Preparation of Granular Activated Carbons from Petroleum Residues James
S. Mattson
Division of Chemical Oceanography, Rosentiel School of -Marine and Atmospheric Science, University of *Miami, M i a m i , Fla. 331 @
Asphaltic petroleum residues can be transformed into a considerably more valuable article of commerce, granular activated carbon. The carbons prepared in the fashion described in this paper offer considerable promise as waste water treatment granular carbons. Economic considerations, which were investigated by Gulf Research and Development Co. (Harmarville, Pa.), indicate that the process i s one which should be of general commercial interest, yielding an excellent return on investment.
A c t i v a t e d carbon is available in two forms, granular and powdered. The granular grades are more expensive than the powdered, and of considerably better quality. Granular carbons are manufactured from bituminous coal, lignite, sulfonated petroleum residues (from “ M hite oil” processing), cocoanut shells, pecan shells, birch and maple wood, and a few other raw materials. Granular activated carbon made from petroleum residues, primarily aliphatic in nature and containing a large portion of “asphaltene,” provides a n economically attractive method of production. The fact that the product takes on a granular form of about ideal size for waste water treatment is attractive. I n this paper, the properties of granular activated carbons prepared from petroleum residues are presented with a view toward their end use in waste water treatment. Experimental Section
Propane-butane-extracted residuals (Gulf Research and Development Co., Harmarville, Pa.) were subjected to sulfonation as described by Goren and Elkins (1957). The sulfonated residues were subsequently activated with steam or CO?. The properties of the starting materials are presented in Table I. The first step in the activation process was sulfonation. Concentrated sulfuric acid was added to the solid (at room temperature) propane-butane-extracted asphaltene, in a ratio of 3.7 to 1. This inhomogeneous mixture was stirred constantly as the temperature was brought up to 100”. After 2 hr a t looo, the temperature was slowly raised to 450°, where it was maintained until the mixture was nearly dry. The temperature profile is hhown in Figure 1. Occasional stirring was employed while the mixture remained fluid. As Figure 1 illustrates, the surface area of the sulfonated asphaltene began to increase steadily after the temperature 1% as raised above 250’. Prior to the treatment, the asphaltene was benzene soluble and about 70y0pentane soluble aq well. The reaction product became insoluble in benzene, concentrated KOH, aiid other common laboratory solvents after only 5 min of contact. Infrared spectroscopic analyses of various starting materials indicate that they are about 7.590% aliphatic. Infrared spectroscopic internal reflection analysis of the 5min aliquot of the sulfuric acid-asphaltene reaction shows only the very intense sulfonate absorption band. Following the sulfonation step, the solid, granular residue was sieved to 12 X 40 (U.S. Sieve) mesh. This sized, sulfo31 2 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 4, 1973
nated asphalt was then heated for 30 min a t 500°, in a fluidized bed with a continual flow of nitrogen, in order to remove volatile matter. Activation of the starting material was then carried out, also under fluidized conditions, using either steam a t 900-920’ for 1-2 hr or COz a t 900-950” for 3-4 hr. One of the COZ activations was sampled throughout the run. The surface area and mercury pore volume data obtained are presented in Figure 2. As Figure 2 illustrates, the surface area increased steadily until it reached a maximum, beyond which the erosion of pore walls tended to increase the “diameters” of the micropores. Raw Materials Required. The following data are based on a unit weight of starting material. The experimental yields in Table I1 can be used t o calculate the amount required per unit weight of product. i.Sulfuric Acid. Either concentrated or 30% fuming sulfuric acid could be employed. We employed 200 m1/100 g of asphalt (3.7 kg of concentrated HnS04/kg of asphalt). Of this amount, most of it was returned directly as SO2 during the nitrogen “flushing” step. The sulfonated asphalt contained approximately 5% sulfur, so a small amount of makeup sulfuric acid would be required. The total amount of makeup acid would be about 6% of the ureight of the starting asphaltene. ii. Nitrogen. Sitrogen was used in the 30-min, 500’ step. About 9.5 l./min of Nz was required to maintain a fluidized bed in a 2-in. diameter tube with a charge of 70-80 g of sulfonated asphalt. Fluidization, however, was unnecessary, and a n Nz flow of 3.0 l./min (at 300°K) per 100 g mas sufficient to carry away the volatile components. iii.Steam o r CO,. The activating atmosphere of steam or CO? had to be supplied a t a flux sufficient to maintain a fluidized bed. Several examples of flow rates required for COZ activation are given in Table 111. (The activation tube uas of 2-in. i.d. unless otherwise noted.) I n general, a n expected final yield of 37% (based on the weight of asphaltene) was typical for steam activation of material similar to that described in Table I aiid 25% for COz activation of such material. The optimum COz activation time was 3 hr. This compares to 6G90 min for steam. For run 20, the COS used was 29 kg/kg of charge. However, the charge weight did not appear to be a limiting factor, in that the CO, was not completely exhausted by the time the influent gas reached the top of the activating column. I n run 27, the amount of COz required for activation
~~
~~~~
~~
Table II. Reaction Yields
Table I. Typical Properties of Starting Material.
A. Sulfonation and Removal of Volatiles
1 042 1 04 87 89 24 7
Specific gravity
% sulfur yo carbon % carbon residue (Conradson) Viscosity (SUS), see Softening point, "C a Propane-butane-extracted residual.
Run no.
5797 (at 149') 77
Starting material no.
16
14
18, 19
14
21,22 24 25,26 27
1 1 1 3
Yield,
%
80 (before removing volatiles) 68 (after removing volatiles) 65 as 12 X 45 mesh 68 (after removing volatiles) 61 as 12 X 45 mesh 72 (after removing volatiles) 52.2 as 12 x 45 mesh 4 9 . 1 as 12 X 40 mesh 42.1 as 12 X 40 mesh
B. Activation
P
c
Run no.
21 22 23 24a 24b 26 27a
I a
Figure 1 . Temperature program and development of surface area with time during H4SO4 treatment of South Louisiana-Nigeria propane-butane-extracted asphalt
750
Gas
coz coz
HzO Hz0 HzO Hz0
coz
Time, hr
3 3 1 1 1.5 1 3.5
Temp,
%
Surface area, m%/g
46.2 64.6 57.6 65.6 58.8 54.1 30
1390 569 786 a 1001 1037 1644
Yield,
O C
920-930 905-920 900-910 900-905 900-910 900 850-905
Not applicable.
Table 111. COz Flow Required to Maintain Fluidized Bed during Activation Step. Run no.
Temp, O C
COz flow, I./min at 300'K
16 900-950 2.8-4.5 16 950 7.9 17 900 5.5-6.3 18 920-940 5.8-6.4 ( 7 . 5 a t end) 20 900-920 4.5 21 920-930 4.5 22 910-920 1.2-1.4 (1-in. tube) 0 , 8 (1-in. tube) 27 900 a Average CO1 flux (300'K) is 1.63 l./(min in.2).
i
0 T I R E , HRS
Figure 2. Development of surface area (circles) and mercury pore volume (triangles) as a function of activation time in COZ at 930-950'. Data taken from run no. 20
was 6.8 kg of COz/kg of charge. The results of the activation in run 27 were optimum so it seems safe to assume that a maximum of 6.8 kg of COZ/kg of charge will be required for activation. The theoretically required amount of CO, can be approximated by examining the reaction scheme
C(s)
-
+ coz 17 CO(s) + CO(g) cob)
CO(d
(la) Ob)
Charge wt, g
66.9 49.1 13 , 0 4 0 13.0-50 13.1-50 69-150 37-57 13-44
The reaction of C 0 2 with carbon, which was discussed in more detail elsewhere (Ergun and Jlenster, 1965; Mattson and Mark, 1971), involves the reduction of COz to form a surface oxide intermediate (reaction l a , followed by the evolution of CO from the carbon surface (reaction l b ) ) . This reaction scheme is complicated in practice by the accompanying water gas shift reaction, reactions with the "impurities" present in the starting material, etc. However, the theoretical amount of COz required for activation, assuming a burn-off of 50Y0 of the charge by reactions la-lb, would be 7.35 kg of CO,/kg of charge. Thus, the experimentally obtained value of 6.8 kg of C02/kg of charge must be reasonably close to the maximum efficiency attainable. For steam, the flow rate required for fluidization was greater than that required for CO, by the inverse ratio of their molecular weights. The amount of water required for activation should closely approximate the value obtained for C02, as the steam activation reaction scheme can be represented by
C(S)
-
+ Hz0 J_ CO(s) + Hz CO(s)
CO(d
@a) (2b)
During steam activation, the starting material (5.1770 S) was also desulfurized (
