Study of an ethylic biodiesel integrated process: Raw-materials, reaction optimization and purification methods

TL;DR: In this article, the authors evaluate the effectiveness of water-free purification methods for the use of a cation-exchange resin and a ceramic membrane for water free purification.

About: This article is published in Fuel Processing Technology.The article was published on 2014-08-01 and is currently open access. It has received 19 citations till now. The article focuses on the topics: Waste oil & Vegetable oil.

Summary

2.2.3. Evaluation of raw materials and biodiesel quality

• After, the solid was treated with 5 mL of nitric acid and heated at 200 ºC until reduced to 200 µL.
• Finally, 5 mL of nitric acid were added and this solution was diluted with distilled water up to 50 mL, for further analysis.

3.1 Raw materials

• The virgin oil presents the characteristics required to be used for food purposes and it was used as reference oil for preliminary experiments and for comparison with the results obtained with the waste oil.
• The characteristics of both oils agree with the range of values reported in the literature and reference books [3, 10, 22] .

3.2 Preliminary experiments

• The reaction conditions were established taking into account a literature review, namely considering the review by Brunschwig et al. [17] that evaluates bioethanol use for biodiesel production.
• Taking into account the great amount of work on ethanolysis conducted at 80 C, initially, experiments were conducted at that temperature and by varying the ethanol:oil molar ratio, the catalyst concentration and the reaction time.

Results are presented in Table 1 (exp. 1 -6).

• It can be seen that using a lower ethanol to oil molar ratio, of 7:1 (experiments 1 -4), independently of the catalyst concentration and reaction time, there was no phase separation, reason why such conditions were considered to be inefficient; also, using 2.0 wt.% of catalyst, a great amount of soap was observed.
• Using this oil, such molar ratio, and at a catalyst concentration of 1 wt.%, immediate soap production occurred which impaired the reaction (experiment 10).
• The best preliminary reaction conditions, that led to a product conversion of 97.7 wt.% were found after 1 h of reaction using 1 wt.% of catalyst (experiment 14).
• The ethyl ester content of waste frying oil biodiesel (WFOB) is very close to the one obtained with the SFOB, meaning that the reaction time of 1 h is also adequate for the conversion of this oil.
• Since the European Standard is based on rapeseed oil, it makes sense the differences found, that agree with studies on the use of such type of oil [3] ; the iodine value of the WFOB shows similar degree of unsaturation.

3.3 Evaluation of purification methods

• On the other hand, the ceramic membrane seemed to retain the fatty acids [20] allowing the reduction of this parameter to acceptable values.
• The raw materials water content was between 600 and 700 ppm (section 3.1) and although the resin selectively absorbs hydrophilic components, the membrane did not retain the water molecules and did not enable a low water content of the product.
• As previously stated, the final purity obtained was lower than that obtained with the water washing method.
• Finally, although these methods are referred to as effective for catalyst removal [20, 21, 25] , to confirm the efficiency towards sodium removal, sodium was measured in the water washed product as well as in the product purified with the water free methods, when the virgin oil was used as raw material.
• Better results might be achieved by optimization studies, since membrane separation efficiency depends upon conditions such as temperature, transmembrane pressure and flow [19] .

Conclusions

• The present work allowed the study of an integrated biodiesel production process through ethanolic route, using virgin and waste oil as raw materials.
• The preliminary results on ethanolic biodiesel production using sunflower oil showed the importance of optimizing reaction conditions and the difficulties and complexity of this process.
• Taking into account the results from preliminary and optimization experiments, the best conditions were selected as: reaction temperature of 45 ºC and 6:1 ethanol:oil molar ratio (considering 1.0 wt.% of catalyst and 1 h of reaction).
• Under such conditions, a good quality product could generally be obtained after water washing, using both the virgin and the waste oil.

Figures

Fig. 3. Ethyl ester content (A) and water content (B) of soybean oil biodiesel (SOB) and 551 waste frying oil biodiesel (WFOB) after treatment with different amounts of resin; results 552 for water washed soybean oil biodiesel (WWSOB) and water washed waste frying oil 553 biodiesel (WWWFOB), in solid line, as well as the EN 14214 standard requirement for 554 methyl esters (dashed line) are presented for reference.555

Fig. 2. Ethyl ester content and viscosity of the waste frying oil biodiesel, obtained in the 546 optimization experiments; max and minimum values relate to standard EN 14214 on 547 methyl esters. 548 549

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Study of an ethylic biodiesel integrated process: raw-materials," ?

In this paper, a transesterification reaction is reversible and involves three steps to convert the initial triglyceride into a mixture of biodiesel and the by-product glycerol. 

Q2. What is the main reason why biodiesel is used in soy?

Vegetable food oils, such as soybean 46 oil, rapeseed oil, palm oil and sunflower oil are used in more than 95 % of biodiesel 47 production plants throughout the world [4]. 

Q3. How much of the biodiesel production costs are derived from vegetable oils?

57 Virgin vegetable oils might account for up to 95% of the biodiesel production costs [6]; 58 therefore, raw-material diversification might have significant impact on improving the 59 economic viability of the process. 

Q4. How many experiments were conducted in order to evaluate the biodiesel production process?

In order to evaluate the biodiesel production process, 14 preliminary experiments were 218 conducted, by varying the reaction temperature, time, ethanol:oil molar ratio and 219 homogeneous catalyst (NaOH) concentration aiming to select the best conditions to 220 obtain high conversion and identify key reaction parameters. 

Q5. How much Na was present in the membrane purified product?

The 417 membrane purified product presented 69 ppm of Na, whereas the product purified with 418 the resin presented 108 ppm of Na. 

Q6. What were the conditions used for the conversion of ethanol to oil?

351 Taking into account the results obtained during preliminary studies and also that the use 352 of high alcohol:oil molar ratios in the transesterification reaction is known to 353 significantly increase separation and purification costs [20], the optimized conditions 354 were selected as 45 ºC and 6:1 ethanol to oil molar ratio. 

Q7. What was the reaction temperature at which the experiment was conducted?

Taking into account the great amount of work on ethanolysis 230conducted at 80 C, initially, experiments were conducted at that temperature and by 231varying the ethanol:oil molar ratio, the catalyst concentration and the reaction time. 

Q8. What were the experimental planning for the 320 experiments?

The 319 experimental planning included performing all experiments in duplicate except for the 320 central point that was performed in triplicate (19 experiments were performed). 

Q9. how many ethanol:oil ratios were used in the same experiment?

It can be seen that, using a 9:1 ethanol:oil molar 326 ratio, minor effects were found on varying the temperature; in this case, the purity was, 327 in average 92.3 ± 0.7 and the viscosity 4.76 ± 0.04 mm2 s-1. 328 When using 6:1 and also when using 12:1 ethanol:oil molar ratio, a more significant 329 effect was found by varying the temperature, with the highest purity being obtained at 330 40 ºC and 6:1 ethanol:oil molar ratio and at 30 ºC, using 12:1, being in both cases very 331 similar (close to 96 wt.%). 

Q10. What is the way to achieve a high ethanol:oil ratio?

The results showed that to achieve high 449 conversions at a relatively low temperature, of 30 ºC, a high ethanol:oil molar ratio is 450 required (12:1); on the other hand, no benefit results from increasing the temperature up 451 to 50 ºC using such a high ethanol:oil molar ratio. 

Q11. What was the reaction temperature at which the product was removed?

To do that, after 1 h 255 the reaction was stopped, the products were settled and glycerol was removed as 256 described in section 2.2.1. 

Q12. How is the biodiesel process compared to the methanolic route?

The ethanolic route is in fact 84 more promising; however, the process is much more sensitive and it still needs to be 85 optimized, namely regarding reaction conditions and product separation constraints, to 86 be competitive with the methanolic route [17].