modeling the reactions of coal liquids

The second step of the modeling procedure is to determine the rates and routes of the reactions of the functional groups by examining the reactions of pure compounds containing the same functionalities. The aim of this thesis is to start the development of a kinetic model of the reactions of complex hydrocarbon mixtures, such as coal liquids. The chemical properties of the complex mixtures are characterized by determining the concentrations of a representative range of functional groups.

The kinetic behavior of the mixture can then be modeled by determining the reaction rates of a set of functional groups. 2] Identification of the main reaction pathways of functional groups and determination of rate parameters. The scope of the work presented here is limited to the characterization of complex mixtures with respect to their functional groups and some initial studies of reaction pathways.

The intensity integrated across each of the bands is proportional to the number of protons in the binding environment assigned to the band. However, in the case of crude oils, the aliphatic part of the spectra shows considerable detail and more information can be derived from the spectra.

AROMATIC ALPHA BET AMM

This is done by relating the concentrations of the functional groups to the experimental data through a series of equilibrium equations. Yn are chosen to minimize a function P(y1, ..yn) depending on the constraints of equations 1 and 2. The shape of the function P depends on what data, if any, is available in addition to elemental analysis and NMR. . Data other than elemental analysis and NMR can be introduced as additional balance equations or can be included in the function P. The method of processing the data is chosen based on the accuracy and precision of the data.

Another assumption is that a concise set of functional groups can be used to represent all the structures assigned to the peaks. Structures are assigned to the peaks resolved in the low-resolution spectrum, and estimates of the functional group concentrations are calculated. Functional group analysis results (concentrations in mol/100 g sample). spectra are given in Table · 8. Examination of the functional group concentrations reveals the following trends.

Finally, the results of the functional group analysis method were compared with the results of an established structural analysis method. The purpose of functional group analysis is to calculate the concentrations of functional groups present in the sample. The relative concentrations of functional groups determine the chemical behavior of liquids.

Not included in the nominal reaction time was the reactor warm-up time, i.e. the time required for the reactor internal temperature to reach within 1 °C of the sand bath temperature. The results of the elemental analysis and the yield of the extractions are listed in Table 3. For each liquid sample, the concentrations of the functional groups listed in Figure 1 were calculated.

The results of functional group analysis for both sets of samples are discussed below. Functional group analysis was applied to each of the ten fractions and the resulting concentrations are given in Table 5. The functional group concentrations of the total heavy distillate were determined from the concentrations and yields of each of the fractions.

Application of the proposed functional group analysis method to two sets of coal-derived fluids provided the following conclusions. The peaks observed in the mass spectra determine the empirical formula of the structures present in the sample. A comparison of 13C data and carbon distributions derived from functional group concentrations is given in Table 5.

The form of the function P depends on the type of data available for the structural characterization.

150 Figure 2 13c NMR Spectrum of a Heavy Crude Oil Distillate

I I MAJOR REACTIONS

The rates of diffusion-limited reactions were estimated from the viscosity of the liquid using the Stokes-Einstein equation {12). All but two of the rate parameters used in the calculations were estimated by thermochemical methods or by analogy with reactions with known parameters. Therefore, LCA was used to determine the concentration pathways for the simplified reaction system consisting of reactions (2)-(11).

The sensitivity of the results of the LCA to the values of each of the four rate constants and to temperature is given in Table IV. Values of the rate parameters derived by analogy with similar reactions in the literature and by thermochemical estimations provided an excellent fit to the data. The activation energy of reaction (9) is increased by 2 kcal/mol to account for the improved stability of the dialylene radical over the tetralyl radical.

The A factors vary with the size of the rings and the substituents on the rings connected by methylene bridges. The results show that the reactions of multicomponent mixtures such as coal liquids are much more complex than the sum of the reactions of the components. The agreement between model predictions and experimental values is very good considering that almost all rate parameters have been estimated a priori by thermochemical techniques or by analogy with similar reactions.

To determine the sensitivity of calculated concentrations to the estimated rate parameters, each of the rate constants was varied individually and the kinetic differential equations were integrated as before. The sensitivity of the model to reactions 15–31 has been described elsewhere.7 The model is most sensitive to changes in initiation and termination rates and to the rate of attack of hydrogen atoms on the methylene bridge of DNM. The only differences between the two mechanisms are the values of the rate parameters of the addition-displacement reaction, the viscosity of the mixture, and the RSE of the diphenylmethane radical.

These various complications make the development of a quantitative model for the reactions of this mixture very difficult. Another piece of information that can be obtained from the data in Table 3 concerns the effect of phenolic substituents on the rate of the aromatic substitution reactions. These approximations may prove useful in developing models for the reactions of complex mixtures.

A comprehensive model of the reactions of coal liquids would require a staggering number of studies of model compound systems. Selected model compound experiments could be performed to investigate the possibilities of homogeneous catalysis (eg, the basic nitrogen-catalyzed decomposition of ether bridges).