PROSPECTING THE BIOFUEL POTENTIAL OF THE UAE’S ‘ALLIG’ DATE SEED

The date palm is the iconic plant of the UAE. Its slender trees dot every neighborhood and its fruits are synonymous with Emirati hospitality. Beyond providing beauty and nourishment, scientists believe the crop can also be a source of energy and greater environmental wellbeing for the UAE.

Reusing waste is considered an important part of protecting the environment and is of particular concern for the UAE, as it has one of the highest waste per capita rates in the world. In Abu Dhabi alone in 2018, total waste was reported at more than 9.8 million tons, of which agricultural waste accounted for 13%. In the same year, the UAE Cabinet passed a federal draft law for integrated waste management that mandated the separation of agricultural waste and supported its use to produce fertilizer, biogas, and bioenergy.

With about 40 million date trees producing enough fruit to place the UAE among the world’s top 10 date producers, a team of researchers, led by Dr. Emad Elnajjar, Associate Professor of Mechanical Engineering at the United Arab Emirates University (UAEU), is exploring date seed waste as a potential biofuel source. The UAE’s date fruit industry produces approximately 1 million tons of date seed waste yearly. Some of this date seed waste is used to make products like animal feed, beverages, and water purification material, but the rest is discarded. Given the composition of date seeds – more than 60% carbohydrate, approximately 12% fat, and 5% protein – the research team believes it may be more suitably used to create biofuel.

“Worldwide, fossil fuel depletion and accompanying environmental problems, like the increasing presence of greenhouse gases in the atmosphere, have resulted in the need for sustainable and environmentally friendly sources of energy. Within the UAE itself, there is an increasing focus on channeling waste that would otherwise be sent to landfill into meeting energy needs. With dates representing a major crop in the UAE, we believed it was worthwhile to explore the energy potential of date seeds,” explained Dr. Elnajjar.

Over the past decade, the UAE has been working towards increasing the share of renewable and alternative energy in its oil and gas dominant energy mix, beginning with the UAE Vision 2021 target of generating 27% of national energy requirements from clean energy sources. The UAE Energy Strategy 2050, launched in 2017, has a larger goal of 50% clean energy, of which 44% is to come from renewable sources like solar and biofuel, and 6% is to come from nuclear power.

In light of these national goals and challenges, Dr. Elnajjar worked with UAEU Professor of Chemical Engineering Prof. Sulaiman Al Zuhair, Research Assistant Shereen Hasan, PhD student Saleha Almardeai, Professor of Mechanical Engineering Dr. Salah Al Omari, and Abu Dhabi Polytechnic Director Dr. Ali HilalAlnaqbi, to characterize the energy potential and chemical composition of date seed waste. A paper on their research was recently published in the highly ranked international journal Energy.

“Compared to all other biomass waste resources, we believe date seeds to be by far one of the best candidates to be used as a source of renewable energy. Its composition suggests it would be a

Associate Professor of Mechanical Engineering at the United Arab Emirates University valuable feedstock to produce biodiesel,” Dr. Elnajjar said.

Among all the potential biofuels, biodiesel is considered to have one of the lowest barriers to entry. This is because biodiesel works the same as diesel, meaning it is compatible with the existing diesel infrastructure. Wherever diesel fuel is used, biodiesel can be substituted. That is why biodiesel is considered a ‘drop-in’ biofuel, as it can be dropped into the existing fuel framework without requiring investment in specialized storage, logistics, or fuel consumption technologies.

The first step for the research project was the preparation of the date seed material. The researchers received ‘Allig’ variety dates from the company Liwa Dates, and manually separated the seed from the date fruit. The seeds were then washed, cleaned, sun-dried, and ground into a powder. The powder was sieved to filter out any particles larger than 0.3 millimeters, as previous research had shown the 0.1 to 0.3 millimeter range to be ideal for oil extraction.

The date seed powder was then run through the processes of three different oil extraction methods – Soxhlet, Folch, and CO2 supercritical – to determine which would be the most productive. The oil yield of the three methods was similar – between 9.5% and 10.15%. Chemical analysis also found that two chemicals present in the original date seed powder – potassium and chromium – did not transfer into the biodiesel and instead remained in the powder after oil extraction.

DATE SEEDS ARE WASTE BIOMASS MATERIALS WHICH CAN BE USED OVER AND OVER IN MULTI-LEVEL PROCESSES, TO PRODUCE ENERGY AND OTHER USEFUL PRODUCTS

The powder left behind after oil extraction was also tested to determine its heat value and chemical properties. It was found to have nearly the same heat value before and after oil extraction. This means that the post-extraction date seed powder can also be utilized as fuel in direct combustion, pyrolysis, or gasification. Direct combustion refers to directly burning the fuel material – in this case, date seed powder. Pyrolysis is way of extracting energy from organic material by heating it to high temperatures in the absence of oxygen, which breaks down the material into combustible gases and charcoal. Gasification is a similar process to that of pyrolysis, where a material is exposed to high temperatures with limited oxygen and/ or steam, which produces a synthetic gas.

“The most important finding from our research is that date seeds are waste biomass materials which can be used over and over in multi-level processes, to produce energy and other useful products. The oil can be extracted from date seeds for biodiesel production, while the leftover date seed powder can be used in a pyrolysis process to generate gaseous fuel, and the char left over from the pyrolysis product can also be used in different applications, such as soil fertilizers and the removal of toxic substances from their solutions,” Dr. Elnajjar explained.

The process to convert date seeds into fuel, which was tested through the project, could also be scaled up for commercial use, to provide a stream of biofuel to the UAE.

“Our study was performed at a laboratory scale. However, with the further supply of date seeds and proper government support, this project could be expanded to a large scale to be economically and environmentally effective,” Dr. Elnajjar said.