PREPARATION OF RAW AND TREATED FLAX STRAW SORBENT FOR OIL SPILL CLEANUP
Date
2018-11-29
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Oil spill incidents occur around the globe and recovering spilled oil from water or soil has become an important subject. One of the significant methods of oil spill cleanup is known as sorption. Most sorbents are made from synthetic materials. Replacing them with a natural and bio friendly material is a sustainable practice. Flax is grown in Canada and specifically in Saskatchewan. In this study, the possibility of developing a natural sorbent from a by-product of linseed oil production is investigated.
Two flax based sorption materials were chemically analyzed: as-received flax straw and processed flax fibers. Various sections of the straw and fiber were observed using scanning electron microscopy (SEM) to view the structure of the plant. The flax straw was cut into small particles of different lengths in order to study the effect of particle size on light and heavy oil uptake. The effect of sorbent density on oil sorption was also determined as well as the effect of shive and fiber. One of the main hinderance to utilizing natural sorbents for oil sorption in aqueous situation is their tendency to adsorb water. To illustrate the behavior of the flax straw in aqueous situations, two experiments were performed on the samples: water uptake and the oil/water selectivity. In order to address the adsorption of water, a chemical acetylation treatment and a proposed novel method for coating sorbents with linseed oil was accessed. Both acetylated and oil coated samples were compared with raw straw to investigate changes in surface morphology, chemical structure, thermal properties, oil sorption and water uptake.
The result of chemical analysis showed the cellulose content of flax fiber was higher than flax straw while its hemicellulose and lignin contents were higher. Based on SEM observations, the major portion of the flax straw stem consisted of a hollow inner tube surrounded by xylem and phloem vascular tubes. The vascular tube area is also known as shives and was considerably porous. Hence, shives may be a promising location for depositing oil in oil sorption projects. Also, it was observed the flax and shives were covered with plant wax, and this wax was mostly removed by the acetylation treatment. In the linseed oil coated samples, the plant wax was covered with a thin layer as well as fiber and shive particles. Fourier-transform infrared (FTIR) spectroscopy revealed changes in the intensity of bands related to -OH groups and acetyl groups which is an indication of a successful acetylation treatment. FTIR results of coated samples showed blockage of hydroxyl functional groups and appearance of C-H functional groups related to the linseed oil backbone. The success of acetylation was also validated by thermal gravimetric analysis (TGA). The acetylated samples were observed to have a lower thermal stability compared to raw samples due to a decrease in the number of hydrogen bonds. The TGA results of coated samples were similar to those of raw samples as the coating agent was physically bonded to the sample surface and hence it did not change the structure of the coated sample. In terms of oil sorption capacity, the raw sample is capable of adsorbing 13.6 g/g and 11.2 g/g for heavy and light oil, respectively. The amount of water uptake was 6.9 g/g after 5 min. This number increased to 8.2 g/g after 45 min of soaking within the artificial sea water. Despite the high oil uptake capacity in a dry condition, in aqueous situation raw flax straw only adsorbed 5.6 g/g of heavy oil and 4.6 g/g of light oil. Similarly, the amount of water uptake was more than oil, at 7.6 g/g and 8.5 g/g from the mixture of water and heavy and light oil, respectively. The oil sorption of acetylated samples increased by 6.6 % and 9.8 % for heavy and light oil, respectively compared to raw flax straw. This may be due to the partial elimination of surface wax on the fibers and shives during acetylation which resulted in more regions being accessible within the sorbent particles. Acetylation treatment of flax straw also improved oil/water selectivity. While the amount of water uptake reduced by almost 44 % from the mixture of heavy oil and water, the oil uptake capacity improved by 9 %. For linseed oil coated samples, a considerable improvement of 32 % was observed in water adsorption compared to raw samples during the artificial sea water uptake experiments. Moreover, a drop of 81 % in water uptake and an increase of 38 % for light oil sorption was observed in oil/water selectivity tests for the linseed oil coated samples compared to the raw samples. As a final study, the possibility of reusability and disposal of the oily sorbent within a landfill was examined. It was observed that the linseed oil coated samples maintained 89 % of the oil sorption capacity after four sorption/desorption cycles for light oil and 92 % for heavy oil. It was determined the sorbents can be deposited in a landfill after one cycle of centrifuging based on the code of federal regulations (CFR).
Description
Keywords
sorbent, sorption, oil coated, SEM flax, linseed oil, fiber and shive, acetylation of natural fiber
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering