Abstract

Extinguishing foams are commonly used for extinguishing fires of flammable liquids, whereby their insulating, choking and quenching effects are exploited. In an attempt to contain petrol fires, locally produced red palm oil was used to synthesize environmental friendly fire-fighting foam agent which is less dense than petroleum motor spirit (PMS). Trans-esterification of palm oil and ethanol in an acidic medium was carried out by refluxing for 18h at 358K to produce palm oil ethyl ester (POEE), which was reduced with sodium metal. Sodium salts of POEE obtained which was highly viscous at room temperature had a pH of 10.2. The optimum foam agent concentration obtained at ratio of 1:8 moles of the foam agent to water had its foaming characteristics sustained for about 29 days. Some physical properties of the resultant foam were tested and extinction performance of the foam agent was confirmed as well.
KeywordsPalm Oil, Trans-esterification, Petrol Fires, Palm oil ethyl ester, Extinguish.

Author and Article information

Author info
1. Material Science Research Laboratory, Department of Chemistry Abubakar Tafawa Balewa University Bauchi, PMB 0248, Bauchi - Nigeria

RecievedNov 4 2013　　AcceptedNov 21 2013　　PublishedDec 4 2013

CitationRaphael Shadai Oguike (2013) STUDY OF FIRE FIGHTING FOAM AGENT FROM PALM OIL FOR EXTINGUISHING OF PETROL FIRES. Science Postprint 1(1): e00007. doi:10.14340/spp.2013.12A0002

Copyright©2013 The Authors. Science Postprint published by General Healthcare Inc. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 2.1 Japan (CC BY-NC-ND 2.1 JP) License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

FundingCollins U. Oguike is acknowledged for financing the publication of the paper. This research received no external funding.

Competing interestThe research work is independent.

DonationPetrol fire has been a menace to our modern society and fire fighting agents needs to be eco-friendly. In this research work, we were able to locally produce a soap-base fire fighting foam agent which is cheap, efficient as well as eco-friendly. Funds are required to carry out the work on a large scale thereby making the product available to the public. Further work on nitrogenating the foam agent and even pulverizing the foam agent to ascertain same fire fighting efficiency is necessary also.

Corresponding authorRaphael Shadai Oguike
AddressMaterial Science Research Laboratory, Department of Chemistry, Abubakar Tafawa Balewa University Bauchi, PMB 0248, Bauchi – Nigeria.
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Introduction

Fire is of great concern in our environment and incidences of fires are usually devastating to both lives and properties. In fire science, there are four classes of fires namely; class A, B, C and D. Class A fire involves common combustibles such as wood, paper and rubber materials, class B fire involves flammable liquids such as PMS, AGO, DPK, gas and grease, class C fires involve energized electrical equipment, conductors or appliances while class D fires involve combustible metals such as magnesium, titanium, potassium and sodium 1-2. Petrol fires classified as class B fire is a product from a rapid chemical reaction in which the combustion of fuel in sufficient quantity of air volume generates flame, heat and gaseous products such as CO₂ and CO simultaneously 3. It is a self – sustaining reaction to the extent that it continues until the fuel supply is completely consumed. It is also an exothermic reaction and depends majorly on three factors; fuel, air and heat. In fire fighting, many kinds of fire extinguishers have been patented and used over the years, but it is worthy of note that none has been reported to effectively quench petrol fires satisfactorily 3. Some of the fire extinguishers include; water, metal/sand mixture, wetting agents, fog, carbon (iv) oxide, halons, halotrons, dry chemicals, water mist, foam agents and FFFP foam (film-forming-fluoroprotein) 2. FFFP foam, Halons and halotrons can be used for class B fires while water cannot be used for class B fire because it will increase the surface of the blazing liquid thereby making matters worse. Halons proved to be good but it generates deadly phosgene gas in very hot fire and has been banned since 2000AD 4. Halotrons give good results but it emits gases that deplete the ozone layer and has been given till year 2015 for its usage to stop 5. Dry chemicals, carbon (iv) oxide and FFFP are also good but they make a mess after extinction thereby recovery of product is not feasible. Sand might have been good being a bad conductor of heat but sand might contain combustible materials that might as well worsen the matter 6.

The fire extinction mechanism is an attempt to remove one or more of the factors responsible for the blazing inferno based on the triangle of fire which include one or all methods of extinction in fire science namely; starvation, cooling and smothering. Starvation (isolation) deprives the blazing inferno of the fuel necessary to maintain combustion, cooling (refrigerating) reduces the heat that accompanies the fire below its ignition temperature while smothering (choky) involves the removal of oxygen or the dilution of air in the vicinity of the fire base or blanketing the fuel surface 3,7. Fire-fighting foam is an extinguishing agent composed of numerous bubbles formed mechanically or chemically from liquid. These are commonly used to reduce the spread and extinguishing of Class B fires and to prevent re-ignition while in certain conditions can be applied to extinguishing Class A fires 8. Extinguishers containing soap-based components permit fire fighters to extinguish fires much quicker than water alone because the foam floats at the fire/material interface creating a superior foam blanket when mixed with air due to the characteristic properties of the soap-based foam 9. In view of the increasing environmental awareness, researches are now focused on fire extinguishers of natural product origin 9. Local palm oil, in addition to being environmentally friendly is ecologically acceptable, inexpensive, readily available and a renewable source of materials. The present study investigates the use of fire-fighting foams agent to curb petrol fires. Local palm oil was used to synthesize a foam agent capable of extinguishing PMS fires. The physical parameters of the synthesized foam were carried out and dissolution of foam agent after PMS fire extinction was also performed.

Materials and Methods

Local red palm oil was prepared by boiling freshly harvested palm fruits in Nekede, Owerri, Imo state and squeezing out the oil from the fruits. The palm oil was collected in a stainless steel basin and stored in glass bottles. All chemicals and reagents used were of BDH analytical grade obtained from Araria Int’l market Aba, Abia state.

Synthesis of palm oil ethyl ester (Acid catalyzed trans-esterification)

100ml of red palm oil, 150ml of ethanol and 50ml of absolute HCl were put in a 500ml three neck round bottom flask with boiling chips added. This was transferred to a thermostated water bath and a wide bore reflux condenser was attached to the centre neck 10-11. A stirring rod was attached to one of the side necks while the other neck was corked in place. The setup was refluxed for about 18h with continuous stirring at 358K. The mixture was allowed to cool and then transferred to a separating funnel. The acid catalyst was neutralized by addition of CaCO₃ suspension and warm solutions of 0.1M NaCl was used to wash the mixture and it was left to stand until distinct layers were seen. The top layer was retained by discarding the lower layer through the tap of the separating funnel. The product was collected, weighed and stored in a reagent bottle.

Hydrolysis of palm oil ethyl ester

125ml of absolute toluene was measured with a measuring cylinder then transferred into a 500ml three neck round bottom flask and 68.89g of sodium metal was added into flask with boiling chips. The mixture was fitted with a wide bore reflux condenser with a wooden stirrer attached to one side neck. The setup was transferred to an oil bath to dissolve the sodium metal after which the mixture was steam distilled to remove the toluene 12. 78.84g of POEE was mixed with 50ml of ethanol and introduced into the reaction flask through one of the side necks of the flask containing molten sodium metal. There was a vigorous reaction for the space of about 2mins and at the subsidence of the reaction (4mins after), the setup was transferred quickly to a water bath and then refluxed for about 5h with continuous stirring. The mixture was allowed to cool after steam distilling to remove any remaining toluene and all ethanol. After cooling, the content of the flask was transferred into a separating funnel where it was washed with water and left to stand for separation to occur. The bottom layer was discarded through the tap. The upper layer was collected, weighed and stored in a reagent bottle.

Foaming and Mechanical stability

The foaming ability test was done according to 13. Eight empty bottles of total volume 1500 cm³ were used and to each, 20, 40, 60, 80, 100, 120, 140 and 180 cm³ volume of water was added respectively. 10 cm³ of the foam agent was added to each bottle and shake vigorously for about 3 mins in each case, the time and foam height was recorded. The foam was also left to stand for 5mins and their heights were measured again, this was then left to stand for 5days, and the heights measured. Finally, foams formed were left to stand until collapse and the time recorded for each foam agent concentration.

Efficiency of foam agent

2L of PMS poured into a basin in an isolated area which was lit from a long wooden splinter, an inferno resulted. 0.7L of the foam agent was introduced through a long hose at the base of the petrol fire 14. The time interval between application time and total extinction time was recorded. After extinction, dissolution of the froth was carried out using water at 27 and 60°C, also dissolution with brine water was studied. These were tested in duplicate and the average reported.

Results and Discussions

Trans-esterification

Trans-esterification is a reversible reaction and a temperature controlled equilibrium reaction. The maximum yield of product does not depend on how fast the reaction occurred but on how complete they have reacted before equilibrium was reached. Maximum yield was obtained by use of excess of ethanol 11 and the reaction catalyzed with absolute HCl which was neutralized at the end of the reaction using equation 1. As can be seen in Fig. 1, the mechanism of trans-esterification is similar to that of acid-catalyzed ester hydrolysis 10 which involves the protonation of the carbonyl oxygen of the ester followed by a nucleophilic attack of an alcohol molecule on the carbonyl carbon of the protonated ester. This results in the exchange of an alcohol molecule for a water molecule as represented by the final step in Fig. 1. After the trans-esterification reaction, CaCO₃ solution was added to the mixture to neutralize the HCl used as catalyst as seen in equation 1. The resulting POEE obtained was 78.84g.

2CaCO₂ + 4HCl → 2CaCl₂ + 2CO₂ + 2H₂O (1)

Fig. 1: Scheme of trans-esterification mechanism 11

Purification of the palm oil ethyl ester

Toluene was used to melt sodium metal because it is inert. A very reactive metal such as sodium needs an inert solvent to dissolve in. If the sodium metal was heated to dissolve on its own, it may decompose exothermally leading to class D fires 6. The sodium metal was dissolved to increase its surface area for effective yield and reduction of the palm oil ethyl ester. The addition of ethanol to POEE before mixing with the molten sodium metal was to act as a dehydrating agent to mitigate reactions between sodium metal and water. For effective reduction, conversion and yield, excess of the sodium metal was used that is, 1:3 moles of POEE and sodium metal respectively 15. The mechanism of hydrolysis of palm oil ethyl ester is similar to that of Fischer esterification as shown in Fig. 2. The reaction involves nucleophilic attack by cations on the carbonyl carbon of the ethyl ester which proceed via a tetrahedral intermediate but the reactants and products are trigonal 11. The sodium salts formed is majorly collection of palmitic and oleic acid was transferred into a separating funnel to separate after which two lower layers were seen and the lower was discarded through the tap. Warm NaCl solution was added to wash the product which was allowed to stand until distinct clear separation occurred. The washing was done to remove all sodium alkoxide in the mixture while the NaCl was added to increase ionic strength of the mixture. The upper layer was collected by running off the lower layer and weighed. 54.8g of the fire fighting foam agent was obtained which was a liquid at 76°C and highly viscous at room temperature.

Fig. 2 Scheme of ethyl ester hydrolysis mechanism 10

Foaming ability and Mechanical stability

Fire fighting foams used today are primarily of the mechanical type. This means that before being used, they must be proportioned (mixed with water) and aerated (mixed with air). Four elements are necessary to produce a quality foam blanket and they include: foam concentrate, water, air and aeration (mechanical agitation) 16. The fire fighting foam produced is highly viscous and has its melting point at 75.6°C which is comparable to the melting point of palmitic acid at 64.8°C 17. When 10cm³ of the foam was added to 20cm³ of water, a viscous-cream liquid was formed with little foam on top. The foam height increased with increase in water volume until concentration ratio of 1:8 foam agent to water respectively and the highest foam height was observed. After this point further increase in water volume results in a decrease in the foam height as shown in table 1. In the process of fire fighting, foams are constantly disrupted by the influence of heat of ignition, internal force of foam and hot surface of burning liquid 18. Also the degradation rate of foam by flame heat effect is much smaller than by the actual surface of the heated evaporating liquid 3,6. The water accompanying the foam agent produced acts as a coolant and the heat resistance of the foam agent was seen to be good. Perusal of table 1 also shows that the froth after petrol fire extinction can best be dissolved by water at 60°C while water at 27°C had longer dissolution time but addition of NaCl to the water had little effect on the dissolution time of the froth.

Fig. 3 showing various foam heights in different volumes of water as a function of time.

Fig. 3 shows time of depletion of the various foam concentrations. The optimal foam to water ratio of 1:8 gave a half life of 345h as seen in table 2. It was observed that the ratio of 1:8 foam to water which had an appreciable time of collapse as compared to other water ratio concentrations. This indicates that the foam agent had longer duration of stability than most foaming agent prepared from detergents which must be freshly prepared prior to use. Further increase in water volume after the optimal foam concentration resulted to decrease in foam height, hence a decrease in foam agent stability as observed in Fig. 4.

Fig. 4 Shows the time of collapse of the fire fighting foam agent as a function of foam concentration

Density and pH of foam agent

Fire-fighting foam is a stable mass of small bubbles produced by mixing air into a foam solution that contains water and foam concentrate which has lower density than most flammable liquids and water. The density of the foam agent was determined using the density bottle 19-20. The Relative density of the foam agent was calculated to be 0.2138gcm^-3 which is less dense than water and PMS. This implies that the foam agent produced is able to float on PMS surface hence reducing the surface area available for the fire. The fire fighting foam functions by constituting a blanket over the liquid surface which consequently blankets the surface from air. The pH value of the foam was taken at different intervals, an average value of 10.2 was recorded. This is shows that the foam agent is alkaline foam.

Efficacy and Solubility of foam agent

The efficiency of the foam agent towards the blazing PMS fire relies on its ability to float on the liquid fuel and continuously spread from the point of application at the edge of the fire into the blazing flame 9,20. As the foam floats and spreads, it eclipses the surface of the blazing liquid and consequently blankets the fuel/air interface. It is interesting and fascinating to observe the gradual quenching of the blazing inferno as the fire fighting foam produced reduces the surface area of PMS and eventually puts off the fire. The water content accompanying the foam provides a cooling effect on the heat generation thereby preventing any possible reflash after extinction. By these juxtapose action, the PMS fire is effectively and efficiently extinguished within seconds of its application. The heat resistance is the ability of the foam bubbles to withstand direct flame impingement or contact with elevated temperature surfaces, with little or no destruction to the foam bubbles which is often called burnback resistance 15. The foam agent used in extinguishing the PMS fires was found to have a good burnback resistance while its knock down speed measured according to Onuchukwu 9 was 7 seconds from the time of foam release through the hose pipe and the time of total fire extinction. Knockdown is the speed at which foam spreads across the surface of a liquid. Dissolution of the foam was carried out to ensure that the foam does not constitute an environmental hazard and that the petrol might be recovered after PMS fire extinction. A study of table 1 shows that the solubility of the foam was best done with water at 60°C. The brine water and ordinary water at room temperature hardly dissolved the foam completely. It was also observed that after the dissolution of the foam, the fuel which has a lesser density than water was on top while the dissolved froth settled beneath, making it possible for PMS to be decanted.

Conclusions

Today, we know many types of fire-fighting foams, which have different physical and extinguishing properties. Each of them has its own pros and cons, as was shown by literature. The sodium salt of palm oil ethyl ester produced was found to be dense than PMS and the water content of the fire fighting foam acts as a refrigerant to prevent a possible reflash. The foam had good heat resistance as well as knockdown speed. The optimal fire fighting foam concentration of 1:8 ratio, foam to water respectively gave the highest foaming characteristics which had a half life of 345 hours. The dissolution of the forth after extinction of fire was possible, hence no mess of the environment is left. The foam agent is a suitable and cheaper alternative for fighting petrol fires.

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Correction notice

In the article titled "STUDY OF FIRE FIGHTING FOAM AGENT FROM PALM OIL FOR EXTINGUISHING OF PETROL FIRES" ( http://www.spp-j.com/spp/1-1/spp.2013.12A0002 ), a copying from another publication without proper citation and clear differentiation from the author's words was suggested by a reader. Our Editorial Office took action to ask author to explain and paraphrase the phrase in author's own words, and the correction was made in the following way in the Introduction section.

[Previous version] ...Extinguishers containing surfactants in major proportions allows fire fighters to extinguish a fire much faster than water alone because the foam agents reduce surface tension of water, and create a superior foam blanket when mixed with air due to the characteristic properties of surfactants [9]...

[Correction] ...Extinguishers containing soap-based components permit fire fighters to extinguish fires much quicker than water alone because the foam floats at the fire/material interface creating a superior foam blanket when mixed with air due to the characteristic properties of the soap-based foam [9]...