Argent Energy

Producing high grade biodiesel from waste

When they said would you like to visit a distillery in Scotland I was definitely up for it. Perhaps there’ll be samples to try I thought. OK, so it wasn’t what I might have expected but meeting up with Dickon Posnett, Development Director of Argent Energy and seeing round their Motherwell facility, was definitely worth the trip. No, they don’t make whisky; what Argent distills is very clean biodiesel from waste products.

There is a very long history of manufacturing diesel fuel from substances other than crude oil or shale, indeed when Rudolph Diesel first invented the diesel engine he ran it on a fuel derived from vegetable oil. What Argent does is take waste fats, whether from tallow, sewage treatment plants, acid oils, cooking fat, out of date mayonnaise or some other form of fat yielding waste and put it through a series of industrial processes before, in most cases, blending with standard diesel stocks to produce a diesel that can be used rear round in diesel engines without amendment to the system. The pure 100% biodiesel they produce (B100) can also be used in buses and trucks to achieve the greatest environmental benefits though this does require alterations to the vehicle in order for it to work efficiently throughout the year.


There are sound environmental reasons for using biodiesel produced from waste rather than fossil fuels and also some operational advantages. In terms of GHG (greenhouse gas) emissions, waste derived biodiesel is between 80-90% better than fossil based fuel.

Waste based biodiesel is low in particulate matter, which means that a DPF filter will block more slowly, in addition to which, because it burns slightly hotter, the DPF system should trigger more efficiently. Biodiesel is slightly less dense than normal diesel but has a high cetane value, so it burns more thoroughly and creates significantly less particulate matter.

Tallow based biodiesel is also high in lubricity which reduces engine wear. Furthermore, it is low in water content, which makes the combustion process more efficient.

Biodiesel is fully interchangeable with fossil based diesel at blends of up to B30 and beyond in some circumstances. Unlike many alternatives to fossil derived diesel fuels, there is no requirement to make any significant change to maintenance regimes at blends of up to B30, although considerable changes would be needed if burning pure biodiesel B100. Furthermore pricing is more or less the same as standard diesel and ex-plant it can be cheaper.

A further advantage of the waste based biodiesel Argent supplies is the customer support representative system. Under this the company inspects tanks, takes fuel samples and reports back to the customer, always happy to help with ensuring the integrity of a customer’s fuel system.


In terms of sustainability, waste derived biodiesel is not only much better than fossil based diesels, it is also superior to vegetable based oils, many of which fall foul of the food versus fuel debate. Dickon explained that, when biofuels started being commercially available, they were all generally seen
as good, but then it was appreciated that palm oil for fuel was being grown on land that had
previously been forest and opinion went the other way. It resulted in a reappraisal and an emphasis on true sustainability.

Under the European Renewable Energy Directive a calculation has been developed that shows the carbon emissions of any biofuel against any carbon based comparator in terms of greenhouse emissions on a well to wheel lifecycle analysis. Against a standard diesel GHG figure of 83.8gm, B100 biodiesel from waste has a well to wheel GHG emission figure of 10gm. In comparison, wheat derived ethanol, rape seed biodiesel, soybean diesel and palm oil diesel all have GHG figures well in excess of 40gm and even sugar cane ethanol creates more than twice the emissions.

To reflect the differing sustainability of different bio-fuels, Europe has studied the effects of an Indirect Land Use Charge (ILUC). Under this, if you grow wheat or rapeseed fuel on land that was growing food or feed there is an ILUC factor applied. As a result, Member States will have to cap the amount of bio-fuels made from crops and from 2020 the intention is to ban them, though Dickon says this may not happen. Waste based bio-fuels continue to be encouraged under EU legislation.

Furthermore, TfL has said that it wants all diesel buses running in the capital to be using waste-based B20 by 2020.

Dickon also pointed out that bus operators using high blend biodiesel in Scotland can benefit from an enhanced BSOG rate relative to the amount of biodiesel that is added to their standard diesel. Apart from Stagecoach, one Scottish operator using it already is E&M Horsburgh.

Asked about fuel economy, Dickon said that it depended a lot on the work cycle. Tests show that with blends of between B20 and B30 there is a small improvement in fuel efficiency because the fuel has a higher cetane level. This drops off as the blend level is increased to 100% and below B20 the advantage is less marked. Dickon believes that, in practice, you are likely to see the best improvements on longer routes rather than on shorter stop/start cycles.

Disadvantages and myths

It should be remembered that by law there is a small amount of biodiesel in all UK diesel stocks. B30 high bio-blends act as a direct fossil based diesel replacement. In pure B100 form vehicles do need to be modified for year round operation because B100 does not flow in colder temperatures. For this reason, buses running on B100 also have a small fossil diesel tank used for starting the bus and the bus switches to biodiesel once the system has warmed up. There is obviously a cost to fitting and maintaining the additional tank.

Some operators do run buses fuelled with 100% biodiesel. An example is the Kilmarnock depot of Stagecoach where they have been using it since 2008. A scheme which saw the operator take in people’s used cooking oil in return for a travel discount continues to operate there. ‘They are genuinely saving huge amounts of carbon by using renewable rather than fossil based fuel,’ said Dickon.

Another issue is that there are not many suppliers doing it at present. As well as supplying Stagecoach throughout Scotland and Northern England, Argent supplies B20 into London, both B100 and B20 to Kent and the South coast and B20 to Scotland, Merseyside, Manchester, the Midlands, Cumbria, the North East, Cambridge and Oxford, and forthcoming changes will expand this availability.

Dickon admitted that some vehicle manufacturers have been slow to review warranty issues for
high blends diesels in the light of recent developments, although this should rapidly become less of
an issue.

There have been instances in the past of fungal growth in storage tanks caused by higher levels of water, either in the diesel or biodiesel. The water limit in biodiesel is 500ppm, compared with 200ppm in fossil derived diesel, but because of the distilling process used, Argent’s waste based biodiesel is normally between 60ppm and 90ppm. On the day of my visit it was 79.9ppm, Dickon told me. In addition, when the company starts supplying it arranges for the tanks to be cleaned to ensure a clean, dry storage facility.

Though there is no denying the raw material used does, waste based biodiesel does not smell, even in B100 form. It is also completely biodegradable and non-toxic. As Dickon put it, ‘it is regarded as biodegradable as sugar and as toxic as salt.’

Argent Energy

The history of the plant is that there were once a number of linked companies in the food and meat industries with a rendering plant near Motherwell. In search of a better use for the high energy animal fat (tallow) Argent worked with an Austrian Company, BDI, to develop a method of converting it to biodiesel. The BSE crisis meant the waste tallow started to be sent to landfill, helping spur Argent to build its plant next door to the rendering facility.  This had not been done anywhere else before, though it had been done with vegetable oils. It became the demonstration plant for Europe for the technology. Since 2005 distilling has been undertaken at the site and since 2008 Argent has concerned itself solely with the manufacture of biodiesel and related products.

Brian Souter’s Souter Investments organisation once held a stake in Argent Energy but along with the other stakeholders sold out in 2013 to the Swire Group. Today it is part of the Green Division John Swire & Sons Ltd, a family company with vast and varied interests in the property, aviation, beverage, maritime services and trading and industrial sectors, including stakes in well known companies such as Cathay Pacific and Akzo Nobel.


The different waste products arrive at the plant in tankers or in containers of varying sizes and are unloaded. I’m not going to pretend to you, it is pretty smelly and I think I was lucky because a lot of what was being used on the day I visited was not the most smelly material. The oils are then pre-treated in cleaning, sterilisation and filtration processes. With such a huge spectrum of wastes used, this pre-treatment is very important to obtaining a high grade final product. This stage of manufacture is carried out in a large building to the left hand side of the site, beyond the office complex.

The next stage is a chemical process known as transesterification and for this the pre-treated oils are pumped to the biodiesel plant to the south of the site. This turns the oils into esters which gives them the correct structure for burning as diesel. In order to obtain the most thorough reaction possible, the transesterification process is undertaken twice.

After transesterification, the final stage in producing Argent’s biodiesel is purification through a distilling process. At the end of this there are three products. By far the majority, something around 95%, is very clean, very pure, biodiesel that fully meets the EN14214 standard. It is so pure, that were you to freeze it, it would return to exactly the same state once thawed. Also produced are glycerol, which goes to water treatment works to help the anaerobic digestion process at their plants and Potassium Sulphate K2SO4 which is used as a fertiliser in agriculture.

Between the pre-treatment and biodiesel production plant is a towering tank farm where raw materials, glycerol, standard diesel for blending and finished biodiesel is kept. The all important blending processes are also undertaken in these tanks. Dickon stressed how important the blending of the different additives is to ensure that what goes to the operator and into the fuel tank is of the same specification throughout. Failing to blend thoroughly can cause filter blocking. The company will blend in other additives for a customer if requested which ensures that they are far more thoroughly mixed than can possibly be achieved if you are pouring something into a tank at a depot. It also ensures that the quantities mixed in are correct. Additives such as Envirox can be used in conjunction with biodiesel as long as they are blended and dosed correctly.

Supporting the operation are laboratories where every ingredient is analysed and every batch produced is also checked thoroughly at various heights within the tanks to ensure thorough blending.

Recently, a new test for filter blocking has been introduced into the British Fuel Standard. The maximum FBT (filter blocking tendency) permitted is 2.52. Dickon said that standard diesel from a good refiner will be around 1.1. He checked the biodiesel in the three tanks on site (using an app on his telephone) and the readings were 1.04, 1.05 and 1.04. He told me that day to day readings are typically 1.03 to 1.06. He also believes that some imported diesel has had relatively high FBT figures, as has some imported biodiesel if it has not been distilled.

Whilst always complying with British Standards, the labs have to predict what the exact fuel formulation needs to be by analysing conditions such as the weather in advance. Nothing is released for use until the laboratories have tested and approved it.

Another key role for the laboratories is in helping operators check out problems they have with fuel, whether or not they are related to Argent supplied products. ‘We work really closely with customers on fuel,’ said Dickon. I also met James Bennett, one of Argent’s Customer Support representatives, who visits operators every day, talking about fuel and taking samples that go to the lab to be analysed. ‘We monitor every tank,’ he said.

Annually, the Motherwell plant produces 60m litres of waste based biodiesel. This gives it the theoretical capability of supplying 240m litres of B25 biodiesel annually, although it doesn’t actually do this because some of the unblended biodiesel produced goes directly to other oil companies for incorporation in their products.

Producing biodiesel from waste is considerably more expensive than producing biodiesel from other sources because it requires so much more infrastructure to do it. It would not be viable doing so were it not for the incentive of RTFO, the Renewable Transport Fuel Obligation, which makes it a requirement that all fuel companies ensure a percentage of all fuel they supply is from renewable sources. Currently up to 7% of standard diesel is already biofuel. It is the RTFO certification mechanism (which enables Argent to sell certificates granted in respect of some of the biofuel it produces to oil companies) that enables it to offer B25 at competitive prices.


As well as the manufacturing plant at Motherwell, Argent already has a blending facility on the Thames in London to help it serve London and the South East. To increase capacity it is constructing a new biodiesel plant at Ellesemere Port that will be 50% bigger than Motherwell. Dickon told me, ‘Argent is increasing its production of waste based biodiesel. We have blending and distribution there already and next year phase one will see a pre-processing plant added. Then, in 2017, we will open a distilling function which will have a capacity of 75,000 tonnes of biodiesel. So our capacity to supply across the UK is going to be increased.’

Argent already operates a fleet of 25 articulated tankers. With the new developments the current workforce of 75 people will rise substantially in the coming year.

Summing up the companies aims, Dickon said, ‘We are focussing on being a good supplier of diesel fuel to the bus and truck industry, supplying direct to fleets nationally. We are developing our supply points across the UK and helping companies reduce their greenhouse gas emissions, cost effectively and in a sustainable way.’



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