It is a more moderate poison compared to contaminants like sodium or arsenic, but it nonetheless results in activity loss of the order of 5-10☏ (3-6☌) for each 1.0 wt% Si deposited on the hydrotreating catalyst. Once the silicon is bound to the alumina surface, it cannot be removed by regeneration or other means. In the hydrotreater, the silica fragments from the antifoam agent undergo a condensation reaction with the alumina surface of the catalyst, forming a strong chemical bond. It has also been found that silicon additives are sometimes used in barge unloading. In addition, it is becoming more common to use silicon additives in the drilling process, and for pipeline companies to use them for both flow enhancing performance and foaming issues. These refineries have begun processing synthetic or other opportunity crudes and the process of making synthetic crude often involves a coking step. More recently, even refineries that do not have cokers are experiencing silicon poisoning of hydrotreating catalysts once thought unlikely since their feed source comes directly from the refiner’s crude unit. As a result, these compounds tend to concentrate in the overhead products and, as a general rule of thumb, 70-80% of the silicon at the coker ends up in the coker naphtha fraction. These species are volatile at coker temperatures, with boiling points ranging from 270-475☏ (132-246☌). The siloxane complex breaks down in the coking process to primarily cyclic methylsiloxane trimers. The main source of silicon is from delayed coker operations, which use an anti-foam agent based on polydimethylsiloxane to suppress foaming in the coker drums. Silicon is probably the most widespread catalyst poison encountered in hydrotreater feeds. ART has seen an increase in the number of units experiencing poisoning from these contaminants in recent years as significantly more of these opportunity feeds are processed. Many of these new feeds contain unknown levels of catalyst poisons such as silicon (Si) and arsenic (As). These diseases include rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis (scleroderma).While these opportunity feeds can help improve profitability, there can be some unpleasant consequences. Autoimmune Disease – Studies of workers have shown that silica exposure is associated with increased risk for a variety of autoimmune diseases.Kidney Disease – Studies of workers have shown that increasing levels of silica exposure are associated with increasing risks for chronic kidney disease.
#Silica poisoning series
This video series provides impact stories from patients and discussion from a physician on the disease. The National Occupational Research Agenda (NORA) Respiratory Health Cross-Sector Council produced Faces of Work-related COPD. Symptoms of COPD include shortness of breath, coughing or wheezing, phlegm or sputum production, and trouble breathing. Chronic Obstructive Pulmonary Disease (COPD) – COPD includes chronic bronchitis and emphysema.Cancerous cells from the lung can also invade other parts of the body, a process known as metastasis. Lung Cancer – Lung cancer results from cells in the body that grow out of control and develop into tumors.Workers exposed to silica and those who have silicosis are also at increased risk of tuberculosis (TB), a contagious and potentially life-threatening infection.Įxposure to respirable crystalline silica puts workers at risk for developing other serious diseases including the following: There is no cure for silicosis and some patients may require lung transplantation. Silicosis can develop or progress even after workplace exposures have stopped. However, the disease can occur much more quickly after heavy exposures. Silicosis results in permanent lung damage and is a progressive, debilitating, and sometimes fatal disease.Ĭhronic silicosis typically occurs after 10 or more years of exposure to respirable crystalline silica. The particles also reduce the lungs’ ability to take in oxygen. Silica dust particles become trapped in lung tissue causing inflammation and scarring. Photo by NIOSH.īreathing in dust from silica-containing materials can lead to silicosis. An x-ray of a lung with silicosis and progressive massive fibrosis (PMF).
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