Process for the preparation of hydrogen and carbon monoxide

Details Process for the preparation of hydrogen and carbon monoxide Process for the preparation of hydrogen and carbon monoxide

2000-04-11

2004-01-06

Silverman, Stanley S. (Department: 1754)

Compositions

Gaseous compositions

Carbon-oxide and hydrogen containing

C423S651000

Reexamination Certificate

active

06673270

ABSTRACT:

The invention relates to a process for the preparation of hydrogen and carbon monoxide by the catalytic partial oxidation of appropriate feedstocks.
The partial oxidation of gaseous hydrocarbons, in particular methane or natural gas, in the presence of a catalyst is an attractive route for the preparation of mixtures of carbon monoxide and hydrogen, normally referred to as synthesis gas. The partial oxidation of gaseous methane is an exothermic reaction represented by the equation:
2CH
4
+O
2
→2CO+4H
2
There is literature in abundance on the catalysts and the process conditions for the catalytic partial oxidation of, in particular, methane. Reference is made, for instance, to EP-A-303 438, EP-B-262 947, U.S. Pat. No. 5,149,464, International patent application publication No. WO 92/11199 and to publications by D A Hickman and L D Schmidt (“Synthesis Gas Formation by Direct Oxidation of Methane over Pt Monoliths”, J of Catal. 138, 267-282, 1992), A T Ashcroft et al. (Selective oxidation of methane to synthesis gas using transition metal catalysts”, Nature, vol. 344, No. 6264, pages 319-321, 22
nd
March, 1990), P D F Vernon et al (“Partial Oxidation of Methane to Synthesis Gas”, Catalysis Letters 6 (1990) 181-186), R H Jones et al. (“Catalytic Conversion of Methane to Synthesis Gas over Europium Iridate, EU
2
Ir
2
O
7
”, Catalysis Letters 8 (1991) 169-174) and J K Hockmuth (“Catalic Partial Oxidation of Methane over a Monolith Supported Catalyst”, Applied Catalysis B: Environmental, 1 (1992) 89-100), and EP-A-656 317.
In EP-A-656 317 the catalytic partial oxidation of methane at high gas hourly space velocities, i.e. in the range of from 20,000 to 100,000,000 h
−1
, is mentioned.
It will be clear that because of the H/C atomic ratio of methane (4), it is the best feedstock when large amounts of hydrogen are to be produced. When considering other sources for producing hydrogen it will be clear that hydrocarbons having more than 1 carbon atom have a lower H/C ratio which makes them less ideal.
Moreover, there is a well-known tendency of hyrocarbons having more than 1 carbon atom to be susceptible to the pyrolitic production of carbon rather than producing optimal amounts of H
2
and CO. This tendency becomes more pronounced as the number of carbon atoms in the hydrocarbon molecule increases. Apart from this tendency to form pyrolytic carbon, higher hydrocarbons also suffer from the intrinsic properties that mixtures of such hydrocarbons with air are very unstable and may lead to pre-emission ignition which is highly undesired.
Further, it is well-known that carbon deposits may also be caused by catalytic reactions and, again, this tendency will be more pronounced subjecting higher hydrocarbons to catalytic processes.
The catalytic partial oxidation of hydrocarbons which are liquid under conditions of standard temperature and pressure to hydrogen and carbon monoxide has been disclosed in U.S. Pat. No. 4,087,259. Liquid hourly space velocities (LHSV), i.e. litres hydrocarbon per litre catalyst per hour, of from 2 to 20 h
−1
are exemplified, which is equal to a gas hourly space velocity of up to 75,000 h
−1
for a mixture of air and gasoline. It is explicitly mentioned that a LHSV greater than 25 h
−1
will result in incomplete partial oxidation and thus in a lower yield.
In EP-A-262 947 the catalytic partial oxidation of hydrocarbons having 1 to 15 carbon atoms is disclosed. For methane, GHSV's of up to 42,500 h
−1
are described. It is mentioned in EP-A-262 947 that for higher hydrocarbons a lower GHSV will be chosen than for hydrocarbons having a lower number of carbons. For hexane, very low throughputs, i.e. 6.25 and 12.5 g/h, are exemplified. These throughputs correspond, with GHSV's below 1,000 Nl/kg/h. For a oxygen-to-carbon ratio in the range of from 0.3 to 0.8, the hexane conversion is, even at these low throughputs, below 80%.
The aim of the present invention is to provide a process for the preparation of hydrogen and carbon monoxide from organic feedstocks that are liquid under conditions of standard temperature and pressure (25° C. and 1 atm) at a very high yield, while avoiding the accumulation of carbon deposits on the catalysts.
Surprisingly, it has now been found that these requirements can be fulfilled by performing a catalytic partial oxidation process with organic feedstocks that are liquid under conditions of standard temperature and pressure at an oxygen-to-carbon ratio in the range of from 0.3 to 0.8 and at very high gas hourly space velocities.
Accordingly, the present invention relates to a catalytic partial oxidation process for the preparation of hydrogen and carbon monoxide from an organic feedstock, which process comprises contacting the organic feedstock and an oxygen-containing gas, in amounts giving an oxygen-to-carbon ratio of from 0.3 to 0.8, with a catalyst at a gas hourly space velocity in the range of from 100,000 to 10,000,000 Nl/kg/h, in which process the organic feedstock used is a feedstock containing hydrocarbons and/or oxygenates, which feedstock is liquid under conditions of standard temperature and pressure and has an average carbon number of at least 6.
The average carbon number can be calculated by a summation of the carbon number times the mole fraction for all fractions. Thus, the average carbon number n is defined as:
n=&Sgr;n
i
.x
i
wherein n
i
is the carbon number of a fraction i and x
i
is the mole fraction of fraction i.
In particular, the feedstocks to be used in the process according to the present invention contain hydrocarbons or mixtures of hydrocarbons boiling in the range of from 50° C. to 500° C., preferably in the range between 60° C. and 350° C. Suitable feedstocks comprise kerosene feedstocks boiling between 150° C. and 200° C., synthetic gasoil feedstocks boiling between 200° C. and 500° C., in particular between 200° C. and 300° C. The hydrocarbons to be used may be derived from biomass, such as for example biodiesel.
In order to measure the suitability of the feedstocks to be used in the process according to the invention, it may be useful to refer to the smoke point of the feedstock envisaged since the smoke point of the feedstock is an indication of the propensity of the feedstock towards the generation of carbonaceous deposits.
In general, smoke points (as determined by ASTM-D 1322-96) of more than 15 are representative of the feedstock for the catalytic partial oxidation. Preferred feedstocks have a smoke point of at least 18, more preferred above 25 whilst feedstocks having a smoke point of more than 60 such as synthetic gasolines (e.g. as produced via the Shell Middle Distillate Synthesis process can be suitably applied).
Another indication of the propensity of the feedstock towards the generation of carbonaceous deposits is the content of sulphur and metals such as Ni or V in the feedstock. Suitably, the sulphur content of the feedstock used in the process of the invention is below 150 ppm, preferably below 100 ppm. The content of Ni or V is suitably below 0.2 ppm, preferably below 0.1 ppm.
It is possible to have hydrocarbonaceous material present in the feedstocks to be used in the process according to the present invention which are gaseous under standard conditions of temperature and pressure provided the requirements of the feedstock being liquid under standard conditions of temperature and pressure and having an average carbon number of at least 6 are still met.
Hydrocarbons which are liquid under standard conditions of temperature and pressure contain up to 25 carbon atoms in their molecules.
The process according to the present invention can also be carried out when the feedstock contains oxygenates being liquid under standard condition of temperature and pressure and having an average carbon number of at least 6.
Oxygenates to be used as (part of) the feedstock in the process according to the present invention are defined as molecules containing apart from carbon and hydrogen atoms at least 1 oxygen atom which is linked to either one or

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