fourth step in TEB synthesis were sensitive to reaction conditions, so it was developed a strategy to try to optimize the third step and obtain TEB with higher yields. An approach, which tries to optimize also the fourth step, will be developed in further works. Several γ-hydroxy-α,β-unsaturated acetylenic ketones can be prepared from 3,3,4,4- tetraethoxybut-1-yne. TEB and γ-hydroxy-α,β-unsaturated acetylenic ketones have been previously synthesized in good yields using various reaction routes. In this work will be shown the synthesis of 1,1-diethoxy-5-hydroxyhex-3-yn-2-one, 1,1-diethoxy-5-hydroxyundec-3-yn-2-one and 1,1-diethoxy-5-hydroxydodec-3-yn-2-one, which will react with ethyl acetoacetate to give, respectively, ethyl 4-(3,3-diethoxy-2-oxopropyl)-2,5-dimethylfuran-3-carboxylate, ethyl 4-(3,3-diethoxy-2-oxopropyl)-5-hexyl-2-methylfuran-3-carboxylate and ethyl 4-(3,3-diethoxy-2-oxopropyl)- 5-heptyl-2-methylfuran-3-carboxylate furan derivatives. This thesis project was carried out during the year 2011, at the Department of Chemistry of the University of Bergen

A study of selectivity in the reactions of unsymmetrical trialkylboron compounds

The reaction of disiamylborane with enol acetates derived from an aldehyde bearing two α-hydrogen atoms involves a slow anti-Markownikoff hydroboration followed by rapid elimination and re-hydroboration reactions. Selectivity between reaction of the cis and trans isomers is far smaller than for the corresponding olefinic hydrocarbons. Enol acetates derived from ketones are generally unreactive to disiamylborane. The extent of reaction of propionic acid with a representative series of trialkylboranes depends on the steric resistance of the borane to the initial co-ordination of the acid. The extent of protonolysis decreases with an increase in the total number of alkyl substituents at the α- and β-carbon atoms to boron. With an unsymmetrical trialkylborane the selectivity between the breaking of secondary and primary carbon-to-boron bonds is small. A very large selectivity is found in favour of the removal of a primary—rather than a tertiary—alkyl group. This is thought to be due to steric and not electronic factors. [Continues.

Finding the Markers of Fungal and Bacterial Infections in Allium cepa L.

Common onion (Allium cepa L.) is considered as one of the most important vegetables due to the extensive usage in industrial food production. The production of dried onions is more than 88 million tons every year. However, onions are prone to several microbial infections reducing their yield and quality within a short period. The early stages of infection cannot be detected in onions by the conventional analytical methods. It can be assumed that the pattern of chemical compounds is altered by the action of pathogenic bacteria and fungi. In this project, we aim to identify the markers of infection in Allium cepa L. which can help to provide early detection of common onion diseases. Five microbial strains including: Fusarium oxysporum, Fusarium proliferatum, Penicillium sp., Botrytis aclada, and Erwinia carotovora, were used to infect onion bulbs. Healthy and infected bulbs were extracted with ethyl acetate. The extracts have been analyzed using HPLC to define potential infection markers. Two new peaks were observed and suggested to be markers for the infections. Fractions were further investigated to charactarize their chemical structures by HPLC/MS, HRMS, UV, IR, and NMR. For the quantitative determination of both marker compounds, dimethyl dihydrofuranone (DMDHF) was served as an internal as well as external standard. Seven other Allium species were also studied to investigate the presence of the same markers. In addition, some experimental work was done to synthesize the markers and detect them using GC and IMS. The bioactivity of the new substances in infected onion extracts was also studied. The structures of the two markers obtained after infection were confirmed as 2-hexyl-5-methyl-3(2H)-furanone and 2-octyl-5-methyl-3(2H)-furanone. These compounds could only be detected after infection, and they could be considered as markers of fungal and bacterial infections in Allium cepa L. The concentration of the markers varied between 1 and 30 ppm depending on the fresh mass of onions. The exact concentration might depend on the grade of infection. These investigated markers also appeared in A. altaicum Pall., A. . pskemense B. Fedt., A. cornutum Clementi ex Vis., A. fistulosum L., and A. porrum L., whereas they could not be detected in Allium sativum L. In bioactivity tests, no significant antifungal or antitumor activity could be recorded. The results showed also increases in free quercetin in infected onion bulbs in comparison to the healthy ones. The 3(2H)-furanones have already been reported in previous studies as normal aroma substances located in Allium cepa. The production of 3(2H)-furanones in plants after infection could be an indirect defense strategy to confuse the quorum sensing in bacteria and other microorganisms

Precursor reaction kinetics control compositional grading and size of CdSe1-xSx nanocrystal heterostructures

We report a method to control the composition and microstructure of CdSe1-xSx nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 degrees C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents (k(E)) spanning 1.3 x 10(-5) s(-1) to 2.0 x 10(-1) s(-1). Depending on the relative reactivity (k(Se)/k(S)), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe1-xSx alloys (k(Se)/k(S) = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed

Liquid-liquid phase equilibrium and interaction exploration for separation of azeotrope (2,2,3,3-tetrafluoro-1-propanol + water) with two imidazolium-based ionic liquids

For separating azeotropic mixture 2,2,3,3-tetrafluoro-1-propanol (TFP) and water, two kinds of imidazolium-based ionic liquids 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([HMIM][OTf]) and 1-octyl-3-methylimidazolium trifluoromethanesulfonate ([OMIM][OTf]) were adopted to separate TFP and water. The liquid-liquid equilibrium behavior for the mixtures (water + TFP + [HMIM][OTf]) and (water + TFP + [OMIM][OTf]) were measured at temperature of 298.15 K and pressure of 101.3 kPa. The extraction ability of [HMIM][OTf] and [OMIM][OTf] was explored with partition ratio and selectivity. In the meantime, the hydrogen bond lengths, total electron density, interaction energies and deformation electron density were calculated to analyze the interactions between the [HMIM][OTf]/[OMIM][OTf] and (TFP/water). Also, the liquid-liquid equilibrium data was fitted by the NRTL model.This work was supported by National Natural Science Foundation of China (Grant 21978155), Shandong Provincial Key Research & Development Project (2018GGX107001)

Extractive distillation with ionic liquids as solvents : selection and conceptual process design

Extractive distillation technology is widely used in the chemical and petrochemical industries for separating azeotropic, close-boiling and low relative volatility mixtures. It uses an additional solvent in order to interact with the components of different chemical structure within the mixture. The activity coefficients are modified in such a way that the relative volatility is increased. Therefore, the choice of the solvent determines the effectiveness of this process. Several solvent selection methodologies had been developed in the literature. They are based on one-way interaction parameters, meaning interactions of the components to be separated with the solvent. It has been widely accepted to consider as a promising solvent the one which is able to increase the relative volatility the most. However, the total annual cost (TAC) and the energy demand influence the final selection. Ionic liquids (ILs) are promising replacements of existing volatile solvents in extractive distillation. However, at this moment insufficient knowledge exists on the optimal properties for ionic liquids to be employed and their implementation in actual process systems. The main goal of this research was to analyze the selection and performance of ionic liquids in extractive distillation processes for three separation cases which differ from each other in polarity and chemical structures: 1-hexene/n-hexane, methylcyclohexane/toluene and water/ethanol. Theoretical ionic liquid design and selection for each mixture is done using COSMOtherm software (version C2.1, release 01.11a) by predicting activity coefficients at infinite dilution. Experimental selectivities and relative volatilities of real solutions were measured in order to choose the most suitable ionic liquids. At last, different extractive distillation processes using ionic liquids were proposed and analyzed. 1-Hexene/n-hexane separation Olefins are important base chemicals used for the manufacture of poly(olefins), plasticizers, etc. and according to Sasol, the projected demand for 2012 of C6-C8 olefins is around 0.85x106 ton. Due to the small differences in boiling temperatures and to the low relative volatility of the system, the separation of olefins and paraffins is energy intensive, meaning that all the commercially available processes for the production of olefins use several fractional distillation columns. In this work, 1-hexene and n-hexane were chosen as representative olefin and paraffin components. Extractive distillation using N-methyl-2-pyrrolidone (NMP) has been used to separate this mixture. COSMOtherm activity coefficients at infinite dilution were used to select suitable ionic liquids for this case study. Non-cyclic, cyclic and aromatic-like cations were tested in this software in combination with 27 different anions. According to the activity coefficients predicted with COSMOtherm, the solubility and selectivity of ionic liquids in 1-hexene and n-hexane is very low. This was confirmed experimentally for the selected ionic liquids using vapor – liquid equilibrium data. None of the ILs studied in this work is able to significantly increase the relative volatility in comparison with the conventional solvent NMP. Only the ionic liquid 1-hexyl-3-methyl-imidazolium tetracyanoborate [HMIM][TCB] reached a slightly higher relative volatility (1.63) than the conventional solvent NMP (1.55). However, the increase is not large enough to consider this solvent as a suitable replacement. Besides this, the ionic liquids have solubility constraints which force the use of large solvent to feed ratios to avoid the formation of two liquid phases. Methylcyclohexane/toluene separation Aromatics are among the most important chemical raw materials for the manufacture of plastics, synthetic rubber and synthetic fiber. The total production in 2009 in Western Europe of benzene, toluene and p-xylene was about 7.2x106, 1.6x106 and 1.7x106 tons, respectively. Because of the low relative volatility, external agents are used to increase the economic feasibility of the distillation units, e.g. N-methyl-2-pyrrolidone, sulfolane. The activity coefficients at infinite dilution for the mixture methylcyclohexane (MCH) and toluene with ionic liquids predicted with COSMOtherm showed a clear compromise between selectivity (easiness of separation) and solubility. Aromatic-like cations in combination with bis((trifluoromethyl)sulfonyl)imide (BTI) and tetracyanoborate (TCB) anions were selected and experimentally investigated. The relative volatility of the mixture MCH + toluene increased when any of the selected solvents (including the conventional solvent NMP) was added. The results showed that the TCB anion performed better than BTI. Therefore, the ILs 1-hexyl-3-methyl imidazolium tetracyanoborate [HMIM][TCB] and 1-butyl-3-methyl imidazolium tetracyanoborate [BMIM][TCB] seem to be the most promising replacements of NMP in the extractive distillation of methylcyclohexane and toluene. Binary and ternary liquid-liquid experimental data for the systems methylcyclohexane + toluene + [HMIM][TCB] and [BMIM][TCB] were collected and correlated with the NRTL and UNIQUAC thermodynamic models. The binary correlations were less satisfactory than ternary correlations. The results showed that UNIQUAC represented the experimental data better than the NRTL model, with a root mean square error below 0.02. The parameters obtained from the regressions of liquid-liquid equilibrium data were used to predict the vapor-liquid equilibrium (VLE). These were compared with experimental data taken by a headspace technique which showed that UNIQUAC and its parameters are able to predict the VLE of the ternary systems with a maximum error of 0.2. The non-aromatic/aromatic selectivities and relative volatilities of the ionic liquids make them suitable solvents to be used in extractive distillation processes. After obtaining the parameters for the thermodynamic model, process simulations for the extractive distillation technology using the IL [HMIM][TCB] were performed and compared with the benchmark solvent NMP. The process variables (reflux, solvent flow and number of stages) are obtained such that the energy requirements of the process are minimized. Just in the extractive distillation column, the process using the ionic liquid requires 43% less energy than the conventional solvent. Several recovery technologies were analyzed (e.g. flash evaporation, stripping with hot nitrogen, supercritical CO2, and stripping with hot MCH). The most energy efficient process (using [HMIM][TCB]) saves up to 50% of the energy requirements compared to the conventional solvent. This optimized process requires an extractive distillation column of 22 equilibrium stages, using a molar reflux ratio of 0.2 and a solvent to feed mass ratio of 2.03. The recovery of [HMIM][TCB] is done in a stripping column using part of the distillate product of the extractive distillation column as the stripping agent. Ethanol/water separation Ethanol is an important base chemical which is produced from petrochemical streams or bioprocesses. It has been used as solvent, in cosmetic and food industry, among others. However, ethanol as a (partial) replacement of gasoline has influenced its worldwide demand. Just in USA, 42x106 m3 (33x106 tons) of ethanol were added to gasoline in 2009 accounting for about 8% of gasoline consumption by volume. Water is involved in the ethanol production chain. This mixture forms an azeotrope with an ethanol mass composition of 0.956 and its challenging energy-efficient separation has been widely reported. Extractive distillation using ethylene glycol (EG) is commonly used to separate this mixture. Selectivities and activity coefficients at infinite dilution were predicted using COSMOtherm. In this case, the activity coefficients showed high attractive forces among the most promising ionic liquids and water, meaning that these ionic liquids are highly hydrophilic. The experimental relative volatility can be increased up to 23% when the conventional solvent is replaced by 1-ethyl-3-methyl-imidazolium acetate [EMIM][OAc] or 1-ethyl-3-methyl-imidazolium dicyanamide [EMIM][DCA]. These ionic liquids seem to be promising solvents for the extractive distillation of water and ethanol. Ternary VLE data were collected for the systems ethanol + water + [EMIM][OAc] and [EMIM][DCA]. In this case, the NRTL model correlates the data better than UNIQUAC, with a value for the root mean square error below 0.02. The ionic liquids are able to increase the relative volatility of the mixture ethanol – water by strongly attracting the water and making it "less volatile" which makes the recovery of the solvent rather challenging and energy intensive. Only after heat integration, the use of ILs appeared to be more attractive, yielding 16% of energy savings compared to the heat integrated conventional process. The recovery conditions and the relatively low energy savings might limit the applicability of ILs for the separation of ethanol – water by extractive distillation. Overall Finally, it can be concluded that, although ionic liquids can be suitable extractive distillation solvents, special attention should be paid to the solvent recovery technology and its heat integration with the extractive distillation column. In this study the most successful case was the separation of toluene/methylcyclohexane, where tetracyanoborate-based IL [HMIM][TCB] yielded 50% energy savings compared to the conventional solvent