To get some idea of the prices to be expected for compounds produced with these approaches, we have estimated the total cost of producing 10,000 tons per annum of 1-octanol from «-octane, based on data collected for this conversion by P. oleovorans, during growth in a two-liquid-phase system containing 15% (v/v) hexadecane as a carrier phase.47 n-Octane is dissolved in the carrier phase to a concentration of 5 -10% (v/v), converted by the P. oleovorans cells in the aqueous phase, and the product 1-octanol dissolves in the hexadecane phase once more. Downstream processing consists of a phase separation, followed by two distillation steps. In the first step, the C8 alkane/alkanol are separated from the hexadecane, which is recycled into the bioreactor. In the second step, the n-octane is distilled off the n-octanol: the octane is recycled to the bioreactor, and the octanol is collected as the desired product. This approach leads to a very clean product stream of >98% pure 1-octanol.48
The total cost of the process was estimated to be about 8 US$ per kg product (Figure 15.13). The most significant cost item (ca. 40% of the total) was due to the glucose and salts necessary to support cell growth; that is, these are part of the biocatalyst formation costs. Biocatalyst costs can be reduced by increasing specific activities per g cells, and by extending the useful lifetime of whole-cell biocatalysts. We estimate that reductions in biocatalyst cost and associated process costs might lower the preceding estimate to 5 US$ per kg product. Although the estimate described here was carried out for a specific
alkane-to-alkanol conversion, it applies to similar hydroxylations or oxidations of other apolar compounds. A key parameter in all such estimates is the specific activity per g cells that can be achieved. Typical activities are in the order of 5 to 50 U/g cell dry mass, where U is the international enzyme activity unit, expressed as mmol of product formed or mmol substrate utilized per minute.
The preceding estimate suggests that products valued at more than 10 US$ per kg are potential targets for biocatalytic production, provided the market is sufficiently large. Clearly, compounds valued at 50-100 US$ or more per kg are interesting biocatalysis targets. However, high tonnage targets of 5-7 US$ per kg are still worth investigating.
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