Cetane Number Improvement of Distilled Diesel from Tawke Wells

The current research aims to improve the cetane number of diesel extracted from the crude oil of Tawke region in Iraqi Kurdistan. A specific mixture of chemical compounds was prepared which included m-nitrophenol, 4-nitro toluene, and nitrobenzene. The components' effects were investigated with regard to the cetane number, flash point, viscosity, and refractive index of diesel. The quantity of each compound mixed with diesel was prepared based on the statistical analysis of the experiment device (Box–Behnken Designs-BBDs). The tested mixture showed a good agreement and improvement of cetane and flash point and a very low effect on viscosity and refractive index. According to the statistical analysis, the main influence on cetane number and the flashpoint was from m-nitrophenol. The investigation showed that the best results were acquired from the samples of 25PPM 4nitro toluene and 50PPM m-nitrophenol with a cetane number of 65.3. The correlation and the interaction of the regression equation were linear with all cases. It is worth mentioning that all additives positively influenced the cetane number in the regression equation. The sulfur content was measured as well, and the obtained weight percentage of sulfur was 0.8404%. Keywords-diesel improvers; cetane number; flash point; viscosity


INTRODUCTION
Additives are mixed with fuel to improve its quality and to enhance its efficiency. This process is termed as mixing with fuel of the trace elements. Fuel in various forms like diesel and benzine does not perform well or reach the required international standards without improvers [1]. Therefore, the search for new improvers is in great demand. The utilizing of influential improvers is very essential in order to reach the requested mechanical and environmental standards [2]. In the past, attempts have been made to ignite fuel readily and thus upgrade ignition quality. Nitro compounds are commonly used as cetane number additives and such chemicals make the delay time of fuel ignition shorter and as a result the rate of knocking decreases [2]. Such additives can be utilized with bio-diesel, which commonly has low cetane number [3]. The cetane number is affected by physical and chemical properties of fuel such as density, viscosity, surface tension, and vaporization. The cetane number is also influenced by the molecular structure of fuel and additives [4].
number. The improvement of diesel properties like viscosity, flash point, density, cloud point, water content, and sulfur content were investigated in [10]. The Design of Experiment (DOE) to study any oil sample represents a significant part of chemo measurements (effects of chemicals on the yield). The universal benefit of DOE is to ensure that the conditions between any test parameters and their yield of the reactions can be evaluated dependably with low cost and exertion with an insignificant number of trials and less amount of chemicals. DOE can be isolated into a few subtopics, for example, confirming factors from an enormous arrangement of factors which is called screening structures, finding the impact of a blend organization on the reaction factors tended to blend plans, and discovering wellsprings of error in estimation frameworks. This leads to concocting ideal conditions inconsistent procedures (evolutionary operation), batch process (response surface methodology), or planning tests for ideal parameter estimation in numerical models (optimal design or optimization) [11]. Different statistical DOE models have been utilized to smooth out factors in the exploratory plan. Accordingly, this helps to select the impact of exploratory factors by conventional methodologies. Tests have been conducted with conscious changes of the specific boundaries. These assessments should be repeated to each boundary effect achieving a reliable number of runs [12].
Numerous studies have been carried out to study the extracted crude oil from the wells of Tawke region in Iraqi Kurdistan [13], but the investigation in crude oil and its components from the specific wells requires more investigations to reach the desired characteristics and to improve its properties. The tests described in the current paper were performed using a sample consisting of diesel mixed with a measured amount of m-nitrophenol, 4-nitro toluene, and nitrobenzene to aggregate the effect of those components on the diesel.

II. EXPERIMENTAL SETUP AND METHODS
The portable analyzer instrument SHATOX SX-100M was used as the main device to analyze the octane/cetane numbers and to determine cetane and octane number, while a device NCL 120 -CLEVELAND OPEN CUP FLASH POINT TESTER MANUAL120 ASTM D 92, IP 36, ISO 2592 was utilized for flash point temperature determination as shown in Figure. 1.  M-nitro phenol, 4-nitro toluene, and nitrobenzene supplied from Germany were used as received. Solutions of mnitrophenol, 4-nitro toluene, and nitrobenzene 50mL/L (PPM) were prepared in diesel and then were diluted to solutions according to Table I. The prepared solutions were covered by aluminum foil and kept in dark to avoid the photodegradation of the 13 samples. Diesel was brought from Tawke oil well distillery and was used as received. Different concentrations of improvers were prepared according to the needs of the experiments as shown in Table I. Table II shows the physicchemical properties of the additives.
It is essential to fit a logical model in order to depict the response directly in the test field by choosing the DOE. Generally, this model is suitable for illustrating a plane surface, as indicated by: where R is the response, βo is the constant term, βi represents the coefficients of the linear parameters, Xi represents the parameters, and ε is the irregular error or commotion to the response. On specific events, it is called the essential impacts model since it incorporates just the principle impacts of the factors as explained intensively in [14]. If the interaction between the parameters is contained, then the first-order model becomes: where βii indicates the quadratic coefficients of the variables and i < j.
Response Surface Methodology (RSM) was applied to identify the positive and negative effects of each factor. The experimental Box Behnken Design (BBD) was also utilized to select the number of required experiments for the present research as represented in [14,15]. The effect of cetane number was studied. All tests were carried out based on the experimental design that is derived from the Minitab16 program (version 2018) as in Table III, where the estimated exact cetane number and the quantities of the mixed additives are stated. Flash point, viscosity, and the refractive index were measured. The solutions were taken for each run according to the run order and levels as illustrated in Table III and Table I. The mixtures were then put aside for 24 hours in order to assure solubility. In each run, before testing, the mixtures were shaken well for total miscibility. The readings were taken from the octane meter and flash point temperature meter. All runs were performed at ambient temperature and on the same day to avoid any environmental effect on the outcome. III. RESULTS AND DISCUSSION Statistical analysis was employed to determine the effect of each additive and their interactions in order to indicate the best model. All models were studied. During the present study, the linear model showed the best agreement among other models and regression equations as in (1) and (2) were opbtained. The regression equation shows that all parameters have a positive effect on the cetane number. However, the effect is rational on octane number and flash point which means there is a negative effect from some additives. The effect of each parameter is determined by a factor in regression equations. Figure 2 demonstrated the relationship between the contour plot of the determined additives and cetane number, while Figure 3 showed the surface plot of the obtained additives and cetane number. The effect of the additives m-nitrophenol, 4-nitro toluene, and nitrobenzene on cetane number was positive. The greatest estimated impact was recorded from nitro phenol followed by 4-nitro toluene, and nitrobenzene by 0.3545, 0.0054, and 0.0035 respectively as shown in regression equation (1). The correlation between the parameters is very strong and equal to 98.92%. Table IV contains the coefficients and ANOVA parameters obtained from the current experiment, and Table V demonstrates the cetane numbers results from the tested samples.     Table VI illustrates the coefficients and ANOVA parameters estimated from the runs, whereas Table VII consists of the results of all tests with their run order. It is worth mentioning that the mixture flash point reaches the requirement of the international standards which is about 51-60 [17].

C. Effect of the Added Chemicals on Viscosity
The effect of the selected additives are exhibited in Figure  6. All additives had a negative effect on viscosity. This means that when the concentration of additives increased, viscosity decreased by the factors of -0.000080, -0.00044, and -0.00008 as shown in (5). Nevertheless, the effect is very weak.

D. Effect of the Added Chemicals on Refractive Index
The influence of the chosen additives is shown in Figure 7. M-nitrophenol, 4-nitro toluene, and nitrobenzene were studied with regard on their effect on the refractive index. The additives presented a very low impact on the refractive index which means their effect is negligible as shown in regression equation (6).

IV. CONCLUSION
The current statistical and experimental analyses have been performed to study the effect of three aromatic compounds as diesel cetane number improvers and their impact on flash point, refractive index, and viscosity of Tawke oil well diesel. Sample 6 gave the best result. To the best of our knowledge, no similar study has been conducted with the certain components to contrast the present outcome, however, many investigations to improve the cetane number of fuel have been performed including the transesterification and higher alcohol-diesel blends [17], the oxygenated compound for cetane number improvement di-n-pentyl-ether (DNPE) [18], and the ethanol with 2-ethyl hexyl nitrate (EHN) component [3].
Mixtures of additives were added to the diesel samples and were measured regarding the cetane number improvement and