Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Patent
1987-04-21
1988-09-06
Konopka, Paul E.
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
423461, 502418, C01B 3112, B01J 2020
Patent
active
047693592
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of adsorbent carbon, in particular active carbons suitable for adsorbing gases e.g. hydrocarbons such as methane.
It is disclosed in U.S. Pat. No. 3,764,561 that activated carbon may be made by treating finely divided coal with a small quantity of an inorganic potassium salt. The specification states that both solid salts and aqueous solutions may be used. The Examples show the formation of a mixture of coal and powdered salts which is then carbonised at low temperatures e.g. 450.degree.-700.degree. C. The specification indicates that the quantity of inorganic potassium salt should not be more than about 2.5% by weight.
U.S. Pat. No. 4,082,694 discloses that activated carbon may be made by heating coal or coal coke or petroleum coke with hydrous KOH so as to dehydrate the mixture, followed by a second heating step at a higher temperature to give the active carbon. The carbon feed is intimately mixed with solid or liquid hydrous KOH. The upper limit of 25% water in the hydrous KOH is set by the ease of handling the alkali and the feed mixture. The description is generally directed to the use of solid KOH rather than liquid.
We have now found a method of producing active carbons which enables high adsorption of gases per unit volume to be obtained.
According to one aspect of the present invention the process for the production of active carbon by treating a carbonaceous feed with KOH and subsequently carbonising the carbonaceous feed is characterised in that the carbonaceous feed is intimately mixed with a hot liquid mixture comprising KOH and NaOH in a molar ratio of NaOH to KOH of from 80:20 to 20:80, heating the mixture to a temperature of at least 500.degree. C., in an inert atmosphere maintaining the mixture at this temperature for not less than 5 minutes, then allowing the carbon to cool in an inert atmosphere to below combustion temperature, followed by washing to remove alkali metal compounds.
The carbonaceous feed may for example be any of the feeds used in the process of U.S. Pat. No. 4,082,694. An example of suitable feedstocks are Pittsburgh No 8 (HVBA) coal cokes and chars. Brown coals or lignites may be used as feed. However, it is particularly preferred to use high rank coals. In particular it is preferred to use coals with the following characteristics: (as defined by the British Coal Classification System 1956).
Carbon content greater than 92.0 wt %,
Hydrogen content less than 3.9 wt %,
Volatile matter content less than 9.0 wt %.
All values are on a dry mineral matter free basis. Where a coal coke or char is used it is preferably prepared by carbonising at not more than 800.degree. C., preferably not more than 500.degree. C.
The carbonaceous feed preferably has low ash content preferably not more than 5% wt. The content of carbonate ash in particular is preferably low.
The particle size of the carbonaceous feed is preferably not more than 1 mm.
The mixture of NaOH and KOH preferably contains NaOH and KOH in the molar range ratio of 70:30 to 30:70. It is particularly preferred to use mixtures whose composition is close to that of the eutectic mixtures, e.g. 65:35 to 57:42 and 45:55 to 55:45 (NaOH:KOH).
A mixture of NaOH and KOH in a molar ratio of 1:1 form an eutectic mixture melting at 170.degree. C., which has a low viscosity.
The hot liquid mixture of NaOH and KOH is preferably at a temperature of at least 100.degree. C. and is preferably not more than 300.degree. C. Commercially available KOH usually contains a proportion of water (10-20% by weight). The presence of this water does not have an adverse effect on the production of the carbon. However in order to minimise energy consumption in the production of the carbon it is preferred to have not more than 20% wt water present in the mixture of KOH and NaOH.
The intimate mixture of carbonaceous feed and molten NaOH/KOH mixtures is preferably formed by introducing carbonaceous feed into the molten liquid with agitation to aid in the wetting of the carbonaceous feed with the molt
REFERENCES:
patent: 3166483 (1965-01-01), Masiantonio
patent: 3387941 (1968-06-01), Murphy et al.
patent: 3764561 (1973-10-01), Nishino et al.
patent: 4082694 (1978-04-01), Wennerberg et al.
Audley Gary J.
Holder Keith A.
Konopka Paul E.
The British Petroleum Company p.l.c.
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