This chapter proposes to offer an overview of different processes used to convert DD to biodiesel/biofuel. Additionally, different processes to recover valuable minor components are described where conversion of FFA and/or acylglycerols to FAME (fatty acid methyl ester) was applied in order to facilitate their purification. However, most of the literature study targets either quality of biodiesel/biofuel or quality of the minor components and seldom offer aspects regarding the overall quality of obtained by-products.

22.3.1 Introduction

An overview of the described routes for biodiesel/biofuel production was given by Echim et al. (2009). Biodiesel/biofuel can be produced from DD by direct esterification (Fig. 22.1) of the FFA or by conversion of FFA to acylglycerols prior to transesterification (Fig. 22.2).

22.3.2 Production of biodiesel/biofuel by direct conversion

Chemically catalyzed process

Soragna (2009, personal communication) described the industrial process for the conversion of FFA into FAME using heterogeneous catalyst, called FACT (Fatty Acid Conversion Technology). This technology is an alternative option compared to the classical technology using homogeneous catalyst, consisting of a continuous countercurrent multiple step esterification using solid catalyst in fixed bed reactors, at 90°C and 0.35 MPa. Production of biodiesel/biofuel from feedstocks with high acidity by direct conversion was registered as a ‘stand-alone process’ Fig. 22.3(a).

For feedstocks with medium/high acidity an ‘integrated process’ was applied (Fig. 22.3b) where a transesterification step for the conversion of the acylglycerols was also included. The FFAs were distilled off and further esterified to FAME before the transesterification of the residual acylglycerols.

The advantage of these processes is the possibility to process high diversity acidity feedstocks (up to 100%) with a conversion of up to 99.8% without limitation in capacity, no usage of liquid acids, higher quality by-products and mild operating conditions.

Verhe et al. (2008) reported a process of converting the DD to biodiesel using sulfuric acid as catalyst, at 75°C for 5 h. The FFA and MAG have undergone esterification, resulting in methyl esters. The crude biodiesel was further washed, dried and distilled in order to increase the quality of the methyl esters. The distillation pitch was further processed for the recovery of sterols and tocopherols.

An extensive study was carried out by Chongkhong et al. (2007) on the palm fatty acid distillate (PFAD) (93% FFA), as feedstock for a batch and continuous production of biodiesel. For the continuous process (CSTR), the amount of FFA was reduced from 93% to less than 2% at the end of the esterification process. A further treatment consisting of neutralization of the FFA and transesterification of the glycerides was required in order to obtain biodiesel which complies with the specifications.

Facioli and Barrera-Arellano (2002) described a process to obtain ethyl esters from soybean oil deodorizer distillates (SODD) using concentrated H2SO4 as catalyst. The DD contained 47% FFA, 26% acylglycerols and 26% unsaponifiable matter.

A conversion of 94% of the fatty acids to ethyl esters was achieved. However, the acylglycerols were not affected and the losses of tocopherols were around 5.5%. A molar excess of ethanol in relation to SODD:FFA was found to be necessary to obtain the best conversion.

Hammond and Tong (2005) described a three-stage acid catalyzed esterification. The reaction mixture was centrifuged, the supernatant lipid phase was separated from the sludge (glycerol, water, acid and methanol), and further reacted with methanol and acid. The maximum FAME conversion obtained for 12-tested acid oils averaged 81%. However, the ester phase could not be increased above 85% even after a fourth-stage reaction or if a basic catalyst was used in large excess. Unknown materials were reported in both FAME and in the sludge phase having a hydrophobic and hydrophilic behavior, respectively. The former compound caused an increase of the biodiesel viscosity and is hypothetically attributed to the presence of polymers.

The polymers might have been formed during the soap acidulation process or during the esterification reaction, due to the limited supply of methanol and the long reaction time. The compound could not be further removed by distillation.