(66f) Novel Process of Biofuel Production from Acid Oil and Hydrous Bioethanol Using Ion-Exchange Resin; I. Experimental Optimization of Operating Conditions

Introduction

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%) and biodiesel, or fatty acid methyl ester (FAME), is also used as a fuel alternative (100%) to petroleum diesel. 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 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 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 this research (Part I), 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 improved¹⁾. 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 alcohol²⁾. This means that the catalytic activity of the resin is not inhibited by water. Thus, using the cation-exchange resin 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.

Materials and methods

The cation-exchange resin, Diaion PK208LH (Mitsubishi Chemical Co., Ltd., Tokyo, Japan) with a high catalytic activity is used²⁾. The resin was supplied in an activated H-form swelled with water. For pretreatment, the resin was packed with the column and ethanol is supplied to remove water in the resin before the esterification. In the batchwise esterification, the preheated mixed-solution at the molar ratio of oleic acid and ethanol, 1:3, and 33 wt% of the resin were added to the glass bottle. The bottle was well shaken in a thermal bath at 50 °C. At specific time intervals, samples of the solution were collected and the concentrations of the reactants and products were analyzed. The water content in ethanol is set at 0, 5, and 10 wt%.

In the continuous esterification, the column packed with the resin was kept constant at 50 °C. For the pretreatment, ethanol with a certain water content was supplied similarly to the batchwise system. Then, the mixed solution of oleic acid and the ethanol at the same molar ratio as that in the batchwise system was supplied to the bottom of the column by a pump. Under each water content in ethanol, the residence time through the resin bed was regulated by changing the feed flow rate. The effluent solutions from the top of the column were collected and the concentrations of the reactants and the products in the solution were also determined.

Results and Discussion

In the batchwise system, using anhydrous ethanol for both pretreatment and esterification, the complete conversion was reached after 50 h. Using ethanol with 5wt% water content, the esterification rate became slower and more than 90% conversion was obtained at 120 h. After the pretreatment using ethanol with 5wt% water content, the water content in the resin was higher than that in the resin pretreated with anhydrous ethanol, so that the lipid soluble reactant, FFA, was hard to transfer into the resin to lower the esterification rate.

In the continuous system, the conversion was determined after steady state was reached under each condition. Using anhydrous ethanol, the complete conversion was obtained at the residence time through the bed of 10 h. Using ethanol with 5wt% water content, more than 95% conversion was attained at the residence time of 35 h and the complete conversion was also obtained at 60 h. Using ethanol with 10wt% water content, more than 90% conversion was obtained at 60 h. In the continuous system, the esterification rate became slower with increasing water content in ethanol, but its effect was smaller than that in the batchwise system. This was because the water formed by esterification was accumulated in the batch system, whereas the water was removed by continuous flow in the continuous system. Therefore, the continuous esterification using the column reactor packed with the resin is very effective for utilization the hydrous ethanol.

Lower esterification rate leads to an increase in energy consumption, thus contributes negatively from a life cycle perspective by inducing more environmental impacts associated with energy. On the other hand, increased water content means lower duty for distillation of ethanol. In another part of this research (Part II), to allow a system-wide optimization, 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.

Reference

1)N.Shibasaki-Kitakawa et al., Kagaku Kogaku Ronbunshu, 42 (2016) 30-36

2)N.Shibasaki-Kitakawa et al., Fuel, 139 (2015), 11-17.