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Thread: Phosphorus and Nitrogen in Crude Oil

  1. #1
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    Phosphorus and Nitrogen in Crude Oil

    By the Redfield Ratio, marine microalgae contains carbon, nitrogen and phosphorus in the ratio C:N:P 106:15:1 (or 117:14:1).

    Since algae is the source of crude oil, I thought that crude oil would also contain CNP in this ratio. And therefore that crude oil would be a source of nitrate and phosphate. But my study of simple summary material on oil chemistry does not discuss this, as far as I have been able to find.

    Can anyone explain what happens to the nitrogen and phosphorus relating to crude oil?

    Thank you.

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    Before you get oil you have the ->humin->kerogen steps. During the formation of humin clays tend to absorb phosphorus from it, as part of the phosphorus cycle. During the formation of kerogen anything which doesn't form dense, aromatic hydrocarbons tends to be left out of the structure. A lot of the functional groups phosphorus and nitrogen are part of get removed throughout the process by incorporation into fulvic and humic acids.

    Sorry, that is not a 100% answer, I'm not a geochemist! But it looks like you have a process which favours the concentration of carbon and hydrogen into efficiently packed aromatic forms with few functional groups and at least two sinks (incorporation into acids, absorption onto clays) removing other elements.

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    According to this presentation, nitrogen levels in crude oil vary from 0.1 to 2% by weight (mostly at the low end).

    Organic nitrogen compounds occur in crude oils either in a simple heterocyclic form as in pyridine (C5H5N) and pyrrole (C4H5N), or in a complex structure as in porphyrin. The nitrogen content in most crudes is very low and does not exceed 0.1 wt%. In some heavy crudes, however, the nitrogen content may reach up to 0.9 wt %.
    I couldn't find a good reference on phosphorous. I believe it is low (from working on catalyst supports - people are sometimes concerned about nitrogen, but I don't recall concern about phosphorous).
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    Thank you very much Shaula and Swift for these informative helpful replies.

    My reason for asking the question is that I am studying the production of algae at sea as a method of mining carbon from the air. To operate at a scale relevant to anthropogenic emissions (10km3 Carbon/year), the question has arisen if it is feasible to pump the required P and N to the surface from Deep Ocean Water (DOW). The problem is that the amount of C in DOW, given by the Redfield Ratio, could displace any carbon from the air, undermining the CO2 removal objective. So I was wondering how biocrude production from a high (0.5%) phosphorus source would relate to crude oil processing, from which phosphorus appears almost completely absent.

    A recent paper, Edmundson, S., Algal Research (2017), http://dx.doi.org/10.1016/j.algal.2017.07.016 which I discovered in following up Shaula's comment on the geological loss of phosphorus from crude oil, explains that Hydrothermal Liquefaction (HTL) of algae to produce biocrude can produce phosphorus as a byproduct, and this phosphorus can be recycled through the algae farm at the surface as fertilizer, enabling the algae farm to mine atmospheric carbon.

    The world ocean contains more than 100 km3 of phosphorus and 20,000 km3 of nitrogen,* so if this and other valuable products can be mined in the context of biocrude production from algae it may help biocrude to become economic.

    It is still unclear to me why the phosphorus disappears from crude oil, although Shaula's summary comment about humin is a good starting point. The useful information is that the phosphorus in algae is retained in HTL production of biocrude.

    * My calculation from source: Karl K Turekian:*Oceans. 1968. Prentice-Hall

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    Phosphorus ends up trapped in mineral form, while nitrogen-containing compounds form nitrogen gas as they decompose. Water soluble phosphates and gaseous, almost-inert nitrogen are not likely to recombine with the liquid hydrocarbon mixture that forms from the remaining organic material. Some of the nitrogen does stick around long enough to get sealed in with the organic material and contaminate natural gas formed from it.

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    Quote Originally Posted by Robert Tulip View Post
    By the Redfield Ratio, marine microalgae contains carbon, nitrogen and phosphorus in the ratio C:N:P 106:15:1 (or 117:14:1).

    Since algae is the source of crude oil, I thought that crude oil would also contain CNP in this ratio. And therefore that crude oil would be a source of nitrate and phosphate. But my study of simple summary material on oil chemistry does not discuss this, as far as I have been able to find.

    Can anyone explain what happens to the nitrogen and phosphorus relating to crude oil?

    Thank you.
    The molecule of crude oil is not located at the original deposit. It started out as a carbohydrate in sediment. In high pressure and temperature environments atoms rearranged to form the hydrocarbon. The hydrocarbons can pass through some porous rock. Oil fields are located below layers of non-porous rock that trap them. Phosphates are likely to bind in the original sediment.

    Oil companies frequently use water and sometimes salt water to pressurize the oil field and help flush out the crude. Removing the salt water is a significant operation. Saudi oil fields pump out 30% salt water 70% crude. Some Texas and mid-west oil fields are 90% water. Piping is a major part of an oil field operation. Dealing with 9 barrels of water for every barrel of oil is expensive. If you had phosphorous in a crude oil source the phosphates would stay in the water. Phosphates are very hydrophilic.

    Refineries have de-salting units. They are intended to remove chlorine but phosphate would come out too. If you are planning on using the phosphorous for agriculture then sewage would be a much better source.

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    Deep Ocean Water for Carbon Removal

    Quote Originally Posted by cjameshuff View Post
    Phosphorus ends up trapped in mineral form, while nitrogen-containing compounds form nitrogen gas as they decompose. Water soluble phosphates and gaseous, almost-inert nitrogen are not likely to recombine with the liquid hydrocarbon mixture that forms from the remaining organic material. Some of the nitrogen does stick around long enough to get sealed in with the organic material and contaminate natural gas formed from it.
    Quote Originally Posted by NearABE View Post
    The molecule of crude oil is not located at the original deposit. It started out as a carbohydrate in sediment. In high pressure and temperature environments atoms rearranged to form the hydrocarbon. The hydrocarbons can pass through some porous rock. Oil fields are located below layers of non-porous rock that trap them. Phosphates are likely to bind in the original sediment.

    Oil companies frequently use water and sometimes salt water to pressurize the oil field and help flush out the crude. Removing the salt water is a significant operation. Saudi oil fields pump out 30% salt water 70% crude. Some Texas and mid-west oil fields are 90% water. Piping is a major part of an oil field operation. Dealing with 9 barrels of water for every barrel of oil is expensive. If you had phosphorous in a crude oil source the phosphates would stay in the water. Phosphates are very hydrophilic.

    Refineries have de-salting units. They are intended to remove chlorine but phosphate would come out too. If you are planning on using the phosphorous for agriculture then sewage would be a much better source.
    Thanks for this helpful information which provides the answer to my question. Here is the discussion note I circulated about use of phosphates in relation to production of biocrude.

    Deep Ocean Water for Carbon Removal

    Proposals to raise deep ocean water (DOW) to the surface as a climate mitigation technology have been criticised for producing warming. These problems may not arise if DOW is used for algae production with full recycling of nutrients.

    Atmospheric consequences of disruption of the ocean thermocline, (Kwiatkowski et al 2015 Environ. Res. Lett. 10 034016) found that artificial vertical mixing of ocean water for local cooling, such as in the proposed ‘Lovelock Pipes’, would actually produce wider warming, reversing the intended benefit. Any proposed applications of large scale ocean pumping to mitigate climate change would need to address the problems modelled by this and related studies.

    In considering use of ocean pumping for large scale algae production, recycling of deep ocean nutrients may be a key method to address such problems. A recent scientific paper, Phosphorus and nitrogen recycle following algal bio-crude production via continuous hydrothermal liquefaction, ( Edmundson, S., Algal Research (2017), http://dx.doi.org/10.1016/j.algal.2017.07.016), explains how hydrothermal liquefaction (HTL) to produce algae biocrude can separate and recycle the phosphorus and nitrogen in algae for ongoing reuse as fertilizer.

    This finding could enable ocean based algae production to mitigate climate change by recycling oceanic phosphorus and nitrogen in combination with carbon dioxide mined from the air. Subject to modelling assessment, my hypothesis is that the climate benefit of efficient removal of carbon from the air in this way would outweigh any warming effects.

    If nitrogen and phosphorus from deep ocean water are used to fertilize a contained algae pond at sea, and the algae is then converted to biocrude by HTL, then the finding that phosphorus and nitrogen in the algae can be separated from the biocrude enables continuous reuse of these nutrients. This changes the parameters for analysis of deep ocean water climate impact. Recycling of oceanic nutrients in algae farms presents a possible path to enable efficient mining of carbon from the air at scale.

    If nutrients can be used in combination with atmospheric CO2 for ongoing repeat fertilization of the algae farm, this HTL nutrient separation process means DOW could potentially provide the nutrients required to grow algae on the scale needed to reverse global warming.

    For algae factories at sea using HTL and recycling nutrients, my calculations of orders of magnitude are as follows.
    · Ocean water below the thermocline has 3 micromoles of phosphate per litre, equal to 90 tonnes of phosphorus per cubic kilometre (per Sverdrup).
    · The scale of carbon removal to reverse climate change requires removal of more than the ten gigatons of carbon in CO2 added to the air every year.
    · To push back from the brink of possible climate tipping points, a reasonable goal is to remove twenty gigatons (petagrams) of carbon from the air every year (one gigaton of water has volume one cubic kilometre).
    · Converting twenty gigatons of carbon from CO2 to hydrocarbons and other products for storage in stable useful form (plastic, soil, bricks, roads, etc) would require 172 million tonnes of phosphorus and 2.6 billion tonnes of nitrogen to grow algae at the Redfield Ratio (C:N:P=117:14:1).
    · With complete retention of mined phosphorus and nitrogen via HTL, about two million cubic kilometres of water would need to be processed to obtain that amount of nutrient.

    The attached diagram of a tidal pump may be one way to shift this volume of water. For the entire annual goal of 20gt of carbon, my estimate is that pumping arrays of 500,000 km2 located on continental shelves with twice daily tidal range 0.5 metres would take ten years to pump two million km3 of water to the surface, in order to mine the required amount of phosphorus and nitrogen from deep ocean water.

    These nutrients would then be available for permanent recycling. This process would also deliver other useful dissolved minerals, and would continue indefinitely, enabling economic use of the vast dissolved mineral wealth of the seas. That scale of pumping operation is about 2% of the world continental shelf area as an eventual goal, and would depend on the availability of suitable locations, which in turn would depend on demonstrated environmental benefit. The algae farm area would be about six million km2, or 2% of the world ocean surface.

    The use of hydrothermal liquefaction at such a scale would require innovative technology. HTL requires pressure equal to water pressure at two kilometres deep in the ocean, and temperature above 300°C, to make the algae cell wall break down to produce biocrude. The best way to subject algae slurry to such heat and pressure may be to pump it down to the deep ocean floor, and develop controlled automated sea floor systems for processing, as per the attached sketch. The feasibility of that method has not been assessed.

    In summary, the demonstration that ‘Lovelock Pipes’ would have unforeseen warming effects does not mean raising DOW is unfeasible as a climate change response, and the ability to use HTL to recycle oceanic nutrients means that large scale ocean based algae production could be an effective method for carbon mining to deliver climate stability.

    Robert Tulip
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