Pyrolysis and combustion kinetics of date palm biomass using thermogravimetric analysis

Abstract

The present research work is probably the first attempt to focus on the kinetics of pyrolysis and combustion process for date palm biomass wastes like seed, leaf and leaf stem by using Thermogravimetric Analysis (TGA) technique. The physical properties of biomass wastes were also examined. Proximate and ultimate analysis of the date palm biomass was investigated. FT-IR analysis was conducted to determine possible chemical functional groups in the biomass. Results showed that date palm seed and leaf can be characterized as high calorific values and high volatile content biomass materials as compared to the leaf stem. Kinetic analysis of this biomass was also given a particular attention. It is concluded that these biomasses can become useful source of energy, chemicals and bio-char.

Introduction

Saudi Arabia and its surrounding regions are the home land of the date palm (Phoenix dactylifera) trees. Palm tree is perhaps one of the oldest trees in the world. Recent statistics showed that Saudi Arabia has about 23 millions palm trees, which produce about 780 thousand tons of dates per year (Al-Abdoulhadi et al., 2011). Dates have high nutrition values and provide excellent health benefits. Each date provides about 20 calories, and is a good source of carbohydrate, fiber, and potassium, with smaller amount of calcium and iron along with other vitamins and minerals. Hence, large amount of dates are consumed as a dietary and its significance is published elsewhere (Ismail et al., 2006).

Annually a huge amount of date palm biomass waste is generated while processing date palm fruit. One more feature of the date palm leaf is that it does not fall from the tree even after getting dry. It stays attached to the date palm tree until it is removed manually. This preserves it from getting lost or wasted. However, excess amount of these date palm leaves can cause environmental hazards such as fire, bait for insects and diseases (Ali, 2008). Interesting to refer that date seeds represents about one third of the date weight. These excess date seeds are not utilized and hence can serve as a potential source of energy or it can be converted into value-added chemical products. Very recently, Joardder et al. (2012) produced bio-oil and activated carbon from date palm seeds in a fixed bed reactor using pyrolysis technique. Not much information is available regarding utilization of date palm biomass for energy or as fuel.

Nevertheless, studies cited in the literature are usually related to farming applications or conversion of date palm biomass into activated carbon for purification purpose or chemical characterization. For instance, Besbes et al. (2004), analyzed two types of date palm seeds in order to investigate its chemical composition. Briones et al. (2011) produced Polyol by chemically modifying date seeds through oxypropylation and liquefaction techniques (using organic solvents in the presence of a catalyst). Recently, production of porous activated carbon from date seed was performed in a tubular furnace with CO₂ as activating agent (Reddy et al., 2012).

Thermo-chemical process plays an important role in rejuvenation of biomass into energy. Thermogravimetric analysis was used to evaluate kinetic parameters of various biomasses and it has been investigated by numerous researchers (Munir et al., 2009, Ounas et al., 2011, Skreiberg et al., 2011, Syed et al., 2011, Mehrabian et al., 2012, Tiwari and Deo, 2012). Recently, Cai and Chen (2012) determined combustion kinetics of pyrolysis char using iterative linear integral isoconversional method. A TGA study of date seed is available in the literature (Briones et al., 2011), however, little information is available about devolatilization behavior and no kinetic data was provided. The paper was focused on production of polyol from chemical modification of date seeds. Therefore, none has attempted to perform detailed combustion and pyrolysis kinetic analysis of date palm biomass including seed, leaf and leaf stem. Prior knowledge of reaction kinetics is crucial before any attempt to utilize biomass as a feedstock for thermo-chemical processes. It is worth noted that Saudi Arabia and other surrounding Gulf countries are considered to be major oil producing regions in the world. Therefore, so far none has looked into date palm and other biomass in these regions as potential renewable source of energy.

The main objective of this research work was to identify the thermo-chemical characteristics data of date palm biomass. For this, TG analysis was used to investigate the combustion and pyrolysis behavior of date palm biomass such as seeds, leaf and leaf stem. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) was also used to identify the types of chemical functional groups present in the biomass. Proximate and ultimate analysis of the date palm biomass was evaluated. Lastly, the kinetics of pyrolysis and combustion of the date palm biomass is being studied for the first time.