# Utilization of Polymeric Materials toward Sustainable Biodiesel Industry: A Recent Review
## 3 Polymeric Catalysts
### Naturally Derived Polymeric Catalysts  
Naturally derived polymeric catalyst are natural polymers with a little modification that have the ability to catalyze the triglycerides transesterification and FFA esterification reactions. Those kinds of polymeric materials are considered as green, recyclable, and biodegradable catalysts. Despite being supportive for the green chemistry, the naturally derived polymeric catalysts are feasible economically since they are derived from low-cost feedstocks. Chitosan is one of the most abundant natural polymers. It can be extracted from marine crustaceans, insects, and fungi. Natural chitosan can be used as a catalyst for biodiesel production. The functionality of chitosan comes from hydroxyl and amino groups obtained from alkaline deacetylation of amide groups of chitin (poly(\(\beta\)-(1-4)-N-acetyl-D-glucosamine) [24; 72]). [PERSON] et al. [73] adsorbed Cu ions into chitosan to synthesize CCu catalyst which was employed on babassu oil under optimized reaction conditions to yield 76.8% biodiesel. However, the yielded biodiesel percentage was increased to 97% when chitosan immobilized with CaO and employed on soybean oil [74]. The increased thermal and mechanical stability of chitosan with supportive CaO may be the reason behind increasing biodiesel production once this basic polymeric catalyst was used in the transesterification reaction [24]. In contrast, other heterogenous acidic catalysts were successfully synthesized from natural chitosan. Sulfonic group -SO\({}_{3}\)H was inserted into chitosan structure once the sulfosuccinic acid (SSA) was crosslinked into chitosan. The new polymeric composite successfully yielded 89% of palmitic acid under optimized parameters [75]. HTCC/Na\({}_{2}\)SiO\({}_{3}\)/ECH catalyst was synthesized by interlinking sodium silicate Na\({}_{2}\)SiO\({}_{3}\) and chitosan chloride (HTCC) with epichlorohydrin (ECH). The nanoparticles composite of Na\({}_{2}\)SiO\({}_{3}\) formed bridge to chitosan which led to increase the catalytic activity and biodiesel yield to 97% from soybean oil [76]. Beside chitosan, alginate is another naturally occurring biopolymer derived from brown seaweeds and marine algae [77]. With a little modification, alginate have been used to catalyze esterification/transesterification reactions toward biodiesel production. [PERSON] et al. [78] synthesized ferric alginate to esterify lauric acid. They obtained 99% conversion percentage of methyl laurate. More interestingly, [PERSON] et al. [79] prepared Tin (Sn\({}^{2+}\)) alginate catalyst to esterify oleic acid with conversion efficiency 98.7 and reusability possibility till the eighth cycle with 97.6% efficiency. Cellulose is another naturally occurring polymeric material sourced from plants wood that can be used in biodiesel catalysis. In addition to the availability and feasibility, other characteristics, e.g., biocompatibility, modification suitability, and porosity, make cellulosic materials high featured catalysts [24]. CB-(AST-HPW) catalyst was synthesized from porous cellulose beads. The catalyst successfully esterified 96% of yellow horn oil under optimized conditions with 70% efficiency after seventh cycle [80]. Cellulosic nanocomposite was modified and subjected to magnetic adsorption of hybrid organic/inorganic acids to produce sulfonated cellulose-magnetic nanocomposite (MSNC) catalyst. The cellulosic nano-catalyst had an efficiency to esterify 96% of oleic acid in the first run and 95% in the fifth cycle [25]. Enzymes are also considered naturally derived catalysts. Lipase enzyme is widely used as a catalyst for biodiesel production. It is usually extracted from the activity of living things. Recently, lipase was immobilized onto polymeric and inorganic materials to increase the efficiency and decrease the costs of lipase extraction [24]. Lipase PS was extracted from species _Burkholderia cepacia_ and capsulated inside \(\kappa\)-carrageenan biopolymer. Then, it was used as a catalyst for the palm oil transesterification reaction.