Conditioning of waste cooking oil for bioethylene production

Abstract

The cracker is the unit where ethylene and polyethylene, among other products, are produced. The conventional cracker unit has had a feed that comes from crude oil, the main raw material being naphtha, but it is a non-renewable source. For this reason, the aim is to reduce the amount of traditional raw material and add one that is recycled and also comes from a renewable source, such as used cooking oil (WCO). The main disadvantage of using WCO as a raw material is the limitations that the feed has to be processed by the cracker, as the restrictions are aimed at reducing the poisoning of the catalyst present in the cracker, at reducing corrosion, and also at reducing the formation of coke, as if the amount deposited is considerable, the cracker must be stopped. Therefore, it is necessary to develop a pre-treatment to reduce the components limited by the cracker and for this reason, the present project is developed with the objective of developing a process for the pre-treatment of second-generation vegetable oil (called as WCO, waste cooking oil), so that such raw material fulfils the requirements to be processed without limitations in the cracker unit to produce ethylene. To achieve the objective, the WCO has been characterised based on a literature search and with the oil characterised, the necessary pre-treatment operations can be selected to meet the specifications for the cracker feed. The pre-treatment must have operations that remove metals, chlorides, nitrogen, ash and solid particles, free fatty acids, phosphorous, oxygen and water. The processes selected to remove metals are degumming, bleaching, desalting, membrane extraction, ion exchange, and settling with skimming. The processes selected to remove chlorides are degumming, desalting, membrane extraction and settling with skimming. For the removal of nitrogen, they are deodorization and hydrotreating. For the removal of ash and solid particles, the processes are degumming, desalting, membrane extraction and settling with skimming. Free fatty acids are removed by degumming and deodorization. Phosphorus is removed by degumming, bleaching and desalting. Oxygen is removed by bleaching, deodorization and hydrotreating. Finally, to remove water there are the processes of degumming, deodorization, desalting and settling with skimming. The future steps for the development are to check experimentally if the proposed pre-treatment is enough to achieve the requirements of the cracker, furthermore, experimentation will give a clearer picture and it is preferable to do this before industrial scale-up. In addition, an economic study should be carried out to check whether or not the pre-treatment process is viable with the proposed processes. Furthermore, the economic study together with the experimental verification will allow to decide whether all the operations are necessary or not, as the components can be removed by different processes. On the other hand, the economic viability is favoured by the use of processes that are well known in petroleum refining such as desalting, membrane extraction and hydrotreatment.