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    Kinetic Study on a Commercial Amorphous Hydrocracking Catalyst by Weighted Lumping Strategy

    Sadighi, Sepehr, Ahmad, Arshad, Irandoukht, Akbar
    International Journal of Chemical Reactor Engineering, 2010, Vol.8(1) [Peer Reviewed Journal]
    Walter de Gruyter GmbH
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    Title: Kinetic Study on a Commercial Amorphous Hydrocracking Catalyst by Weighted Lumping Strategy
    Author: Sadighi, Sepehr; Ahmad, Arshad; Irandoukht, Akbar
    Publisher: De Gruyter
    Subject: Hydrocracking ; Vacuum Gas Oil ; Lump Kinetic Model ; Amorphous
    Description: Hydrocracking is an important upgrading process in the petroleum refinery, and it is generally used to process feedstocks ranging from vacuum gas oil (VGO) to vacuum residue. In this work, hydrocracking of VGO using a dual functional amorphous catalyst was carried out at a pilot scale unit under the following reaction conditions: liquid hourly space velocity (LHSV) from 1 to 1.5 hr-1 and reaction temperatures of 360-440°C at the constant pressure and hydrogen to oil, 156 bar and 1780 Nm3/m3, respectively. The effluent of the reactor was characterized to dry gas, naphtha, kerosene, diesel and unconverted VGO or residue. The pilot tests demonstrated that performing experiments beyond the temperature, recommended by catalyst vendor, lead the process to unstable hydrocracking. To describe the yield of hydrocracking products a five-lump discrete lumping approach with ten reactions was proposed. At first, the kinetic model contained twenty kinetic constants which were estimated by using the conventional objective function. The estimated parameters showed that the tendency of the catalyst to convert VGO to gas and naphtha was negligible whilst rate constants for hydrocracking of VGO to middle distillates were considerably high which was compatible with the nature of amorphous hydrocracking catalysts. After evaluating the magnitude of reaction rates and eliminating the ignorable constants, the network was reduced to six reactions in which only nine parameters were needed. The predictions indicated that the latter network could fit the yield of products more acceptable as if the average absolute deviation between experimental and calculated yields was descended from 16.25% to 12.6%. Then, to have a better prediction, a weighted objective function was used in which weight factors were calculated by a proposed weighted least square expression. The results confirmed that this approach could reduce average absolute deviation of model to 10.75%, and it created a fairly even distribution of deviation between hydrocracking products.
    Is part of: International Journal of Chemical Reactor Engineering, 2010, Vol.8(1)
    Identifier: 1542-6580 (E-ISSN); 10.2202/1542-6580.2193 (DOI)

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    4-Lump kinetic model for vacuum gas oil hydrocracker involving hydrogen consumption

    Sadighi, Sepehr, Ahmad, Arshad, Rashidzadeh, Mehdi
    Korean Journal of Chemical Engineering, 2010, Vol.27(4), pp.1099-1108 [Peer Reviewed Journal]

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    Comparison of Lumping Approaches to Predict the Product Yield in a Dual Bed VGO Hydrocracker

    Sadighi, Sepehr, Ahmad, Arshad, Shirvani, Mansoor
    International Journal of Chemical Reactor Engineering, 2012, Vol.9(1) [Peer Reviewed Journal]
    Walter de Gruyter GmbH
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    Title: Comparison of Lumping Approaches to Predict the Product Yield in a Dual Bed VGO Hydrocracker
    Author: Sadighi, Sepehr; Ahmad, Arshad; Shirvani, Mansoor
    Publisher: De Gruyter
    Subject: Hydrotreating ; Hydrocracking ; Lump Kinetic Model ; Hydrogen Consumption ; Dual Bed Hydrocracking Reactor
    Description: In this research, to predict the product yields of a pilot scale VGO hydrocracking reactor charged with mono functional hydrotreating and hydrocracking catalysts, two different four-lump models are developed. The first one, called combined bed model, is a simplex in which there is no boundary between hydrotreating and hydrocracking reactions through the reactor. The second one, called dual bed model, is a rigorous model in which hydrogen consumption and hydrotreating reactions are included. In this way, the reactor is subdivided into two different layers, so the effect of hydrotreating reactions on the hydrocracking section can be considered. Results show that the absolute average deviation (AAD%) of the yield prediction for the combined bed and the dual bed models are 8.23 percent and 5.87 percent, respectively. The main reason for the lower average deviation of the dual bed model is its higher accuracy to predict the yield of gas which is also the major advantage of this approach. However, the simplicity of the combined bed model can make it more applicable and attractive, especially when hydrogen consumption as well as sulfur, nitrogen and aromatic specifications of the feed and products are not accessible.
    Is part of: International Journal of Chemical Reactor Engineering, 2012, Vol.9(1)
    Identifier: 1542-6580 (E-ISSN); 10.1515/1542-6580.2519 (DOI)

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    Effect of Lump Partitioning on the Accuracy of a Commercial Vacuum Gas Oil Hydrocracking Model

    Sadighi, Sepehr, Ahmad, Arshad, Masoudian, Seyed Kamal
    International Journal of Chemical Reactor Engineering, 2012, Vol.10(1) [Peer Reviewed Journal]
    Walter de Gruyter GmbH
    Available
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    Title: Effect of Lump Partitioning on the Accuracy of a Commercial Vacuum Gas Oil Hydrocracking Model
    Author: Sadighi, Sepehr; Ahmad, Arshad; Masoudian, Seyed Kamal
    Publisher: De Gruyter
    Subject: Hydrocracking ; Lump Kinetic Model ; Vacuum Gas Oil ; Partitioning ; Separation
    Description: In an industrial hydrocracking plant, except to the reactor, the separation section can affect the accuracy of the developed mathematical model. In this study, two combined-bed six and seven-lump kinetic models for the hydrocracking of vacuum gas oil in a real refinery are developed and their accuracies for the prediction of product yields are compared. In the six-lump model, the engaged components are selected according to the actual products of the plant, but the seven-lump one is included of lumps which are partitioned based on the specified initial and final boiling points.For both approaches, a complete kinetic network with the catalyst-decay functions is considered. It is found that over a 17-month period of operation from the start of run, the average absolute deviation (AAD%) of the six-lump and the seven-lump models for the yield prediction are 20.51% and 5.21%, respectively for all products. Additionally, the sum of residuals for the seven-lump model has been appreciably decreased in comparison to the six-lump one. Therefore, it is confirmed that partitioning of the products to the lumps with specific boiling points can acceptably decrease the deviation of the prediction. So it is conclusive that including the operation of the separation section in commercial models can effectively increase the accuracy of the model and smooth the prediction error.
    Is part of: International Journal of Chemical Reactor Engineering, 2012, Vol.10(1)
    Identifier: 1542-6580 (E-ISSN); 10.1515/1542-6580.2616 (DOI)

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    6-Lump Kinetic Model for a Commercial Vacuum Gas Oil Hydrocracker

    Sadighi, Sepehr, Ahmad, Arshad, Seif Mohaddecy, S. Reza
    International Journal of Chemical Reactor Engineering, 2010, Vol.8(1) [Peer Reviewed Journal]
    Walter de Gruyter GmbH
    Available
    More…
    Title: 6-Lump Kinetic Model for a Commercial Vacuum Gas Oil Hydrocracker
    Author: Sadighi, Sepehr; Ahmad, Arshad; Seif Mohaddecy, S. Reza
    Publisher: De Gruyter
    Subject: Vacuum Gas Oil ; Hydrocracking ; Lump Kinetic Model ; Catalyst Life ; Isomax
    Description: A 6-lump kinetic model, including a catalyst decay function for hydrocracking of vacuum gas oil in a commercial plant, is proposed. The model considers vacuum gas oil (VGO) and unconverted oil, having boiling point higher than 380-°C (380+°C) as one lump. Other lumps are diesel (260-380-°C), kerosene (150-260-°C), heavy naphtha (90-150-°C), light naphtha (40-90-°C) and gases (40-°C) as products. Initially, a kinetic network with thirty coefficients is considered, but following an evaluation using measured data and order of magnitude analysis, mainly the route passes of converting middle distillates to naphtha lumps are omitted; thus the number of kinetic coefficients is reduced to eighteen. This result is consistent with the reported characteristics of amorphous catalyst, which has the tendency to produce more distillates than naphtha. By using catalyst decay function in the kinetic model and replacing days on stream with a noble term, called accumulated feed, the prediction of the final approach during 1.5 years is in good agreement with the actual commercial data. The average absolute deviation (AAD%) of the model is less than 5% for all main products. If the residue or unconverted VGO is considered, the error only increases to 6.94% which is still acceptable for a commercial model. The results also confirm that the hydrocracking of VGO to upgraded products is represented better by a second order reaction.
    Is part of: International Journal of Chemical Reactor Engineering, 2010, Vol.8(1)
    Identifier: 1542-6580 (E-ISSN); 10.2202/1542-6580.2164 (DOI)