The production of synthesis gas by either partial oxidation or steam-reforming is well known and there are extensive literature references to these processes. The processes may be used separately or they may be combined. Thus, the steam-reforming reaction is highly endothermic and is described as: EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 ( 1)
while the partial oxidation reaction is highly exothermic and is described by: EQU CH.sub.4 +O.sub.2 .fwdarw.CO+H.sub.2 +H.sub.2 O
The combined reaction employing a 2/1 CH.sub.4 /O.sub.2 feed ratio is described as: EQU 2CH.sub.4 +O.sub.2 .fwdarw.2CO+4H.sub.2
In addition to these reactions, the mildly exothermic water gas shift reaction also occurs: EQU CO+H.sub.2 O.fwdarw.H.sub.2 +CO.sub.2
The representation of the combined process shows that the ratio of produced hydrogen to carbon monoxide is 2/1; the approximate stoichiometric hydrogen/carbon monoxide ratio for producing higher hydrocarbons by a hydrocarbon synthesis process, such as the Fischer-Tropsch process over a catalyst with little or no water gas shift activity.
A number of patents illustrate these processes, and U.S. Pat. No. 4,888,131 contains an extensive, but not exhaustive listing thereof.
Fluid bed processes are well known for the advantages they provide in heat and mass transfer characteristics. Such processes allow for substantially isothermal reactor conditions, and are usually effective in eliminating temperature runaways or hot spots; however, with O.sub.2 injection while complete elimination of hot spots is impossible although the fluid bed does tend to minimize the intensity thereof. They are not, however, without their disadvantages: catalyst strength or attrition resistance is important for maintaining the integrity of the catalyst and minimizing the formation of fine particles that may be lost from the system, especially those particles not recoverable by use of cyclones and deposited in down stream equipment causing fouling or reverse reactions as temperature is decreased; erosivity, or the tendency to erode equipment must be contained, since attrition resistance is often an inverse function of erosivity.
Additionally, the relatively high temperatures, e.g., above about 1650.degree. F., found in reforming reactions where oxygen is present can cause agglomeration of the catalyst particles leading to lower catalytic efficiency (e.g., lower conversion), larger particles that are more difficult to fluidize, greater wear on equipment due to greater momentum and impact forces, and clogging of lines. For example, a common catalytic material, nickel, even when deposited in small amounts on a suitable carrier, e.g., less than about 5 wt. % nickel on a support, tends to soften at reaction temperatures (due to its reactivity with the support phase with concomitant formation of reactive/lower melting mono- and polymetalic oxide phases), which become sticky, and generally lead to particle agglomeration. Particle agglomeration, in fact, tends to increase as the amount of nickel present in the catalyst bed increases or as the Ni containing phase is subjected to multiple oxidizing and reducing cycles as it is transported through the fluid bed. The behavior of Ni/Al.sub.2 O.sub.3 in H.sub.2 and steam rich environments has been reported, E. Ruckenstein et al, J. Catalysis 100 1-16 (1986). Thus, maintaining the amount of nickel at rather low levels in the catalyst bed minimizes particle agglomeration. On the other hand sufficient nickel is required for providing economical feed conversions to synthesis gas, i.e., within about 200.degree. F. approach to equilibrium, thereby minimizing the level of CH.sub.4 exiting the syngas generation zone.
Processes similar to fluid-bed steam-reforming processes for the preparation of synthesis gas are also illustrated by U.S. Pat. No. 4,758,375 and European patent publication 0163 385 B1 relating to spouted-bed technology and the use of inert materials in the bed.
An object of this invention, therefore, is taking advantage of fluid-bed or spouted-bed processes for the production of synthesis gas from lower alkanes, e.g., C.sub.1 -C.sub.4, feeds while substantially eliminating particle growth at elevated temperatures. Another object of this invention is approaching a minimum nickel concentration in the reactor while continuing to provide economic conversion levels.