Solid enthalpy

Physical property data for many of the key components used in the simulation for the ethanol-from-lignocellulose process are not available in the standard ASPEN-Plus property databases (11). Indeed, many of the properties necessary to successfully simulate this process are not available in the standard biomass literature. The physical properties required by ASPEN-Plus are calculated from fundamental properties such as liquid, vapor, and solid enthalpies and density. In general, because of the need to distill ethanol and to handle dissolved gases, the standard nonrandom two-liquid (NRTL) or renon route is used. This route, which includes the NRTL liquid activity coefficient model, Henry s law for the dissolved gases, and Redlich-Kwong-Soave equation of state for the vapor phase, is used to calculate properties for components in the liquid and vapor phases. It also uses the ideal gas at 25°C as the standard reference state, thus requiring the heat of formation at these conditions. 

A great number of studies related to thermochemical properties of QDO and PDO derivatives have been recently described by Ribeiro da Silva et al. [98-103]. These studies, which have involved experimental and theoretical determinations, have reported standard molar enthalpies of formation in the gaseous state, enthalpies of combustion of the crystalline solids, enthalpies of sublimation, and molar (N - O) bond dissociation enthalpies. Table 5 shows the most relevant determined parameters. These researchers have employed, with excellent results, calculations based in density functional theory in order to estimate gas-phase enthalpies of formation and first and second N - O dissociation enthalpies [103]. 

Of the many solid enthalpy of formation values determined for anthracene, ref. 4 chose only one, at that time the newest A newer solid enthalpy of formation (see ref. 52) later became available, which although somewhat less positive than the earlier value is compatible with it because of the relatively large uncertainty interval (Aff((c) = 125.54 5.6 kJ moP ). The weighted average is... 

The inconsistency of the cited enthalpies of sublimation of naphthacene is a problem. Of five citations since 1951 including the newest, three are ca. 125 kJ moP. A 1952 determination is 8 kJ moP less and a 1980 determination is 18 kJ moP higher. There is only one solid enthalpy of formation. Ref. 4 recommends an average (291.4 9.4 kJ moP ) of the two gaseous enthalpies of formation calculated using the highest enthalpy of sublimation as well as the median value. 

If the sorption isotherm is temperature-independent the heat of sorption is zero therefore a number of sorption isotherm equations used in agricultural sciences are useless from the point of view of dryer calculations unless drying is isothermal. It is noteworthy that in the model equations derived in this section the heat of sorption is neglected, but it can easily be added by introducing Equation 3.59 for the solid enthalpy in energy balances of the solid phase. 

Wet solid enthalpy (per unit mass of dry solid) can now be defined as... 

Substance (aqueous or solid) Enthalpy H°, Kcal/mole Free Energy AG , Kcal/mole... 

The maximum-likelihood method is not limited to phase equilibrium data. It is applicable to any type of data for which a model can be postulated and for which there are known random measurement errors in the variables. P-V-T data, enthalpy data, solid-liquid adsorption data, etc., can all be reduced by this method. The advantages indicated here for vapor-liquid equilibrium data apply also to other data. 

The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

Immersion of a solid in a liquid generally liberates heat, and the enthalpy of immersion may be written... 

Accurate enthalpies of solid-solid transitions and solid-liquid transitions (fiision) are usually detennined in an adiabatic heat capacity calorimeter. Measurements of lower precision can be made with a differential scaiming calorimeter (see later). Enthalpies of vaporization are usually detennined by the measurement of the amount of energy required to vaporize a known mass of sample. The various measurement methods have been critically reviewed by Majer and Svoboda [9]. The actual teclmique used depends on the vapour pressure of the material. Methods based on... 

To write an unsteady state enthalpy balance we require the enthalpy per unit volume of the gas-permeated solid matrix. This is given by... 

Equations (12.13) and (12.14) may be approximated by rather simple equations in most conditions of physical interest. This is possible because of the relatively large value of the thermal conductivity of the solid matrix, which has two important consequences. First, the conductive enthalpy flux, represented by the second term on the left hand side of... 

The tables in this section contain values of the enthalpy and Gibbs energy of formation, entropy, and heat capacity at 298.15 K (25°C). No values are given in these tables for metal alloys or other solid solutions, for fused salts, or for substances of undefined chemical composition. 

The values of the thermodynamic properties of the pure substances given in these tables are, for the substances in their standard states, defined as follows For a pure solid or liquid, the standard state is the substance in the condensed phase under a pressure of 1 atm (101 325 Pa). For a gas, the standard state is the hypothetical ideal gas at unit fugacity, in which state the enthalpy is that of the real gas at the same temperature and at zero pressure. 

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