The ester plant is a highly automated and flexible batch plant located indoors. The plant was commissioned in 1998 and is capable of processing a wide range of ester products. Alcohols and fatty acids are initially prepared in a weigh-vessel before being transferred to the reactor vessel. Reacted ester is then cooled while transferring to the bleacher vessel. The ester is further refined in the bleacher vessel before being filtered though a pressurized 5,000 liter Dr. “M” Fundabac candle filter into dedicated storage tanks. The filter is used to remove the carbon which was added for color control.
The main process operation steps for the manufacture of all products are: pre-weighing of fatty acid and alcohol in the pre-weigh vessel, followed by esterification in the reactor to produce the crude ester, and finally neutralization, bleaching, filtration, and deodorization of the product in the bleacher vessel to meet the finished product specifications (normally acid value, color, and odor).
The rectification of the low boiling alcohols, methanol and isopropanol, is carried out using the reactor column when sufficient alcohol has accumulated in the wet alcohol storage tanks.
The pre-weigh vessel is a stainless steel tank with 33 m³ capacity. It is mounted on load cells with internally fitted hot water heating coils, agitator, and nitrogen blanket. The reactor charge recipe of fatty acid, alcohol, carbon, and catalyst are weighed into the pre-weigh and warmed to a maximum of 80°C while the reactor is occupied. Alcohols used in this process are glycerol, propylene glycol, butyl alcohol, octyl alcohol, and tri-methylol propane (TMP).
The reactor capacity is 30 m³, which will give an actual product yield of 22-23 metric tons per batch. The reactor vessel is fitted with an agitator, high-pressure steam heating coils, low-pressure nitrogen sparge and blanket, alcohol injection sparge, top charge entry from the pre-weigh vessel, wash water entry via high-pressure spray balls, and vapor take-off via fractionating column to the condensers.
Discharge from the reactor is via the reactor transfer pump to the bleacher through the product coolers mounted above the bleacher. The reactor pressure is controlled using the vacuum transmitter on the vapor outlet on the top of the second condenser. Catalysts are used to initiate and speed up the reaction sequence. Para-toluene sulphonic acid and hypo-phosphorous acid are typically used.
This reaction is reversible and to obtain a completely one-way reaction, the generated water (reaction water) must be drawn off as it is formed. The reaction water is boiled off and condensed in the two overhead condensers combined with a fractionating column. Non-condensables that pass through the condensers are run through a water scrubber to remove any VOCs prior to releasing to atmosphere.
The fractionating column is packed in two sections (1.7 m at the bottom and 2.8 m at the top), with the vapor from the reactor entering below the bottom bed. This allows for future modification to give the option of middle vapor entry for in-situ alcohol (methanol or isopropanol) rectification during reaction. This would also make middle liquid feed possible as an alternative to batch rectification of the wet alcohol. For column cleaning and cooling of hot spots, 40 psig steam can be injected into the vapor space below the bottom bed. All of the charge injection valves with the exception of nitrogen and the low-pressure steam to the column base are interlocked so that only one can be opened at once. Liquid can be collected independently from the base of the column and the condensers to either of two 5.6 m³ receivers. The receivers are discharged to the appropriate alcohol storage tank or to effluent. The vessel high pressure safety relief from the rupture disc and relief valve is directed to atmosphere via a cyclone separator, allowing the liquid component to be collected into an enclosed 4 m³ accumulation tank.
The bleacher capacity is 30 m³, which will give an actual product yield of 22-23 metric tons per batch (same as the reactor). The unit operations of neutralization, drying, bleaching, filtration, and deodorization are carried out on the crude product in the bleacher. These are the processes of refining to remove residual reaction components and catalyst and improve the color and odor of the ester as necessary to meet the product specification.
Catalyst and residual fatty acid impurities are reduced to an acceptable level by neutralization, addition of bleaching earth, drying, and filtration carried out in the bleacher. The refining of crude reaction products manufactured using acid catalyst (low or medium temperature injection) is performed by neutralization with 28% sodium hydroxide solution, addition of a minimum quantity of bleaching earth to adsorb the catalyst salt, followed by drying and filtration. Additional earth and carbon is used in the process of bleaching to improve color during refining. Crude high temperature esterification products are treated with 50% phosphoric acid solution to aid in catalyst removal with bleaching earth adsorption and filtration.
Neutralization is performed with either sodium hydroxide or phosphoric acid. Bleaching is performed with bleaching earth and carbon black. Filtration is done with a Dr. “M” candle filter. Deodorization is done with carbon black and steam heat.
Process control systems and programming are completely up-to-date and are for sale with the facility. They are Siemens PCS7 and Fisher-Provox systems. Promace is used as the process information management system (PIMS).
Click Here for the Process Flow Diagram