The present invention relates to an integrated process for the conversion of flare gas to hydrogen with hydrogen storage, and a corresponding integrated unit.

Gas flaring is the burning of natural gas as associated with oil extraction. According to the World Bank, the practice has persisted from the beginning of oil production and takes place due to a range of issues. Hence, flaring constitutes waste of a valuable natural resource that should either be used for productive purposes, such as generating power, or be conserved. The amount of gas that is currently flared each year is about 142 billion cubic meters (World Bank 2020). Flaring persists to this day because it is a relatively safe, though wasteful and polluting, method of disposing of associated gas. Utilizing associated gas often requires economically viable markets for companies to make the investments necessary to capture, transport, process, and sell the gas. In 2015, the World Bank and the UN Secretary-General launched the Zero Routine Flaring by 2030 (ZRF) initiative, which commits governments and oil companies to not routinely flare gas in any new oil field development and to end existing (legacy) routine flaring as soon as possible and no later than 2030.

The present invention addresses the issues associated with flaring.

In a first aspect, the invention related to an integrated process. In a second aspect, the invention relates to a corresponding integrated unit, receiving the raw flare gas, separating-off of methane (CH4), cracking the methane in a pyrolysis process, to hydrogen (H2) and solid carbon (C), and storing the hydrogen in a Liquid Organic Hydrogen Carrier (LOHC) substrate.

[1] The integrated process for the conversion of flare gas according to the first aspect comprises i) feeding flare gas to a gas separation stage a), the gas separation stage providing one or more a1 ) methane-containing streams comprising at least 95 percent by weight of methane, and one or more a2) a gas separation off gas streams, the one or more a2) a gas separation off gas streams comprising less than 2 percent by weight of the methane comprised in the flare gas feed; ii) feeding at least part of the a1 ) methane-containing stream to a pyrolysis stage b), the pyrolysis stage b) providing b1 ) a hydrogen-containing stream comprising at least 95 percent by weight of hydrogen, and b2) a carbon-containing stream comprising at least 95 percent by weight of carbon; iii) feeding at least part of the b1 ) hydrogen-containing stream to c) a stage providing electrical energy; and iv) feeding at least part of the b1 ) hydrogen-containing stream to d) a Liquid Organic Hydrogen Carrier (LOHC) hydrogenation stage; the LOHC hydrogenation stage providing a hydrogen- loaded LOHC (LOHC+) stream.

The flare gas that is fed to gas separation stage a) is a flammable gas that would otherwise be released into the atmosphere. Non-avoidable flare fractions are recovered according to the invention, to minimize greenhouse gas (GHG) emissions, by converting to carbon and hydrogen.

Fig. 1 shows a process scheme and is a preferred embodiment of the invention.

The purpose of the methane gas separation step is to generate a clean methane gas stream out of compressed vent gas/flare gas. Separated-off impurities are (heavy) hydrocarbons, water, and hydrogen sulphide, if necessary in two or more steps to remove hydrogen sulphide first. The specific membrane material (e.g., polymer) allows a selective permeation and purification of methane. The membrane units are installed in the existing infrastructure as plugin replacements. The recovered natural gas liquids (NGL) can be converted to liquefied petroleum gas (LPG) for further use. The membrane unit is scalable in wide range of volume flows (10 - 1 ,000 Nm ³ /h) and in a pressure range of 5 to 70 bar, e.g., preferred range 20- 50 bar operating pressure. Methane purities of > 99% can be achieved. The purpose of the methane pyrolysis process is to convert methane from flare gas into clean hydrogen and solid carbon, to prevent/minimize CO2 emissions from flare operation. The main component of natural gas, methane, is broken down at high temperature in the absence of oxygen: Specific process characteristics are:

- Use of zero emission energy to generate electrical power for reactor heating (Fuel cell, ORC, other)

- Hydrogen storage in LOHC,

- Hydrogen use for synfuel production.

The reaction is an endothermic process. Compared to other hydrogen production routes, the thermodynamic analysis of an ideal pyrolysis process shows energetic advantages. The energy required to provide hydrogen during pyrolysis (37.8 kJ/mol H2) is significantly lower than the energy required to produce hydrogen from natural gas using steam reforming (63.3 kJ/mol H2) or to provide renewable hydrogen using electrolysis (285.9 kJ/mol H2).

The history of commercial thermal decomposition of methane dates back to the 1920’s and is well documented in the scientific literature. Reactor thermodynamics and design are described in “Technology Development and Techno-economic analysis of hydrogen production by thermal decomposition of Methane’’ by T. Keipi, Tampere University of Technology, 2017, which is incorporated herein in its entirety. The use of catalysts determines reaction temperature and carbon product type (source of Fig. 2 and 3: Ind. Eng. Chem. Res. 2021 , 60, 1 1855-1 1881 “Methane Pyrolysis for zero emission hydrogen production”).

Fig. 2 shows the temperature range of applicability of different catalysts for methane pyrolysis.

Fig. 3 shows alternative reactor configurations for the pyrolysis stage.

[2] Preferably, pyrolysis stage b) comprises an offheat recovery stage. More preferably, the offheat recovery stage is an Organic Rankine Cycle (ORC) stage.

The purpose of the Organic Rankine Cycle (ORC) unit is to produce electrical and thermal power from recovered waste heat sources in a kWh to MWh scale, to enhance the overall efficiency. The electrical power output may be used to energize the various stages of the process. State of the art ORC turbogenerator equipment in this application can produce up to 40 MW of electric power per single generator. Examples for energy sources: Reaction heat in general, especially ~9 kWh/kg H2 from the Hydrogenation of LOHC at a temperature level of 150 - 200 °C. The working principle of such an ORC unit is as follows: the working fluid is pumped to a boiler where it is evaporated, passed through an expansion device (e.g. turbine, screw, scroll, or other expander), and then through a condenser heat exchanger where it is finally re-condensed.

The purpose of the LOHC hydrogenation/storage unit is to perform a chemical reaction, binding gaseous hydrogen in a safe, stable, and easily-transportable liquid organic hydrogen carrier (LOHC) for storage at ambient conditions. In this liquid form, hydrogen can be handled on a large scale within existing infrastructure, and can be transported globally over large distances without hydrogen loss.

The hydrogenation step is an exothermic chemical reaction between molecular H2 and another compound (carrier) in the presence of a catalyst. The carrier, e.g., dibenzyltoluene (DBT) oil, is an organic compound that provides ideal thermal stability, making it a suitable reversible hydrogen carrier (see e.g. A. Wunsch, T. Berg and P. Pfeifer, Materials (Basel). 2020 Jan; 13(2):277). Alternatively, monobenzyl toluene may be used as the LOHC substrate.

Reaction parameters are preferably pressures of 25 to 50 bar and temperatures of 150 to 200 C in the presence of catalysts specially developed for this application.

The LOHC molecule can be hydrogenated, i.e., hydrogen can be chemically bound. The reaction heat is 9 kWh/kg H2 (DBT system). Hydrogen storage capacity: 57 kg H2 in 1 m ³ of LOHC. The waste heat developed in this unit can be used in other processes (see ORC) and thus increases the overall system efficiency.

If the hydrogen is needed again, for example in chemical process plants, the steel industry, or to supply fuel cells to use electrical energy, it can be extracted from the LOHC in a dehydrogenation reaction. LOHC is stable and can be reused in a cycle up to ~ 7 years and then cleaned for further use.

[3] Preferably, the c) stage providing electrical energy is a fuel cell.

[4] Preferably, the c) stage providing electrical energy provides electrical energy to the pyrolysis stage b).

[5] Preferably, the d) LOHC hydrogenation stage comprises an offheat recovery stage; preferably wherein the offheat recovery stage is an Organic Rankine Cycle (ORC) stage.

[6] In a preferred embodiment, gas separation stage a) has a hydrogen sulphide separation step prior to methane separation.

[7] The integrated unit for the conversion of flare gas according to the second aspect of the invention comprises i) gas separation means A), the gas separation means comprising means for providing one or more a1 ) methane-containing streams comprising at least 95 percent by weight of methane, and one or more a2) a gas separation off gas streams, the one or more a2) a gas separation off gas streams comprising less than 2 percent by weight of the methane comprised in the flare gas feed; ii) pyrolysis means B) comprising means for pyrolyzing at least part of the a1 ) methane- containing stream, the pyrolysis means comprising means for providing b1 ) a hydrogen-containing stream comprising at least 95 percent by weight of hydrogen, and b2) a carbon-containing stream comprising at least 95 percent by weight of carbon; iii) means for providing electrical energy C) from at least part of the b1 ) hydrogencontaining stream; and iv) Liquid Organic Hydrogen Carrier (LOHC) hydrogenation means D) comprising means for providing a hydrogen-loaded LOHC (LOHC+) stream.

Preferably, the integrated unit according to the invention is comprised of standard containers, such as 20 ft or 40 ft containers. For instance, means A) to D) may each be housed within a dedicated 20 ft or 40 ft container.

As shown in Fig. 1 , passing a flare gas stream of 526 m ³ per hour (353 kg per hour) to gas separation stage a) or unit A) captures 98% of the methane therein. Subsequent pyrolysis of the methane-containing stream will provide 259 kg per hour of carbon product, consuming 837.5 kW per hour of energy from a PEM fuel cell. Subsequent hydrogenation of the LOHC gives 630 liter of LOHC+ per hour, with generation of 22.5 kW per hour of hydrogenation offheat.