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The economic feasibilities of four continuous processes to produce biodiesel, including both alkali- and acid-catalyzed processes, using waste cooking oil and the 'standard' process using virgin vegetable oil as the raw material, were assessed. Although the alkali-catalyzed process using virgin vegetable oil had the lowest fixed capital cost, the acid-catalyzed process using waste cooking oil was more economically feasible overall, providing a lower total manufacturing cost, a more attractive after-tax rate of return and a lower biodiesel break-even price. On the basis of these economic calculations, sensitivity analyses for these processes were carried out. Plant capacity and prices of feedstock oils and biodiesel were found to be the most significant factors affecting the economic viability of biodiesel manufacture.

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Cardiolipin (CL) is found in inner mitochondrial membranes and the plasma membrane of aerobic prokaryotes. CL is tightly bound to those transmembrane enzymes associated with oxidative phosphorylation. CL has earlier been reported to have a single pK at low pH. We have titrated CL in aqueous suspension (bilayers) and in solution in methanol/water (1:1, vol/vol) and found it to display two different pK values, pK1 at 2.8 and pK2 initially at 7.5 but shifting upwards to 9.5 as the titration proceeds. The unusually high pK2 might be explained by the formation of a unique hydrogen bond in which the free hydroxyl on the central glycerol forms a cyclic intramolecular hydrogen-bonded structure with one protonated phosphate (P-OH group). We have therefore chemically synthesized the 2'-deoxycardiolipin analogue, which lacks the central free hydroxyl group, and measured its pH-dissociation behavior by potentiometric titration, under the same conditions as those for CL. The absence of the hydroxyl group changes the titration dramatically so that the deoxy analogue displays two closely spaced low pK values (pK1 = 1.8; pK2 = 4.0). The anomalous titration behavior of the second dissociation constant of CL may be attributed to the participation of the central glycerol OH group in stabilizing the formation of a cyclic hydrogen-bonded monoprotonated form of CL, which may function as a reservoir of protons at relatively high pH. This function may have an important bearing on proton pumping in biological membranes.