Quantitative Analysis of Infrared Spectra of Binary Alcohol + Cyclohexane Solutions with Quantum Chemical Calculations.

Hydrogen bonding has profound effects on the behavior of molecules. Fourier-transform infrared spectroscopy is the technique most commonly used to qualitatively identify hydrogen-bonding moieties present in a chemical sample. However, quantitative analysis of infrared (IR) spectra is nontrivial for the hydroxyl stretching region where hydrogen bonding is most prominently expressed in organic alcohols and water. Specifically, the breadth and extreme overlap of the O-H stretching bands, and the order of magnitude variability of their IR attenuation coefficients complicates the analysis. In the present work, sequential molecular dynamics simulations and quantum mechanical calculations are used to develop a function to relate the integrated IR attenuation coefficient to the vibrational frequencies of hydroxyl bands across the O-H stretching region. This relationship is then used as a guide to develop an attenuation coefficient scaling function to quantitatively determine concentrations of alcohols in a hydrocarbon solution from experimental IR spectra by integration across the entire hydroxyl frequency range.

Infrared quantification of ethanol and 1-butanol hydrogen bonded hydroxyl distributions in cyclohexane.

Quantifying the mid-range infrared hydroxyl stretch absorbance region has traditionally been a challenge due to the wavenumber dependence of the attenuation coefficient. Interpretation often assigns a single attenuation coefficient to each type of hydrogen-bonded aggregate. This work leverages a recently developed technique of scaling hydroxyl stretching absorbances in the mid-infrared region with a continuous attenuation coefficient function that produces integrated areas which directly correlate to hydroxyl concentrations. After scaling, the hydroxyl absorbance is fitted with five curves, of which four are dominant. These four curves represent unique hydroxyl configurations and translate to specific aggregate structures. The technique is applied to ethanol and 1-butanol. The resulting population distributions of hydrogen-bonded hydroxyl configurations are compared with the resummed thermodynamic perturbation theory (RTPT) model for linear chains as a function of concentration and temperature. The model is demonstrated to capture the critical features of the distributions.

A novel process for recovery of fermentation-derived succinic acid: process design and economic analysis.

Recovery and purification of organic acids produced in fermentation constitutes a significant fraction of total production cost. In this paper, the design and economic analysis of a process to recover succinic acid (SA) via dissolution and acidification of succinate salts in ethanol, followed by reactive distillation to form succinate esters, is presented. Process simulation was performed for a range of plant capacities (13-55 million kg/yr SA) and SA fermentation titers (50-100 kg/m(3)). Economics were evaluated for a recovery system installed within an existing fermentation facility producing succinate salts at a cost of $0.66/kg SA. For a SA processing capacity of 54.9 million kg/yr and a titer of 100 kg/m(3) SA, the model predicts a capital investment of $75 million and a net processing cost of $1.85 per kg SA. Required selling price of diethyl succinate for a 30% annual return on investment is $1.57 per kg.

Butyric acid esterification kinetics over Amberlyst solid acid catalysts: the effect of alcohol carbon chain length.

The liquid phase esterification of butyric acid with a series of linear and branched alcohols is examined. Four strong cation exchange resins, Amberlyst™ 15, Amberlyst™ 36, Amberlyst™ BD 20, and Amberlyst™ 70, were used along with para-toluenesulfonic acid as a homogeneous catalyst. The effect of increasing alcohol carbon chain length and branching on esterification rate at 60°C is presented. For all catalysts, the decrease in turnover frequency (TOF) with increasing carbon chain length of the alcohol is described in terms of steric hindrance, alcohol polarity, and hydroxyl group concentration. The kinetics of butyric acid esterification with 2-ethylhexanol using Amberlyst™ 70 catalyst is described with an activity-based, pseudo-homogeneous kinetic model that includes autocatalysis by butyric acid.

A kinetic model of the Amberlyst-15 catalyzed transesterification of methyl stearate with n-butanol.

An attractive approach to improving cold flow properties of biodiesel is to transesterify fatty acid methyl esters with higher alcohols such as n-butanol or with branched alcohols such as isopropanol. In this study, the reaction kinetics of Amberlyst-15 catalyzed transesterification of methyl stearate, a model biodiesel compound, with n-butanol have been examined. After identifying conditions to minimize both internal and external mass transfer resistances, the effects of catalyst loading, temperature, and the mole ratio of n-butanol to methyl stearate in the transesterification reaction were investigated. Experimental data were fit to a pseudo-homogeneous, activity-based kinetic model with inclusion of etherification reactions to appropriately characterize the transesterification system.

Application of catalytic ozone chemistry for improving biodiesel product performance.

Ozonolysis of methyl soyate (biodiesel) was conducted in the presence of methanol, dichloromethane (solvent), and triethylamine (catalyst) at -75 degrees C. Structural analysis, including FTIR, GC, and GC-MS, showed that the total amount of double bonds in the mixture was reduced by more than 90% after 2 h of ozonolysis. All of the esters predicted by this novel application of ozone reaction chemistry were successfully produced. Other major components were identified by GC-MS. Thermogravimetric analysis showed a dramatic decrease in the onset volatilization temperature from 135 to 73 degrees C, making ozonated biodiesel fuel comparable to diesel fuel (76 degrees C). Differential scanning calorimetric studies showed that the cooling curves for both methyl soyate and ozonated methyl soyate displayed two exothermic regions. The onset freezing temperature of ozonated methyl soyate in the "colder" region was significantly reduced from -63 to -86 degrees C. Furthermore, the degree of crystallinity in the "hotter" region was also reduced.