Directly
upgrading natural gas is limited by the stability of its
primary component, methane, and process economics. Since the 1980s,
oxidative coupling of methane (OCM) has shown potential to produce
ethylene and ethane (C2s). The typical OCM approach catalytically
converts methane to C2 products using molecular oxygen,
reducing process efficiency. To overcome this, chemical looping OCM
converts methane to hydrocarbons via intermediate oxygen carriers
rather than gaseous cofed oxidants. The chemical looping approach
for OCM has been studied mechanistically for the first time with a
Mn–Mg-based catalytic oxygen carrier (COC). The COC delivered
stable performance in a fixed bed for 100 cycles for more than 50
h with a 63.2% C2 selectivity and 23.2% yield. These experimental
results and original process simulations of an OCM chemical looping
system for C2 or liquid fuel production with electricity
cogeneration present a direct method for methane utilization.
We describe novel Staphylococcal Protein A ligands that enable milder elution pH for use in affinity chromatography. The change in elution pH is the result of point mutations to the protein sequence. Two novel ligands are investigated in this study. The first, designated Z(H18S)4, represents a histidine to serine substitution single mutation. The second, designated Z(H18S, N28A)4, is a double mutant comprising histidine to serine and asparagine to alanine mutations. Both are compared against the unmutated sequence, designated Z4, which is currently utilized in a commercially available Protein A stationary phase for the purification of molecules containing Fc domains. The ligands are coupled to a chromatography support matrix and tested against a panel of antibodies and an Fc fusion protein for elution pH, dynamic binding capacity, step-wise elution, and capture from clarified culture media. Results demonstrate that the novel ligands result in milder elution pH, on average >0.5 pH units, when tested in a pH gradient. For step-wise elution at pH 4.0, the Z(H18S, N28A)4 ligand showed on average a greater than 30% increase in yield compared to Z4. Importantly, for the antibodies tested the mutations did not result in a decrease in dynamic binding capacity or other desirable attributes such as selectivity. A potential application of the novel ligands is shown with a pH sensitive molecule prone to aggregation under acidic conditions.
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