Kinetic Study of α-cellulose Hydrocracking Using Ni and Pd Supported on Mordenite Catalysts

Kinetic study of liquid product formation from hydrocracking of α-cellulose using Ni and Pd supported on Mordenite (MOR) catalysts had been conducted. The hydrocracking was performed in a semi-batch reactor with hydrogen flow (30 mL min-1). The catalysts were prepared by wet impregnation. The catalysts were characterized using Fourier Transform Infrared (FTIR), X-Ray Diffractometer (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray Spectrometer (SEM-EDX) and Inductively Coupled Plasma-Emission Spectroscopy (ICP-ES). Liquid product formed in hydrocracking of α-cellulose was measured under time variations of 30, 60, 90, and 120 min. at 450oC for each catalyst. The results showed that impregnation of metals increased the acidity and didn’t damage the crystallinity of MOR. The kinetics of liquid product formation using MOR, Ni/MOR and Pd/MOR catalysts followed the first order reaction with rate constant of liquid product formation (kL) of 0.0050, 0.0180 and 0.0069 min-1, respectively.


INTRODUCTION
Hydrocracking reaction can be carried out thermally or catalytically.The thermal hydrocracking reaction took a longer time to convert the feed into fractions with light carbon compounds 1 .The addition of catalyst in the cracking process will decrease the decomposition temperature so that it will lead to more efficient process 2 .The catalyst used in hydrocracking can be a bifunctional catalyst comprising a metal carrying on a carrying material.Trisunaryanti et al., (2012) compared mordenite and Y-zeolite activities for the hydrocracking of tires, and proved that mordenite had higher activity than Y-zeolite 3 .Mordenite, because of its uniform, small pore size, high internal surface area, flexible framework, and controlled chemistry, was widely used in catalysis, separation and purification [3][4][5] .Mordenit had been proved that it could be used as catalyst in hydrocracking process to convert low density polyethylene (LDPE) and tire waste to fuel fractions 6,7 .
The concept of a bifunctional catalyst had two active sites, in which the metal on the surface of supporting material act as an active site provides the hydrogenation/de-hydrogenation process and another site acted as acid sites that provided cracking reactions 8,9 .The interaction between metal and supporting material provided a very crucial role to increase catalytic performance and as a key factor in the dispersion, stabilization, and active side activity of the catalyst 10 .The Ni metal selected for its high stability, low price and great availability 11 .The use of Ni as a catalyst had been widely studied because it had good catalytic activity and cheap price.In addition, Ni catalysts had an advantage that was relatively high during reaction and can easily be recycled due to its magnetic properties 12 .The Pd metal had good chemical stability, thus acting as a good hydrogen adsorbent medium in hydrogenation reaction 13 .The effect Pd metal on mordenite and clinoptilolite had been studied and showed that Pd density increased significantly on zeolite surface area 14 .
In the bifunctional catalyst system, the reactant was dehydrogenated on the metal side, then diffuses at the Brønsted acid site so that it can be protonated into carbonium ions.The carbonium ion formed will undergo rearrangement or may create β-scission to form carbonium ions with shorter chains.The carbonium ion further diffused to the metal side and undergoes hydrogenation 15 .
Kinetic studies considering each compound and all the possible reactions were complex due the huge number of hydrocarbons involved.However, they permitted a mechanistic description of hydrocracking based on the detailed knowledge of the mechanism of the different reactions.Most of the times, applying this method to hydrocracking of real feeds was difficult because of analytical complexity and computational limitations 16 .
Mamleev and co-workers 17 , using Broido-Shafizadeh (BS) model, conducted kinetics study of cellulose conversion through two approaches: intermediate reactions between the starting material and the final product, and the formation of two end products i.e. volatile and coke products.Burnham group 18 approached the kinetic model through reacting fractions and volatile products.The result showed that reaction followed one-order reaction.Knowledge of chemical kinetics in degradation of solid compounds became a very important stage in the making of optimal reactor design and operation.By knowing the value of the constant rate of reaction it can be obtained an estimate value of the resulting conversion 19 .Although many reviews on hydrocracking had been published, kinetic aspects in hydrocracking had not received too much attention.
Lignocelluloses consist of 40-50% cellulose, 20-40% hemicellulose, and 20-30% lignin.Cellulose which was the main constituent of lignocellulose made it very crucial in the production of fuel and chemicals 20 .The cellulose crystal structure as well as the intermolecular and intramolecular hydrogen bonds made the cellulose difficult to dissolve in water as well as other conventional solvents.This problem induced a new challenge to produce fuel and chemicals directly from cellulose. 21sed on the explanation above, the author investigated kinetic study of liquid formation of α-cellulose hydrocracking using Ni and Pd metals supported on mordenite as catalysts was carried out by measuring the formation of liquid product at time variations of 30, 60, 90, 120 minutes.

Procedure Catalyst Preparation and Characterization
Metals (Ni and Pd) were loaded onto Mordenite (MOR) and were prepared by wet impregnation method using metal salt solution.Solution was filtered and evaporated at 100 O C, after that calcinated at 450 O C for 3 h and continued by reduction (20 mL min -1 hidrogen flow) for 3 h producing Ni/MOR and Pd/MOR catalysts.The crystallinity of MOR, Ni/MOR and Pd/MOR was investigated by XRD.Surface morphology of catalysts was analyzed using SEM.The metal content on catalyst was investigated using EDX and ICP-ES.Catalysts powder were pelleted using KBr and were analyzed at 4000-300 cm -1 using FTIR.

Kinetic study of liquid poduct formation
α-cellulose and catalyst in a weight ratio of 10:1 were loaded in a semi-batch reactor (h: 30.0 cm; l: 30.0 cm; o.d.: 4.50 cm; i.d.: 3.75 cm).The reaction time was varied for 30, 60, 90, and 120 min at 450 O C for 4 h with 30 mL min -1 hydrogen flow.The reactor was connected with condenser and the liquid product was collected in an ice-bath system.

Catalyst Characterization
Catalyst characterization were analyzed with FTIR, XRD, SEM-EDX and ICP-ES from our previous study 22 .Based on FTIR analysis indicated that the amount of acid sites increased after metals (Ni and Pd) impregnated on mordenite.Total acid sites of MOR, Ni/MOR, and Pd/MOR were 0.48; 2.46; and 4.75 mmol g -1 .The XRD analysis showed that there was no damage structure in the MOR after the metals impregnation, indicating that no crystalline transformations occurred during the impregnation of metals onto Mordenite.Based on the SEM image there was no changing in the surface morphology of the catalyst after the impregnation of metal on the mordenite.This result indicated that no crystalline transformations occurred during the impregnation of metals onto the mordenite.Based on ICP-ES analysis, metal impregnated on mordenite catalyst was 0.32 wt.% and 0.50 wt.% for Ni/MOR and Pd/MOR respectively.

Kinetic Study
The catalyst and feed were placed on different lumps, the catalyst was located above the feed and separated by wire net.The feed would evaporate when the heating energy provided was sufficient, the feed vapour reached catalyst and catalytic reaction occured.The catalyst would speed up the cracking process so that the liquid product would flow out of the reactor and reached the condenser.Products with smaller molecular mass and smaller C atoms could not be condensed into liquid products and exited the reactor system as a gas product.Effect of feed evaporation on the reactor system used in this study was only caused by the heat given when it did not reach catalyst yet.The liquid product formation occurred when cleavage of the feed formed high boiling point compounds so that it can be condensed and became a liquid product (P).The number of liquid product yields will be proportional to the reaction time (t) till reached the maximum reaction.The unevaporated feed became the residue (A).The formation of a liquid product over time can be modelled through a kinetics study of