Chemical engineering and transport fuel

The economic growth of the 20th Century was to a large degree driven by the reduction in cost and increase in speed of transportation. Without this decrease in cost, the economies of scale of the 20th Century industrial revolution could not have been realised. Today, goods can be manufactured in a relatively few locations and shipped at acceptable cost to global markets. The internal combustion and jet engines were the drivers for these changes. These in turn were made possible by the availability of liquid fuels tailored to them. Simply burning crude oil was not a practical solution. Chemical Engineers were needed to design and manage the refineries to distil the oil into its fractions. The C4 to C12 (i.e., four carbon atom hydrocarbon – butane to twelve carbon atom hydrocarbons) fraction forms the gasoline pool for spark ignition engines used in private cars. C6 to C16 is the Kerosene pool, now largely used for gas turbine jet engines for aircraft. C10 to C15 is the diesel pool for diesel engines that rely on the autoignition of the fuel under compression and used for cars and for larger road transport vehicles. The residue from crude oil C20 up to C50 was traditionally used for ships, either in steam boilers or large diesel engines. According to the BP Statistical Review, in 2020, global capacity in refineries amounts to 101 million barrels of oil per day (i.e., approximately 14 million tonnes per day). 

Crude oil comes in a wide range of compositions. These do not match the market demands for the different fuels. Residual fuel was normally over supplied and priced at a discount to crude oil. Gasoline is the premium product with automotive diesel and aviation kerosene often priced just a little less. Chemical Engineers constantly strive to keep the supply and demand for each product in balance by adjusting the blending for the final products and through a range of processes to transform longer chain molecules into shorter. These are achieved either by adding hydrogen or removing carbon to split the molecules. The optimisation process is driven Chemical Engineers using linear program software that almost constantly seeks the best operational combination. 

Up until the 1970’s, fuels were developed to improve efficiency and power from engines. For gasoline, this was through higher Octane number fuels that could be used in high compression engines. The solution used was to add Tetra Ethyl Lead (TEL) in small quantities. This is a highly toxic material that required chemical engineers to design special areas on the refinery to handle. 

After the 1970s, the emphasis switched to reduce the environmental impact from using fuels. Initially this was by removing TEL and maintaining the Octane rating by adding other less hazardous materials and further processing the gasoline components. For diesel fuels, the emphasis was to reduce the sulphur in the fuel. For gasoline, diesel and kerosene sulphur can be removed by using hydrogen in hydrotreaters. Achieving very low levels in diesel was more costly. Sophisticated analysis of the costs and benefits was undertaken to justify the reduction in sulphur in automotive fuels.  

In the late 1990’s the European Commission undertook the Auto Oil II Programme to decide what level of sulphur was appropriate to meet air quality targets in major cities in Europe. This multi-disciplinary programme involved inputs from vehicle manufacturers on what can be done with engines, air quality modellers on the how automotive emissions would be dispersed and chemical engineers to determine the cost to the refining industry and hence the increase in price needed on the fuels. The contract to do the modelling work on the refineries was won by Bechtel Consulting (the contract was novated to Nexant Ltd, a Bechtel spin-out in 2000). I was leading Bechtel Consulting from London at the time and became the Managing Director of the spin-out. The hard work was done by a team of process engineers and linear program modellers from Bechtel’s process group, led by Peter DuPreez using the PIMS program, with Neil Richardson handling the liaison from Brussels. The European refining sector could be sub-divided into North and South, which helped to simplify what was an extremely large and challenging LP model into two very large challenging and weakly connected models. The model itself had to stand scrutiny by the European refining industry lobby group, who were anxious not to be burdened with costs at a time when the industry was unprofitable due to overcapacity. After several months of hard work, the Bechtel / Nexant team had produced a solution that showed that the proposed tightening of sulphur standards could be accommodated without the European refining industry being burdened with excessive costs. There would be winners and losers among refineries, but this is normal in a competitive industry. The project was named as the winner of the British Consultants and Construction Bureau (BCCB – now British Expertise International) award for 2000 as the outstanding example of British expertise for an intangible project, i.e., not a physical structure. 

The recent change has been the reduction in permitted sulphur levels of ocean transport. Traditionally ships mainly used residual fuel oil, which was very high in sulphur. It was thought that the acidic pollution at sea was not an issue. Ship bunkers (fuel) provided a convenient market for refineries to dispose of residue. Since January 2020, the IMO (International Maritime Organisation) has imposed a global limit of 0.5% sulphur in marine fuels or the ship must be equipped with a scrubber to remove SOx. The sulphur content of many crude oils is around 3%. In Emission Control Areas, such as the coastal areas of many countries, the limit is 0.1%. Unlike diesel and gasoline, heavy fuel oil cannot be easily de-sulphurised using hydrotreaters. The catalysts used in these units quickly suffers from the heavy metals and coke in the heavy fuel oil. Desulpurising residue requires more severe conditions, which is very costly and results in the long molecules being split into the diesel range as well as the sulphur being removed as hydrogen sulphide. To meet the new specification, residual fuel is now usually supplied for ship bunkers blended with more expensive diesel to meet the sulphur target – ocean transport has become a little more expensive. Chemical Engineers are key to this supply of fuel and to the design of scrubbers on ships if high sulphur fuels are used. 

The challenge for the future is to decarbonise transport.

Private cars will probably be electric. Chemical engineers are working on how to reduce costs of manufacturing the chemicals needed for the batteries required. 

Heavy vehicles could possibly be electric, but currently there appear to be challenges concerning the weight and size of batteries required. Alternatives such as biofuels or hydrogen from renewable power are also being tested. Chemical engineers are working on how to manufacture these at an acceptable cost and safely.  

Aircraft may use batteries for short range and hydrogen or biofuels or offsetting (i.e., growing trees or bogs to capture carbon) for longer range. 

For the Marine sector, batteries are being tried for short distance use on ferries. For ocean going vessels, alternative fuels such as hydrogen, ammonia or LOHC (liquid organic hydrogen carriers) are being proposed. Chemical engineers are developing how to manufacture and handle these without creating serious hazards and at an acceptable cost. Some of the alternatives, such as ammonia and liquid hydrogen present serious safety challenges.  

Sequestration of carbon may also present interesting challenges for chemical engineers if the shipment of carbon dioxide is considered desirable. Some observers have suggested the problem would easily be solved by say shipping LNG from the Middle East to markets and the ships returning with liquid carbon dioxide to be injected back into the gas fields. This would present some massive challenges for cargo containment and ship design due to liquid carbon dioxide’s density being more than double methane. Carbon dioxide is also tricky as it can easily turn to a solid (dry ice) if conditions are wrong. This would require some serious engineering to work out what to do if this happened to a cargo of several hundred thousand tonnes of CO2. 

In the early 1990’s, Bechtel were commissioned by the European Commission to evaluate the economics of simply piping CO2 into the Atlantic to a sufficient depth it would be a liquid. This idea seems to have been forgotten perhaps because no one at the time could work out what the environmental impact might be or if the CO2 would remain as a liquid blanket at the bottom of the Atlantic.