Characterization of solidifiers used for oil spill remediation

Highlights

• Oil solidifier products were characterized with FTIR, XPS, SEM, EDX.

• Most products were low density polymers or copolymers with trace amounts of Ca and Si.

• Products with decreasing carbon content, increasing Ca content, and decreasing bulk density performed best.

• Inter-particle void volume and intra-particle pore size contribute towards product oil-removal efficiency.

• Cohesiveness, consistency, and ease of removal of the final product were better for the low density polymeric solidifiers.

Abstract

The physical characteristics and chemical composition of oil spill solidifiers were studied, and correlation of these properties with product effectiveness enabled determination of characteristics that are desirable in a good solidifier. The analyses revealed that the commercial products were primarily comprised of organic polymers and a few trace elements. A natural sorbent, which was composed entirely of plant based matter, was also evaluated, and it had the highest oil removal capacity, but it did not produce a solid mat-like final product. Generally, solidifiers with a carbonate group, pore size greater than 5 μm, and bulk densities lower than 0.3 g cm⁻³ were found to have better efficiency and produced a cohesive rubbery final product that facilitated removal compared to sorbents. The importance of bulk density and pore size in the performance of the solidifier suggest that the primary mechanism of action was likely physical sorption.

Introduction

Solidifiers are high molecular weight polymers that have porous matrices and large oleophilic surface areas and are introduced during an oil spill to chemically bond the solidifier with the oil and transform the physical and chemical properties of the oil (Fingas, 2013) into a cohesive mat that can easily be removed from the environment. An added advantage of using solidifier materials for oil spill cleanup is that these materials can, in some cases, be recycled by introduction into other industrial processes, such as asphalt modifications and rubber additives (National Response Team, 2007). They are used mainly on small, thin slicks near shorelines (Fingas and Fieldhouse, 2011), where they are appropriate for removing residual sheen.

Currently the most commonly used materials include styrene-butadiene and related polymers (Fingas, 2013). The exact details of most products are proprietary, and thus only a general understanding of the solidifier products is possible. Rea (1991) tested seven pure polymeric or cross-linking chemicals with diesel fuel. The products tested were two forms of norbornene, two forms of styrene-ethylene butylene-styrene block copolymer, and three types of styrene-butadiene block copolymers. The study concluded that the addition of the polymeric gelling agents (which are generally in the form of white powder flakes) reduced the fluid properties of oil (i.e., increased viscosity, plasticity, etc.), resulted in long term increases in physical solidification, and reduced emissions of volatile organic compounds from the gelled fuel. However, meaningful differences among the performances of the different types of solidifier were not obtained. Different forms of polypropylene nonwoven sorbents were evaluated by Wei et al. (2003) with the conclusion that the sorbent with a higher porosity has a higher initial oil pickup, but poor retention capacity. In another study, the sorption capacity of exfoliated graphite on different grades of heavy oil was found to be highly dependent on bulk density, indicating the importance of grain size, void volume, and packing density of the solidifier on oil removal capacity (Toyoda and Inagaki, 2000). The performance of a solidifier product is expected to depend on its bulk powder density, which takes into consideration the size of the powder particles and the spatial arrangement of particles in the powder bed. The effectiveness of five solidifiers in removing Prudhoe Bay crude oil slicks was evaluated by Rosales et al. (2010), and the results showed the removal was non-selective and both n-alkanes and polycyclic aromatic hydrocarbons (PAHs) reacted at a similar rate for each solidifier. Three of the solidifiers used in their study showed similar performance under similar conditions and contained carbonate functional groups, which generally resulted in better performance.

The evaluation and pre-authorization of solidifier products are essential to serve as a strategic planning tool for regional response teams and state or federal on-scene coordinators. The solidifiers were tested under various conditions to account for the many factors that could influence solidifier effectiveness (Sundaravadivelu et al., 2014, Sundaravadivelu et al., 2015). In this study, we focused on characterizing the 12 solidifiers by using different analytical techniques. Currently, no studies have appeared in the literature that examines the physical and chemical features of oil solidifiers. Measuring and correlating properties that describe a solidifier with its oil removal capacity will enable determination of the characteristics that define a good solidifier.