Feasibility of semi-artificial photosynthesis

Abstract

Green hydrogen, produced from renewables, will play a key role in decarbonization in a wide range of industries. As renewables remain in short supply, hydrogen from photocatalytic water splitt ing is gaining more interest as an alternative. Pannwitz et al. proposed in 2020 a novel approach by mimic nature and embed photosystems and hydrogenase in artificial bilipid layers for hydrogenproduction. But conventional phospholipids are unstable at high temperature , low pH and oxidative conditions conditions that arise during water splitting. T his paper proposes a new approach for this semi artificial pho to synthetic system (SAPS) based on more stable photosynthetictetra hetral lipid (TEL) liposomes Photo Somes. The goal of this thesis is a feasibility study for a potential scale up the semi artificial photosynthetic particulate, suspended fully biological lipidbased PhotoSome hydrogen production process. An overview of the H 2 value chain with current and future H 2 demand, standards and requirements is presented. H 2 production methods especially greenH 2 methods have been described, and compared on their level of development and cost effectiveness with a focus on solar H 2 and photo catalytic production methods. A holistic review of publications on the topic of H 2 producing s emi artificial photo synthetic photocatalytic has been written.The PhotoSomes are described and , studies about stability, limitations and option for of the main components photosensitizer , charge carrier and catalytic center are given. Based on this insight a safe separation approach for the potentially explosive oxyhydr ogen gas mixture based on dilution by nitrogen was developed. A basic process design, with analysis of all unit operations was carried out.For the scale up and cost analysis 2 concepts, one based on a 2 stage gas permeation and pressure swing adsorption (PSA CONCEPT) and a second based on a hypothetical electro chemical hydrogen compressor (EHC CONCEPT) for hydrogen separation, with a daily hydrogen production comparable to a 1 MW electrolyzer have been designed for comparison. A pure PSA system and a cryogenic separation were ruled out in advance because of the low hydrogen concentration in the diluted gas stream.As an electro chemical hydrogen separation via EHC of a diluted oxyhydrogen gas mixture hasn’t been described in literature, a separation of a H 2 O 2 CO 2 gas mixture was carried out 15.5% of H 2 wereseparated at a potential of 1 V and an energy consumption of 33.3 kWh/kg H 2 equivalent to 100.07%of lo w er heating value of hydrogen. Heavy oxidation occurred on the current collector plates.Based on a 7% solar to hydrogen efficiency and lifetime of 6 months of the PhotoSomes, t he system would require an area of around 80 000 m 2 . The PSA CONCEP T achieved a cost of 41.16 €/kg H 2 andthe EHC CONCEPT of 30 49 €/kgH 2 at a daily production of 483 kgH 2 . The power requirement during operation reaches 5.429 MW for the PSA CONCEPT and 3.532 MW EHC CONCEPT producing hydrogen without net energy gain. T he biggest obstac les for a cost effective Photo Some process is theenergy consumption of the gas separation process, the cost of TEL lipids and the cost of stainless steel for the construction of the photoreactors. The inherent intermittence of solar irradiation, subzero temperatures, and the real behavior of PhotoSomes are open question s .A suspended single catalyst PhotoSome hydrogen production system is not cost effective! Further research should focus on synthesis of higher value product s such as acetate and form eatavoiding flammable gas atmosphere in the first place.