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Abstract. Size distributions of particles formed from sulfuric acid(H2SO4) and water vapor in a photolytic flow reactor (PhoFR) weremeasured with a nanoparticle mobility sizing system. Experiments with addedammonia and dimethylamine were also performed. H2SO4(g) wassynthesized from HONO, sulfur dioxide and water vapor, initiating OHoxidation by HONO photolysis. Experiments were performed at 296 K over arange of sulfuric acid production levels and for 16 % to 82 % relativehumidity. Measured distributions generally had a large-particle mode thatwas roughly lognormal; mean diameters ranged from 3 to 12 nm and widths(lnσ) were ∼0.3. Particle formation conditions werestable over many months. Addition of single-digit pmol mol−1 mixing ratios ofdimethylamine led to very large increases in particle number density.Particles produced with ammonia, even at 2000 pmol mol−1, showed that NH3is a much less effective nucleator than dimethylamine. A two-dimensionalsimulation of particle formation in PhoFR is also presented that starts withgas-phase photolytic production of H2SO4, followed by kineticformation of molecular clusters and their decomposition, which is determined by theirthermodynamics. Comparisons with model predictions of the experimentalresult's dependency on HONO and water vapor concentrations yieldphenomenological cluster thermodynamics and help delineate the effects ofpotential contaminants. The added-base simulations and experimental resultsprovide support for previously published dimethylamine–H2SO4cluster thermodynamics and provide a phenomenological set ofammonia–sulfuric acid thermodynamics.
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This content will become publicly available on April 30, 2026
Impacts of Sulfur Impurity and Acid Pretreatment on Catalytic Depolymerization of Corn Cob Lignin
When fractionating corn cobs using the acetosolv process, the type of acid catalyst and their concentrations significantly affect the structure of the resulting lignin fraction as well as its catalytic deconstruction to aromatic monomers. Gel permeation chromatography (GPC) results show that the average molecular weight (~55,750 g/mol) of the sulfuric acid-pretreated corn cob lignin (H2SO4-CCL) is much greater than that (~39,400 g/mol) of hydrochloric acid-pretreated corn cob lignin (HCl-CCL) at similar acid concentrations, suggesting increased condensation reactions when using sulfuric acid. Further, a significant amount of bound sulfur content (~2900 ppm) was measured in H2SO4-CCL. This sulfur presence poisons the Pd/C catalyst used in the downstream catalytic conversion of the lignin in methanol to form monolignols and derivatives thereof. X-ray photoelectron spectroscopy (XPS) results reveal that both sulfide and sulfate groups are formed with the surface Pd sites, rendering them inactive and amenable to possible leaching. Elemental mapping of spent catalysts using scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF)/energy dispersive x-ray (EDX) technique corroborate overlapping presence of Pd, S and O in the micrographs. 2D 1H/13C HSQC nuclear magnetic resonance (NMR) spectroscopy reveals that the use of H2SO4 preserves aryl ether linkages only at low concentrations. In contrast, the use of HCl in the acetosolv process preserves such linkages even at high concentrations while also mitigating sulfur poisoning of the Pd/C catalyst. Consequently, the yield of aromatic monomers during catalytic fractionation of HCl-CCL was doubled compared to H2SO4-CCL at identical operating conditions.
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- PAR ID:
- 10597859
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Industrial & Engineering Chemistry Research
- Volume:
- 64
- Issue:
- 17
- ISSN:
- 0888-5885
- Page Range / eLocation ID:
- 8630 to 8641
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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