Modelling Sulfonation Kinetics On The Sodium Lignosulphonate Synthesis From Black Liquor

Surfactant is a compound that has the ability to lower the interfacial tension between the face of two phases (liquid). The need of surfactant has increased along with the development of the industrial sector. One example is sodium lignosulfonat (SLS) which is useful to improve oil acquisition in its application for EOR (Enhanced Oil Recovery). SLS is a result of the reaction between lignin, NaHSO3 (bisulfite) and sodium hydroxide as catalyst. The purpose of this research is to determining the reaction mechanism and determining the value of the reaction rate constant (k). The sulphonation kinetics of lignin was carried out in various temperature (50, 60, 70, 80, and 90C). From this research obtained a positive (linear) response between sulfonation temperature against reaction rate constants. The lowest k values obtained k50 = 2,05 x 10 minute and the highest one is k90= 3,35 x 10. From graphycally calculation obtained the value of A is 0,015 and the energy activation (Ea) is -11,708 kJ/mol with R = 95,69%. The correlation of the temperature influence to the constant of reaction rate espressed in arhenius equation as follows : k = 0,015 exp (-1408,3/T)


Introduction
Black liquor (BL) is side result of pulp processing with lignin as main component approximately 46% of total solid [1].In successive year, Black liquor production increase as the growth of paper demand.This solution is stable, complex, smelly and has toxic compound such hidrogen sulfide, methyl mercaptan.It means, dumping to the environment cause pollution.Nowadays, the utilization of BL only for energy source for pulp mill, and use as biofuel [2].Black liquor has high of density is caused by black liquor also has high of solid content [3].
Surfactant are compound that lower the interfacial tension, between two liquids.It compose of polar (hydrophilic) and non polar (lypophilic).The need of surfactant in Indonesia increase a long with the development in the industrial sector.During this time, surfactant commonly used is petroleum-based.This surfactant have good performance, but not ecofriendly, hard to degrade, comes from non-renewable materials [10].Therefore, it takes an effort to create a new surfactant with the same good or better performance and more sustainable.Development of surfactants is being carried out which one of them is sodium lignosulfonat (SLS) from biomass such as lignin.SLS can be produced from lignin through a sulfonation process.This process aim to substitute hydroxyl groups with sulphonate groups which is more polar (Fig. 1).The use of this surfactant such as emulsifying agents, emulsion stabilizer, dye dispersant, floacculants [11], for mud viscosity control during deep oil well drilling, corrosion inhibitor [13].
This research is intended to study the kinetic reaction of sulfonation process in batch reactor.It becomes important to determine the chemical reaction mechanism and determine the value of reaction rate constant (k).The reaction rate is defined as increasing Corresponding author: pramudono2004@yahoo.com Lignin is a major wood component beside cellulose and hemicellulose, consists of three dimensional monomer namely p-coumaryl alcohol (H), koniferil alcohol (G) and sinapyl alcohol (S) [4].Lignin are formed by polymerization of monomers which differ structure depending on plant type.It means that, each plant type have different structure of lignin [5].Lignin is colorless, amorphorus, renewable [6].Usually, lignin is used as a cement water reducer, composite materials [7], surfactant and dispersant for cement admixture [8], Flocculants for waste water [9].Basicly lignin is hydrophobic in nature, so lignin insoluble in water, acid, and hydrocarbon but soluble in alkali solution.It means, lignin from BL can be isolate by acid.

Kinetic Reaction
Experiment performed in batch reactor with fix volume, and temperature condition.Follow as 2 nd order reaction.

Analysis
UV spectrophotometric method is the best suited for determining the concentration of component like lignin, sodium bisulfit, and sodium lignosulfonat (SLS).In this experiment concentration were analyze by UV mini -1240 spectrophotometer pharco -300.Each component have different wavelength, for lignin λ = 205 nm [14] , for sodium bisulit λ = 288 nm, and for Sodium lignosulfonat λ = 232 nm [15].Based on fig. 2 and table 1 known that at the higher temperature of sulfonation process, reaction rate constant also higher.This is due to at the higher temperature (T) , the reactant molecular activation and the collision factor also increase.The reaction rate constant were increase at 1,1 fold every 10oC increment.based on the "rule of thumb" which states that every 10 degree temperature rise, the reaction rate constant (k) will increase twice as much.But in this study, only 1.1 times increased.It's cause the sulfonation reaction rate is affected by the concentration of the lignin active site and the total SO2 ion concentration.This result corresponds to the arrhenius equation, that temperature is proportional to the reaction rate constant (k).

Determine A and Ea
Ea (activation energy) is the minimum energy required for the reaction occur.Activation energy determined using Arrhenius equation.

Validation of reaction kinetics model
Reaction kinetics model used for the calculation of reactor capacity, in order to scale up the capacity of production.The best condition of sulfonation process is 90 o C in temperature, with reaction rate constant 3,35x10 -4 .Validation process is performed by comparing the value of Ca lab 90oC and Ca calc 90C .ln (Cb/Ca) = (Cb 0 -Ca 0 ) k.t + ln M (5) Ca = Cb/M.e (Ca0-Cb0).k(6) Based on the data, it can be concluded that reaction kinetics model is acceptable.From the calculation, the average of %error kinetics model is 1,091%.

Conclusion
Lignin sulfonation reaction kinetics follow as 2 nd order with the highest reaction rate constant occur at 90 o C, with k = 3,35x10 -4 and give 1,1 fold every 10 o C increment.The activation energy, collision factor (A) is 11,708 kJ/mol and 0,0015.Validation indicate that laboratory data (Ca lab ) and calculation (Ca calc ) result in similarity, so the reaction kinetics model is acceptable.
[out] + [rate of rx] = [acc] Batch reactor, so V = constant 0 -0 -C.V. k = dVC/dt If conversion of A = Xa, and initial concentration of A and B symbolized as Ca 0 , Cb 0 so we get (1) If C b0 = M.C a0 , so M = C b0 /C a0 and we get

Fig. 3 .
Fig. 3. ln k vs 1/T Based on fig.3, show that slope representing the value of -Ea/R and the intercept representing ln A. From the calculation, value of -Ea (with R = 8,314 J/K.mol) is 11,708 kJ/mol and the collision factor 0,015.The results showed that the value of Ea in this study was smaller when compared to the ismiyati (2013) in which Ea obtained was 21.27 kJ/mol.It is indicates that the energy required for sulfonation reaction is smaller.For this data experiment, reaction rate constant follow this equation : k = 0,0015.e -1408,3/T

Table 1 .
Reaction rate constant vs T

Table 2 .
Validation of Ca Calculation (at 90 o C)