Steam reforming

Abstract

A process is described for steam reforming a hydrocarbon-containing feedstock, comprising passing a mixture of the hydrocarbon-containing feedstock and steam through a catalyst bed comprising an eggshell nickel steam reforming catalyst disposed within a plurality of tubes in a gas-heated reformer and recovering a reformed gas from the plurality of tubes, characterised in that the catalyst bed has an inlet temperature in the range of from 400 to 560 °C, an exit temperature ≤ 850 °C, and the pressure of the mixture of the hydrocarbon-containing feedstock and steam is in the range of from 30 to 100 bar abs.

Description

[0001] Steam Reforming

[0002] This invention relates to a process of steam reforming hydrocarbons to produce a synthesis gas and to apparatus for carrying out the process.

[0003] Synthesis gas comprises hydrogen and carbon oxides (carbon monoxide and carbon dioxide) and may contain nitrogen and other gases such as argon and low levels of methane. The synthesis gas may contain greater or lesser amounts of hydrogen and carbon oxides suited to the particular end use, such as hydrogen manufacture for refineries or fuel cells, ammonia synthesis, methanol synthesis, dimethylether synthesis or the Fischer-Tropsch process for the synthesis of liquid hydrocarbons. Synthesis gas is often produced by a steam reforming process.

[0004] In a steam reforming process, a mixture of a hydrocarbon feedstock and steam, and in some cases also carbon dioxide, is passed at an elevated pressure through particulate catalyst-filled tubes, which are externally heated by a hot gas mixture, typically formed by a combusting fuel in a fired reformer. The particulate steam reforming catalyst is normally in the form of shaped units, e.g. cylinders having a plurality of through holes, and is typically formed from a refractory support material, such as alpha-alumina, calcium aluminate or magnesium aluminate, impregnated with a suitable catalytically active metal such as nickel.

[0005] Eggshell catalysts, in which the active nickel component is present as a thin layer at the surface are disclosed in WO2010125369 A1 . These catalysts advantageously contain lower levels of nickel than conventional impregnated or precipitated catalysts.

[0006] WO2022034283 A1 discloses the use in a steam reforming process of an eggshell steam reforming catalyst comprising 2.5 to 9.5% by weight nickel, expressed as NiO, wherein the nickel is provided in a layer at the surface of the catalyst and the thickness of layer is in the range of 100 to 1000pm.

[0007] Gas-heated reformers, where the catalyst-filled tubes are heated by convection rather than radiation using a hot gas, often a synthesis gas generated by partial oxidation or secondary autothermal reforming, provide a steam reforming processes with reduced carbon dioxide emissions. However, the inlet temperatures normally used are generally too low for eggshell catalysts to perform efficiently. Furthermore, compared to fired steam reformers, the heat exchange profile in gas-heated reformers means that a greater proportion of the catalyst operates at a lower temperature, which also is disadvantageous for eggshell catalysts. We have found that certain types of eggshell catalyst may be surprisingly effective when operated at elevated pressures in gas-heated reformers.

[0008] Accordingly the invention provides a process for steam reforming a hydrocarbon-containing feedstock, comprising passing a mixture of the hydrocarbon-containing feedstock and steam through a catalyst bed comprising an eggshell nickel steam reforming catalyst disposed within a plurality of tubes in a gas-heated reformer and recovering a reformed gas from the plurality of tubes, characterised in the catalyst bed has an inlet temperature in the range of from 400 to 560 °C, an exit temperature < 850 °C, and the pressure of the mixture of the hydrocarbon- containing feedstock and steam is in the range of from 30 to 100 bar abs.

[0009] The use of eggshell catalyst in gas-heated reformers overcomes several problems associated with the use of conventional nickel catalysts in fired steam reformers or gas-heated reformers.

[0010] The hydrocarbon-containing feedstock fed to the process may comprise any gaseous or low boiling hydrocarbon feedstock, such as natural gas, associated gas, LPG, petroleum distillate, diesel, naphtha or mixtures thereof, or off-gases from chemical processes, such as a refinery off-gas, or a pre-reformed gas. The hydrocarbon-containing feedstock preferably comprises methane and may be a pre-reformed gas, an associated gas or natural gas. Natural gas is an especially preferred feedstock. The feedstock may be compressed to a pressure in the range 30 to 100 bar abs. The pressure of the hydrocarbon-containing feedstock may usefully govern the pressure throughout the process. The pressure of the mixture of the hydrocarbon- containing feedstock and steam is in the range of 30 to 100 bar abs. The pressure of the mixture of the hydrocarbon-containing feedstock and steam is preferably in the range of 35 to 100 bar abs, more preferably 40 to 80 bar abs, most preferably 60 to 80 bar abs as this provides an enhanced performance from the process.

[0011] If the hydrocarbon-containing feedstock contains sulphur compounds before or, preferably, after compression, the feedstock may be subjected to desulphurisation. Desulphurisation may comprise hydrodesulphurisation using CoMo or NiMo catalysts, and absorption of hydrogen sulphide using a suitable hydrogen sulphide absorbent, e.g. a zinc oxide adsorbent. An ultrapurification adsorbent may usefully be used downstream of the hydrogen sulphide adsorbent to further protect the steam reforming catalyst. Suitable, ultra-purification adsorbents may comprise copper-zinc oxide / alumina materials and copper-nickel-zinc oxide / alumina materials. To facilitate hydrodesulphurisation and / or reduce the risk of carbon laydown in the reforming process, hydrogen may be added to the compressed hydrocarbon-containing feedstock. The amount of hydrogen in the resulting mixed gas stream may be in the range 1 to 20% vol, but is preferably in the range 1 to 10% vol, more preferably in the range 1 to 5% vol. If the hydrocarbon-containing feedstock contains other contaminants, such as chloride or heavy metal contaminants, these may be removed, prior to reforming, upstream or downstream of any desulphurisation, using conventional adsorbents. Adsorbents suitable for chloride removal are known and include alkalised alumina materials. Similarly, adsorbents for heavy metals such as mercury or arsenic are known and include copper sulphide materials.

[0012] Where the hydrocarbon-containing feedstock is a pre-reformed gas containing methane, this may be formed by subjecting a hydrocarbon I steam mixture to a step of adiabatic low temperature steam reforming. The hydrocarbon may be a rich natural gas, naphtha or other hydrocarbon-containing feedstock containing hydrocarbons heavier than methane. Prereforming processes are known. In such processes, the hydrocarbon / steam mixture is heated, typically to a temperature in the range 400 to 650 °C, and then passed adiabatically through a fixed bed of a suitable particulate steam reforming catalyst, usually a precipitated catalyst having a high nickel content, for example above 40% by weight, expressed as NiO. During such an adiabatic low temperature reforming step, any hydrocarbons higher than methane react with steam to give a pre-reformed gas comprising a mixture of methane, carbon oxides and hydrogen. The use of an adiabatic reforming step, commonly termed pre-reforming, is desirable to ensure that the feed to the tubular steam reformer contains no hydrocarbons higher than methane and also contains a significant amount of hydrogen. This is desirable in order to minimise the risk of carbon formation on the catalyst in the downstream tubular steam reformer.

[0013] The hydrocarbon-containing feedstock is mixed with steam to form a reforming feed gas. The steam introduction may be performed by direct injection of steam and / or by saturation of the feedstock by contact of the latter with a stream of heated water. In some embodiments, the hydrocarbon-containing feedstock is saturated in a saturator fed with hot water to form a saturated gas mixture. The steam content of the saturated gas mixture may, if desired, be increased by the direct addition of steam. The water preferably comprises one or more of condensate streams recovered from the reformed gas, water recovered from the bottom of the saturator, and other condensate produced in the process. The amount of steam introduced is desirably sufficient to give a steam to carbon ratio of at least 1.8:1 , i.e. at least 1 .8 moles of steam per gram-atom of hydrocarbon carbon in the feedstock. It is preferred that the steam to carbon ratio is in the range 1 .8:1 to 5:1 , more preferably 2.0:1 to 3.5:1 , especially 2.0:1 to 3.2:1 as this provides an optimal balance of hydrogen production and efficiency.

[0014] The reforming feed gas mixture is then desirably pre-heated prior to reforming. This heating may be achieved in exchange with hot synthesis gas or another heated gas mixture. Desirably, the mixed stream is heated to an inlet temperature in the range 400 to 560 °C or 440 to 560 °C. The temperature of the catalyst bed mid-way along the catalyst-filled tubes is preferably in the range of 560 to 640 °C.

[0015] During the reforming process, methane reacts with steam to produce hydrogen, carbon monoxide and carbon dioxide. Any hydrocarbons containing two or more carbon atoms that are present are converted to methane, carbon monoxide and hydrogen. In addition, the water- gas shift reactions occur. Overall, the process is endothermic, requiring heating of the tubes and catalyst to maintain the reaction and achieve the desired conversion. The heat input to the steam reformer is typically such that the temperature of product gas stream at the outlet of the tubes is higher than the inlet temperature. The outlet or exit temperature is < 850 °C.

[0016] The gas-heated reformer contains a plurality of catalyst-containing tubes, usually arranged vertically, through which the gas mixture may be passed, and to which heat is transferred by means of a hot gas flowing around the exterior surfaces of the tubes. The hot gas may comprise a synthesis gas formed from a reformed gas recovered from the plurality of tubes. The tubes have inlets typically at the top end such that the feed gas mixture is typically fed to the top of the gas-heated reformer and flows downward through the tubes. Thus the gas- heated reformer may have an inlet for the feed gas, an outlet for a reformed gas mixture, and a plurality of vertical tubes in communication with the inlet through which the gas mixture may be passed, and to which heat is transferred by means of a hot gas flowing around the tubes in a heat exchange zone. The tubes may have a circular cross section and may have a length of 5 to 15 m and preferably a diameter in the range 5 to 30 cm.

[0017] In the present invention the tubes contain an eggshell catalyst. By the term “eggshell catalyst” we mean that the nickel in the catalyst is not uniformly distributed within the catalyst support but is concentrated at the surface and therefore forms a thin layer, with nickel being essentially absent beneath this layer. The thickness of the eggshell layer in the present invention is preferably in the range of 250 to 750pm, more preferably in the range 300 to 500pm, most preferably in the range 350 to 450pm and particularly about 400pm. These thicknesses particularly provide the necessary conversion at the pressures used in the process. The thickness of the layer may readily be established using electron probe microanalysis (EPMA) or optical microscopy on cross-sectioned catalysts.

[0018] The nickel in the eggshell catalyst is supported on a shaped particulate catalyst support. The shaped particulate catalyst support may be formed from any suitable material, such as a refractory metal oxide comprising alumina, titania or zirconia or an alkaline earth metal aluminate, preferably one or more calcium aluminate compounds and / or magnesium aluminate. Eggshell catalysts supported on alkaline earth metal aluminates are preferred because they have higher stability and strength in use and may be more resistant to unwanted carbon formation than alumina-supported catalysts. Calcined shaped alkaline earth metal aluminate supports may be prepared by forming a calcium aluminate cement powder and / or a magnesium aluminate powder, optionally with additional alumina and / or lime, into a shape and subsequently calcining the shape. Other oxidic materials, e.g. titania, zirconia or lanthana, may be present in the support. A particularly suitable support comprises 30 to 70% by weight of a calcium aluminate cement (comprising 65 to 85% by weight of alumina and 15 to 35% by weight of CaO) mixed with 24 to 48% by weight of alumina, 0 to 20% by weight of lime. The catalyst support may, if desired, be “alkalised” by impregnation with a solution of an alkali such as potassium hydroxide. This serves to minimise lay down of carbon on the catalyst during steam reforming resulting from high temperature cracking of hydrocarbons and from the reaction of carbon oxides with hydrogen. Alkali oxide, e.g. potash, levels of up to about 5% wt on the calcined support may be used. If desired, the catalyst support may be treated with a solution of an alkaline earth metal, such as Ca or Mg. The catalyst support is desirably shaped using known pelleting techniques but may also be prepared by extrusion. The shaped support may be in any suitable shape but preferably the support is in the form of cylinders, which may have one or more through holes. Suitable diameters for cylindrical pellets are in the range 3-40 mm and the aspect ratio (length / diameter) is preferably < 2. The cylinders may be domed or flat-ended. More preferably the shaped support is in the form of a cylindrical pellet having between 1 and 12 holes extending there-through, especially 3 to 10 holes, preferably of circular cross section. The shaped support may additionally have between 2 and 20 flutes or channels running along the length of the pellet. Preferred shapes include a 4-hole quadralobe, a 5-hole pentalobe, a 7-hole cylinder and a 10-hole cylinder.

[0019] The eggshell catalysts may be prepared by impregnating a suitable nickel compound or salt, such as nickel nitrate or nickel acetate, into the shaped support. In order to form the desired eggshell layer, the shaped support may be treated with water to change the surface chemistry of the support, or impregnation conditions adjusted to cause deposition of the nickel just at the surface of the support.

[0020] Methods for preparing suitable eggshell catalysts are described in WO2010 / 125369 A1 and WO2012 / 056211 A1.

[0021] The nickel content of the eggshell catalyst, expressed as NiO, is preferably in the range 2.5 to 9.5% by weight, more preferably 2.5 to 5.5% by weight. Nickel contents, expressed as NiO, in the range 2.5 to 5.5% by weight are surprisingly effective and have the advantage of using less nickel than conventional steam reforming catalysts, thereby reducing exposure to the metal oxide and metal during manufacture, installation and discharge of the catalyst. The risk of selfheating of the catalyst on discharge is also reduced. Thus, one impregnation may be sufficient to generate the desired catalyst. However, if desired, impregnation may be repeated until the nickel content of the catalyst is at the desired level.

[0022] The nickel metal surface area in the eggshell catalyst may be 100m2 / kg or higher.

[0023] One or more promoter compounds may also be present but are usually not necessary and their inclusion in the eggshell catalyst is less preferred. If it is wished to include a promoter, one or more promoter compounds may be included in the nickel impregnating solution or the promoter may be added previously or subsequently by a separate impregnation. The promoter may be confined to the eggshell layer or may be distributed throughout the catalyst support. Promoters include platinum group metals such as platinum, palladium, iridium, ruthenium, rhodium and gold. Lanthanide metals such as lanthanum and cerium may also be included as promoters. Water-soluble salts, particularly nitrates, may be used as sources of the metal promoters.

[0024] More than one promoter may be present and additional alkali may also be added. The amount of promoter metal, if used, will typically be in the range 0.1 to 5% by weight on the active catalyst.

[0025] The eggshell nickel catalyst may be the sole catalyst or may be used in combination with other nickel steam reforming catalysts provided as layers within the tubes, wherein at least the layer of steam reforming catalyst adjacent the outlet is the eggshell nickel steam reforming catalyst. Thus, there may be a single eggshell catalyst in each tube, in which case the catalyst bed in the tubes consists only of the nickel eggshell catalyst. Alternatively, there may be two, three or more layers of nickel steam reforming catalysts in the tubes wherein in each case at least the layer adjacent the outlets of the tubes is the eggshell nickel catalyst. The tubes may therefore comprise a non-eggshell steam reforming catalyst upstream of the eggshell catalyst or another different eggshell catalyst may be present. The relative amounts of the steam reforming catalysts may vary in thickness to produce the desired conversion. In some embodiments comprising a layer of non-eggshell catalyst and a layer of eggshell catalyst adjacent the outlets of the tubes, the eggshell catalyst layer may comprise 95% to 5% of the volume of the bed or may comprise 80% to 20% of the volume of the bed or may comprise 75% to 25% of the volume of the bed. The other layers of steam reforming catalyst in the catalyst bed in the remaining part of the tube may be the same or different to the eggshell nickel steam reforming catalyst.

[0026] Where the catalyst bed consists of two or three layers of nickel steam reforming catalyst, the catalyst layers at the inlets of the tubes preferably have the same or a higher nickel content as the eggshell nickel catalyst layer adjacent the outlets. Where non-eggshell catalysts are employed upstream of the eggshell nickel steam reforming catalyst, the non-eggshell catalysts preferably have nickel contents, expressed as NiO, in the range 10% to 30% by weight. Thus, in some embodiments, the catalyst tubes may comprise or consist of two layers of nickel steam reforming catalyst wherein the catalyst layer adjacent the outlets of the tubes is the eggshell nickel steam reforming catalyst, preferably containing 2.5% to 9.5% by weight nickel, expressed as NiO, and the catalyst layer adjacent the inlets of the tubes is a non-eggshell nickel steam reforming catalyst, preferably containing 10% to 30% by weight nickel, expressed as NiO.

[0027] The catalyst is typically provided to the tubes of the tubular steam reformer in an oxidic form and activated by reduction of the nickel oxide, to form elemental nickel, in-situ. For example, the catalyst in oxidic form may be placed in the tubes, and the nickel oxide reduced with a reducing agent, such as a hydrogen-containing gas. Known reduction techniques may be used to generate the active catalyst for steam reforming.

[0028] Alternatively, nickel oxide in the catalyst may be reduced ex-situ and then the elemental metal coated with a thin passivating layer of oxide using an oxygen containing gas, such as air or nitrogen-diluted air. A mixture of oxygen and carbon dioxide, optionally with nitrogen, may also be used. In this way the reduced catalyst may be transported safely to the user, and the time to generate the active catalyst and quantity of hydrogen used during the subsequent activation, reduced.

[0029] A reformed gas, or crude synthesis gas, is recovered from the plurality of tubes. The reformed gas contains hydrogen, carbon monoxide, carbon dioxide, steam and methane.

[0030] The reformed gas recovered from the plurality of tubes is preferably subjected to a step of autothermal secondary reforming or partial oxidation to convert remaining methane and heat the resulting synthesis gas to a temperature where it may be used effectively to heat the tubes in the gas-heated reformer. Autothermal reformers and partial oxidation reactors are known and may be used for the process.

[0031] Preferably the plurality of tubes in the gas-heated reformer are heated by a synthesis gas, formed from a reformed gas recovered from the plurality of tubes, wherein the synthesis gas is at a pressure less than 10 bar below, preferably less than 5 bar below, more preferably less than 2 bar below, the pressure of the mixture of the hydrocarbon-containing feedstock and steam. Having allow differential pressure between the mixture of hydrocarbon and steam on the tube-side of the gas-heated reformer and the synthesis gas heating medium on the shell side of the gas-heated reformer allows the gas-heated reformer to operate safely at elevated pressures with a lower risk of tube rupture. The process of the present invention may be used as part of a process for the manufacture of hydrogen, methanol, dimethyl ether, olefins, ammonia, urea or hydrocarbon liquids, e.g. diesel fuels, obtained by the Fischer-Tropsch synthesis. Thus, the reformed gas may be subjected to further processing including one or more steps of cooling to below the dew point of the steam, separation of condensate, hydrogen separation, carbon dioxide separation, methanol synthesis, dimethyl ether synthesis, olefin synthesis, ammonia synthesis, or hydrocarbon liquid synthesis. Known processes may be used to accomplish these steps.

[0032] The invention is further described by reference to the following Examples and Figures 1 , 2 and 3, in which:

[0033] Figure 1 is a graph depicting a surface normalised methane steam reforming reaction rate in a pellet with varying nickel layer thicknesses at 440 °C and at pressures in the range 20-80 bar abs;

[0034] Figure 2 is a graph depicting a surface normalised methane steam reforming reaction rate in a pellet with varying nickel layer thicknesses at 634 °C and at pressures in the range 20-80 bar abs; and

[0035] Figure 3 is a graph depicting pressure versus required nickel layer thicknesses to achieve an equivalent rate of steam reforming reaction for a pellet at 616 °C.

[0036] Example 1

[0037] The effect of pressure and nickel layer thickness on the performance of an eggshell catalyst pellet was modelled. The steam reforming reaction modelled was:

[0038] CH4+ H2O ->• CO + 3 H2

[0039] This reaction is endothermic and so increasing the inlet temperature drives the reaction forward. However, gas-heated reformers use relatively low inlet temperatures. Furthermore, the increase in molecular number from the reactant to product side of the reaction, means that from an equilibrium point of view the process is favoured by lower pressures. The gas-heated reformer conditions were selected as follows:

[0040] The 440 °C temperature is an example of an inlet temperature. The 634 °C temperature is an example of a temperature of the catalyst bed mid-way along the catalyst-filled tubes. The diffusion and reaction of the process gas through a single pellet at steady state was modelled programmatically using Froment kinetic equations to calculate the reaction profile through the pellet. The geometry of the pellet used in the model was based on a 4-hole quadralobe pellet depicted in WO2010125369 A1 . The geometry was converted into an infinite slab for the purposes of the modelling. The nickel surface area was set at 100 m2 / kg. The model was used to study the effect on methane conversion at pressures of 20, 30, 40, 60 and 80 bar. The normalised rate of reaction through the profile of the pellet at 440 °C is depicted in Figure 1 . The rate of reaction was normalised against the rate at the surface (depth 0).

[0041] Figure 1 illustrates that at a low inlet temperature of 440 °C, at 20 bar the normalised rate of reaction within any point of the pellet requires a thicker egg-shell layer than at the higher pressures for equivalent normalised reforming rate. Only at the thicknesses above about 700 to 800 microns is the difference removed. Hence, Figure 1 shows that eggshell catalysts with thinner nickel layers and lower amounts of nickel are more effective above 30 bar abs, especially above 35 or 40 bar abs. Alternatively, Figure 1 illustrates that any given reforming rate of reaction may be achieved at a smaller relative depth when the pressure is increased.

[0042] The effect of increasing temperature is illustrated by Figure 2, which shows that at temperatures above the gas-heated reformer inlet temperature, such as at a example of a temperature of the catalyst bed mid-way along the catalyst-filled tubes, the differences between the pressures is reduced for thicker eggshell layers but even then, at about 400 microns the 20 bar normalised reaction rate is observably larger than the higher pressures. This means that through the length of the catalyst bed, higher pressures and thinner eggshell catalyst layers may be effective for achieving the desired methane conversion.

[0043] This is further illustrated by Figure 3 which demonstrates that to get an equivalent rate of reaction at 616°C a catalyst impregnated to a depth of about 360 microns may operate at about 40 bar, whereas a catalyst impregnated to a relative depth of 180 microns is equally effective at 75 bar, showing that satisfactory performance can be achieved with a thinner eggshell layer by increasing the pressure. Thinner eggshells result in catalysts with lower Ni contents. Thus, the invention surprisingly finds effective conversion with thinner layer eggshell catalysts, having lower Ni contents, at increased pressures.

Claims

Claims.1 . A process for steam reforming a hydrocarbon-containing feedstock, comprising passing a mixture of the hydrocarbon-containing feedstock and steam through a catalyst bed comprising an eggshell nickel steam reforming catalyst disposed within a plurality of tubes in a gas-heated reformer and recovering a reformed gas from the plurality of tubes, characterised in that the catalyst bed has an inlet temperature in the range of from 400 to 560 °C, an exit temperature < 850 °C, and the pressure of the mixture of the hydrocarbon- containing feedstock and steam is in the range of from 30 to 100 bar abs.

2. A process according to claim 1 , wherein the hydrocarbon-containing feedstock comprises methane.

3. A process according to claim 1 or claim 2, wherein the mixture of hydrocarbon-containing feedstock and steam has a steam to carbon ratio in the range 1 .8:1 to 5:1 , preferably 2.0:1 to 3.5:1 , more preferably 2.0:1 to 3.2:1 .

4. A process according to any one of claims 1 to 3, wherein the temperature of the catalyst bed mid-way along the catalyst-filled tubes is in the range of from 560 to 640 °C5. A process according to any one of claims 1 to 4, wherein the mixture of hydrocarbon- containing feedstock and steam is at a pressure in the range 35 to 100 bar abs, preferably 40 to 80 bar abs, more preferably 60 to 80 bar abs.

6. A process according to any one of claims 1 to 5, wherein the nickel is supported on a shaped particulate catalyst support.

7. A process according to claim 6, wherein the nickel is provided in a layer at the surface of the catalyst and the layer has a thickness in the range of from 250 to 700 pm, preferably 300 to 500 pm, more preferably 350 to 450 pm.

8. A process according to any one of claims 1 to 7, wherein the eggshell catalyst has a nickel content, expressed as NiO, in the range 2.5 to 9.5% by weight, preferably 2.5 to 5.5% by weight.

9. A process according to any one of claims 1 to 8, wherein the catalyst bed consists of one, two, three or more layers of nickel steam reforming catalyst wherein the layer of steam reforming catalyst adjacent outlets of the tubes is the eggshell nickel catalyst.

10. A process according to claim 9, wherein there are two or more layers of steam reforming catalyst within the tubes and the eggshell catalyst layer comprises 95% to 5% of thevolume of the bed, preferably 80% to 20% of the volume of the bed, more preferably 75% to 25% of the volume of the bed.

11. A process according to any one of claims 1 to 10, wherein the reformed gas is subjected to a step of autothermal secondary reforming or partial oxidation to form a heated synthesis gas and wherein the heated synthesis gas is used to heat the plurality of tubes in the gas-heated reformer.

12. A process according to claim 11 wherein the heated synthesis gas is at a pressure less than 10 bar below, preferably less than 5 bar below, more preferably less than 2 bar below, the pressure of the mixture of the hydrocarbon-containing feedstock and steam.

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