The present application is directed to the preparation of methanol synthesis gas. More particular, the invention uti lizes carbon dioxide introduced together with a hydrocarbon feed stream into a two-step reforming stage.

Production of synthesis gas e.g. for the methanol synthesis with natural gas feed is typically carried out by steam re forming or a combination of steam reforming and oxygen re forming .

The principal reaction of steam reforming is (given for me thane) :

CH ₄ + H ₂ 0 ¾ 3H ₂ + CO

And oxygen reforming (given for methane) :

CH ₄ + ½02 ¾ 2¾ + CO

Similar reactions occur for other hydrocarbons. Any reform ing is usually accompanied by the water gas shift reaction:

CO + ¾0 ¾ C0 ₂ + H2

Performing steam reforming, also known as SMR, and oxygen reforming, also known as autothermal reforming or in short ATR, in series is known as two-step reforming.

More details of steam reforming and 2-step reforming can be found in the literature. The product gas from 2-step reforming comprises hydrogen, carbon monoxide, and carbon dioxide as well as other compo nents usually including methane and steam.

Methanol synthesis gas has preferably a composition corre sponding to a so-called module (M= (H2-CO2) / (CO+CO2) ) of 1.90-2.20 or more preferably slightly above 2 (eg.2.00- 2.10) .

2-step reforming produces the above mentioned preferred stoichiometric module.

It is an increasing desire in the chemical industry to re duce emission of carbon dioxide and/or to utilize carbon dioxide as feed or a part of the feed in the production of chemical products.

In existing or new methanol plants employing or designed with two-step reforming in the preparation of methanol syn thesis gas, use of carbon dioxide as at least a part of the reforming feed is not an option because two-step reforming produces the stoichiometric correct synthesis gas for the methanol production leaving limited or no possibility for adding carbon dioxide to the reforming process.

We have found a method for the production of methanol syn thesis gas utilizing carbon dioxide by combining two-step reforming with a hydrogen preparation step arranged in par allel to the two step reforming, allows use of carbon diox ide as part of the feed in a two step reforming based meth anol plant. Thus, this invention provides in one aspect a method for the preparation of methanol synthesis gas comprising the steps of

(a) providing a first feed stream comprising hydrocarbon and steam;

(b) providing a second feed stream comprising carbon diox ide in amount to result in a carbon dioxide/hydrocarbon ra tio of between 01. and 0.8, preferably between 0.15 and 0.7 if the second feed stream is mixed with the first stream;

(d) introducing the first and second stream into a two-step steam reforming stage comprising a steam reforming step and an autothermal reforming step;

(e) withdrawing a first synthesis gas stream;

(f) providing a third feed stream comprising hydrogen; and

(g) applying the first synthesis gas stream together with the third feed stream as methanol synthesis gas.

The term "methanol synthesis gas" used hereinbefore and in the following description and claims shall be understood as any gas that can be used for methanol synthesis, e.g. make up gas or unconverted methanol synthesis recycled to a methanol reactor in a methanol loop.

Thus, in an embodiment of the invention, the first and a part or all of second feed stream are mixed upstream the steam reforming step in step (d) .

In further an embodiment, a part or all of the second stream is added to the reformed first stream upstream the autothermal reforming step. In an embodiment, the third stream comprising hydrogen is provided by one or more of:

(a) steam reforming of a stream comprising hydrocarbon and steam arranged in parallel with the two-step reforming pro cess;

(b) electrolysis of water;

(c) an external source.

In an embodiment, a further stream comprising carbon diox ide is added in (a) to the stream comprising hydrocarbon upstream the steam reforming.

In still an embodiment, a further stream comprising carbon dioxide is added to the third stream comprising hydrogen.

In an embodiment, the second feed stream comprising carbon dioxide is added to the first feed stream prior to the steam reforming step or to the feed stream leaving the re forming step in step (d) .

In an embodiment, a further stream comprising carbon diox ide is added to the third stream comprising hydrogen.

In an embodiment of the invention, the first synthesis gas has a module M of < 2.3, preferably 1.4 < M < 2.15, where M is (H2-CO2) / (CO+CO2) .

In an embodiment of the invention, the module M in the third stream comprising hydrogen is larger than the module M in the first synthesis gas. In an embodiment of the invention, the module M of the third stream comprising hydrogen is > 1.9, preferably >

2.0.

In an embodiment of the invention, a mixture of the first synthesis gas stream and the third stream with optional CO2 added has a module M of between 1.8 and 2.3.

In an embodiment of the invention, the carbon dioxide in the second feed stream or the further stream comprising carbon dioxide added to the third feed stream is obtained from flue or off-gas.

In an embodiment of the invention, the steam reforming pro cess is performed in a tubular reformer, a bayonet tube re former or a convective reformer.

In an embodiment of the invention, the first synthesis gas stream and the third stream with optional added CO2 is in a further step converted to a methanol product.

A suitable reforming catalyst composition for use in the steam reforming depends on the amount of carbon dioxide added to the feed and the type of reformer used in the steam reforming. In most cases, a nickel catalyst is suffi cient, but for high carbon dioxide contents in the feed, noble metal catalysts may be required for some types of steam reformers.

The carbon dioxide for use in the method according to the invention can advantageously be obtained from flue or off- gasses, such as e.g. flue gas stemming from the burners in the steam reformers.

Depending on the feed composition it might be preferred to desulfurize and prereform the first feed upstream the two- step reforming and/or the second feed upstream the steam reforming .

An advantage of the method according to the invention is i.a. a reduced energy consumption and a reduced CO2 foot print .

An additional advantage is that the method of the invention allows to generate a more reactive synthesis gas for metha nol production than the typical gas generated by two step reforming having a module close to 2. The higher reactivity makes the methanol synthesis reaction proceed faster and thus less reactor volume and catalyst is needed.

As already mentioned hereinbefore, the invention is addi tional useful in increasing production capacity of existing methanol plants based on two step reforming in the produc tion of methanol synthesis gas. Taking advantage of the possibility of generating a more reactive gas with the in ventions opens for the possibility of being able to in crease methanol production without having to add additional methanol synthesis reactor volume and catalyst or at least only a smaller volume than without the invention.

Accordingly, a further aspect of the invention is a method for revamping an existing methanol synthesis gas plant, comprising adding a steam reformer section and/or an electrolysis unit and/or a pipeline connected to an external hydrogen source in parallel to an existing two-step reforming section;

connecting the existing two step steam reforming section and optionally the added steam reformer section and/or electrolysis unit and/or pipeline connected to an external hydrogen source, to a pipeline connected to a carbon diox ide source and;

connecting an outlet line of the existing two-step reform- ing section and an outlet line of the added steam reformer and/or electrolysis unit and/or pipeline hydrogen source to a methanol synthesis plant.

The two outlet lines can be combined before the connection or can be connected separately.