Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link: http://www.jett.dormaj.com  
Structural Information from Ratio Bands in the  
FTIR Spectra of Long Chain and Branched  
Alkanes in Petrodiesel Samples  
Flora Ferati 1*  
Department of Technology, University of Mitrovica “Isa Boletini” Ukshin Kovaqica, Mitrovica, 40000, Kosovo  
Received: 15/06/2020  
Accepted: 14/07/2020  
Published: 20/09/2020  
Abstract  
FTIR is a widely used equipment for determining the chemical structure of organic materials. Vibrational analysis was  
employed to characterize hydrocarbon structure from which depends their quality and environmental effect. The results showed  
that the FTIR spectrum of petrodiesel allowed structural information about degree of branched or aliphatic chain hydrocarbons.  
2 3  
The ratios of aliphatic carbons especially CH /CH (A2920/A2950) and A1376/(A1376+A1460) appeared to be suitable indicators for  
identifying type of alkanes present in petrodiesel samples.  
Keywords: FTIR, Petrodiesel, Hydrocarbon structure  
Introduction1  
others applied NIR-Spectroscopy (4, 15), or NMR (5, 16).  
Most of them use a lot of toxic chemicals also need a lot of  
time for sample preparation and cost analysis are very  
expensive.  
1
Most of air contaminants have origin from diesel  
petroleum which is urgent problem in most world countries  
and simplicity of determination of fuel quality is still  
challenge. Today all European countries have strong quality  
control of quality diesel fuel, but all these quality parameters  
do not involve petroleum hydrocarbons (PHCs) which can  
contain a lot of contaminants, or can initiate formation of  
other air contaminants which can be chemical product in  
engine combustion of diesel petroleum. Nakakita et al.  
reports about diesel fuel which contain branched and ring  
hydrocarbon compounds under engine combustion produced  
high level of PM precursors, such as benzene and toluene  
which are in high level produced from branched paraffins  
compare with n-paraffins where their formation are in low  
level (1, 13). Their funding’s suggest branched  
hydrocarbons to be in low level in diesel fuel because of  
possibility to increase PM emissions in air also particle  
matter of are in strong correlation with composition and  
physico-chemical parameters (1, 14). Anyway, high level of  
n-paraffins or long chain aliphatic hydrocarbons have lower  
impact in PM emissions compared with branched paraffins;  
but also has other negative effect which originates from their  
higher boiling point and under engine incomplete  
combustion some of them can be exhaust gases or can be  
condensed droplets from unburned fuel (2). From this point  
of view it is very important to know what type of  
hydrocarbons contain diesel fuel branched or long chain  
hydrocarbons. Cetane number and molecular composition of  
petrodiesel properties was done by gas chromatography (3),  
Other important parameter used in fuel quality is cetane  
number which depends from organic structure of molecules  
and can be in correlation with molecular structure of  
hydrocarbons but from cetane number is not possible to  
know more details about type of hydrocarbons. Most of  
methods used in cetane number determination are expensive  
and time consuming but using this cetane number is possible  
to know molecular structure of fuel hydrocarbons (6).  
Cetane Number has minimum legislative limit, but not the  
maximum, based on European Commission legislation.  
Cetane number, combustion level and PM emissions are in  
strong correlation between and as a conclusion high cetane  
number provide complete and faster combustions and lower  
PM emissions (7, 17). Our research group proposed FTIR-  
spectroscopy application which has a lot of benefits  
compared with other methods for the reason that it does not  
need any sample preparation, it does not use any hazardous  
chemicals, the cost analysis is cheaper and FTIR-  
Spectroscopy known as green but also as fast and sensitive  
method of analysis. FTIR spectroscopy was applied in order  
to estimate structural information of hydrocarbon molecules  
present in coal using single wavenumber and using ratio of  
frequencies from asymmetric stretching vibrations of  
2 3  
CH /CH ratio (8, 18). Cetane number is one fuel parameter  
which corresponds with ignition delay, but in general this  
depends on the type of hydrocarbons content in fuel. Similar  
application in coal sample characterization was reported  
Corresponding author: Flora Ferati, Department of Technology, University of Mitrovica “Isa Boletini” Ukshin Kovaqica,  
Mitrovica, 40000, Kosovo. E-mail: flora.ferati@umib.net.  
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Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
about using same ratio of frequencies to find branched  
aliphatic degree and long chain side of hydrocarbons (9).  
They found correlation between intensity ratio and type of  
hydrocarbons (long or short chain and branched degree) as  
follows:  
For comparison between branched and long chain  
compounds was used two standard compounds one as a long  
chain aliphatic compounds was used hexadecane >99 %  
Sigma-Aldrich (below STD1) and isocetane as highly  
branched alkane reference compound 2.2.4.4.6.8.8-  
heptamethylnonane Sigma-Aldrich, 98 % (below STD2).  
The assignment of bands was done by comparison with  
literature spectral data and with reference compounds  
spectra included in the software spectral library. Height and  
area of each band were measured and calculated by the  
essential FTIR software. Cetane Number were determined  
according to the standard methods EN ISO 5165 method  
(11).  
Decrease or lower ratio- High level of branched degree  
or shorter aliphatic chain  
Increase or high ratio-Longer aliphatic chain of alkanes  
are present or less branched.  
Other authors’ reports about other ratio combinations  
that determine the branched degree of alkanes following  
1376/(A1376+A1460) apply in oils from reservoirs (10). The  
A
intensity of this ratio is in correlation with branched degree  
of hydrocarbons which means that high intensity of this ratio  
corresponds with the highest branched hydrocarbon  
structure. There are published reports about the use of the  
ratio of frequencies, but not directly about fuel analysis and  
their usage as indicators for type of hydrocarbons which still  
remain unclear. Novelty of this proposed method is the  
promotion of FTIR-Spectroscopy as an alternative method  
of cetane number determination and to give information  
about type of hydrocarbons. This FTIR offers opportunities  
to detect the type of hydrocarbons branched or long chain  
which is sufficient information for monitoring contaminants  
in air and their origin of contamination. The aim of this  
research is to optimize FTIR-Spectroscopy method by using  
those two types of ratio frequencies from two different IR  
region of methyl and methylene vibrations. Challenge is to  
determine exact type of hydrocarbons in petrodiesel samples  
present in different diesel fuels from 5 different brands of  
fuel companies around Kosovo in comparison with cetane  
number as a standard method.  
3 Results and Discussion  
Based on reported results (Table 2a) sample number 4  
has higher cetane and also based FTIR results has similarity  
in ratio 2925/2954 and conclusion is they are not different  
which means their chemical structure is very similar between  
standard long chain molecule and real analyzed sample.  
From this point of view higher cetane number are in  
correlation with long chain aliphatic molecules. All other  
analyzed petrodiesel samples are classified as different  
compared with standard long chain compound because  
relative difference is higher than 10 %. Same samples were  
analysed by FTIR Spectroscopy and all results were  
compared with branched aliphatic standard compound  
results presented in Table 2b, relative difference is lower  
than 10 % classified as Not Different chemical structure  
except in sample 4 where relative difference is higher than  
10% and it is classified as different chemical structure.  
Conclusion based on a standard compounds was confirmed  
from both compounds long and branched aliphatic  
compounds and based on this sample 1,2,3 and 5 contain  
branched aliphatic compounds and only sample 4 has long  
aliphatic chain molecules. In Figure 1 are shown scanned  
FTIR spectra of petrodiesel compounds and their  
characteristic band of methylene and methyl vibrations of  
hydrocarbon molecules and in Table 1 are presented group  
frequencies for crucial type of vibrations in petrodiesel  
samples. Ratio I was used to compare standard analyzed  
compounds and both reference compounds and sample 4 has  
similarity with STD1 or long chain aliphatic compounds and  
all other samples has similarity in intensity ratio with STD2  
or branched aliphatic reference compounds Figure 2.  
2
Experimental  
2
.1 Samples and applied Measurements  
Diesel fuel purchased from local and international  
brands in Kosova were used and analyzed by FTIR-  
Spectroscopy. An Irrafinity-1 Shimadzu FT-IR  
spectrophotometer equipped with a deuterated triglycine  
sulfate (DTGS) detector was used to acquire FT-IR spectra.  
Fuel sample were deposited between two CaF transparent  
2
-
windows. All spectra were recorded from 4000 to 1000 cm  
1
and processed using IR-Solution Software for Windows  
(
Shimadzu). After each operation, the CaF window was  
2
thoroughly cleaned up, washed with acetone and then dried.  
Table 1: Selected FTIR spectra peak frequencies in petrodiesel (12).  
-
1
Functional Group  
Region (cm )  
3010~3080  
2950~2975  
Intensity*  
Comments  
Str.  
asym.str.  
sym.str.  
asym.str.  
sym.str.  
Str.  
asym.def  
sym def.  
acissors vib.  
Ar‒H  
m
m-s  
m
m-s  
m
w
m
m-s  
m
CH  
3
2
865~2885  
2915~2940  
840~2870  
2880~2890  
1440~1465  
CH  
2
2
CH  
CH  
3
1
370~1390  
1440~1480  
CH  
2
*w = weak; m = medium; s = strong; vs = very strong; v = variable; asym= asymmetric; str.= streching  
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