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Item type:Publication, Access status: without files , Enzyme Accelerated Carbon Capture in different Contacting Equipment - A Comparative Study(Elsevier, 2016-11); ; ; ; CO2 capture is an essential step for providing a sustainable and ecological solution to cope with increasing energy supply burning fossil fuels. However, industrial application of current CO2 capture technologies is limited due to the significant energy penalty. In order to reduce this energy penalty two different approaches of process intensification are examined in this study. The first approach aims at the intensification of mass transfer to compensate for low absorption rates of solvents with high capacity that would allow for more energy-efficient CO2 capture. Here the tertiary amine methyldiethanolamine (MDEA) is combined with a highly efficient biocatalyst, the enzyme Carbonic Anhydrase (CA), for which significant enhancement of absorption performance was demonstrated in literature. In addition to the intensification of the solvent system, the contacting of gas and liquid streams in ab- and desorption can be improved in intensified contacting devices (ICD). Here especially membrane contactors (MC) and rotating packed beds (RPB) are promising alternatives to classical packed columns. MC provide a well-defined interfacial area that is orders of magnitude higher than for conventional equipment and introduces additional operational flexibility, expressed by the independent flow ratio between liquid and gas phase. In a RPB centrifugal forces are exploited to increase acceleration of the liquid and improve turbulence and mass transfer. The rotational speed of the rotating packing introduces an additional degree of freedom compared to common static equipment. Both ICDs offer a very compact design. While both, ICD and the improved solvent system with CA, can significantly intensify the CO2 capture process, research on the combination of both is scarce. In order to evaluate the potential benefit of a joint implementation, a first step of imminent importance is to characterize the operating windows of such an intensified process. Based on prior results concerning the energy requirements for solvent regeneration, an aqueous amine solution with 30 wt.-% MDEA is investigated in this study without and with dissolved CA. In order to evaluate the potential improvement of a joint application of the ICD and the application of CA absorption experiments in a packed column and in the two ICDs are performed. While all three devices show similar absorption performance without CA added, the RPB offers the advantage to handle exceptionally high gas loads while the MC can be operated over a much wider range of liquid loads. When CA is added to the solvent system the packed column and the RPB show superior performance compared to the MC. While none of the combinations is generally superior, the different means for process intensification extent the operating window and facilitate improved absorption performances.Publicationtype: Conference Paper36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Different Strategies for Accelerated CO₂ Absorption in Packed Columns by Application of the Biocatalyst Carbonic AnhydraseWithin this work, the combination of an energetically favorable aqueous N-Methyldiethanolamine (MDEA) solution and the enzyme carbonic anhydrase is investigated in a packed column pilot plant. The use of aqueous MDEA solution for CO2 separation is already known from natural gas applications, for which an increased driving force due to the higher partial pressures of CO2 overcompensates reaction kinetic limitations. The objective of the addition of carbonic anhydrase is to countervail the loss of separation efficiency caused by the lower driving force in CO2 capture from power plant flue gases. Hence, carbonic anhydrase acts as a key to harness the energetic advantage of these solvent systems. However, application of the enzyme also poses restrictions on the process. Especially compliance with the enzyme stability limits is challenging for desorption, which is generally performed at high temperatures. In order to determine an optimal implementation of the enzyme into the process the current work presents different strategies how to apply CA as a biocatalyst in reactive absorption processes and shows how absorption efficiency is influenced. For introducing the enzyme to a packed column two approaches are investigated in this study. The simplest way of application is to dissolve the enzyme in the solvent. This allows the enzyme to work exactly where the reaction kinetic limitation can be found, in the liquid boundary layer. However, due to the temperature sensitivity of the enzyme an additional enzyme recovery step prior to the desorber might be necessary if desorption is to be performed at high temperatures. The immobilization of the enzyme inside the absorption column presents an alternative to prevent this additional separation, but may cause additional mass transfer limitations at the solid particles in which the enzyme is immobilized. The immobilization and the necessity of a suitable packing in which the enzyme particles can be filled, also makes this strategy more complicated but allows placing the enzyme at a location of most suitable process conditions in the column. But most importantly it completely avoids that the enzymes experience high temperature in the desorber. Systematic investigations of the influence of specific liquid load, liquid inlet temperature, MDEA-concentration and enzyme immobilization on absorption performance are conducted. Dissolved enzyme showed a nearly three times higher absorption performance than the immobilized enzyme under equivalent operating conditions, however the immobilized enzyme concentration used was effectively 50 times lower, meaning the result is actually quite promising for immobilized CA. From the investigated operating conditions, a liquid inlet temperature of 20 °C, a MDEA concentration of 30 wt.-% and a liquid flow rate of 24 m3 m-2 h-1 showed the best absorption performance with the dissolved enzyme. The measured absorption rate was 7.57 times higher than without enzyme added.Publicationtype: Conference Paper102