**4. Gasification**

Gasification is a well-established process for the conversion of many non-renewable sources, like petroleum resids, petcoke or coal. In general, it can process any carbonaceous material into a valuable mixture of hydrogen, carbon monoxide and carbon dioxide – called syngas (synthetic gas). Syngas itself is a source of hydrogen and carbon monoxide used for various chemical processes or as fuel when separated into pure streams, or as a high calorific fuel or feedstock for chemical synthesis into other chemicals, like methanol, ethylene glycol, acetic anhydride and hydrocarbons (via Fischer-Tropsch synthesis) when not separated. Examples of syngas applications are presented in **Figure 5**. As polyolefins consist of carbon and hydrogen, these can be very good feedstock for gasification.

#### **4.1 Gasification reaction**

Gasification is a complex process with several reactions taking place between carbon-based material, oxygen and steam at high temperatures (700–1500°C). Examples of reactions that take place during gasification are presented in **Table 3**.

The hydrogen to carbon oxide ratio in obtained syngas varies significantly (from 0,7 to 6 for different fossil fuels) depending on the type of the raw material and technology. For different applications, different ratios are required. It is technically possible to obtain every required syngas composition from every feedstock, but it has economic limitations [28].

#### **Figure 5.**

*Overview of potential syngas applications [28].*


#### **Table 3.**

*Examples of gasification process reactions [28].*

#### **4.2 Gasification of plastic waste**

Polyolefin waste is potentially a very good source of carbon for gasification. What is more, as biomass and other plastic wastes are also reach in carbon, mixed wastes streams can be used. Gasification of waste has the following steps: drying, pyrolysis, cracking and reforming, char gasification. Drying of plastics has an insignificant role but might be important when plastics are processed with biomass, unlike the pyrolysis step, which is key in the gasification of plastics. The poor heat conductivity, sticky nature, high content of volatiles created during pyrolysis of polyolefins, and relative low char and high tar yields make the process different from coal or biomass gasification challenging but also promising. Air and steam gasification processes are proposed with different pros and cons. Finally, co-gasification with fossil-based feedstock or other waste streams is possible, expanding the flexibility of the process. The variability of quality and composition of the feedstock is a significant problem [40].

Gasification seems to be a promising alternative to pyrolysis for chemical recycling of plastic waste, which can produce chemicals or fuels without detailed *Chemical Recycling of Polyolefins (PE, PP): Modern Technologies and Products DOI: http://dx.doi.org/10.5772/intechopen.99084*

separation and washing of the feedstocks. It is attractive due to the versatility of potential products. On the other hand, it is related to high capital and operational costs [41]. What is more, currently, only fuels are produced, which might be related to instability of the waste streams, which may cause problems with keeping proper hydrogen to carbon oxide ratio.

Canadian company Enerkem provides the most advanced waste pyrolysis technology. The company currently operates a commercial (TRL 9) plant in Edmonton with a capacity of 38 000 m3 /a of methanol and ethanol used as a fuel. Another plant in Canada for fuels and chemicals production with a capacity of 125 000 m3 /a is under construction, and two more projects with capacities of 270 000 m3 /a of methanol each are developed currently in Europe [42]. Ebara Environmental Plant and Ube Industries from Japan provide gasification of plastic waste through partial oxidation by oxygen and steam. 70 000 tons of plastic waste is processed at Showa Denko's Kawasaki Plant since 2003. Currently, a feasibility study for the next plant in South Korea is being processed [43].
