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Recovering sulphur

We are developing methods to recover and reuse the sulphur in hydrogen sulphide (H2S) from natural gas.

Technology

At our laboratories we are studying new processes for separating and reusing sulphur, which, in the form of hydrogen sulphide, is normally found in natural gas. Altogether, the recovery cycle comprises three phases. First of all hydrogen sulphide is separated from the natural gas, then sulphur is extracted, then this element is used as a component in new products. For each of these phases we are testing alternative processes that could be more efficient than current one. For separation, for example, we are assessing the use of ionic liquids, absorbent substances that are more innovative and advantageous than those currently used in the chemical industry. For the successive phase of conversion, we are studying a process known as Hydro Claus, which is simpler than current technologies. As for use, we are studying how to use sulphur to produce polymers by inverse vulcanisation, which lets us insert a very high proportion of this element. 

Context

H2S (hydrogen sulphide) is one of the secondary components of natural gas. Unfortunately, unlike methane and other useful ingredients, hydrogen sulphide is a toxic, corrosive acid gas, which absolutely must be removed and prevented from escaping into the environment. The treatments for doing so, however, are complex and costly. In the petrochemical industry, H2S is currently converted into elemental sulphur through the Claus process, which is rather complicated. Moreover, the market for pure sulphur has been going through a slump in the last few years, because production is overtaking demand. To get over both of these obstacles, we are working on two fronts. On one hand, we are using cheaper and more efficient processes to separate H2S. On the other, we are coming up with new ways to use sulphur to get useful and therefore marketable products.

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How to capture and convert H2S - Energy Transition | Eni Video Channel

Technological challenge

The goal of our research into recovering sulphur is to find new ways of using this element, and we are using three technologies to do so, each of them focused on one phase of the process. For the first phase, separating hydrogen sulphide from natural gas, we are taking into consideration the use of ionic liquids and absorbent compounds with innovative properties. Thanks to their chemical and physical properties, in fact, these substances have a higher absorption density and can be used more simply in operations compared to traditional amines. Other advantages are that they do not evaporate easily at room temperature, are not flammable, do not decompose and are not aggressive chemically. For the phase of converting H2S into elemental sulphur, we are using the Hydro Claus process, which is simpler than the conventional process known simply as Claus. Here the advantage lies in a part of the reaction taking place in a watery environment, at a low pressure and temperature, to obtain a hydrophilic sulphur that is particularly useful in farming, either as slurry or powder. For the final phase, use, we are thinking of alternative uses of sulphur, in which it might provide a base for producing polymers. The innovation here lies in the use of a process known as inverse vulcanisation. Whereas traditional vulcanisation adds a small dose of sulphur to rubber strengthen its structure, the inverse variety uses a large quantity of this element, along with a small added organic component that acts as a cross-linker, to stabilise the polymer's structure. This allows us to produce a polymer made of up to 90% sulphur. 

Industrial integration

For technological projects on recovering sulphur, the goal is to turn a problem into an opportunity, reusing a pollutant, namely Hydrogen sulphide, as raw material for useful, safe, sustainable new products for the market. Given the frequency of H2S in the Upstream fields we work in, managing this compound is very important in our activity. The technologies available for separating and converting it into sulphur have been strengthened, but our goal is to identify new solutions that will simplify treatment of acid gases while maintaining safety, efficiency and sustainability, both economic and environmental. In line with the principles of the circular economy, we want to exploit this waste component to create new commercial opportunities. The products we are focusing on are innovative polymers, as well as fertilisers and soil improvers for farming. Made up mostly of sulphur, the polymers can be used in the electronics sector and widely used plastic materials. Based on hydrophilic sulphur, the fertilisers and soil improvers are particularly suited to improving saline or alkaline land undergoing desertification, which is typical in the areas we work in.

Environmental impact

At the centre of our industrial research into sulphur recovery is natural gas, a mix of multiple hydrocarbons in which methane is prevalent, and which we consider fundamental to our decarbonization strategy because it produces about 60% less CO2 than coal when burnt. To be processed, however, natural gas must first be purified of any polluting substances, like hydrogen sulphide, or H2S, a toxic, corrosive acid gas. Thanks to the technologies we are developing, our treaters for acid gases will be less cumbersome and more versatile, as well as more efficient and environmentally sustainable. Focusing on ionic liquids, we can get greater absorption density than with traditional amines, and therefore reduce the size of treatment systems. Being able to get elemental sulphur from hydrogen sulphide, and above all being able to use it for useful new products, is what makes these technologies even more interesting from an environmental point of view. Fertilisers and soil improvers for agriculture, based on hydrophilic sulphur, could make a big contribution to treating saline and excessively alkaline soil, and reclaiming areas undergoing desertification.