Search

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

Anthropogenic emissions of CO2 have nearly exhausted our carbon budget, putting the world on a trajectory toward irreversible climate change. CO2 emissions must be reversed in coming decades to avoid global warming past the 2 °C target. Recent approaches have focused on recycling CO2 into fuels and chemicals to create sufficient financial incentives to pay for CO2 removal and geological sequestration. These technologies aim to produce fuels and chemicals at quantities relevant to global markets while also recycling a meaningful amount of CO2. While promising, these technologies are CO2-neutral at best. Truly negative emission technologies will require significant quantities of durable, fungible products that sequester hundreds of millions of tonnes of CO2. We present an economically viable approach to sequestering hundreds of thousands of tonnes of CO2 per year in polymer composites made from CO2-functionalized lignin or lignite fillers mixed with a high-density polyethylene (HDPE) matrix. CO2 is chemically fixed to polymeric phenols via C–C bond formation at the lignin or lignite surface, storing about 2–4.2 wt% of CO2. Composites produced with the CO2-functionalized fillers and HDPE have mechanical properties that meet international building code standards for decking, a multi-billion-dollar market. A techno-economic analysis and life cycle assessment suggest that CO2-functionalized lignin and lignite fillers have favorable economic potential. These composites could reduce greenhouse gas emissions up to 62% over conventional wood plastic composites or be CO2-negative within 20 years when manufactured with renewable electricity, recycled high-density polyethylene and if extra CO2 is captured and sequestered in the ground. The composites can achieve a net-negative global warming potential after 54 years for the CO2 solely stored in the composites. [ABSTRACT FROM AUTHOR]

Switchable ionic liquids (SWILs) derived from organic bases and alcohols are attractive due to their applications in gas capture, separations, and nanomaterial synthesis. However, their exact solvent structure still remains a mystery. We present the first chemical mapping of a SWIL solvent structure using in situ time-of-flight secondary ion mass spectrometry. In situ chemical mapping discovers two coexisting liquid phases and molecular structures vastly different from conventional ionic liquids. SWIL chemical speciation is found to be more complex than the known stoichiometry. Dimers and ionic clusters have been identified in SIMS spectra; and confirmed to be the chemical species differentiating from non-ionic liquids via spectral principal component analysis. Our unique in situ molecular imaging has advanced the understanding of SWIL chemistry and how this "heterogeneous" liquid structure may impact SWILs' physical and thermodynamic properties and associated applications.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to analyze poly(ether ether ketone) (PEEK) based membranes. PEEK membranes have been shown to be effective in the separation of CO2 from flue gases (post-combustion technique). The PEEK membranes were synthesized using novel aromatic ether-ketone linkages inspired by PEEK with polymeric backbone bistriflimide [Tf2N]− counterions. One of the keys to advancing this technology is developing membranes that are selective and permeable toward CO2, in which PEEK based membranes have been shown to be. Furthermore, the compatibility between various water lean solvents also needs to be investigated. Surface analytical techniques such as x-ray photoelectron spectroscopy and ToF-SIMS are useful for investigating chemical changes between membranes. Herein, we present ToF-SIMS data obtained in the negative ion mode for four different PEEK membranes designed for use in CO2 capture systems. Positive ion mode spectra are reported in Paper I. [ABSTRACT FROM AUTHOR]

Static time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed for acquiring the high-resolution surface spectra of four types of synthesized imidazolium ionene membranes. These novel membranes have aromatic ether–ketone–ether linkages inspired by poly(ether ether ketone) (PEEK). The PEEK-ionenes synthesized for this study have imidazolium cations placed in the polymeric backbone with bistriflimide [Tf2N]− counterions. The attention given to synthetically modified PEEK derivatives, such as PEEK-ionenes, is considerable due to their ability to selectively capture CO2 molecules and other light gases. Therefore, it is important to characterize the surface of these synthesized novel PEEK-ionenes. In this work, characteristic and unique peaks were identified in the positive spectra of each sample. The differences in mass spectra among the samples provide insights for optimizing or fine-tuning the PEEK-ionenes synthesis to achieve a high-performance CO2 separation membrane with enhanced permeability, selectivity, and mechanical stability. The SIMS spectra and identified characteristic peaks of these synthesized ionenes will serve as a reference in the positive mode, complementing the corresponding spectra reported in the negative ion mode (Paper II). [ABSTRACT FROM AUTHOR]

Ionenes, polymers with ionic groups incorporated directly within the backbone are a highly versatile class of materials, although they have received much less attention than polyelectrolytes which have ionic groups pendant from the polymer backbone. By designing ionenes that incorporate robust properties of poly(ether ether ketone) (PEEK), we have achieved new imidazolium-containing PEEK–ionene architectures that create opportunities for enhanced CO2 separation membranes. To achieve these materials, an new imidazole-functionalized PEEK oligomer (ImK(EEK)2KIm) was synthesized through facile and straightforward routes. This molecule was then polymerized via condensation reactions with two different aromatic (α,α′-dibromo-p-xylene) and aliphatic (dibromohexyl containing-bis(imidazolium)hexane dibromide salt) comonomers and exchanged with bistriflimide ([Tf2N]) anion to obtain two unique PEEK–ionenes containing distinct PEEK and ionic segments: p([ImK(EEK)2Im-p-xyl][Tf2N]2) and p([ImK(EEK)2(ImC6)3][Tf2N]4). While the neat PEEK–ionenes exhibited high molecular weight but were not able to form high-quality films, adding stoichiometric amounts of "free" IL (1-methyl-3-butylimidazolium bistriflimide, [C4mIm][Tf2N]), greatly improved the flexibility and processability of the resultant membranes. Further, the structure–property relationships of bulk PEEK–ionenes and corresponding composites were extensively characterized by different analytical techniques (thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and solid-state NMR). The gas separation properties were investigated, with the PEEK–ionenes + IL composites exhibiting CO2 permeabilities of 14–94 barrer and good CO2/N2 permselectivities of 26–35, indicating that new designs of segmented ionenes and composites with ILs a promising material design strategy for developing gas separation membranes. [ABSTRACT FROM AUTHOR]

Efficient direct air capture (DAC) of CO2 will require strategies to deal with the relatively low concentration in the atmosphere. One such strategy is to employ the combination of a CO2‐selective membrane coupled with a CO2 capture solvent acting as a draw solution. Here, the interactions between a leading water‐lean carbon‐capture solvent, a polyether ether ketone (PEEK)‐ionene membrane, CO2, and combinations were probed using advanced NMR techniques coupled with advanced simulations. We identify the speciation and dynamics of the solvent, membrane, and CO2, presenting spectroscopic evidence of CO2 diffusion through benzylic regions within the PEEK‐ionene membrane, not spaces in the ionic lattice as expected. Our results demonstrate that water‐lean capture solvents provide a thermodynamic and kinetic funnel to draw CO2 from the air through the membrane and into the bulk solvent, thus enhancing the performance of the membrane. The reaction between the carbon‐capture solvent and CO2 produces carbamic acid, disrupting interactions between the imidazolium (Im+) cations and the bistriflimide anions within the PEEK‐ionene membrane, thereby creating structural changes through which CO2 can diffuse more readily. Consequently, this restructuring results in CO2 diffusion at the interface that is faster than CO2 diffusion in the bulk carbon‐capture solvent. [ABSTRACT FROM AUTHOR]

An efficient and selective heterogeneous catalyst is identified for the condensed‐phase hydrogenation of captured CO2 in the presence of an advanced water‐lean post‐combustion capture solvent, (N‐(2‐EthoxyEthyl)‐3‐MorpholinoPropan‐1‐Amine), 2‐EEMPA. The catalysts commonly used for gas‐phase CO2 hydrogenation (e.g., Cu/Zn/Al2O3) cause deactivation of amine promoters via N‐methylation by CO cleavage of formamide intermediates. A heterogeneous catalyst system that suppresses N‐methylation of amine solvents is identified, demonstrating how Pt, supported by reducible metal oxides CeO2 or TiO2, can be selective for CN cleavage to produce methanol. This is the first known demonstration of integrated low‐temperature thermocatalytic capture and conversion of CO2 to methanol in an economically viable CO2 capture solvent. Technoeconomic analyses performed on the state‐of‐technology suggest that methanol can be produced with a minimum selling price of $4.4/gallon ($1,460/metric ton) when using CO2 captured from a 650 MW natural gas combined cycle plant. Ultimately, a road map of how realistic and achievable improvements to space velocity and methanol selectivity of this integrated process can enable near cost parity to fossil‐derived methanol, with a selling price of ≈$1.4/gal ($470/metric ton), is presented. [ABSTRACT FROM AUTHOR]

Amidines are reported to react with CO2 to form a stable and isolable zwitterionic adduct. However, spectroscopy of the reaction between DBU and CO2 detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO2.

A combined experimental and theoretical study has been carried out on the wetting and reactivity of water‐lean carbon capture solvents on the surface of common column packing materials. Paradoxically, these solvents are found to be equally able to wet hydrophobic and hydrophilic surfaces. The solvents are amphiphilic and can adapt to any interfacial environment, owing to their inherent heterogeneous (nonionic/ionic) molecular structure. Ab initio molecular dynamics indicates that these structures enable the formation of a strong adlayer on the surface of hydrophilic surfaces like oxidized steel which promotes solvent decomposition akin to hydrolysis from surface oxides and hydroxides. This decomposition passivates the surface, making it effectively hydrophobic, and the decomposed solvent promotes leaching of the iron into the bulk fluid. This study links the wetting behavior to the observed corrosion of the steels by decomposition of solvent at steel interfaces. The overall affect is strongly dependent on the chemical composition of the solvent in that amines are stable, whereas imines and alcohols are not. Moreover, plastic packing shows little to no solvent degradation, but an equal degree of wetting. [ABSTRACT FROM AUTHOR]