There was continued interest within the exploitation of the world’s petroleum residues for reasons associated to each economic and market forecasts as well as causes of national curiosity to those nations wherein the residues are generated and accumulated. The petroleum residue is a possible supply of artificial fuels and valuable chemicals. With a purpose to successfully use these petroleum residues, it is critical that they be upgraded. Several options are available to accomplish this upgrading. Catalytic upgrading of the residue is necessarily costlier because of the upper catalyst and hydrogen consumptions. Usually, some hydro-processing shall be required to eventually produce finished products however the high funding and operating prices of hydro-processing could be mitigated by the introduction of non-catalytic processes to upgrade residues [Bello, et. al., 2001]. Among the upgrading processes, delayed coking is more important due to its low investing and operating prices, broad feed inventory applicability and excessive conversion [Elliot, et. al., 1981]. Delayed coking is a severe form of thermal cracking during which the viscosity and pour point of the liquid hydrocarbon base material is permanently lowered after it has been subjected to extreme temperature for a time frame at comparatively low stress under inert condition.
A number of investigators Jiazhi, et. al., 2002a; Zacheria, et. al., 1982; Bonila, 1982; Jiazhi, et. al., 2002b] have reported the outcomes of deasphalting and thermal conversion of Athabasca oil sands, Arabian heavy crude, Orinoco heavy crude, Lloydminster heavy oil, Loda (Nigeria) tar sand and Marguerite lake bitumen as feedstock beneath variety of working situations. For the reason that petroleum residue characteristics differ drastically from one area to a different, delayed coking application issues and options also differ. Process conditions which might be efficient in a single system usually are not at all times successful in others as a result of most purposes are these developed for tar and oil sand bitumen and not from petroleum derived fluids or petroleum primarily based fractions.
While the problem of delayed coking upgrading has been addressed by numerous research [Bello, et. al., 2001; Ukwuoma, 1993; Elliot, et. al., 1981; Schucker, 1983; Zacheria, et. al., 1982; Bonila, 1982; Jiazhi, et. al., 2002b], info relating delayed coking product spectrum to Nigerian petroleum residue traits shouldn’t be out there. Such info may foster design concepts and optimization methods for utilizing a vast accumulation of petroleum residues in all the nation’s refineries. The current work tries to offer a greater description of the conversion of Nigerian petroleum refinery residue to synthetic fuels and chemicals using delayed coking reactor system at varied operating circumstances. The effect of course of variables corresponding to temperatures, response time and chemical additives on the natural liquid product (OLP) yield and kinetics was studied.
Materials AND Methods
The vacuum residue of Nigerian medium gravity crude was used in this examine. The bodily properties of the residue are given in Desk 1. Detailed procedures for characterizing the residue has been reported elsewhere [Bello, et. al., 2001].
The experimental elements of the current study consist basically of (a) thermal conversion of the residue with methanol-potassium hydroxide and methanol followed by (b) chromatographic evaluation of the samples of the merchandise obtained from the thermal upgrading experiments.
Gear and Experimental Procedure
The thermal conversion of the petroleum residue was studied in a delayed coking reactor system with additive focus and additive-to-residue ratio been different. The system is comprised of the following elements; reactor and transport, a trapping and analyzing. This reactor was used to thermally crack the petroleum residue, which was adopted by upgrading with the additive techniques. The reactor was manufactured from 316 stainless steel tubing, 50mm in inside diameter enclosed in a much bigger cylindrical pipe of about 80mm in outdoors diameter. The tubular vessel and its larger enclosure were each held in place by a flange of 80mm outside diameter with 19.1mm thickness. The annulus consists of an electric heater capable of heating the feed pattern to the desired temperature. Here, underneath precise temperature control, the desired sample cracking can be achieved. The carrier gas, which is nitrogen gasoline, transports the cracked pattern to the shell and tube condenser. It has been demonstrated that the residence in the reactor doesn’t fluctuate by more than ±10% [Jiazhi, et. al., 2002a]. The reactor is able to being operated at temperatures of as much as 600ºC and at residence time of zero to a hundred and twenty minutes. The merchandise of thermal conversion are cooled in a shell and tube condenser, collected, characterized and analyzed utilizing analytical equipment. The schematic diagram of the experimental setup is shown in Figure 1.
The experimental runs have been carried out at low pressure in a batch response system operated within the temperature vary of 200-6000C and residence time of 30 to one hundred twenty minutes. In a typical run, the petroleum residue was fed into delayed coking reactor. Prior to delay cooking conversion course of, the Nigerian refinery fuel oil was purged with nitrogen within the reactor for 10 minutes to take away residual oxygen. The Nigeria refinery gas oil was heated at 8000C/s to response temperatures between one hundred and 6000C and maintained at that temperature for 30 to 120 minutes. Using a shell and tube condenser, the resulting gaseous product stream was condensed and colleted in a vessel. On the conclusion of each run, the yields were measured. For some experiments, the Nigerian residue samples charged into the reactor was dosed with assorted amounts of methanol and alcoholic potassium hydroxide loading and additive-to-residue ratio. A T-shaped agitator was used to realize correct mixing throughout response to make sure uniformity of response. The procedure was repeated for every 30 minutes, until the whole residence time for every isothermal operation was one hundred twenty minutes. The gaseous product steam was passed by means of a condenser and the liquid product collected.
The liquid product had a single homogeneous section, and a few of those product samples have been distilled at 2000C and 172 Pa utilizing a Buchi GKR-56 distillation unit. No residue was noticed after this distillation. This exhibits that substantial cracking of the non-risky fraction of the petroleum residue had occurred during the upgrading course of. Subsequently, all different liquid products have been directly analyzed by a gas chromatography (Carle GC-500) with a banded non-polar (methyl silicone) 50m x zero.2mm i.d. capillary column and a flame ionization detector (FID). The compounds present within the liquid product had been identified by using commonplace compounds and by GC-MS (Finningan/MAT-4500). The full weight of each part class of the distillate was determined from the share of each element class in the entire products collected.
Thermal Upgrading of the Petroleum Refinery Gasoline Oil within the Delayed Coking Reactor
The petroleum residue samples were tested on the apparatus and delayed coking assessments were performed for every petroleum residues at eight reaction temperatures (250, 300, 350, 450, 500, 550, and 600ºC). The outcomes reported listed below are averages of a minimal of 4 assessments carried out per petroleum residues at each reaction temperature. The product yields are listed in Desk 2. The product yields from exams performed at 4000C temperature had been repeatable as illustrated by the standard deviation of the measured gentle oil given in Table 2. The standard deviation was between 0.2 and 4.0% and was usually less than 2.0%. Approximately 0.5% of this variation may be because of the accuracy of the steadiness used to find out the yields.
Experiments were carried out also to study the characteristics of solid and liquid merchandise obtained from eleven samples of petroleum residues with totally different properties (specific gravity, obvious viscosity, pour point, sulfur content material, and so forth) have been used as feed. Various physical traits of the liquid product obtained through the thermal remedy of petroleum residues are additionally introduced in Tables 2 and 3. A comparability of the physical properties of complete petroleum residues and liquid product derived from thermal upgrading of petroleum residues reveals that the viscosity and density of liquid product had been lower than those of the unique petroleum refinery gasoline oil. Chemical composition of the liquid product obtained during thermal treatment of petroleum residues is presented in Desk four. The liquid product consisted of 49.1 wt% aliphatic hydrocarbons, 23.5 wt% aromatic hydrocarbons, and 12.Four wt% naphthenic hydrocarbons, other than minor fraction of phenols, ketones, alcohols, acids and esters. For a given treatment time, the 2 products yields elevated with remedy temperature, the results are proven in Figures 2 and 3. The noticed pattern of the yield confirmed that rising the therapy temperature and time might enhance the yield of the two products.
Effects of Additive System and Additive-to-Residue Ratio on Product Characteristics and Reaction Kinetics
The relative proportions of the merchandise spectrum obtained from with using methanol and methanolic potassium hydroxide mixture at numerous solvent-to-residue ratios used are as proven in Table 4. For the 2 additive programs, the proportion of the aromatic compounds improve with increasing ARR. However, the share is larger at each stage obtained with methanolic potassium hydroxide mixture than within the methanol system. This could also be as a result of the truth that these chemicals had undergone cracking reaction involving rupture of carbon-carbon bonds yielding lighter hydrocarbons Nonetheless, since an aliphatic content material of lower than forty.0wt% was reported for the petroleum residue used [Bello, et. al., 2001], the trend should be attributable to methanol enhancing impact involving the seize of carbon species by free radical created during the delayed coking reaction. The excessive yield of aliphatic hydrocarbons within the presence of methanol and potassium hydroxide strongly indicate these additives to be promoters of the cracking reaction. This is likely to be resulting from the fact that there was elevated response on account of addition of methanolic potassium hydroxide aiding decomposition of petroleum residue pattern.
It would even be on account of the truth that alcohol and potassium hydroxide present the opportunity for chemical reaction through the conversion due to the nucleophilicity of the alcohol hydroxyl group and the tendency of the alcohol to act as a hydrogen donor. It’s thought that such methanol enhancing effect could involve the seize of carbon species by free radial created throughout the delayed coking cracking reaction. This outcomes in the return of more cracked liquid reactant fraction to the vapor section. Thus, the methanol gives a better share of aromatic hydrocarbons than methanolic potassium hydroxide, probably resulting from its larger selectivity in the direction of aromatics. The results of feed conversion and distillate yields as features feed properties, various methanol and potassium hydroxide concentrations and ARR at reactions temperatures and time of 400ºC and a hundred and twenty minutes respectively are as presented in Table 4. Within the absence of methanol the yield of coker distillate elevated as coking temperature was elevated from 100oC to 500ºC, at 250ºC no appreciable change in the yield of coker distillate was noticed for petroleum residue samples containing as much as 5 % methanol.
Figures 4 shows the result of kinetic analysis of the process response, with the conversion for given reaction temperatures and concentrations plotted as a features of time. The degree of the conversion reaction was observed to rely on the response focus and temperature. The upper conversion from the progress of reaction plots is that noticed when 24% methanol was added. Figure four also exhibits the effect of initial focus of methanol on the speed of conversion of the petroleum residue to hydrocarbons. As might be seen, the methanol has comparatively excessive effect on the overall conversion course of. It’s thought that such methanol enhancing effect may contain the seize of carbon species by free radical created throughout the delayed coking reaction. This results within the return of more cracked liquid reactant fraction to the vapor section. The reaction price data obtained in this study have been analyzed using first-order reaction mannequin. This model is the one which greatest suits the result of previous staff for the kinetics of heavy oil conversion course of. The current study confirms this mechanism. Arrhenius plots for the rate constants obtained from the least-sq. regression utilized to the database is shown in Determine four. Activation power of 24.5Kcal/mol was obtained. Efficiency of the petroleum residues thermal course of enhance with the rise in temperature and preliminary potassium hydroxide concentration. A conversion process effectivity of 70% was achieved at operating temperature of 500ºC, 24% methanol and 0.6M potassium hydroxide. On the premise of the kinetic research and outcome presented the knowledge of the conversion kinetic will facilitate the design of effectively operating delayed coking batch reactor. Also, limitation in the equipment used on this examine did not permit finishing up the method below continuous conditions. Such work should be undertaken if the method is to be absolutely evaluated for doable industrial utility of petroleum residues thermal conversion course of.
The exploratory research of upgrading Nigerian petroleum residue in a delayed coking reaction system has indicated that it’s sensible to produce high quality liquid products by delayed coking of the petroleum residue at excessive temperature and low stress with chemical additives. Outcomes obtained from the experimental work reveals that working temperature, residence time, additive concentration loading and additive-to-residue ratio have important influence on the effectivity of petroleum residue to fuels and chemicals. The OLP and aromatic hydrocarbon selectivities adopted the order methanolic potassium hydroxide > methanol > no additive. High Previous and aromatic hydrocarbon selective for methanol potassium hydroxide had been as a consequence of methanol enhancing effect involving the seize of carbon species by free radical created throughout the delayed coking reaction.
The OLP yield was most at 350ºC and a maximum fraction of 83 wt% of OLP consisted of aromatic hydrocarbons using two methanol-potassium hydroxide at optimum reaction temperature and a residence time of two hours. The OLP obtained with out methanol additive consisted of a higher fraction of aliphatic hydrocarbons whereas that with methanol-potassium hydroxide mixture contained more aromatic hydrocarbons. The OLP yield was approximately ¼ of the petroleum residue with 83wt% selectively for aromatic hydrocarbons. Higher residence time was fascinating for high OLP yield in all the three thermal conversion instances. Subsequently, it’s endorsed that an analysis of this process under continuous mode could also be carried out.
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