Multiscale Mechanistic Insights into Hydrogen Production from Microalgae via Molten Hydroxide-Mediated Thermochemical...

[NNadir]

...Conversion.

The paper I'll discuss in this post is this one: Multiscale Mechanistic Insights into Hydrogen Production from Microalgae via Molten Hydroxide-Mediated Thermochemical Conversion Jun Li, Ling Lei, Dian Zhong, Hongyang Zuo, Han Zhu, Kuo Zeng, Haiping Yang, and Hanping Chen Environmental Science & Technology ]2026 60 (9), 7054-7066

It's written by scientists in China.

Since the paper involves the preparation of hydrogen from algae, one could argue, that it is literally "green" hydrogen, as chlorophyll is "green," although as we can easily see, the environmental sense of the word - which is widely abused, very, very, very often in connection with hydrogen scams - does not apply.

The um, introduction to the paper is rather cute:

The rising global energy demand and pressing environmental challenges, particularly climate change, have intensified the pursuit of sustainable and clean energy alternatives. Hydrogen, characterized by its high energy density and zero carbon emissions during utilization, stands as a key energy carrier for a future low-carbon economy. Biomass thermochemical conversion presents a promising pathway for renewable hydrogen production. (1) Among various feedstocks, microalgae offer distinct advantages due to their rapid growth rate, short cultivation cycle, and ability to thrive on nonarable land without competing with food production, (2,3) making them a highly sustainable and hydrogen carriers for hydrogen production.

Conventional thermochemical processes for microalgae, such as pyrolysis and gasification, are often constrained by persistent tar formation, ash clogging, and insufficient hydrogen yield/purity, (4−6) which adversely affect process efficiency and economic viability. In response, molten salt technology has emerged as a promising alternative, with molten hydroxides proving particularly effective. (7) These salts serve simultaneously as an efficient heat transfer fluid, an effective cracking catalyst, and a selective CO2 absorbent. (8,9) Previous work by the authors has demonstrated the superior effectiveness of molten hydroxides for microalgae processing, achieving a hydrogen yield of 67 mmol/g-microalgae with a purity of 80% while reducing tar formation by over 99%. (10,11) Approximately 58% of this hydrogen originated from the hydroxide itself, with the hydrogen utilization efficiency from the algae reaching 84.86%. This integrated performance outperforms that of the majority advanced catalytic and chemical looping systems in terms of clean and efficient hydrogen production...

During utilization, you don't say? Does this mean that we should ignore how hydrogen is made?

The IEA reports (as do many scientific papers) the carbon impact of hydrogen production:

IEA GHG Emissions of Hydrogen and Its Derivatives:

]In 2023, global hydrogen production emitted 920 Mt CO₂. Nearly two-thirds of production was from unabated natural gas, which emits 10‑12 kg CO₂-equivalent (CO₂-eq)/kg H₂; about 20% was from unabated coal, which emits 22-26 kg CO₂-eq/kg H₂. Between 75% and 95% of these emissions occur directly at the point of production, and can be reduced by carbon capture, utilisation and storage (CCUS). For hydrogen from steam methane reforming (natural gas), abatement costs are estimated at around USD 60-85/t CO₂ for capture rates of 55-70%, and USD 85-110/t CO₂ for rates above 90%. However, carbon capture alone is not sufficient; upstream and midstream emissions must also be tackled...

Perhaps they are discussing a perpetual motion machine, where the heat to melt group I hydroxides is provided by, um, hydrogen. Somehow I don't think so.

The molten hydroxide in this case is sodium hydroxide, mixed with sodium carbonate. The melting temperature of NaOH, a very caustic material, is 323 °C (598K). We may ask, whence the heat? (The authors reveal it at the end of the article by their affiliations.)

The experimental conditions:

The schematic of the experimental setup for thermochemical conversion of tar model compounds in molten salt is shown in Figure S1. The system primarily consists of a reactor (cylindrical crucible made of Hastelloy C276), a feeding unit, an electric furnace, and a gas product collection unit. Feedstock pellets were initially stored in the feeding unit and then delivered via a feeding tube into the molten salt. Throughout the process, N2 was continuously introduced through both the feeding tube and a bubbling tube to maintain a positive internal pressure and to agitate the molten salt, thereby ensuring uniform dispersion of the pellets. The molten salt level was maintained at approximately 40 mm to provide sufficient residence time for pyrolytic volatiles. Further details of the reactor configuration are available in previous work. (11) Before each experiment, the reactor was purged with N2 to remove air. The electric furnace was then activated to heat the molten salt. Once the temperature reached 750 °C, about 2 g of feedstock pellets were introduced into the molten salt and allowed to react for 10 min. Given the low boiling points of the tar model compounds (218–342 °C), the resulting volatiles were rapidly carried out of the reactor by the N2 stream...

Hastelloy is a nickel alloy with multiple other metals mixed in. It has been used in molten salt nuclear reactors, reactors I might note that have some rather serious materials science issues, particularly with respect to helium generation from neutron interactions with some of the lighter isotopes of nickel. (This is a problem.)

Some figures from the text:




The caption:

Figure 2. Functional groups evolution of volatiles during microalgae thermochemical conversion: (a) without and (b) with molten salt.

This indicates that the hydrogen produced will not be pure and will contain multiple compounds, one of which is carbon monoxide. Mixtures of hydrogen and carbon monoxide are known as "syn gas" from which petroleum like mixtures can be obtained using "FT chemistry," Fischer-Tropsch (which was industrialized in Nazi Germany and in Apartheid era South Africa). However the nitrogenous compounds are likely to poison FT catalysts.

The lab scale reactor used in the experiments:



Note that the hydrogen is carried out of the molten hydroxides in a stream of nitrogen, meaning, again, that additional steps would be required to purify the already challenging hydrogen gas, a nightmare to store.

An additional note:

The evolution of typical tar species (benzene, toluene, and naphthalene) was detected by MS (Figure 3). Without molten salt, these components were generated between 300–400 °C, mainly by the aromatization of carbohydrates (e.g., furans) and the demethylation of phenolics. At higher temperatures (450–650 °C), these species remained detectable, attributing to secondary cracking of polycyclic aromatic hydrocarbons (PAHs, e.g., phenanthrene) (26) and deep deoxygenation of oxygenated macromolecules (e.g., ethers and phenols). (27) In the molten hydroxide system, the release intensities of all three tar species were notably suppressed and diminished above 500 °C...

Benzene and toluene are both carcinogens, and account for the Proposition 65 notices on gasoline pumps in California:

On every gasoline pump in the State, the notice reads:

⚠ WARNING: Breathing the air in this area or skin contact with petroleum products can expose you to chemicals including benzene, motor vehicle exhaust and carbon monoxide, which are known to the State of California to cause cancer and birth defects or other reproductive harm. Do not stay in this area longer than necessary. For more information go to www.P65Warnings.ca.gov/service-station.

Of course, the fossil fuel marketeers trying to rebrand fossil fuels as "hydrogen" are only interested in cancer and carcinogenesis if they can stupidly tie it to nuclear plants.

Despite these warnings, people are willing to pay a lot of money for gasoline in California, more than ever, actually.

There is, by the way, a lot of nice chemistry in the paper, including a description of the PAHs - fossil fuel carcinogens - generated and the temperatures required to reduce, if not eliminate, them.

Usually, when citing scientific papers here, I often omit the institutions from which the authors come, but it seems important to do so in this case.

Jun Li - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

Ling Lei - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

Dian Zhong - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

Hongyang Zuo - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

Han Zhu - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

Haiping Yang - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China; Orcidhttps://orcid.org/0000-0002-8323-8879

Hanping Chen - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, P. R. China

I added the bold.

This of course, is consistent with current Chinese practice for making hydrogen, using coal, something that is likely to be utilized more than ever for hydrogen production now that the Asian source of dangerous natural gas is constrained by the closing of the Straits of Hormuz has been closed by the stumbling insanity of the orange pedophile in the White House.

Thermochemical reactions for hydrogen production are well known, including the SI process that is now being piloted in China, driven by nuclear heat, which obviously is superior to coal except in the minds of German antinukes and, um, fossil fuel salespeople working to rebrand fossil fuels as "hydrogen" with slick commercial videos. The SI process does not require fossil fuels, and is catalytic water splitting via the generation of SO₂ from the thermal decomposition of sulfuric acid followed by the iodine mediated Bunsen reaction.

Anyway, there's a lot of interesting stuff in this paper in a purely chemical mechanistic sense, and I've long had ideas about the use of molten hydroxides, although my interest is primarily in a highly radioactive hydroxide, cesium hydroxide, which has some very wonderful properties.

This said, this lab scale process, like much of the other hydrogen bullshit that flies around here, is not really useful.

Have a nice weekend.