Styrene Lab Report

CHAPTER 1

1.1 Chemical reactions with descriptions of starting raw materials

Ethylbenzene will undergo catalytic dehydrogenation to produce styrene. The dehydrogenation reaction of ethylbenzene is an endothermic and reversible reaction. The optimum temperature for the reaction to occur is 590℃ to 650℃ and pressure of 200 mmHg or slightly above atmospheric pressure (Meyers, 2004). The required catalyst is potassium-promoted iron oxide in the presence of steam. The dehydrogenation process can be represented by the following chemical reaction:

The main by-products produced from the dehydrogenation of ethylbenzene are benzene and toluene, which can be represented by the following chemical equations:

The starting raw materials for

The first step is to form ethylbenzene from alkylation of benzene with ethylene. Then ethylbenzene is dehydrogenated to form styrene (final products). In the industrial process, the first stage is the formation of ethylbenzene. In the main reactor, alkylation process of benzene undergoes in the presence of an aluminium chloride (AlCl3) catalyst complex. In the convention of the AlCl3 process, three phases are present in the reactor. They are aromatic liquid, ethylene gas, and a liquid catalyst complex phase. Dry benzene, recycled polyalkylbenzenes and some catalyst complex are continuously fed to the reactor. Agitation occurs to disperse the catalyst complex phase in the aromatic phase. Ethylene and the catalyst promoter (HCl) are introduced into the reactor through sparges and effectively all ethylene is converted into ethylbenzene. Low ethylene and high benzene ratios are used in order to give desired yield of ethylbenzene. Most commercial plants operate at the ratio if 0.3-0.35 because as the ratio increased, more side reactions will occur such as transalkylation and isomeric rearrangement. Further alkylation of ethylbenzene will leads to formation of polyalkylbenzenes. The loss in net yield can be recovered by recycling the material to the alkylation

To produce pure styrene, it must undergo distillation process through 3 towers which are under low temperature and vacuum condition (low pressure to reduce boiling point) to reduce polymer formation of styrene (Inc, 2016). Firstly, benzene and toluene are removed. Toluene is sent to toluene dehydrogenation plant to remove toluene for sale while benzene is being recycled. The feed then enters the second distillation tower which is below 100°C where unconverted ethylbenzene is separated and recycled in the reactors. In the third distillation tower (<20°C), styrene is distilled away from tars. The organic phase must be transported completely and non-stop into the distillation column under vacuum which works at 20m bar. The motor driven control valve is used to check the pressure difference which is adjusted automatically or by manual control inside the distillation column (Behr, 2005). Styrene can be polymerized easily, therefore inhibitor is added. In this case, 4-tert-butylcatechol (TBC) inhibitor is added by pump inside the third distillation tower. The distillation tower contains a structured packing of stainless steel mesh which is tantamount to 36 theoretical plates. Ethylbenzene and styrene, both are having similar boiling points, require 70–100 trays for their separation. Since styrene and ethylbenzene almost have similar boiling points, their