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Jan-2018

Oxidation catalysts for VOC reduction

How destruction of volatile organic compounds at lower temperatures is positioning catalytic oxidation systems for the future

MIKE SHAO
Clariant
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Article Summary
With an ever increasing number of processing plants coming on stream worldwide to keep up with the burgeoning petrochemical industry, the focus on the release of volatile organic compounds (VOC) into the atmosphere is coming under intense scrutiny by environmental authorities. The release of VOCs from industrial processes not only poses a potential hazard to human health, but can also represent a risk of financial losses to the operator. Emissions and pollution control issues are a priority the world over, both in developed and developing economies, and VOC emission control is high on the agenda.

Omnipresent VOCs
VOCs are effectively petrochemicals of different kinds. They are numerous, varied and ubiquitous, emanating mostly from hydrocarbon processing plants. VOCs are among the most common air pollutants emitted from chemical, refining, petrochemical and other allied industries. They are one of the main sources of photochemical reaction in the atmosphere, leading to countless environmental hazards, although in some cases, if captured, they can have good commercial value.

VOC pollutants can emanate from the inevitable venting and loading losses from storage tanks, via open vessel tops, vents, or leakages from pipes, valves, flanges and other equipment. And, of course, they are the result of combustion based processes, being present in exhaust gases or ‘off gases’ which are emitted as a result of the combustion of fuels including natural gas, diesel and biodiesel blends, gasoline and others.

A major source of man-made VOCs is solvents. As with other VOCs, when solvents increase in temperature, as in a production process exhaust stream, they evaporate and enter the atmosphere where they create a foul smell, potentially causing a variety of health problems and also requiring the company concerned to purchase the solvents lost in the process.

The most common VOCs are halogenated compounds, aldehydes, alcohols, ketones, aromatic compounds, and ethers. VOCs include most solvent thinners, degreasers, cleaners, lubricants, and liquid fuels. Some of those solvents include acrylic acid, acetone, benzene, formaldehyde, methane, methyl methacrylate, ethane, tetrachloroethane, methyl chloride, and many chlorohydrocarbons and perfluorocarbons, among dozens of others.

Growing environmental awareness has resulted in increasingly stringent regulations to control VOC emissions. In such circumstances, it becomes mandatory for each VOC emitting industry or facility to adopt suitable VOC control measures. There are multiple techniques available to control VOC emissions, along with their particular advantages and limitations.

The issue of health
The risks associated with industrial VOCs are aggravated by the fact that hazardous concentrations are usually very low and the health issues they can cause can be cumulative and slow to develop.

The world’s media regularly report that asthma and other respiratory diseases are on the rise, affecting both young and old. While there are many causes of these ailments, it is generally recognised that some VOCs can have severe, adverse influences on human health in several areas. These include sensory stimulation, tissue inflammation, anaphylaxis and nerve toxic reactions. A few VOCs can also easily constrain the normal function of the central nervous system, causing headaches, fatigue, drowsiness and discomfort. Research indicates that alcohols, aromatic hydrocarbons and aldehydes have the potential to stimulate mucous membranes and upper respiratory tracts. Furthermore, a number of VOCs are proven carcinogens or potential carcinogens; for instance benzene, trichloroethylene and formaldehyde.

Hydrocarbons in combination with NOx, in the presence of sunlight, undergo photochemical oxidation, producing a photochemical smog that is environmentally hazardous. VOCs react with nitrogen oxides and other airborne chemicals, in the presence of sunlight 
(photochemically), to form ozone, which is a primary component of smog.

China has several of the world’s most polluted cities within its borders and the effects are becoming a major public health threat. Asthma cases have risen dramatically in China over the past couple of decades along with ever deteriorating air quality according to leading respiratory specialists. In a nationwide epidemiology study1 led by Dr Lin Jiangtao at the Department of Respiratory Diseases, China-Japan Friendship Hospital in Beijing, the resultant report indicated that between 1% and 2% of the population over the age of 14 years experienced the condition, with 16% of cases needing emergency treatment. Additionally, nearly half of respondents claimed to be handicapped by the disease. Dr Jinagtao stated unequivocally that the prevalence of asthma has sharply increased over the past decade and that the significantly rising trend of asthma prevalence is plainly evident.

A potentially fatal disease, asthma is the leading cause of hospitalisation among children in China and carries a significant burden to families and communities. Public awareness campaigns are now commonplace, with videos demonstrating treatment for asthma attacks on social media channels.

The global community is working to improve cooperation between emitting sources, legislative bodies and monitoring systems in order to reduce the number of serious pollutants being released into the air to help mitigate the adverse effects on human health and the environment.

Legislation and regulations
There is a significant amount of legislation – both recent and upcoming – to control VOC emissions from large combustion plants – chemicals, refining, petrochemicals and related industries – in China.

On 1 July 2015, the Chinese government implemented a number of emission standards which would impact the refining, chemical and petrochemical industries: Emission Standard of Pollutants for Petroleum Refining Industry (GB31570-2015); Emission Standard of Pollutants for Petrochemical Industry (GB31571-2015); Emission Standard of Pollutants for Synthetic Resin Industry GB31572-2015; and Emission Standard of Pollutants for Inorganic Chemical Industry (GB31573-2015). Issued by the Ministry of Environmental Protection, the standards specify water pollutants, air pollutant discharge limits, monitoring and supervision management requirements for petroleum refining and petrochemical industrial enterprises and production facilities. While various regions within China were encouraged to implement the upcoming standards as soon as possible (depending on local environmental protection, economic and technical conditions), all industrial plants falling within its remit were required to comply by the July cut-off.

GB31570 is applicable not only to the management of air and water emissions from petroleum refining production facilities but also to crude and refined products storage, during the oil delivery process, as well as plant construction projects.
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