(224d) Fluid Behaviors of Kaolin Slurry

It is well known that Fluid Catalytic Cracking (FCC) process plays an important role in petroleum refining industry, and FCC catalyst is the core of FCC process. Since kaolin was introduced into the manufacture of semi-synthetic FCC catalyst, the rheology of kaolin slurry was potential in catalyst processing such as pipe transporting and stirring. It was found that, with the different conditions of kaolin slurry, the fluid behaviors of slurry could be different. It was expected that the results of this study could provide some basic data for the improvement of commercial FCC catalyst manufacture. 2          Experimental Section

Kaolin slurry was prepared by mixing kaolin clay (Suzhou kaolin clay) and water. In slurry, pH was controlled by adding acid and base. There were different kinds of dispersants including anionic organic dispersants (e.g.PN), cationic organic dispersants (e.g. BO) and non-ionic organic dispersants (e.g. VD).The rheology was measured by Rotovisco RV20 made by HAAK corp. 3          Results and Discussion

Rheology (viscosity and fluid behaviors) of kaolin slurry that was affected by solid content, dispersants and zeolite was discussed in this section. 3.1        Effects of solid content

The effects of solid content were investigated before further study on the slurry affected by the dispersants.

Fig.1. showed that the influence of solid content on the rheology of slurry. The shear stress rose with the increasing of shear rate. The rheology curves approached to Para curves from straight line with solid content increasing. In the same conditions on shear rate, the shear stress increased when solid contents rose. Those mean the viscosity of slurry increased with adding of kaolin.     

Fig.1. Rheology curves affected by solid content

a- solid content  22%; b- solid content  10%£»

c- solid content  7%£»d- solid content  4%£»e- solid content  1%

      Tab.1. showed the fitting results in different conditions of solid content which were taken from the rheology curves in Fig.1. When solid content was 1% and 4%, the formulate suitable to data was chosen as

¦"-¦"_y=¦Ç_pD                          (1)

¦"_y=yield stress

¦Ç_p=plastic viscosity

With solid content in 1% and 4%, the suitable formulate was power-law which was often represented by the following formulate:

¦"=kDⁿ                                     (2)

k=fluid consistency index

n=flow behavior index

It mean that with the increasing of the solid content of kaolin slurry, the viscosity of slurry rose and it became pseudoplastic fluid (the solid content) from Classical Bingham plastic fluid (the solid content).

Tab.1. Fitting results in different conditions of solid content

When solid content was 1% and 4%, yield stress and plastic viscosity of slurry increase with solid content rising. When solid content was 7%, 10% and 22%, fluid consistency index and flow behavior index increased with solid content rising. The dimensions of  K depended upon the value of n, K was therefore not a material property ^[1] .It could be concluded that the meaning of n also depended on K. 3.2        Effects of dispersants

Effects of different types of dispersants were discussed in Tab.2.

Tab.2. Viscosity affected by different dispersants

Solid content =22%,pH=7,shear rate=150s^-1, dispersants/solid content=0.005;

Viscosity of slurry decreased with the addition of PN (anionic organic dispersant), but the additions of BO and VD could not effectively cause the decrease of viscosity.

Tab.3. Fitting results of dispersants

Then different formulates were chosen to fit the curves when the addition amount of dispersant was changed in Tab.3. The slurry approached to Classical Bingham plastic fluid from pseudoplastic fluid, with the increasing amount of PN. When the power-law formulate suit to the curves of slurry, k and n was decreasing with addition of PN. 3.3        Effects of zeolite in different conditions

Tab.4. showed that the fluid behaviors of slurry were affected by zeolite in different conditions.

It was dependent on the conditions of dispersants that the rheology of slurry was affected by the addition of zeolite. When kaolin slurry was mixed with zeolite, the viscosity decreased. VD and BO could not change the fluid behaviors of slurry efficiently, but PN can. If the amount of PN was enough, the mixed slurry would become Classical Bingham plastic fluid.

Tab.4. Fitting results of zeolite in different conditions

4          Conclusion

With the increase of the solid content of kaolin slurry, the viscosity of slurry increased and the slurry became pseudoplastic from plastic fluid. Rheological properties (viscosity and fluid behaviors) of the slurry could be altered by dispersants. With the addition of anionic dispersants (e.g.PN), the viscosity of kaolin slurry was effectively reduced and it became plastic fluid from pseudoplastic fluid. The rheology of slurry was affected by the addition of zeolite depending on the conditions of dispersants.

Acknowledgement

We thank all staff of our institute. This work is supported by SINOPEC.CORP.

Literature Cited

[1]John Harris,Rheology and non-Newtonian flow,Longman,London and New York,1977,5-6

[2]C.Tiu,D.V.Boger, Rheology and non-Newtonian fluid mechanics,Australia,1983,7-14