{"references": ["M. Hassani, G. Amini, G. D. Najafpour, & M. Rabiee, \"A two-step catalytic production of biodiesel from waste cooking oil\". International Journal of Engineering, 26(6), 563, 2012.", "A. Banerjee, & R. Chakraborty, \"Parametric sensitivity in transesterification of waste cooking oil for biodiesel production\u2014a review\". Resources, Conservation and Recycling, 53(9), 490-497, 2009.", "A. Demirba\u015f, \"Biodiesel fuels from vegetable oils via catalytic and non-catalytic supercritical alcohol transesterifications and other methods: a survey\", Energy conversion and Management, 44(13), 2093-2109, 2003.", "A. Gashaw, A. Teshita, \"Production of Biodiesel from Waste Cooking Oil and Factors Affecting Its Formation: A Review\", International Journal of Renewable and Sustainable Energy. 3(5), 92-98, 2014.", "G. Labeckas, & S. Slavinskas, \"The effect of rapeseed oil methyl ester on direct injection diesel engine performance and exhaust emissions\", Energy Conversion and Management, 47(13), 1954-1967,2006.", "I. M. Atadashi, M. K. Aroua, A. A. Aziz, & N. M. N. Sulaiman, \"The effects of water on biodiesel production and refining technologies: A review\" Renewable and Sustainable Energy Reviews, 16(5), 3456-3470, 2012.", "A. K. Endalew, Y. Kiros, & R. Zanzi.\" Inorganic heterogeneous catalysts for biodiesel production from vegetable oils\", biomass and bioenergy, 35(9), 3787-3809, 2011.", "K. Watcharathamrongkul, B. Jongsomjit, & M. Phisalaphong, \"Calcium oxide based catalysts for ethanolysis of soybean oil\", Sonklanakarin Journal of Science and Technology, 32(6), 627, 2010.", "S. Gryglewicz, \"Rapeseed oil methyl esters preparation using h\u00e9terogeneous catalysts\", Bioresource Technology, 70(3), 249-253, 1999.\n[10]\tR. I. Kusuma, J. P. Hadinoto, A. Ayucitra, F. E. Soetaredjo, & S. Ismadji, \"Natural zeolite from Pacitan Indonesia, as catalyst support for transesterification of palm oil\", Applied Clay Science, 74, 121-126, 2013.\n[11]\tH. R. C. KambizTahvildari, & P. Mozaffarinia, \"Heterogeneous Catalytic Modified Process in the Production of Biodiesel from Sunflower Oil, Waste Cooking Oil and Olive Oil by Transesterification Method\", acad. res. int. 5, 60-68, 2014.\n[12]\tZ. Yaakob, M. Mohammad, M. Alherbawi, Z. Alam, & K. Sopian, \"Overview of the production of biodiesel from waste cooking oil\", Renewable and sustainable energy reviews, 18, 184-193, 2013."]}

Reduction of fossil fuels sources, increasing of pollution gases emission, and global warming effects increase the demand of renewable fuels. One of the main candidates of alternative fuels is biodiesel. Biodiesel limits greenhouse gas effects due to the closed CO2 cycle. Biodiesel has more biodegradability, lower combustion emissions such as CO, SOx, HC, PM and lower toxicity than petro diesel. However, biodiesel has high production cost due to high price of plant oils as raw material. So, the utilization of waste cooking oils (WCOs) as feedstock, due to their low price and disposal problems reduce biodiesel production cost. In this study, production of biodiesel by transesterification of methanol and WCO using modified sodic potassic (SP) clinoptilolite zeolite and sodic potassic calcic (SPC) clinoptilolite zeolite as heterogeneous catalysts have been investigated. These natural clinoptilolite zeolites were modified by KOH solution to increase the site activity. The optimum biodiesel yields for SP clinoptilolite and SPC clinoptilolite were 95.8% and 94.8%, respectively. Produced biodiesel were analyzed and compared with petro diesel and ASTM limits. The properties of produced biodiesel confirm well with ASTM limits. The density, kinematic viscosity, cetane index, flash point, cloud point, and pour point of produced biodiesel were all higher than petro diesel but its acid value was lower than petro diesel. Finally, the reusability and regeneration of catalysts were investigated. The results indicated that the spent zeolites cannot be reused directly for the transesterification, but they can be regenerated easily and can obtain high activity.