Process for the production of polyhydroxyalkanoates

Abstract

Embodiments of the invention relate generally to processes for the production and processing of polyhydroxyalkanoates (PHA) from carbon sources. In several embodiments, PHAs are produced at high efficiencies from carbon-containing gases through the utilization of a regenerative polymerization system.

Description

RELATED APPLICATIONS[0001]This application claims the benefit of Provisional Application Nos. 61 / 237,606, 61 / 237,609, 61 / 237,635, 61 / 237,603, 61 / 237,616, 61 / 237,615, 61 / 237,620, 61 / 237,643, 61 / 237,633, 61 / 237,630, 61 / 237,626, 61 / 237,642, 61 / 237,639, and 61 / 237,627, all filed on Aug. 27, 2009, the disclosures of which are all incorporated by reference herein.BACKGROUND[0002]1. Field of the Invention[0003]Embodiments of the invention relate to an improved process for the production and processing of polyhydroxyalkanoates, and specifically to a process for the production of polyhydroxyalkanoates from carbon-containing gases.[0004]2. Description of the Related Art[0005]Polyhydroxyalkanoates (PHAs) are thermoplastic polyesters that serve as energy storage vehicles in microorganisms. PHAs are biodegradable in both aerobic and anaerobic conditions, are biocompatible with mammalian tissues, and, as thermoplastics, can be used as alternatives to fossil fuel-based plastics such as polypropyle...

AI Technical Summary

Benefits of technology

[0009]To reduce the carbon input cost of the PHA production process, carbon-containing industrial off-gases, such as carbon dioxide, methane, and volatile organic compounds, have been proposed as an alternative to food crop-based sources of carbon. In addition to the wide availability and low cost of carbon-containing gases, carbon-containing gases also do not present the environmental challenges associated with food crop-derived sources of carbon. Specifically, whereas food crop-based carbon substrates require land, fertilizers, pesticides, and fossil fuels to produce, and also generate greenhouse gas emissions during the course of production, carbon-containing off-gases do not require new inputs of land, fertilizers, pesticides, or fossil fuels to generate. Thus, on both an economic and environmental basis, the utilization of carbon emissions for the production of PHA would appear to offer significant advantages over sugar-based PHA production processes.

[0104]PHA, while able to be treated post-production to reduce pigmentation, is less expensive to produce when lower levels of pigmentation exist. Some microorganisms are more pigmented than others, and therefore in several embodiments, selection against the more pigmented microorganisms results in a less pigmented PHA, which reduces production costs. In some embodiments. the microorganisms cultured and selected for are methanotrophic microorganisms. By manipulating the culture conditions, which benefit certain varieties of microorganisms, a less pigmented culture (and hence a less pigmented PHA) result. In some embodiments, increases in concentration of dissolved oxygen over periods ranging from 1-3 hours, 3-5 hours, 5-7 hours, 7-10 hours, 10-15 hours, or 15-24 hours are used to select for less pigmented microorganisms.

Problems solved by technology

Unfortunately, despite these maximized efficiency advantages, sugar-based PHA production remains many times more expensive than fossil fuel-based plastics production.

Thus, given the apparent efficiency maximization of the high density sugar-derived PHA production process, PHAs are widely considered to be fundamentally unable to compete with fossil fuel-based plastics on energy, chemical, and cost efficiency.

Despite the environmental advantages of PHAs, the high cost of PHA production relative to the low cost of fossil fuel-based plastics production has significantly limited the industrial production and commercial adoption of PHAs.

Unfortunately, the fermentation of carbon-containing gases presents technical challenges and stoichiometric limitations that have, in the past, rendered the gas-to-PHA production process significantly more energy and chemical intensive, and thus more costly, than the food crop-based PHA production process.

Specifically, these technical challenges and stoichiometric limitations include: low mass transfer rates, low microorganism growth rates, extended polymerization times, low cell densities, high oxygen demand, and low PHA cellular inclusion concentrations.

As a result, the ratio of energy-to-PHA required to carry out upstream carbon injection, optional oxygen injection, and culture mixing, as well as downstream PHA purification, significantly exceeds the energy-to-PHA ratio required for sugar-based PHA production methods, thereby rendering the emissions-based process uncompetitive when compared to both petroleum-based plastics and sugar-based PHAs.

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