1. Introduction
This conventional process for biodiesel production using
1) High FFA used cooking oil
2) PFAD
as feedstock is commonly applied by all small scale biodiesel players worldwide particularly in developing countries and those areas where quality issue is not a big deal. This conventional process using H2SO4 (sulfuric acid) as catalyst can be found in many areas in China implemented by small scale (marginal) producers. In Indonesia the implementation of this process is pioneered by BPPT (Agency for Assessment and Application of Technology) in its Engineering Center in year of early 2005 and produced several hundreds to over a thousand liters (depending on PFAD supply) per day and used the biodiesel product for fueling its operational cars. Recently PT. Eterindo Wahanatama Tbk followed the suit producing biodiesel from PFAD using similar process. Another company in Indonesia also has implemented and produced PFAD biodiesel by using this sulfuric acid catalyzed process.
2. About PFAD
PFAD (Palm Fatty Acid Distillate) is a byproduct from CPO (Crude Palm Oil) refinery plant. It is taken as distillate from FFA Stripping Tower. The main product from CPO refinery is RBD (Refined Bleached & Deodorized) Palm Oil which is usually fractionated into RBD Olein and RBD Stearin fractions through cooling-down (or winterizing) and filter pressing. RBD Olein is mainly marketed as cooking oil. While RBD Stearin goes to stearic acid production and some to margarine.
The major component of PFAD is free fatty acids (Oleic, palmitic and stearic), usually in the range of 85 ~ 95%. The balances are oil/triglycerides, squalene, aldehydes, ketons, moisture and other minor impurities. The FFA Stripping Tower is considered to having high process efficiency if the FFA content in PFAD is high and triglycerides content is low. So higher the FFA content higher the process efficiency of the Stripping Tower is.
As PFAD is mainly free fatty acids and contains many impurities the quality is less stable thus its storage life is relatively shorter compared with RBD. So it is important to get relatively fresh PFAD product when purchase it, otherwise the resulted biodiesel quality could be affected.
3. Handling and Storage of PFAD
PFAD is semi/soft solid (paste) at ambient temperature in tropical region and become harder in subtropical region during cold/winter season. Therefore its storage tank needs bottom heating coils and all its loading and unloading pipelines including pumps, valves and fittings requires steam tracing. The required level of temperature is not high, 45~50 oC is usually sufficient. It is recommended not to heating up PFAD into too high temperature during storage and handling as there is a higher risk of oxidation compared with RBD, limit the temperature to just enough to keep it flow-able.
Storage tank construction material should be of SS304 or epoxy-coated SS400 but bottom heating coils should be from SS316L. Pipelines, valves and fittings materials should be from SS316L or SS307 depending on operating temperature.
4. Chemistry
The conversion of PFAD into biodiesel involves esterification and transesterification reactions. Esterification converts FFA into biodiesel and transesterification converts oil/triglycerides into biodiesel. The stoichiometry of the reactions is as follows:
FFA + MeOH = Biodiesel + H2O (1)
Oil + MeOH = Biodiesel + Glycerin (2)
Almost all FFA (at least 98.5%) is converted into biodiesel by reaction (1) which is acid catalyzed esterification that could also converts part of oil into biodiesel. The remaining oil is converted into biodiesel by alkali catalyzed transesterification reaction (2).
As the oil content in PFAD is relatively small (only a few percentages) the glycerin produced is also very small and it is dispersed/dissolved totally in bulk methanol~water~sulfuric phase at the bottom of reactor after reaction is finished.
5. Process Description & Procedures
5.1) MeOH is charge into reactor followed by sulfuric acid and then PFAD. Agitator may be switch-on when starting PFAD feeding (please check with agitator vendor the minimum required liquid level before switch it on, the minimum required liquid level depends on agitator's design).
5.2) While feeding-in PFAD, heating-up could be started. Maintain reactor temperature at 65oC. Reaction time is approximately 3~5 hours depending on reactor size and design. The end point for reaction (1) is acid value. AV should be max. 2 mg KOH/g sample.
5.3) Sample taken from reactor must first be washed with water several times before being used for AV analysis.
5.4) If AV <= 2 then stop agitator and do settling. Drain bottom layer into a suitable container (bottom layer is very acidic, pH <1). pfad =" XX*(end-point" av =" 2;" mg =" 1.5%;" dg =" 1.1%;" tg =" 0.9%" pfad =" XX*(2)" xxx =" 64.19" pfad =" 1000" meoh =" 630" h2so4 =" 50" biodiesel =" 930" excess =" 542" waste =" 50" glycerin =" 0.6" soap =" 10" losses =" the">98%) is not corrosive so it can be stored in carbon steel SS400 tank. But in aqueous H2SO4 will dissociate perfectly into 2 H+ and (SO4)2-. These H+ ions that cause the corrosive properties. It exhibit strong corrosion power at any concentration as long as water is presence at enough amount to dissociate H2SO4 into its ions. It is found that the corrosive power is worst at 60% concentration. At elevated temperature it become stronger. At this condition stainless steel is not suitable even SS316L can not stand long. One year ago the price of SS304 plate was USD3.4/kg. Now its price is USD5.5/kg; and SS316L is USD8.7/kg.
2) As sulfuric acid also has strong hygroscopic and oxidative power especially at high concentration, it is not strange if the color of its biodiesel product is dark. Please be extra carefully with all of your body when handling concentrated H2SO4. It will burn you and turn your finger into charcoal instantly.
3) Recovery of methanol is another major issue as MeOH-Water-H2SO4 solution is corrosive. The concern is the construction material of the methanol recovery column particularly its bottom areas. Besides, with 400% excess methanol requires versus 100% with RBD palm biodiesel, this PFAD process requires higher steam energy.
4) Used sulfuric acid is not recoverable. Its disposal is another big issue. It must be neutralized first with alkali usually caustic soda. For every 50 kg 98% sulfuric acid needs 41 kg of 98% caustic soda for neutralization. Its neutralized product namely Na2SO4 salt is not without problem. If it is discharged into waste water treatment plant it will contribute to high dissolved solid in waste water that give more burden to the waste water treatment plant. This is another additional cost as treatment chemicals are needed to reduce this dissolved solid into allowable level.
8. Challenges to Find Better Process
The author and his team are currently working on alternative catalysts thus processes that are better in many senses than sulfuric acid catalyzed process. With many years and intensive experience the author is confident with the invention of a new process that is less corrosive and giving a better quality of biodiesel product. Besides the possibility of recovery of catalyst so that it is reusable thus eliminating environmental issue.
First we will apply the new process in batch reactor w/o water removal system; then batch process w/ water removal system and later-on complete w/ methanol and catalyst recovery system. Finally it will be applied to continuous process with water removal system plus probably reactive distillation and methanol and catalyst recovery system.
The objectives of new process technology are:
- Much less corrosive process
- Better product quality
- Higher product yield
- Lower methanol consumption
- Lower methanol excess thus lower recovery cost
- Recovery and recycle of catalyst, thus cost saving and
at the same time solving environmental issue created by sulfuric acid.
While the chemistry is quite simple, process engineering for PFAD continuous process is pretty complex. The author foresee, for this PFAD process, maintaining methanol balance which is in combination with water removal system around each of CSTR could be the most challenging issue. However, that is the heart of PFAD biodiesel continuous process and once it is solved the benefit will be great including big reduction in methanol feed rate to reactor from 500% of stoichiometry requirement (i.e. 400% excess) to only 200% of sthoichiometry which is 100% excess.
This conventional process for biodiesel production using
1) High FFA used cooking oil
2) PFAD
as feedstock is commonly applied by all small scale biodiesel players worldwide particularly in developing countries and those areas where quality issue is not a big deal. This conventional process using H2SO4 (sulfuric acid) as catalyst can be found in many areas in China implemented by small scale (marginal) producers. In Indonesia the implementation of this process is pioneered by BPPT (Agency for Assessment and Application of Technology) in its Engineering Center in year of early 2005 and produced several hundreds to over a thousand liters (depending on PFAD supply) per day and used the biodiesel product for fueling its operational cars. Recently PT. Eterindo Wahanatama Tbk followed the suit producing biodiesel from PFAD using similar process. Another company in Indonesia also has implemented and produced PFAD biodiesel by using this sulfuric acid catalyzed process.
2. About PFAD
PFAD (Palm Fatty Acid Distillate) is a byproduct from CPO (Crude Palm Oil) refinery plant. It is taken as distillate from FFA Stripping Tower. The main product from CPO refinery is RBD (Refined Bleached & Deodorized) Palm Oil which is usually fractionated into RBD Olein and RBD Stearin fractions through cooling-down (or winterizing) and filter pressing. RBD Olein is mainly marketed as cooking oil. While RBD Stearin goes to stearic acid production and some to margarine.
The major component of PFAD is free fatty acids (Oleic, palmitic and stearic), usually in the range of 85 ~ 95%. The balances are oil/triglycerides, squalene, aldehydes, ketons, moisture and other minor impurities. The FFA Stripping Tower is considered to having high process efficiency if the FFA content in PFAD is high and triglycerides content is low. So higher the FFA content higher the process efficiency of the Stripping Tower is.
As PFAD is mainly free fatty acids and contains many impurities the quality is less stable thus its storage life is relatively shorter compared with RBD. So it is important to get relatively fresh PFAD product when purchase it, otherwise the resulted biodiesel quality could be affected.
3. Handling and Storage of PFAD
PFAD is semi/soft solid (paste) at ambient temperature in tropical region and become harder in subtropical region during cold/winter season. Therefore its storage tank needs bottom heating coils and all its loading and unloading pipelines including pumps, valves and fittings requires steam tracing. The required level of temperature is not high, 45~50 oC is usually sufficient. It is recommended not to heating up PFAD into too high temperature during storage and handling as there is a higher risk of oxidation compared with RBD, limit the temperature to just enough to keep it flow-able.
Storage tank construction material should be of SS304 or epoxy-coated SS400 but bottom heating coils should be from SS316L. Pipelines, valves and fittings materials should be from SS316L or SS307 depending on operating temperature.
4. Chemistry
The conversion of PFAD into biodiesel involves esterification and transesterification reactions. Esterification converts FFA into biodiesel and transesterification converts oil/triglycerides into biodiesel. The stoichiometry of the reactions is as follows:
FFA + MeOH = Biodiesel + H2O (1)
Oil + MeOH = Biodiesel + Glycerin (2)
Almost all FFA (at least 98.5%) is converted into biodiesel by reaction (1) which is acid catalyzed esterification that could also converts part of oil into biodiesel. The remaining oil is converted into biodiesel by alkali catalyzed transesterification reaction (2).
As the oil content in PFAD is relatively small (only a few percentages) the glycerin produced is also very small and it is dispersed/dissolved totally in bulk methanol~water~sulfuric phase at the bottom of reactor after reaction is finished.
5. Process Description & Procedures
5.1) MeOH is charge into reactor followed by sulfuric acid and then PFAD. Agitator may be switch-on when starting PFAD feeding (please check with agitator vendor the minimum required liquid level before switch it on, the minimum required liquid level depends on agitator's design).
5.2) While feeding-in PFAD, heating-up could be started. Maintain reactor temperature at 65oC. Reaction time is approximately 3~5 hours depending on reactor size and design. The end point for reaction (1) is acid value. AV should be max. 2 mg KOH/g sample.
5.3) Sample taken from reactor must first be washed with water several times before being used for AV analysis.
5.4) If AV <= 2 then stop agitator and do settling. Drain bottom layer into a suitable container (bottom layer is very acidic, pH <1). pfad =" XX*(end-point" av =" 2;" mg =" 1.5%;" dg =" 1.1%;" tg =" 0.9%" pfad =" XX*(2)" xxx =" 64.19" pfad =" 1000" meoh =" 630" h2so4 =" 50" biodiesel =" 930" excess =" 542" waste =" 50" glycerin =" 0.6" soap =" 10" losses =" the">98%) is not corrosive so it can be stored in carbon steel SS400 tank. But in aqueous H2SO4 will dissociate perfectly into 2 H+ and (SO4)2-. These H+ ions that cause the corrosive properties. It exhibit strong corrosion power at any concentration as long as water is presence at enough amount to dissociate H2SO4 into its ions. It is found that the corrosive power is worst at 60% concentration. At elevated temperature it become stronger. At this condition stainless steel is not suitable even SS316L can not stand long. One year ago the price of SS304 plate was USD3.4/kg. Now its price is USD5.5/kg; and SS316L is USD8.7/kg.
2) As sulfuric acid also has strong hygroscopic and oxidative power especially at high concentration, it is not strange if the color of its biodiesel product is dark. Please be extra carefully with all of your body when handling concentrated H2SO4. It will burn you and turn your finger into charcoal instantly.
3) Recovery of methanol is another major issue as MeOH-Water-H2SO4 solution is corrosive. The concern is the construction material of the methanol recovery column particularly its bottom areas. Besides, with 400% excess methanol requires versus 100% with RBD palm biodiesel, this PFAD process requires higher steam energy.
4) Used sulfuric acid is not recoverable. Its disposal is another big issue. It must be neutralized first with alkali usually caustic soda. For every 50 kg 98% sulfuric acid needs 41 kg of 98% caustic soda for neutralization. Its neutralized product namely Na2SO4 salt is not without problem. If it is discharged into waste water treatment plant it will contribute to high dissolved solid in waste water that give more burden to the waste water treatment plant. This is another additional cost as treatment chemicals are needed to reduce this dissolved solid into allowable level.
8. Challenges to Find Better Process
The author and his team are currently working on alternative catalysts thus processes that are better in many senses than sulfuric acid catalyzed process. With many years and intensive experience the author is confident with the invention of a new process that is less corrosive and giving a better quality of biodiesel product. Besides the possibility of recovery of catalyst so that it is reusable thus eliminating environmental issue.
First we will apply the new process in batch reactor w/o water removal system; then batch process w/ water removal system and later-on complete w/ methanol and catalyst recovery system. Finally it will be applied to continuous process with water removal system plus probably reactive distillation and methanol and catalyst recovery system.
The objectives of new process technology are:
- Much less corrosive process
- Better product quality
- Higher product yield
- Lower methanol consumption
- Lower methanol excess thus lower recovery cost
- Recovery and recycle of catalyst, thus cost saving and
at the same time solving environmental issue created by sulfuric acid.
While the chemistry is quite simple, process engineering for PFAD continuous process is pretty complex. The author foresee, for this PFAD process, maintaining methanol balance which is in combination with water removal system around each of CSTR could be the most challenging issue. However, that is the heart of PFAD biodiesel continuous process and once it is solved the benefit will be great including big reduction in methanol feed rate to reactor from 500% of stoichiometry requirement (i.e. 400% excess) to only 200% of sthoichiometry which is 100% excess.
