Esterification Of Citric Acid Research Articles

English

Sulfonated crosslinked chitosan resins (SCCRs) were prepared by firstly crosslinking chitosan to crosslinked chitosan resins (CCRs) using a reverse emulsion crosslinking method, followed by sulfonating CCRs with concentrated H 2 SO 4 as the sulfonation agent. The properties and application of SCCRs as solid acid catalysts were studied. The acidic sites in SCCRs, including C 6 –O and C 2 –N sulfate groups, are all weak acidic sites. SCCRs of higher crosslinking degrees have a higher sulfonation rate of the C 6 primary hydroxyl groups, thus more C 6 –O sulfate groups. High-temperature treatment and TG analysis verified that the crosslinking can improve the thermostability of both SCCR backbone and its acidic groups, and a higher crosslinking degree leads to better thermostability. Catalytic esterification of citric acid with butanol and propionic acid with n-butyl alcohol demonstrated that SCCRs have good catalytic activity and can be repetitively used as efficient solid acid catalysts.

Adsorption of lead(II) onto organic acid modified rubber leaf powder: Batch and column studies

This study evaluated the Pb(II) sorption capacities of two chemically modified biosorbents which are citric acid modified rubber leaf powder (CARL) and monosodium glutamate modified rubber leaf powder (MGRL). The raw rubber leaf powder (RLP) was modified to improve its effectiveness in removing the Pb(II) ions in an aqueous solution. CARL was prepared by esterification of citric acid onto the cellulose structure while MGRL was prepared by functionalising monosodium glutamate onto the epoxy activated rubber leaf powder. The sorption performance of the sorbents was examined by pH, kinetics and isotherm experiments. The adsorption of Pb(II) was much more favourable at higher pH. The rate limiting step in the adsorption process for both adsorbents was chemisorption and both adsorbents had a better fitting to the pseudo-second order kinetic model. The maximum capacities of Pb(II) calculated by the Langmuir isotherm by CARL and MGRL were 97.19 and 109.95mg/g, respectively. In column experiments, the breakthrough time was found to decrease from 25 to 5min for CARL and 37.5 to 10min for MGRL with an increase in Pb (II) concentration from 20 to 60mg/L. The Thomas and Yoon–Nelson models had a good fit with the fixed bed column data. Different column parameters such as column adsorption capacity and 50% adsorbate breakthrough were calculated. It was found that the adsorption capacity and performance of MGRL was superior to CARL in both batch and fixed bed column studies.

Esterification Kinetics of Tributyl Citrate Production Using Homogeneous and Heterogeneous Catalysts

In this work, the production of tributyl citrate via catalytic and self-catalyzed esterification of citric acid with 1-butanol was studied. Both, methanesulfonic acid (MSA) and Amberlyst 70 ion-exchange resin were evaluated as catalysts in the reaction. The kinetic effects of the temperature (353–393 K), the feed molar ratio of alcohol to acid (8:1 to 16:1), and catalyst loadings (0.5–1.5 wt % of MSA, and the equivalent amount of Amberlyst 70) were evaluated. Experiments were carried out using stirred batch reactors under isothermal operation. A Box–Behnken design was used to optimize the number of experiments required to obtain a valid kinetic model. Chemical equilibrium conditions were evaluated independently from kinetic experiments, reducing the number of parameters to adjust during data regression. Self-catalytic rate of reaction was also evaluated, and it was included within the overall kinetic model. The obtained models show good agreement with experiments, and they can be used for process analysis...

Esterification of citric acid with n-butanol over zirconium sulfate supported on molecular sieves

Solid acid catalysts consisting of zirconium sulfate (ZS) supported on a series of molecular sieves including HZSM-5, HMS and MCM-41 were prepared and used in the esterification of citric acid with n-butanol to produce tributyl citrate (TBC). Highly dispersed ZS was supported on 40wt.% ZS/HMS or ZS/MCM-41, whereas HZSM-5 loaded more bulk ZS species. The ZS loading and type of support showed obvious effect on thermal stability, acidity and type of acid sites. In the esterification of citric acid, 40wt.% ZS/HMS or ZS/MCM-41 exhibited higher catalytic activity than pure ZS or 40wt.% ZS/HZSM-5. An investigation focused on ZS/HMS showed that Brønsted and Brønsted+Lewis acid sites acted as the active center for the esterification reaction. 40wt.% ZS/HMS calcined at 180°C obtained the highest conversion of citric acid and TBC yield. The reaction was found to obey an Eley–Rideal mechanism.

A biodegradable thermoset polymer made by esterification of citric acid and glycerol

A new biomaterial, a degradable thermoset polymer, was made from simple, economical, biocompatable monomers without the need for a catalyst. Glycerol and citric acid, nontoxic and renewable reagents, were crosslinked by a melt polymerization reaction at temperatures from 90 to 150°C. Consistent with a condensation reaction, water was determined to be the primary byproduct. The amount of crosslinking was controlled by the reaction conditions, including temperature, reaction time, and ratio between glycerol and citric acid. Also, the amount of crosslinking was inversely proportional to the rate of degradation. As a proof-of-principle for drug delivery applications, gentamicin, an antibiotic, was incorporated into the polymer with preliminary evaluations of antimicrobial activity. The polymers incorporating gentamicin had significantly better bacteria clearing of Staphylococcus aureus compared to non-gentamicin gels for up to 9 days.

A simple route to prepare carbonaceous nanospheres from bagasse

We reported a simple route to prepare carbonaceous nanospheres (CNSs) (20–30nm in diameter) from bagasse using a mixture of phosphoric and sulfuric acids while stirring at 50°C for 30min followed by heating for dehydration at 220°C for 1h. It was found that the CNSs were efficient catalysts and recyclable for the esterification of citric acid with n-butanol, in which the esterification rate reached 87.88% for 4h. Meanwhile, luminescent carbonaceous dots were found on the surface of the CNSs. Their maximum emission wavelength was at 425nm under excitation with 330nm wavelengths. The quantum yield was 2.7% under 330nm excitation wavelengths.

Enzyme‐Catalyzed Synthesis of Monoacylglycerols Citrate: Kinetics and Thermodynamics

AbstractThe kinetics and thermodynamics of the esterification of citric acid (CA) and monoglycerides (MGs) for citrate esters of monoacylglycerols catalyzed by Novozym 435 in tert‐butyl alcohol system was studied in this work. The relationship between initial reaction rate and temperature was established, based on the Arrhenius law. A linear relationship was established between the initial reaction rate and enzyme load up to 3 g/L, which demonstrated that the influence of external mass transfer limitations on the reaction could be eliminated. The reaction kinetics agreed with the Ping‐Pong Bi–Bi mechanism with CA inhibition characterized by Vmax, KB, KA, and KiA, values of 0.7092 mmol/(min g), 0.0553, 0.0136 and 0.1948 mol/L, respectively. The model was used to simulate the reaction process. The values calculated from the kinetic mode agreed well with the experimental rate data under the different MG and CA concentrations.

Preparation and Properties of Copolymer of Degraded Starch and CA-HPA Initiated by HRP/H<sub>2</sub>O<sub>2</sub>/ACAC

Citrate-hydroxypropyl acrylate (CA-HPA) was prepared by esterification of citric acid and hydroxypropyl acrylate. Then a graft copolymer was synthesized by copolymerization of degraded starch and CA-HPA using a complex initiation system of horseradish peroxidase (HRP)/H2O2/acetylacetone (ACAC). The effects of amount of CA-HPA, HRP, ACAC and reaction temperature on grafting efficiency (GE) and grafting percentage (GP) were investigated. The results showed that the graft copolymer with higher grafting level could be prepared by grafting copolymerization of 50 g degraded starch (wt 15%) with 13.9 g CA-HPA in the presence of 6.4 mg HRP/4.7mL H2O2/1.2g ACAC at 35 °C for 5h under system pH 8. The graft copolymer can be used as retannage. The structure of the copolymer was characterized by FTIR, and the mechanism of polymerization was advanced. The retanned leather has the merits of good uniformity fullness softness, strong selecting filling properties and good elasticity.

Preparation and Properties of Copolymer of Degraded Starch and CA-HPA Initiated by HRP/H<sub>2</sub>O<sub>2</sub>/ACAC

Citrate-hydroxypropyl acrylate (CA-HPA) was prepared by esterification of citric acid and hydroxypropyl acrylate. Then a graft copolymer was synthesized by copolymerization of degraded starch and CA-HPA using a complex initiation system of horseradish peroxidase (HRP)/H2O2/acetylacetone (ACAC). The effects of amount of CA-HPA, HRP, ACAC and reaction temperature on grafting efficiency (GE) and grafting percentage (GP) were investigated. The results showed that the graft copolymer with higher grafting level could be prepared by grafting copolymerization of 50 g degraded starch (wt 15%) with 13.9 g CA-HPA in the presence of 6.4 mg HRP/4.7mL H2O2/1.2g ACAC at 35 °C for 5h under system pH 8. The graft copolymer can be used as retannage. The structure of the copolymer was characterized by FTIR, and the mechanism of polymerization was advanced. The retanned leather has the merits of good uniformity fullness softness, strong selecting filling properties and good elasticity.

Synthesis, Characterization of Novel Hexamethyleneiminium-Based Ionic Liquids and their Application in Esterification

Three novel Brønsted acidic ionic liquids (ILs), 1-(3-sulfopropyl) hexamethyleneiminium hydrogen sulfate ([HMIPS]HSO4), 1-(3-sulfopropyl) hexamethyleneiminium tosilate ([HMIPS]OTs) and 1-hexamethyleneiminium hydrogen sulfate([HMI]HSO4), were synthesized and characterized by1H NMR, FT-IR and DSC-TG. Their catalytic activities for the esterification of citric acid with n-butanol were examined and compared with the imidazolium-based ILs. The results showed that the hexamethyleneiminium-based ILs exhibits excellent catalytic activity. By using [HMIPS]HSO4as the catalyst, the yield of tributyl citrate reached 97.5%. Furthermore, the catalysts were reused at least 10 times without significant decrease in activity

Enzymatic synthesis of monoacylglycerol citrate optimized by response surface methodology

The ability of immobilized lipase B from Candida antarctica (Novozym 435) to catalyze the direct esterification of citric acid (CA) and monoglyceride (MG) for citrate esters of monoacylglycerols (CITREM) preparation was investigated. The effects of substrate concentration, molecular-sieve amount, substrate molar ratio, reaction temperature, time, and enzyme load on the conversion of CA in the reaction were investigated. Enzyme screening and the effect of solvent on the esterification were also investigated. RSM was used to optimize the effects of the reaction temperature (45-55 C), the enzyme load (6-10%; relative to the weight of total substrates), and the reaction time (24―48 h) on the conversion of CA. Validation of the RSM model was verified by the good agreement between the experimental and the predicted values of CA conversion. The optimum preparation conditions were as follows: CA concentration 0.12 mol/L, molecular-sieve 120 g/L, molar ratio of MG/CA 2:1, temperature 54.18°C, enzyme load 9.0% (relative to the weight of total substrates), and reaction time 47.5 h. Under the suggested conditions, the conversion of CA was 77.4%. Repeated reaction tests indicated that Novozym 435 could be used eight times under the optimum conditions with 92% of its original catalytic activity still retained.

Reaction Kinetics of the Catalytic Esterification of Citric Acid with Ethanol

Reaction kinetics are presented for the reversible esterification reaction of citric acid with ethanol to form tri-ethyl citrate via mono-ethyl and di-ethyl citrates. The reaction was studied in batch isothermal experiments, self-catalyzed homogeneously by citric acid and the formed mono- and di-ethyl citrates, and heterogeneously catalyzed by macroporous Amberlyst-15 ion-exchange resin catalyst. Experimental data were obtained between 78 and 120 °C at different mole ratios of ethanol to citric acid and catalyst concentrations up to 5 wt % ion-exchange resin. The kinetics of ethanol etherification to form di-ethyl ether were included in the investigation. Kinetic modeling was performed using a pseudo-homogeneous UNIQUAC-based activity model, taking into consideration the rate of self-catalyzed esterification and the side reaction to form diethyl ether. The activity coefficients for the tri-ethyl citrate−ethanol and tri-ethyl citrate−water binary pairs were obtained from experimental vapor−liquid equilibri...