Modelling and optimisation of oxidative desulphurization process for model sulphur compounds and heavy gas oil. Determination of Rate of Reaction and Partition Coefficient via Pilot Plant Experiment; Modelling of Oxidation and Solvent Extraction Processes; Heat Integration of Oxidation Process; Economic Evaluation of the Total Process.

摘要

Heightened concerns for cleaner air and increasingly more stringent regulations onudsulphur content in transportation fuels will make desulphurization more and moreudimportant. The sulphur problem is becoming more serious in general, particularly foruddiesel fuels as the regulated sulphur content is getting an order of magnitude lower,udwhile the sulphur contents of crude oils are becoming higher. This thesis aimed touddevelop a desulphurisation process (based on oxidation followed by extraction) withudhigh efficiency, selectivity and minimum energy consumption leading to minimumudenvironmental impact via laboratory batch experiments, mathematical modelling andudoptimisation.udDeep desulphurization of model sulphur compounds (di-n-butyl sulphide, dimethyludsulfoxide and dibenzothiophene) and heavy gas oils (HGO) derived from Libyan crudeudoil were conducted. A series of batch experiments were carried out using a small reactorudoperating at various temperatures (40 ¿ 100 0C) with hydrogen peroxide (H2O2) asudoxidant and formic acid (HCOOH) as catalyst. Kinetic models for the oxidation processudare then developed based on `total sulphur approach¿. Extraction of unoxidised andudoxidised gas oils was also investigated using methanol, dimethylformamide (DMF) andudN-methyl pyrolidone (NMP) as solvents. For each solvent, the `measures¿ such as: theudpartition coefficient (KP), effectiveness factor (Kf) and extractor factor (Ef) are used toudselect the best/effective solvent and to find the effective heavy gas oil/solvent ratios.udA CSTR model is then developed for the process for evaluating viability of the largeudscale operation. It is noted that while the energy consumption and recovery issues couldudbe ignored for batch experiments these could not be ignored for large scale operation.udLarge amount of heating is necessary even to carry out the reaction at 30-40 0C, theudrecovery of which is very important for maximising the profitability of operation andudalso to minimise environmental impact by reducing net CO2 release. Here the heatudintegration of the oxidation process is considered to recover most of the external energyudinput. However, this leads to putting a number of heat exchangers in the oxidationudprocess requiring capital investment. Optimisation problem is formulated usingudgPROMS modelling tool to optimise some of the design and operating parameters (suchudas reaction temperature, residence time and splitter ratio) of integrated process whileudminimising an objective function which is a coupled function of capital and operatingudcosts involving design and operating parameters. Two cases are studied: where (i) HGOudand catalyst are fed as one feed stream and (ii) HGO and catalyst are treated as two feedudstreams.udA liquid-liquid extraction model is then developed for the extraction of sulphurudcompounds from the oxidised heavy gas oil. With the experimentally determined KPudmulti stage liquid-liquid extraction process is modelled using gPROMS software and theudprocess is simulated for three different solvents at different oil/solvent ratios to select the best solvent, and to obtain the best heavy gas oil to solvent ratio and number ofudextraction stages to reduce the sulphur content to less than 10 ppm.udFinally, an integrated oxidation and extraction steps of ODS process is developed basedudon the batch experiments and modelling. The recovery of oxidant, catalyst and solventudare considered and preliminary economic analysis for the integrated ODS process isudpresented.