Glycerol-based Isobutanol

• In the search for renewable vehicle fuels several different gasoline additives have been discussed and reviewed. Today bioethanol is the most commonly used option, but isobutanol is being proposed as a better alternative by many stakeholders, due to its superior fuel characteristics, e.g. energy density, oxygen content and vapor pressure. The research project “Glycerol-based isobutanol” has investigated the possibility to produce isobutanol from glycerol with respect to feedstock availability, process economics and savings in GHG emissions. The process has been studied both as a stand-alone fuel production process and integrated with an existing petroleum refinery, a case study together with Preemraff Lysekil. The starting point for the process is glycerol, a waste product from the production of first generation biofuels. Glycerol is a significant byproduct from biodiesel production, in which glycerol corresponds to about 10% (w/w) of the total fuel production. The rapidly increasing production of biodiesel, and thus also glycerol, has led to a market collapse for glycerol in the last decade. This has led to an increasing interest in glycerol as a feedstock for renewable fuels and chemicals. Glycerol is also formed as a byproduct in the production of bioethanol, this quantity is however not utilized today, but in future scenarios glycerol volumes corresponding up to 10% (w/w) of the bioethanol production may become available. Projections from IEA and OECD.FAO show that the production of first generation biofuels will continue to increase, indicating that glycerol will continue to be available as a suitable feedstock for renewable fuels and chemicals. The production of glycerol-based isobutanol is divided into three parts. In the first, glycerol is converted to propanal via acrolein; in the second parallel part, methanol is converted to methanal; in the final part methanal and propanal are condensed to methacrolein which is hydrogenated to isobutanol. Methanol and hydrogen are, besides glycerol, important feedstocks for the process. By using process integration methodology, i.e. pinch analysis, the energy demand of the process has been optimized. The possibility to integrate the production process into an existing petroleum refinery, Preemraff Lysekil, has also been studied. A techno-economic assessment of the process has been performed to calculate the capital investment costs and operation costs of the process. Finally, the greenhouse gas emissions from glycerol-based isobutanol have been calculated and compared with fossil gasoline. The results show that the proposed production process is technically viable. The process has a large heat demand, which to a significant degree can be supplied by internal heat exchanging, according to the results from the process integration studies. Integrating the process with an existing petroleum refinery enables the use of existing utilities and hydrogen production capacity which is an important benefit. The techno-economic assessment shows that the cost for production of glycerol-based isobutanol from a stand-alone plant (1 140 $/m3) is 22% higher than from a plant integrated with a refinery (935 $/m3). The largest share of the production cost is due to the cost for raw materials, both for the stand-alone and integrated case. The calculated production cost is significantly higher than for bioethanol, which is considered to be the main competitor among biobased gasoline blendstocks. The calculations on GHG emissions show that glycerol-based isobutanol is a fuel which yields significant reductions – about 55 %% – in emissions when compared to fossil gasoline. As glycerol from biodiesel production is not loaded with any CO2 emissions according to the EU directive on renewable energy the main contributions are due to the methanol and hydrogen consumed in the process, as both are produced from natural gas. Glycerol-based isobutanol is viable from a technical viewpoint, considering both the proposed production process and the suitability of isobutanol as a gasoline blendstock, and the calculated production cost is in a ranger which could make the process also economically feasible.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

glycerol

isobutanol

biofuel

process integration

techno-economic analysis

Publikations- och innehållstyp

rap (ämneskategori)

vet (ämneskategori)