JP4777190B2 - Catalyst for producing hydrogen from hydrocarbon, method for producing the catalyst, and method for producing hydrogen using the catalyst - Google Patents

Description

  The present invention relates to a catalyst for producing hydrogen from hydrocarbons, particularly a hydrogen production catalyst used in a fuel cell, a method for producing a hydrogen production catalyst, and a hydrogen production method.

Conventionally, as a method for producing hydrogen from hydrocarbons, many methods using Ni or ruthenium catalyst and using city gas, LPG, or naphtha fraction as raw materials have been performed.
However, when assuming a small fuel cell power generation system for home use, light hydrocarbons such as natural gas and LPG have a high cost per calorific value, and low cost heavy hydrocarbons such as kerosene are used as raw materials from an economic viewpoint. A hydrogen production method that has been desired is desired.

However, low-cost kerosene and the like are heavy hydrocarbons, so carbon is likely to deposit on the catalyst. Therefore, if H ₂ O / C, which is one of the operating conditions, is increased, carbon deposition on the catalyst can be suppressed. However, since it causes an increase in water vapor intensity (water vapor consumption per product unit amount), It is desirable to make it low.
When a steam reforming reaction is performed using a Ni catalyst and a heavy hydrocarbon such as kerosene as a raw material, violent carbon deposition occurs on the catalyst regardless of the reaction temperature and H ₂ O / C conditions. Ruthenium-based steam reforming catalysts have also been studied as a catalyst with relatively little carbon deposition.

  In addition, when exposed to steam reforming reaction conditions for a long time, the catalyst strength may decrease, and the practical strength may not be maintained. Therefore, it is known to use an α-alumina support as a catalyst having excellent strength as well as activity. In Patent Document 1 (Japanese Patent Laid-Open No. 2001-276623), as a catalyst for efficiently improving the reforming activity of hydrocarbons, ruthenium which is an active component is a portion of up to 1/3 from the catalyst outer surface to the center of the catalyst. Discloses a catalyst using an α-alumina carrier supporting 50% or more of the total amount of ruthenium supported. However, α-alumina has a small surface area, and when a heavy raw material such as kerosene is used, there is a problem that sufficient reforming activity cannot be obtained with conventional catalysts.

JP 2001-276623 A

  An object of the present invention is to provide a hydrocarbon steam reforming catalyst capable of maintaining high activity while having a practical strength even when a hydrogen production reaction using heavy hydrocarbons such as kerosene is performed, and the catalyst And a hydrogen production method using the catalyst.

In order to achieve the above object, the present invention provides a catalyst for producing hydrogen by steam reforming from the hydrocarbons listed in the following 1-3 , and a method for producing hydrogen using the catalyst.
1. On the inorganic oxide carrier containing α-alumina, ruthenium is contained on a catalyst basis, 0.5 to 10% by mass in terms of metal, potassium is contained on a catalyst basis, 0.5 to 10% by mass in terms of metal, and EPMA ( Electron probe microanalyzer), when ruthenium was linearly measured in one direction from the outer surface of the catalyst to the other outer surface so as to pass through the center of the cross section of the catalyst, the length from the outer surface of the catalyst to the center was set to r _0. The sum of the characteristic X-ray intensities of ruthenium at a distance from the outer surface to 0.5r ₀ is in the range of 30 to 70% of the sum of the characteristic X-ray intensities of all rutheniums, and the distance from the outer surface of the catalyst to 0.7r ₀ hydrogen production by steam reforming from hydrocarbons, wherein the sum of the characteristic X-ray intensities of the ruthenium is from 40 to 80% of the sum of the characteristic X-ray intensities of all ruthenium in Catalyst.
2 . Using a solution containing a ruthenium-containing compound on an inorganic oxide carrier containing α-alumina, ruthenium is supported on a catalyst basis, 0.5 to 10% by mass in terms of metal, subjected to alkali treatment, and then at least using a solution containing a compound comprising one potassium, potassium catalyst criteria, after 0.5 to 10 mass% supported in terms of metal, by steam reforming according to the above 1, wherein the drying A method for producing a catalyst for hydrogen production.
3 . In the presence of the catalyst as described in 1 above, a hydrocarbon having a boiling point in the range of 30 to 350 ° C. and a steam having a fraction of 90% by mass or more is reacted with a reaction temperature of 400 to 900 ° C., a reaction pressure of 0 to 5 MPa- A method for producing hydrogen by steam reforming , characterized by reacting under conditions of G and H ₂ O / C (molar ratio) = _{2.5 to} 5.0.

The catalyst of the present invention is unlikely to cause a decrease in strength even when exposed to steam reforming reaction conditions for a long time, and the hydrogen production method using the catalyst of the present invention can be obtained from hydrocarbons, particularly heavy hydrocarbons such as kerosene. In the process for producing hydrogen, hydrogen can be produced while maintaining high activity even under severe reaction conditions for a catalyst of low H ₂ O / C (molar ratio) = _{2.5 to} 5.0.

  Below, the catalyst of this invention, its manufacturing method, and the manufacturing method of hydrogen using the same are demonstrated in detail. The hydrogen production catalyst of the present invention prepares an inorganic oxide containing α-alumina by calcining a raw material containing α-alumina or a precursor thereof at 600 to 1300 ° C., and uses it as a carrier. As the inorganic oxide carrier, α-alumina is preferably used alone, but it may be a composite oxide in which at least one of titania, silica, zirconia, magnesia and the like is mixed with α-alumina. In addition, an aluminum compound that generates α-alumina by firing at 600 to 1300 ° C., such as aluminum hydroxide and aluminum nitrate, can also be used as a carrier raw material.

A carrier can be prepared by heating and baking the above carrier raw material in an oxygen atmosphere, for example, air, at 600 to 1300 ° C. Although baking time is not specifically limited, Usually, it is 1 to 20 hours.
The shape of the carrier may be any shape other than various granular materials such as spherical, elliptical, prismatic, cylindrical, hollow, ring, tableting, etc., and is not particularly limited. A cylindrical or spherical granular material used for the reaction is preferred, and a spherical shape is particularly preferred. The size of the carrier is not particularly limited, but in the case of a cylinder or a sphere, the diameter is usually 1 to 6 mm, preferably 1 to 4 mm. In this case, the carrier can be prepared by firing using the shaped carrier material.

  The catalyst of the present invention contains ruthenium as an active component for hydrogen production in the carrier in an amount of 0.5 to 10% by mass, preferably 1 to 4% by mass in terms of metal. When the ruthenium content is 0.5% by mass or more, the desired number of active sites and the degree of dispersion can be provided, and the catalyst performance can be maintained. Moreover, if it is 10 mass% or less, it is economically preferable. When loading on the catalyst, a solution containing a compound containing ruthenium is used. Examples of the compound include ruthenium chloride hydrate, ruthenium chloride (IV), ruthenium chloride anhydride, ruthenium salts such as potassium ruthenate, ruthenium salts such as ruthenium nitrate, and the like. In addition, as a supporting method, a general metal supporting method such as a precipitation method, an ion exchange method, a coprecipitation method, a kneading method, and an impregnation method can be applied, and an impregnation method is preferable.

The catalyst of the present invention contains an alkali metal. The content of the alkali metal is 0.5 to 10% by mass, preferably 2 to 4% by mass in terms of catalyst and metal. Within the above range, the catalyst of the present invention can be imparted with the ability to suppress carbon deposition and the ability to activate steam, and the performance of the catalyst of the present invention can be kept stable over a long period of time. It becomes possible to highly disperse ruthenium which is an active ingredient on the top.
Examples of the alkali metal include Li, Na, K, Rb, Cs, and Fr. Na and K are preferable, and K is particularly preferable. Any one of these alkali metals may be used alone, or two or more thereof may be used in combination. In carrying the catalyst, a solution containing a compound containing an alkali metal is used. The compound is not limited as long as it is a precursor of an alkali metal, but an alkali metal salt is preferable, for example, nitrate, carbonate or hydroxide is preferable. In particular, with respect to the precursor of K, hydroxide, bicarbonate and carbonate are preferable, and hydroxide is most preferable.
Examples of the method for supporting the alkali metal on the catalyst include, but are not limited to, a precipitation method, an ion exchange method, a coprecipitation method, a kneading method, and an impregnation method.

Furthermore, in the catalyst of the present invention, when ruthenium is linearly measured in one direction from the outer surface of the catalyst to the other outer surface so as to pass through the center of the cross section of the catalyst by EPMA (Electron Probe Microanalyzer), the length to the center and r _0, the sum of ruthenium characteristic X-ray intensity at a distance from the catalyst outer surface to 0.5r ₀ is some 30 to 70% of the sum of the characteristic X-ray intensities of all ruthenium . Furthermore, the sum of the characteristic X-ray intensities of ruthenium at a distance from the outer surface of the catalyst to 0.7r ₀ is in the range of 40 to 80% of the sum of the characteristic X-ray intensities of all ruthenium. By supporting ruthenium, which is an active component, not only on the outer surface of the catalyst but also on the inside, the number of effective active points can be increased.

Next, the manufacturing method of the catalyst of this invention is demonstrated.
In the present invention, ruthenium is first supported on the inorganic oxide support containing α-alumina. For loading ruthenium, a conventional loading method such as a precipitation method, an ion exchange method, a coprecipitation method, a kneading method, and an impregnation method can be applied, but the impregnation method is preferable. A solution containing a ruthenium compound is prepared so that ruthenium is 0.5 to 10% by mass, preferably 1 to 4% by mass in terms of metal based on the catalyst, and the carrier is permeated and absorbed. Examples of the compound include ruthenium chloride hydrate, ruthenium chloride (IV), ruthenium chloride anhydride, ruthenium salts such as potassium ruthenate, ruthenium salts such as ruthenium nitrate, and the like. The temperature of the contained solution is preferably less than 50 ° C., particularly room temperature, in order to avoid decomposition of the ruthenium compound.

  The permeation time is not particularly limited, but is preferably 0.1 to 1 hour. If the time is shorter than 0.1 hour, the solution does not reach the entire catalyst and may become non-uniform. If the permeation time is within this range, the solution spreads uniformly throughout the catalyst, and ruthenium is supported inside. After supporting ruthenium on the inorganic oxide carrier, it is preferable to perform drying at 120 ° C. or lower, preferably 80 ° C. or lower, more preferably 50 ° C. or lower. Although it makes sense to dry in a noble gas such as helium or argon or an inert gas stream such as nitrogen, the amount of oxide produced is small even in the air when operated at 120 ° C or lower. It is not a problem. And if it is 120 degrees C or less, a subsequent reduction | restoration process will advance easily, without producing | generating ruthenium oxide. Moreover, the drying method is not particularly limited, but vacuum drying that can be quickly dried is particularly preferable.

  Subsequently, the carrier carrying ruthenium is immersed in an alkaline aqueous solution 3 times or more in terms of mole relative to the amount of ruthenium carried, and the ruthenium is converted to ruthenium hydroxide so that the ruthenium is insoluble and immobilized on the carrier. . As the alkaline aqueous solution used for insolubilization / immobilization of ruthenium, aqueous solutions of ammonia water, ammonium hydrogen carbonate, ammonium carbonate, sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like can be used. .

  In addition, after ruthenium is insoluble and immobilized as ruthenium hydroxide on the support, it is dried at 120 ° C. or lower, preferably 80 ° C. or lower, under reduced pressure or normal pressure in order to suppress oxidation of this ruthenium hydroxide. Is preferred. It makes sense to dry in a noble gas such as helium or argon, or an inert gas stream such as nitrogen. However, if it is operated at 120 ° C. or lower, the amount of oxide produced is in air. It is scarce and does not matter. In drying in the air, the lower the drying temperature, the more advantageous in terms of suppressing the formation of oxides. However, if the drying temperature is too low, the drying time is significantly increased, so the temperature is about 50 ° C. or higher. It is preferable. Therefore, the drying time may be appropriately selected according to the conditions such as the drying temperature and the amount of the object to be dried, but usually about 1 to 20 hours is preferable.

Next, an alkali metal is supported on the ruthenium-supported carrier. For supporting the alkali metal, a conventional supporting method such as a precipitation method, an ion exchange method, a coprecipitation method, a kneading method, and an impregnation method can be applied, but the impregnation method is preferable. A solution containing an alkali metal compound is prepared so that the alkali metal is 0.5 to 10% by mass, preferably 2 to 4% by mass, based on the catalyst, in terms of metal, and permeated and absorbed in the ruthenium-supported carrier.
The permeation time is not particularly limited, but is preferably 0.1 to 30 hours. More preferably, it is 1 to 30 hours, and usually 1 to 5 hours. By setting it to 0.1 hours or more, the solution can be spread to a desired portion of the catalyst, and can be uniformly permeated and absorbed. Preparation time can be shortened by setting it within 30 hours. Further, within the above range, the longer the permeation time, the higher the activity of the resulting catalyst.

Thereafter, drying is performed to suppress oxidation of ruthenium hydroxide insoluble and immobilized on the support. Here, drying is preferably performed at 120 ° C. or lower, preferably 80 ° C. or lower, under reduced pressure or normal pressure. By doing so, the desired catalyst of the present invention can be obtained.
It makes sense to dry in a noble gas such as helium or argon, or an inert gas stream such as nitrogen. However, if it is operated at 120 ° C. or lower, the amount of oxide produced is in air. It is scarce and does not matter. In drying in the air, the lower the drying temperature, the more advantageous in terms of suppressing the formation of oxides. However, if the drying temperature is too low, the drying time is significantly increased, so the temperature is about 50 ° C. or higher. It is preferable. Therefore, the drying time may be appropriately selected according to the conditions such as the drying temperature and the amount of the object to be dried, but usually about 1 to 20 hours is preferable. Moreover, after carrying | supporting an alkali metal, baking is not performed.

The hydrogen production catalyst of the present invention obtained by the production method of the present invention is preferably used after reducing ruthenium hydroxide insoluble and immobilized on the support before being subjected to the hydrogen production reaction.
Ruthenium hydroxide is reduced to metal ruthenium in a low temperature range of about 60 to 80 ° C. However, in the case of an extremely fine particle active metal, it is conceivable that a very small part of the active sites are affected by heat. In the present invention, in order to maintain stable catalyst performance for a long period of time, the catalyst is reduced at a temperature of 400 to 950 ° C., preferably 400 to 800 ° C., before being subjected to a hydrogen production reaction. If the reduction temperature of the catalyst is within the above range, the metal surface area is not decreased by ruthenium aggregation or sintering, and the desired catalytic activity can be maintained without clogging the pores of the support. As the reducing gas, hydrogen gas, hydrogen / water vapor mixed gas, carbon monoxide, or the like can be used. Among these, hydrogen gas and hydrogen / water vapor mixed gas are preferable, and hydrogen gas is particularly preferable. The reduction time may be appropriately selected according to conditions such as the reduction temperature and the amount of the reducing gas flow, but about 1 to 20 hours is practical.

In the method for producing hydrogen in the presence of the catalyst of the present invention described in detail above, as a raw material, carbonization having a sulfur content of 0.1 mass ppm or less, a carbon number of 1 or more, and a distillation range at atmospheric pressure of 350 ° C. or less. Hydrogen is preferably used, and hydrocarbons having a fraction having a boiling point range of 30 to 350 ° C. of 90% by mass or more are more preferably used, and a kerosene fraction can be particularly preferably used. At this time, the reaction pressure is 0 to 5 MPa-G, H ₂ O / C = 2.5 to 5, and the reaction temperature is not particularly limited, but 400 to 800 ° C. is suitable. The reaction method is not particularly limited, but a batch type, semi-continuous type or continuous type operation using a fixed bed or moving bed reactor is preferable.
In the hydrogen production method of the present invention, the catalyst of the present invention may be used alone or in combination with a catalyst other than the catalyst of the present invention.

In the following examples, the generated gas analysis is performed by filling a stainless steel (SUS) tube (inner diameter: 3 mm, length: 2 m) with a 60-80 mesh filler (Unibeads-C, manufactured by GL Sciences) and separating it. H ₂ , CO, CO ₂ , and CH ₄ were measured using a gas chromatograph (GC-390, manufactured by GL Science) with a thermal conductivity detector (TCD) attached as a column.
In addition, analysis of C _{1 to} C ₅ in the product gas was performed on a gas chromatograph (GC-390, manufactured by GL Science) with a flame ionization detector (FID) equipped with a capillary column of Al ₂ O ₃ / KCl as a separation column. I went. The amount of metal supported on the catalyst was confirmed by inductively coupled plasma emission analysis (ICP analysis).

The ruthenium line analysis was measured in one direction so as to pass through the center of the catalyst using an electron probe microanalyzer (EPMA, JXA-8200 manufactured by JEOL Ltd.). The measurement conditions were an acceleration voltage of 15 kV, an irradiation current of 1 × 10 ⁻⁷ A, an interval between measurement points of 12 to 15 μm, and a counting time of 30 msec. The cross section of the measurement catalyst was prepared by embedding the catalyst in MMA (methyl methacrylate), polishing with a polishing apparatus, and depositing carbon.

The activity of the catalyst of the present invention was evaluated by “raw material C ₁ conversion” obtained from the following formula 1. To indicate that the higher raw material C ₁ conversion is higher reforming ability, it can be said that a high catalytic activity.
The raw material C ₁ conversion was determined from the following formula 1.
[Formula 1]: Raw material C ₁ conversion (%) = [M / M ₀ ] × 100
(M ₀ : number of moles of carbon of feed hydrocarbon per unit time, M: number of carbon moles of C ₁ compound (CO, CO ₂ , CH ₄ ) in product gas per unit time)

Example 1
Alpha alumina powder (200 mesh) is formed into a spherical shape (spherical pellet) with a molding pressure of 2000 MPa (20 tons / cm ² ) and a diameter of 3.2 mm using a tableting molding machine (FK-1 type, manufactured by Systems Engineering). And calcined in a muffle furnace in nitrogen at 950 ° C. for 3 hours to obtain an α-alumina carrier.

Ruthenium chloride hydrate (RuCl ₃ .nH ₂ O, ruthenium content 39% by mass) 1.81 g was dissolved in 12.9 g of water, and this aqueous solution was added dropwise to 30 g of the α-alumina carrier, and the mixture was stirred at room temperature for 1 hour. Left to stand. Subsequently, the spherical pellets were heated to 50 ° C. with an infrared hot plate under a vacuum of about 2.7 kPa (about 20 mmHg) by a rotary evaporator and dried.
Next, the spherical pellet was transferred into about 1 L of 7 mol / L aqueous ammonia (diluted about twice as high as a commercially available reagent special grade), and stirred slowly with a stirrer for 1 hour to insolubilize and fix ruthenium. The spherical pellet was recovered from the aqueous ammonia using a Buchner funnel. The collected spherical pellets were thoroughly washed with ion exchange water. At the end of washing, an aqueous silver nitrate solution was dropped into a part of the filtrate, and the white precipitate of silver chloride was not generated. The washed spherical pellets were dried in a dryer at 80 ° C. for 15 hours. Next, 1.57 g of potassium hydroxide (special grade manufactured by Wako Pure Chemicals, purity of 85%) is dissolved in 14.1 g of ion-exchanged water and added dropwise to the total amount of the alumina carrier carrying ruthenium, so that the aqueous potassium hydroxide solution is uniformly distributed throughout the carrier. The mixture was stirred for 1 hour, allowed to stand for 1 hour, and then dried at 80 ° C. to obtain catalyst A. Catalyst A is composed of 1.9% by mass of ruthenium (in metal), 2.6% by mass of potassium (in metal), and the remaining alumina. Table 1 shows the physical properties of Catalyst A.

The reactor was charged with 2.5 ml of catalyst A, and reduced with hydrogen whose flow rate was adjusted with a mass flow controller at 0.9 MPa-G, 450 ° C., GHSV = 400 (v / v) h ⁻¹ for 1 hour. Subsequently, the desulfurized kerosene listed in Table 2 was introduced into the reactor as a raw material oil together with steam, and the steam reforming reaction was performed at a reaction temperature of 650 ° C., 0.9 MPa-G, H ₂ O / C = 3.0, The test was performed under the condition of LHSV = 5 (v / v) h ⁻¹ . The reaction results are shown in Table 1.

Example 2
Catalyst B was prepared in the same manner as in Example 1 except that the potassium permeation time was 3 hours.

Example 3
Catalyst C was prepared in the same manner except that the potassium permeation time was 24 hours in Example 1.

Comparative Example 1
α-alumina powder (200 mesh) is formed into a spherical shape (spherical pellet) with a molding pressure of 2000 MPa (20 tons / cm ² ) and a diameter of 3.2 mm using a tableting molding machine (FK-1 type, manufactured by Systems Engineering). And calcined in a muffle furnace at 900 ° C. for 3 hours in the air to obtain an α-alumina carrier. Next, 3.11 g of potassium hydroxide was dissolved in 16.5 g of ion-exchanged water, dropped onto 30.0 g of the above alumina carrier, stirred so that the aqueous potassium hydroxide solution was uniform over the entire carrier, and allowed to stand for 1 hour. After that, it was dried. Subsequently, it baked at 950 degreeC in the air in the muffle furnace for 3 hours, and obtained alpha-alumina-potassium oxide complex oxide.

Ruthenium trichloride hydrate (RuCl ₃ · nH ₂ O, ruthenium content 39 mass%) 3.2 g was dissolved in 12.8 g of water, and this aqueous solution was dropped into 30 g of the above-mentioned alumina-potassium oxide composite oxide. And left at room temperature for 1 hour. Subsequently, the spherical pellets were heated to 50 ° C. with an infrared hot plate under a vacuum of about 2.7 kPa (about 20 mmHg) by a rotary evaporator and dried.
Next, the spherical pellet was transferred into about 1 L of 7 mol / L aqueous ammonia (diluted about twice as high as a commercially available reagent special grade), and stirred slowly with a stirrer for 1 hour to insolubilize and fix ruthenium. The spherical pellet was recovered from the aqueous ammonia using a Buchner funnel. The collected spherical pellets were thoroughly washed with ion exchange water. At the end of washing, an aqueous silver nitrate solution was dropped into a part of the filtrate, and the white precipitate of silver chloride was not generated. The washed spherical pellets were dried in a dryer at 80 ° C. for 15 hours to obtain Catalyst D. The catalyst D is composed of 2.0% by mass of ruthenium (in metal), 0.6% by mass of potassium (in metal), and the remaining alumina. Table 1 shows the physical properties of Catalyst D. Reduction was performed in the same manner as in Example 1 to perform a steam reforming reaction. The reaction results are shown in Table 1.

As is clear from Examples 1 to 3, the catalyst according to the present invention is produced by supporting ruthenium and alkali metal in this order on an α-alumina support, and without rubbing after the metal is supported. By containing 0.5% by mass to 10% by mass of each, ruthenium metal is supported inside the catalyst. The heavy hydrocarbon desulfurization kerosene in the steam reforming reaction as a raw material, it is possible to obtain a high raw material C ₁ conversion.
Furthermore, a comparison of Examples 1 to 3, the longer the penetration time of the potassium high raw material C ₁ conversion of the catalyst, it can be seen that highly active catalysts.

Claims (3)

On the inorganic oxide carrier containing α-alumina, ruthenium is contained on a catalyst basis, 0.5 to 10% by mass in terms of metal, potassium is contained on a catalyst basis, 0.5 to 10% by mass in terms of metal, and EPMA ( Electron probe microanalyzer), when ruthenium was linearly measured in one direction from the outer surface of the catalyst to the other outer surface so as to pass through the center of the cross section of the catalyst, the length from the outer surface of the catalyst to the center was set to r _0. The sum of the characteristic X-ray intensities of ruthenium at a distance from the outer surface to 0.5r ₀ is in the range of 30 to 70% of the sum of the characteristic X-ray intensities of all rutheniums, and the distance from the outer surface of the catalyst to 0.7r ₀ wherein the sum of the characteristic X-ray intensities of the ruthenium is from 40 to 80% of the sum of the characteristic X-ray intensities of all ruthenium in, manufactured by hydrogen by steam reforming from hydrocarbons Use catalyst. Using a solution containing a ruthenium-containing compound on an inorganic oxide carrier containing α-alumina, ruthenium is supported on a catalyst basis, 0.5 to 10% by mass in terms of metal, subjected to alkali treatment, and then at least 2. The steam reforming according to claim 1 , wherein a solution containing a compound containing one kind of potassium is used for supporting potassium in an amount of 0.5 to 10% by mass in terms of a catalyst, and then dried. Of producing a catalyst for hydrogen production by the method. In the presence of the catalyst according to claim 1 , a hydrocarbon having a boiling point in the range of 30 to 350 ° C and a water vapor of 90% by mass or more is reacted with a reaction temperature of 400 to 900 ° C and a reaction pressure of 0 to 5 MPa. A method for producing hydrogen by steam reforming , characterized by reacting under the conditions of -G, H2O / C (molar ratio) = _{2.5 to} 5.0.