CATALYST DEVELOPMENT FROM LOCALLY AVAILABLE RESOURCES – (A CASE STUDY OF NICKEL-SILICA CATALYST)

ABSTRACT

The efficacy of silica obtained from our local sand as a carrier in synthesis of Nickel-Silica catalyst  was  investigated.  Six  samples  of  soil  were  collected  from  two  different  sites (comprising five white coloured samples collected from Iva valley,  lower part of Milliken hill,   namely: pottery 2 (P2), down iva (DI), run-off iva (ROI),  pottery rock (POR), white chalk (WTC) and one brown coloured sample (UdS) collected from Udi Siding) in Enugu, Nigeria.  Prior  to  treatment  by flotation  method,  some  properties  that  could  affect  their catalytic use like organic matter content, texture, porosity and pH were assayed. (i) P2 (pH, 4.7; fine sand, 74.29 %; organic matter, 0.26 %), (ii) DI (pH, 4.7; fine sand, 72.72 %; organic matter, 0.26 %), (iii) ROI (pH, 7.4; fine sand, 87.42 %; organic matter, 0.19 %), (iv) POR (pH, 6.4; fine sand, 85.65 %; organic matter, 0.0%), (v) WTC (pH, 4.7; fine sand, 83.59 %; organic matter, 0.07 %) and (vi) UdS (pH, 4.4; fine sand, 32.79 %; organic matter, 0.19 %). Three of the samples with the best results ROI, POR, and WTC as can be seen above were selected. The pre-treated sand was purified by leaching process using 20 % HF, 20 % H2SO4, 10 % NaOH and distilled water. Comparison of the XRD results of the raw sand sample and silica extract showed complete removal of Al, Ca, and other oxide impurities from the raw sand. The silica was coupled with nickel employing two catalyst preparation methods. The Deposition method was used to couple silica with Ni(NO3)2  to prepare the catalyst named DPNN and NiCl2 to prepare the catalyst named DPNC. In the Co-precipitation method, silica was coupled with NiCl2  to prepare the catalyst named CPNC. The surface area, pore volume and particle size distributions of the catalyst samples were determined by N2 adsorption at 77 K using Trister  II Plus BET analyzer.  The elemental  composition  was obtained  by  XRF spectroscopy. Effect of using two different nickel precursors for coupling was investigated; the  result  showed  that  NiNO3   gave  a  higher  degree  of  Ni  dispersion  and  incorporation compared  to  NiCl2.  Effect  of using two  different  catalyst  preparation  methods  was also investigated;  Co-precipitation  method allowed  the  highest  degree of Ni incorporation  and improved surface properties. The results showed that Ni-silica catalysts prepared using silica from the local soil has catalytic properties that are similar to the standard Ni-Silica catalyst, Euro Ni-1, and better catalytic properties than some previously synthesized ones reported by Unichema, C. B. V. (1990), Wang, W. et al (2006), and Hermida, L. et al (2012).

1. INTRODUCTION

1.1 BACKGROUND OF STUDY

CHAPTER ONE

The search for catalysts or improved catalysts seems to be a never ending one since  small reductions in operating temperature and pressure, or small differences in yields or product distribution  affected  by catalysts can have great economic importance  on  the commercial scale.

Catalysts  are chemical substances  that modify the rate of a chemical reaction, usually by acceleration;  while  catalysis  is  the  process  in  which  the  rate  of  a  chemical  reaction  is influenced by a catalyst1,2. Examples of catalysts include hydrogen ion, Vanadium (v) Oxide, nickel etc. Industrial catalytic processes includes: hydrogenation of oils, Ammonia synthesis, cracking of petroleum, Friedel Crafts reaction etc.

In  most  cases,  industrial  catalysts  contain  3  groups  of  components:  catalytically  active materials,  catalyst  support  and  promoters.  Catalytically  active  material  is a  precursor  to industrial catalyst; they possess appropriate catalytic properties (activity and selectivity) but still do not have the complex of properties required for industrial catalyst. The complex of properties  include proper pore structure, long lifetime, high  resistance to deactivation  and poisons,   easy  regeneration,   low   operating   temperature,   high   thermal   stability,   high

mechanical strength, resistance to attrition and low price3.

Sand is everywhere around us, not often used in the chemistry laboratory as it contains a lot of impurities. Adding value to sand by purification turns it into silicon dioxide  which has many applications in chemistry. Furthermore, combination of silica with some catalytically active substances like alumina, nickel, platinum, copper etc makes it improved catalyst with better activity and evenly dispersion of the active agent on the carrier.

Improvements that may result from dispersion of the catalytically active agent include:

    Increase of available surface

    Stabilization against crystal growth and sintering

    Creation of a favourable orientation of surface molecules

    Improvement of mechanical strength

Nickel-silica  catalysts  have  potential  application  generally  for  hydrogenation4,5;  also  in petrochemical industry for processes like deoxygenation, methanation, reforming, and hydro- cracking6.

The existence of raw sand with proper composition and catalytic ability has been reported;

the sand was treated and used to accomplish the catalysis of Friedel Crafts acylation7.

Catalysts  are  employed  in  many  industrial  processes;  special  mention  is  made  of  the processes for the manufacture and upgrading of motor gasoline. This industry is by far the largest  user  of  catalyst  and  has  been  the  inspiration  for  much  of  the  progress  in  the

development of catalysts and the techniques of their manufacture and use8.

Steps involved in catalyst development are as follows:

•     Choice  from  previous  knowledge,  of  the  elements  or  compounds  known  to  be effective in reactions of the type under consideration;

•     Narrowing  down  by actual  experimental  test,  of  the  list  of  possible  catalysts  to identify those that are most promising;

•     Attempting to improve the performance  of the catalysts  selected  by preparing  and testing  their  mixture,  by subjecting  them  to  treatments  designed  to  increase  their specific surface area, by trying different activation methods, and by varying the size of the catalyst particles;

•     Attempting to characterise the detailed form and structure, as well as the properties of the catalyst and to correlate them with the performance of the catalyst.

1.2 Statement of Problem

The use of imported  catalyst  is the order of the day. In our research lab; the small  scale reactions employ expensive imported catalyst, likewise our chemical industries that produce in large scale.

Silica is cheap and readily available, but it is imported; intensive research on purifying our local soil and producing silica based products from it is needed to put our raw materials to use.

Although many efficacious catalysts exist and nickel-silica (Ni-SiO2) has been synthesized6, there is need to develop the best of the catalyst by trying different methods of preparation and comparing  their  products.  Presently,  no  combined  silica  catalysts  have  been  synthesized employing silica from our local soil, to the best of our knowledge.

1.3 Research Objectives

This work is aimed at:

      Testing different  soil samples with the aim of selecting  the sample with the  best surface features for catalyst application;

      Purification  of the samples using both physical  means and chemical  leaching  into silica; this makes it suitable for application in many chemical industries/processes;

      Development of nickel-silica catalyst using silica from the locally available soils by co-precipitation and deposition methods;

    Physico-chemical characterisation of the prepared nickel silica catalysts; and

      Optimization of preparation method for the nickel-silica catalyst and comparing the effect of two nickel precursors on the final product.

1.4      Justification of the Study

The successes of basic research in the field of catalysis have direct effect on solving many fundamental  problems  that  face  humanity.  Examples  of  such  solutions  include:  efficient utilisation of raw materials, mastering of new sources of energy and  improvement  on the

existing ones, and development of efficient systems for environmental protection3. Due to high cost of running high temperature engines coupled with the long duration of some chemical  reactions,  it becomes  imperative  to resort  to use of catalysts  to speed  up such reactions. It is also unreasonable to import expensive and non-specialty catalysts while their alternatives could be synthesized locally.

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