Evaluations of Sustainability of Making Hydrogen from Waste Plastics With Various Approaches.

[NNadir]

The paper I'll discuss in this post is this one: Environmental Sustainability Assessment of Hydrogen from Waste Polymers, Cecilia Salah, Selene Cobo, Javier Pérez-Ramírez, and Gonzalo Guillén-Gosálbez, ACS Sustainable Chemistry & Engineering 2023 11 (8), 3238-3247.

The graphic associated with the abstract of the paper is nicely evocative in terms of money:



The environmental impact, i.e. the external cost, is slightly different, since while dangerous natural gas based hydrogen, which overwhelmingly dominates the source of the world's hydrogen, and has done so for well over half a century - although coal and oil are also often utilized - is a rather large contributor to climate change.

In general, here and elsewhere, people whose focus in the area of energy and the environment who want to talk about monetary costs of energy sources - this only for their own generation, with contempt for future generations - are disinterested entirely in climate change and other impacts of the dangerous fossil fuel game. Seen in a way consistent with what I personally regard as ethics, natural gas/coal/petroleum based hydrogen, on which the world food supply depends for now, has the highest cost, in external costs.

As far as electrolysis, which is hyped endlessly by people embracing the "wind and solar will save us" scam, it is the most expensive for all sources of electricity, both in monetary and environmental terms, since electricity is a derived source of energy, badly thermodynamically degraded, and electrolysis further degrades it thermodynamically and economically.

Electricity is not "green," despite all the horseshit to the contrary one hears. One needs to waste energy to make it.

I am a fan of process intensification, which basically involves using waste heat from one process to power another. Process intensification reaches its highest efficiencies when the initial source of heat is at as high a temperature as can be realized, and the technical driver of this is materials science.

For the record, I find the issue discussed in this paper a worthy pursuit; I often reflect on steam reforming of municipal waste as a possible contributor to addressing climate change, and, albeit at a low level to the extent that municipal waste contains biomass, as a possible contributor to the capture of the dangerous fossil fuel waste CO2 from the atmosphere, indirect air capture.

The paper's introduction begins with a paragraph that is a statement of the problem:

The global demand for polymers is rising, leading to increasing amounts of waste polymers (wP). Only 9% of all plastics produced until 2015 were recycled, 12% incinerated, and the remaining 79% were landfilled or lost to the environment. (1) Moreover, within the plastic packaging sector (USD 80–120 billion annually), (2) 95% of polymers are single-use and have a short lifetime, with a low recycling rate of 14%. (2) In 2013, 72% of the 78 Mt of plastic packaging materials produced were landfilled or dispersed in the environment. (2) This waste mismanagement has detrimental consequences for ecosystems and human health, (3?7) which underlines the need for a circular economy that valorizes wP.

In my generation, we were very proud of our embrace of "recycling" and we have generalized it to other stuff. As the paragraph shows, it's not really working.

The introduction continues:

Chemical recycling has recently gained attention for providing valuable feedstock that could replace fossil resources and help transition to a circular carbon economy, (8?10) thereby avoiding the environmental impacts of incinerating and landfilling wP. (11?13) For instance, waste polyethylene and polypropylene can undergo pyrolysis to recover their respective monomers (14?17) or gasification to produce synthesis gas (a mixture of H2, CO, and CO2), widespread in chemical production. (18,19) Although monomers should be the ultimate goal in chemical recycling, the gasification route appears easier to implement, is more mature, and can handle mixed-polymer inlet streams. (20)

Alternatively, gasification of wP could yield H2 to decarbonize several sectors, (21) including transportation and industry, responsible for 25.7% and 19.7% of all greenhouse gas (GHG) emissions in 2019, respectively. (22) Steam methane reforming (SMR) is currently the preferred pathway to produce H2 from natural gas (gray H2), while blue H2 from SMR coupled with carbon capture and storage (CCS) and green H2 from electrolysis based on renewables or biomass gasification are still marginal. To date, SMR is the cheapest technology, (23) but other alternatives could reduce human health and ecosystems impacts substantially. (24) Notably, previous works applied life cycle assessment (LCA) to H2 pathways, finding that gray H2 embeds the highest global warming impacts (GWI) among existing technologies. (23) Moreover, Verma et al. showed that coupling CCS with SMR significantly reduces fossil-based H2’s net life cycle GHG emissions (to less than half), making blue H2 environmentally competitive against electrolytic H2 from renewables. (25) Moreover, Bhandari et al. found that the electricity source heavily influences the environmental performance of electrolytic routes at the mid- and end point impact levels. (26) On the economic side, Lan and Yao recently discussed that producing H2 via wP gasification in the US could yield competitive costs with blue H2 in the local market. (27)

LCA has become the preferred approach for evaluating the environmental impact of technologies. (28) However, standard LCAs are mostly applied to compare alternatives as they lack thresholds beyond which a system should be deemed unsustainable, making the interpretation phase challenging. Absolute environmental sustainability assessment (AESA) studies have recently emerged to define environmental limits on impact metrics. (30?32) (29...

All this talk of "sequestration" by the way is nonsense. Building vast carbon dioxide dumps is basically an idea - I include solar and wind in this category - which are designed to market the continuous use of dangerous fossil fuels by promoting, as a marketing expense, the idea that fossil fuels will magically become sustainable. They will not. They must be banned to save what is left to be saved, and to restore what can be restored.

The paper defines "SOS" as "Safe Operating Space" and goes on to compare 13 different approaches to the gasification of dangerous polymer waste. (One should keep in mind that almost all of the world's plastic waste, so far as CO2 is concerned, originated from dangerous fossil fuels. Plastic is sequestered carbon.)

The paper begins with a generalized process flow diagram of a reformer system. The issue not shown in this diagram, and which has the most important consequences from an environmental standpoint, is the source of the low pressure and high pressure steam, as well as the mechanical energy associated with compression. Note that the system relies on carbon dioxide dumps. This fantasy should be a nonstarter, but this would be a minor criticism if we substitute CCU (carbon capture and utilization) for CCS, (carbon capture and sequestration.)




The caption:

Figure 1. Process flowsheet of H2 from waste polymers. (a) Waste polymer gasification (wPG). (b) CO2 compression unit for CO2 geological storage. Additional unit for the wPG process coupled with carbon capture and storage (wPG+CCS).

The graphics in this paper are quite evocative. The paper deigns to answer the question of all potential sources of hydrogen, including those involved in the "solar and wind will save us" fantasies:



The caption:

Figure 2. Graphical representation of the studied scenarios. The following acronyms are employed: WASTE P, waste polymers; NG, natural gas; wPG, waste polymers gasification; SMR, steam methane reforming; BG, biomass gasification; CCS, carbon capture and storage; MP, methane pyrolysis; GRID, electricity from the power grid; BECCS, electricity from bioenergy; WIND, electricity from wind power; SOLAR, electricity from photovoltaic cells; HYDRO, hydropower; NUCLEAR, electricity from a nuclear power plant; and PEM, proton exchange membrane electrolysis. The column on the left-hand side of the figure contains the energy sources used for the different technologies. PEM is the only technology that was evaluated with various power sources. The remaining technologies consume electricity coming from the power grid mix of 2018.

Now the authors cut to the chase, global warming impact of all approaches, regrettably including carbon dioxide dumps in their scenarios; the most negative in this diagram, in my view, should be ignored:




The caption:

Figure 3. Global warming impact breakdown of the studied H2 production routes. The following acronyms are employed: wPG, waste polymers gasification; CCS, carbon capture and storage; SMR, steam methane reforming; MP, methane pyrolysis; BG, biomass gasification; PEM, proton exchange membrane electrolysis; BECCS, bioenergy with CCS; nuclear, nuclear power plant; wind, wind power; hydro, hydropower; solar, photovoltaic energy; and 2018 grid mix, electricity from the power grid of 2018.

Here's a table of results, as a graphic, from the paper's described system boundaries, with which I have major quibbles, the biggest being the continued reference to carbon dioxide dumps, and most others connected with I regard as weak appreciation of land use changes, but also because there is a glaring omission in the nuclear case. All of the abbreviations can be found in the caption.




The caption:

Figure 4. Planetary boundaries assessment of the 13 H2 production routes. TL relative to SOSH2,wP,b of the different H2 routes; values labeled as “less than 1” indicate that the scenario in question has not transgressed SOSH2,wP,b; negative values (in green) indicate prevented impacts due to avoided burdens and/or capture and storage of biogenic CO2; the remaining values that range from white to red indicate the TL relative to the corresponding SOS associated with each scenario. The following abbreviations are employed: SOSH2,wP,b, safe operating space for Earth-system process b downscaled to the maximum H2 production from waste polymers (wP); CC, climate change; CO2, atmospheric CO2 concentration; EI, energy imbalance at the top of the atmosphere; SOD, stratospheric ozone depletion; OA, ocean acidification; BGF, biogeochemical flows; P, phosphorus; N, nitrogen; LSC, land-system change; FWU, freshwater use; CBI, change in terrestrial biosphere integrity; wPG, waste polymers gasification; CCS, carbon capture and storage; SMR, steam methane reforming; MP, methane pyrolysis; BG, biomass gasification; PEM, proton exchange membrane electrolysis; BECCS, bioenergy with CCS; nuclear, nuclear power plant; wind, wind power; hydro, hydropower; solar, photovoltaic energy; and 2018 grid mix, electricity from the power grid of 2018.

The glaring omission in the nuclear case is the question of rather than relying on nuclear electricity, one should consider nuclear steam. A nuclear powerplant, and this pretty much covers all existing nuclear plants, is not optimized if the only purpose for it is to make thermodynamically degraded electricity. This idea, of utilizing nuclear heat as a process driver is gaining a huge amount of attention. The nation most advanced in bringing this idea to fruition is probably Poland, where serious design work on using SMR's as process heat providers is actively being planned.

An account of the cost of hydrogen by various discussions of approaches to making it as discussed in the paper.



The caption:

Figure 5. Levelized cost of hydrogen (LCOH) for the alternative production routes, expressed in USD 2019 kg–1 H2. All values of LCOH consider the CAPEX and OPEX of the technology in question, including the pre-energy crisisliterature estimates by Parkinson et al. (23) wPG and wPG+CCS have only central and low LCOH, accounting, respectively, to the cases where the wP feedstock are costly and free. All values were normalized to USD 2019, using the CEPCI.

Note that this paper, as shown in this diagram, treats nuclear plants as electricity generating devices.



The caption:

Figure 6. Results of the cost optimization of global H2 production within planetary boundaries. (a) Case for a high cost of waste polymers. (b) Case where waste polymers are free. Bar plots showcase the contribution of the individual technologies of the optimal portfolio to the transgression level (TLb) relative to the downscaled safe operating space attributed to the global H2 demand (SOSH2,b) for each Earth-system process b. TLb ? 1 indicates that the downscaled SOS defined for Earth-system process b has not been transgressed. The dashed line corresponds to TLb = 1. Pie charts display the contribution of the H2 technologies to the optimal H2 portfolio.

I have lots of quibbles with the paper, particularly the reliance on putative carbon dioxide dumps, and the conservative approach to the use of nuclear energy as a being limited to making thermodynamically degraded electricity.

The paper does not discuss how hydrogen might be used. We hear a lot of stupid commentary on hydrogen cars, trucks, buses, blah, blah, blah. This is not a wise approach to hydrogen utilization; in fact it's a disastrous idea, a waste of money, resources and time. This said, captive hydrogen can play an important role in building environmental homeostasis. It is theoretically possible to close the industrial carbon cycle by the hydrogenation of carbon dioxide to useful chemicals, including, but hardly limited to, sustainable polymers.

Enjoy the rest of the weekend.