**1. Introduction**

Oil palm, commercially named as Elaeis quineensis, is one of the main agricultural crops that thrives in a hot tropical climate. It produces vegetable oil fit for human consumption. As can be seen in **Figure 1a**, the tree is naturally brown and seed reddish in color because of a high betacarotene content. The oil palm industry has been conveniently quoted as the main sector producing abundant biomass as renewable sources in different forms; these include empty fruit bunches (EFB), mesocarp fiber (MF), palm shell (PS), oil palm fronds (OPF) and oil palm trunks (OPT). Palm oil industries face significant challenges in meeting the increasingly stringent environmental regulations on waste disposal.

Palm oil clinker (POC) is a waste by-product generated in one of the oil palm processing phases [1]. It is a residue from the heating zone of a steam boiler during electricity generation produced in huge amount from oil palm fibers and shells calcination in a suitable proportion of (30:70) at 100–850°C [2, 3]. It is subsequently cooled at air atmosphere [4].

Physically, POC shown in **Figure 1b** are naturally porous, flaky, gray in color, irregular in shape, lighter in weight, with rough and sharp broken surfaces [5, 6]. They are mostly presented as solid lightweight materials between the sizes of 2 and 15 cm [7]. POC is made up of inorganic oxides, 3.35% organic carbon and minerals like halite, lysite, eglestonite, elatossite, quartz and cristobalite [8]. Chemical oxides composition of POC highlighted in **Table 1** varies according to several factors. Some of these are: fiber to shell ratio, applied incineration process temperature, palm tree location soil condition, POC form (nano, powder, fine or coarse particle size) etc. [7, 12]. POC is a pozzolanic aggregate capable of producing appropriate attachment in a geopolymer matrix because of alumina-siliceous compounds presence [22]. It is no more news that, pore structure has a close association with the resistance of cement-based substances to fluid infiltration. These include, pore size distribution, interconnectivity and porosity [23].

Oil palm extraction rate has rapidly increased due to the increasing oil palm global demand [24]. As a consequence, fresh porous lumped POC is continuously

**Figure 1.** *(a) An oil palm tree and (b) palm oil clinker chunks.*


*Palm Oil Clinker as a Waste by-Product: Utilization and Circular Economy Potential DOI: http://dx.doi.org/10.5772/intechopen.97312*

> **Table 1.** *Chemical composition of POC.*

generated [25]. The produced POC in the boiler is mixed in suspension, moved from the combustion boiler, and deposited in the factory yard [13]. It is a solid waste product of little to no economic benefit that causes pollution of the atmosphere, soil degradation and ground water contamination [8]. In recent times, it is mostly dumped in landfills that not only causes soil pollution but go as far as contaminating ground water [26]. It is important to note that the continuous dumping activity would cause waste accumulation at the dump site and creates the need to allocate new disposal area. Continuous disposal would result in waste rack up at the dumpsite, necessitating the allocation of new space for landfills. This would have negative consequences for the environment as fertile land is converted into a refuse collection area [27].

Besides overcoming waste disposal problems, integrating low cost and environmentally-friendly waste materials in new and sustainable product development would help in environmental pollution control, appropriate land use and promoting sustainability [14, 28]. Therefore, reusing POC for different applications would assist in natural resources preservation, reduce greenhouse gas emission, pave way for proper consumption and producing cleaner environment [23, 29].

With the technological advancement, there is a need for a change in using traditional old materials for industrial applications. Raw materials used by industries are affecting the environment to a larger extent. There is a dire need to change the current scenario especially for developing countries [21]. To achieve the concept of green technology, many attempts have been carried out to develop low-carbon footprint products or techniques. Due to their high mechanical properties and environmental benefit, POC appear as a future prospective industrial material and have applications in different areas. This article reviews the physical, chemical and microstructural properties of palm oil clinker (POC) by-products of palm oil. It aims to give a comprehensive survey of already-well-established or future potential energy applications of POC. A critical comparison of their use in different area is reported and their modification by various physical and chemical routes is detailed. The new direction beyond the state of the art is the application of POC in Nano form. This is why only one [1] article is found in this chapter.
