(619o) Novel Process of Biofuel Production from Acid Oil and Hydrous Bioethanol Using Ion-Exchange Resin; II. Introducing Life Cycle Perspectives in Optimization of Operating Conditions
Liquid biofuels offer attractive advantages over other forms of biomass energy resources in terms of high energy density and ease of storage and transport. Bioethanol is useful as a gasoline additive (up to 10%), with production worldwide in 2014 of 94 million kL. Biodiesel, or fatty acid methyl ester (FAME), is also used as a fuel alternative (100%) to petroleum diesel, with worldwide production in 2014 at 30 million kL. However, there has been no significant increase in the production of these fuels in the past few years. The reason is that there is no profitability for producers owing to high production cost and no benefits for consumers because of unstable product quality and lower fuel economy and power. Moreover, emergence of next-generation automobiles (e.g., battery-powered and fuel cell electric vehicles) will lower the demand for gasoline. The water content of ethanol used as the gasoline additive should be less than 0.5 wt% and the dewatering process requires a large energy input. Thus, the necessity of anhydrous ethanol as gasoline additive fades and new technology which can use hydrous ethanol is desired. On the other hand, the diesel fuel continues to be used for heavy duty on-road commercial transportation, non-road construction, agricultural machines, railroads, and various types of ocean vessels. If new technology to economically produce high quality biodiesel can be developed, the necessity of biodiesel utilization will increase.
In Part I of this research1), biodiesel is produced in the form of fatty acid ethyl ester (FAEE) using hydrous ethanol by esterification of free fatty acid (FFA). The FAEE has higher cetane number and fuel economy and power than the traditional fatty acid methyl ester (FAME) and FAEEâ??s low temperature fluidity is also improved2). However, the conventional technologies for esterification of FFA never use hydrous ethanol because the water in the reaction solution must be completely removed to obtain a high conversion. We have reported to produce FAME at more than 95% conversion by esterification of acid oil using a cation-exchange resin catalyst without dewatering and adding excess alcohol3). This means that the catalytic activity of the resin is not inhibited by water. Thus, using the cation-exchange resin as solid catalyst the batch and continuous esterification experiments with hydrous ethanol are performed. The maximum water content in hydrous ethanol to obtain high conversion is clarified.
The experimental study exhibited how the rate of esterification reaction slows down as the water content becomes higher. Lower reaction rate leads to an increase in energy consumption, thus contributes negatively from a life cycle perspective by inducing more environmental impacts associated with energy. It will also lead to higher frequency of regeneration of resin, which requires additional loading. On the other hand, increased water content means lower duty for distillation of ethanol. To allow a system-wide optimization, in Part II of this study, modeling of the system with a scope that contains all the relevant product life cycles is performed. Using the data acquired from the experiments with continuous configuration, the abovementioned trade-off is highlighted using a case study with a Japanese example. The systems are modeled so that is possible to conduct a comparative LCA. For the bioethanol, the base case is set at the situation where fermented liquor is distilled and dehydrated to 99.5% to replace gasoline, whereas in the evaluated case, it is used to produce FAEE. For biodiesel, in the base case, FFA and methanol are subject to esterification reaction whereas in the evaluated case, FFA and hydrous ethanol at concentration of 90%-99.5% are assumed to be used for esterification reaction. The inventory data for the continuous production are obtained from the pilot scale experiments performed in this study. The details of the experiments are described in Part I1)of this report. Electricity consumption is continuously measured by built-in Watt-Hour meter. Molasses from cane sugar mills are assumed as the source of bioethanol. Yeast is used for fermentation to convert sugars to ethanol. The yeasts are recycled after the fermentation. Economic allocation is applied to the surplus yeast after fermentation as it is valuable as a fertilizer. In Japan, most of the cane sugar mills produce only the sugar as product, and the molasses are collected by a private company as raw material for other product. Heat and power required for sugar extraction is usually entirely supplied from bagasse boiler attached to the sugar mill. The bagasse is usually not enough if ethanol fermentation and distillation is required. Therefore, combustion of fuel oil in the bagasse boiler is assumed as the source of heat and power for bioethanol production, in the case study. The factors that influence the trade-off in life cycle greenhouse gas emissions and cost of operation over the water content in the bioethanol used for FAEE production is discussed.
1) N. Shibasaki-Kitakawa et al., Submitted for presentation at 2016 AIChE Annual Meeting
2) N. Shibasaki-Kitakawa et al., Kagaku Kogaku Ronbunshu, 42 (2016), 30-36.
3) N. Shibasaki-Kitakawa et al., Fuel, 139 (2015), 11-17.