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In many chemical industrial processes, mass transfer across gas-liquid interfaces accompanied by chemical reaction is the governing phenomena. In case of mass transfer accompanied by a chemical reaction in the liquid phase, the reaction will enhance mass transfer and generally the mass transfer enhancement is quantified in terms of an enhancement factor. Large number of enhancement factor models have been developed in literature and used without critical analysis for analyzing pilot data for CO2 absorption into aqueous amines. In order to perform such a critical analysis, 24 models are tested using lab-scale experimental data from four independent apparatuses for CO2 absorption into MEA solutions covering a range of different conditions such as short and long contact times, with and without gas phase resistance, high and low CO2 loadings and temperatures. Of the 24 enhancement factor models tested only six models were found to satisfactorily predict the experimental CO2 fluxes. These were the models based on the simple pseudo-first order reaction assumption, Emodels 1, 2 and 3 by Hatta [2] and Dankwerts [4] respectively, Emodel 20, the deCoursey and Thring [44] model based on Danckwert's surface renewal theory with unequal diffusivities, Emodel 24, the recently published generalized model by Gaspar and Fosbøl [51] and Emodel 21, the Tufano et al. [67] model based surface renewal theory. All these models were found to work equally well to the discretized penetration model. No significant difference was found between Emodels 1, 2 and 3, indicating that whether one uses as basis a film, penetration or surface renewal model, is of insignificant importance. The success of the simple models is attributed to the short contact times in the experiments used as basis and the accuracy of the kinetic model. Contact times of the same magnitude between mixing points is also encountered in industrial packings and it is believed that the simple enhancement factor models may work well also in these cases if an accurate kinetic model is used.

A detailed kinetic model describing the consumption of key components and product distribution in the Fischer-Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al 2 O 3 commercial catalyst is developed. The developed model incorporates the H 2 Oassisted CO dissociation mechanism developed by Rytter and Holmen and a novel approach to product distribution modeling. The model parameters are optimized against an experimental dataset comprising a range of process conditions: total pressure 2.0-2.2 MPa, temperature 210-230 C, CO conversion range of 10%-75% and feed with and without added water. The quality of the model fit measured in terms of mean absolute relative residuals (MARR) value is 23.1%, which is comparable to literature reported values. The developed model can accurately describe both positive and negative effects of water on the rate kinetics, the positive effect of water on the growth factor, temperature and syngas composition on the kinetics and product distribution over a wide range of process conditions, which is critical for the design and optimization of the Fisher-Tropsch reactors.

By adding energy as hydrogen to the biomass-to-liquid (BtL) process, several published studies have shown that carbon efficiency can be increased substantially. Hydrogen can be produced from renewable electrical energy through the electrolysis of water or steam. Adding high-temperature thermal energy to the gasifier will also increase the overall carbon efficiency. Here, an economic criterion is applied to find the optimal distribution of adding electrical energy directly to the gasifier as opposed to the electrolysis unit. Three different technologies for electrolysis are applied: solid oxide steam electrolysis (SOEC), alkaline water electrolysis (AEL), and proton exchange membrane (PEM). It is shown that the addition of part of the renewable energy to the gasifier using electric heaters is always beneficial and that the electrolysis unit operating costs are a significant portion of the costs. With renewable electricity supplied at a cost of 50 USD/MWh and a capital cost of 1,500 USD/kW installed SOEC, the operating costs of electric heaters and SOEC account for more than 70% of the total costs. The energy efficiency of the electrolyzer is found to be more important than the capital cost. The optimal amount of energy added to the gasifier is about 37–39% of the energy in the biomass feed. A BtL process using renewable hydrogen imports at 2.5 USD/kg H2 or SOEC for hydrogen production at reduced electricity prices gives the best values for the economic objective.