Missing substance properties can become a limiting factor in research and process design. Especially for ionic liquids (ILs), experimental data are often not available and measurement is expensive and time-consuming. To cope with this issue, an estimation scheme for the heat capacity and the thermal conductivity of ILs has been developed. To achieve a wide range of application, first-order group contributions have been chosen to describe the molecular structure of the ions. 2419 experimental heat capacity data points for 106 ILs have been used in two separate subsets for parameter fitting and testing to allow for a reliable external validation. In the case of thermal conductivity, 372 data points for 39 ILs have been processed analogously. The data for ILs from the subset not used for the fitting could be reproduced with a mean absolute error of 5.4% in the case of heat capacity and of 8.1% in the case of thermal conductivity. Using these estimation schemes, it is possible to screen a huge number of potential combinations of cations and anions to find candidates suited best for a specific task before performing the experimental measurement.

Heat capacity is a crucial parameter for process design. Ionic liquids (ILs) offer the opportunity to tailor the relevant properties for many processes, but heat capacity data often are not available. In this work, temperature-dependent contributions to the heat capacity for 39 cations and 32 anions are proposed. A database containing 104 ILs with 2443 data points was used for the development of this model. The experimental data in the test set could be reproduced with a mean relative error of 4.4%. This allows for a systematic screening of a huge IL database to determine the solvent best-suited for a task without the necessity to measure all the missing data. Furthermore, an optimization taking different substance properties into account by using respective mathematical tools is possible by combination with prediction models for other properties.

No abstract

This paper presents the development of the subsystems for stationary biogas powered solid oxide fuel cell (SOFC)-based combined cooling, heat and power (CCHP). For certain applications, such as buildings, a heat-driven operation mode leads to low operating hours per year for conventional combined heat and power (CHP) systems due to the low heat demand during the summer season. The objectives of this study are the evaluation of an adsorber, a steam reformer, a SOFC, and an absorption chiller (AC). Biogas, however, contains impurities in the form of hydrogen sulfide (H2S), hydrogen chloride (HCl), and siloxanes in different concentrations, which have a negative effect on the performance and durability of the SOFC and, in the case of H2S, also on the catalyst of the steam reformer. This paper describes different experimental sections: (i) the biogas treatment with its main focus on H2S separation and steam reforming, (ii) the setup and start-up of a 10 cell SOFC stack, and (iii) test runs with an AC using a mixture of NH3 (ammonia)/H2O (water). The components required for the engineering process of the subsystem's structure are described in detail and possible options for system design are explained. The evaluation is the basis to reveal the improvement potentials, which have to be considered in future product developments. This paper aims at comparing experimental data of the test rigs to develop an understanding of the requirements for a stable and continuous operation of a SOFC-based CCHP operated by biogas.

The coupling of AVLs 6 kW EL SOFC CHP system using an IKTS stack module with a 5 kW COLD absorption heat pump developed by TU Graz will be presented. The exhaust gas heat from the SOFC which is available at >200°C will be used to operate the thermally driven heat pump. The SOFCs fuel capability was extended towards renewable fuels such as biogas, and synthetic diesel using a novel gas cleaning concept. For buildings, a heat driven operation mode leads to low operating hours per year for conventional CHP systems during summer season. Generating cooling power in addition to heat will increase the annual operating hours per year and thus economic efficiency significantly. This analysis presents the capability of the SOFC CCHP system for a flexible and demand-oriented generation of electricity, heat and cooling power and shows how cold and cooling water temperatures influence the overall system size.