Isobutane and olefin are feeds into the alkylation unit which combines the olefin with butane to increase octane and lower the vapor pressure of the product for blending. Alkylation is used in combination with fractional distillation, catalytic cracking and isomerization to increase the yield of automotive gasoline. Either sulfuric or hydrofluoric acid is used as the catalyst for the alkylation reaction. Both catalysts operate at low temperatures and high isobutane-to-olefin ratios to reduce the side reactions and catalyst consumption. Sulfuric acid is a liquid under normal operation conditions, while hydrofluoric acid is a gas. Produced alkylates are passed through caustic to remove residual acids.
Online Acid Strength Determination
Acid acts as a catalyst in a refinery alkylation reaction, therefore, a minimal amount of acid is required to enable the reaction to occur. As acid strength declines, undesirable side reactions increase and can cascade in a runaway manner that consumes all of the acid in the unit. This can lead to undesirable polymer formation or oily sample formation depending on the type of acid used. In the hazardous environment, rugged online analyzers monitor the concentration of acid used in the alklyation
Alkali concentration can be measured using a similar online analyzer.
Monitoring Alkylation by CIC
Insufficient acid strength in the HF Alkylation unit can lead to flurobutane formation. In an acid runaway situation, the amount of organic fluorides in the alkylate product elevates as acid is consumed and exits with the alkylate. Metrohm provides easy to use solutions for the residual organically bound fluoride and sulfur in iso-butane and olefin feeds by Combustion IC with a gas box that can withstand pressure up to 400 psi.
Residual Moisture Content
The alkylate is blended to make gasoline with specific Research Octane Number (RON) values and residual water content in the alkylate can induce corrosion. For finished product quality assurance the moisture content determination in the alkylate product is important.
The 875 KF Gas Analyzer from Metrohm provides predefined methods for water content determination in liquefied and permanent gases.