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Lactic acid is a platform chemical that can be utilized for a variety of applications in food, medical, packaging, and cosmetics industries. The global market for lactic acid is expected to grow substantially from $2.1 billion in 2016 to $9.8 billion in 2025. Lactic acid can be produced from both petroleum and biobased sources; however, the demand for lactic acid produced from biobased feedstock sources is expected to increase due to growing consumer awareness of the need for sustainability, biodegradability, recyclability and green packaging in different industries. Biobased lactic acid can be produced from starch-rich feedstocks, such as corn grain, and lignocellulosic feedstocks, such as corn stover and miscanthus. Lactic acid produced from biobased feedstocks can yield lactic acid isomers suitable for applications in the food and medical industries. Despite huge growth potential, the techno-economics and environmental impacts of different pathways for biobased lactic acid production are not well studied. Thus, the objective of this dissertation was to analyze the techno-economics and life cycle environmental impacts of producing lactic acid from biobased feedstocks, including corn grain, corn stover and miscanthus. These feedstocks were selected based on their current availability and future potential for biorefinery use in the U.S. The study evaluated different logistics and conversion pathways by developing comprehensive techno-economic and life cycle assessment models. The models incorporated data collected from the literature related to biomass production, harvest, post-harvest logistics and conversion to lactic acid. Three grain logistics scenarios were defined based on intermediate grain storage at 1) farm storage structure, 2) country elevator, and 3) both, before the grain delivery to the biorefinery. The 90% central range (CR) for the grain logistics cost, including costs for grain harvest, hauling, and storage, was $36-50 per metric ton (t). The grain logistics scenario with storage at the elevator after harvest and delivery to the biorefinery upon demand had the lowest estimated cost. The estimated logistics cost for the scenario with both farm and elevator storage before delivery to the biorefinery was the highest, but this allows the grain to be sold when its price is high, which would potentially result in higher net profit. The study evaluated three lignocellulosic feedstock logistics scenarios, which included corn stover only, miscanthus only, and combined corn stover and miscanthus feedstocks harvest, collection and delivery to the biorefinery. The 90% CR for logistics costs for corn stover, miscanthus, and combined scenarios were $87-150, $66-116 and $77-134/t, respectively. The feedstock logistics cost for miscanthus was lower than corn stover due to higher miscanthus yield which permits lower transportation distances to supply the feedstock to the biorefinery. Due to current supply limitations, corn stover is the only viable option at present; however, miscanthus is expected to become a major feedstock for biobased industries in the future.This dissertation also evaluated the conversion of corn grain, corn stover and miscanthus to lactic acid using three fermentation pathways involving bacteria, fungi, and yeast. The 90% CR of minimum selling prices (at 10% internal rate of return) per metric ton of lactic acid produced from different feedstocks following different fermentation pathways were $844-1,251 for corn grain, $1,130-1,400 for corn stover and $1,025-1,295 for miscanthus. Lactic acid production costs for different feedstocks were the lowest for yeast-based fermentation pathway ($844/t for corn grain, $1,130/t for corn stover and $1,025/t for miscanthus) because fermentation could be done at low pH, which eliminates the use of many chemicals and reduces waste. The minimum selling price of biobased lactic acid was comparable to the market price of lactic acid.Compared to petroleum-based lactic acid production, the estimated life-cycle global warming and eutrophication potentials for biobased lactic acid production were lower by 64-88% and 64-76%, respectively. The estimated resource depletion potential was 23-92% lower for lactic acid produced from lignocellulosic feedstocks than from petroleum sources. The outcomes of this dissertation can be used as a guide for the selection of viable pathways for commercial-scale lactic acid production from different biobased feedstocks. |
