How to recycle ethyl acetate waste gas? Key points of condensation recovery and condensate acid prevention for ester solvents

Ethyl acetate is a widely used ester solvent in the coatings, ink, adhesive, and pharmaceutical industries. With a boiling point of approximately 77℃, it volatilizes rapidly at room temperature and is slightly soluble in water. Compared to alcohols and ketones, the recovery and preparation of esters have their own unique characteristics: the condensation temperature is not particularly stringent, but one thing must be prevented on the condensate side - hydrolysis. When esters coexist with water, they slowly hydrolyze to produce acids and alcohols. The acidification of the condensate not only affects the quality of reuse but also corrodes equipment. By properly arranging the temperature and hydrolysis, the recovery process of ethyl acetate becomes smooth, and operation becomes less troublesome.

Where does the exhaust gas come from

The evaporation of ethyl acetate in the paint and ink industry is concentrated in the ink mixing, spraying, and drying processes. The exhaust gas from drying, with its high temperature and high concentration, is a stream with concentrated recovery value; the exhaust gas from printing and dry laminating processes is continuous and stable; the reaction exhaust gas from adhesive production and the pharmaceutical industry, as well as the exhaust from vacuum pumps, also carry a large amount. The concentrations of these gases vary greatly, and they are grouped according to high and low concentrations during collection: the non-condensable gases from drying and distillation are processed separately, while the exhaust from spraying and the overall workshop ventilation are combined for treatment, ensuring a stable load in the recovery section.

Ethyl acetate has a low odor threshold, and by the time the workshop perceives a "strong odor," significant amounts have already evaporated. Therefore, the selection and inspection of collection seals are prioritized on the management checklist - most odor complaints initially arise from the sealing process.

Key points of condensation configuration

The dew point of ethyl acetate changes gently with concentration. Under most operating conditions, two stages of water cooling followed by one stage of low temperature section can achieve significant recovery. The key points in temperature level calculation lie in moisture content and mixing: when ethanol and water vapor are mixed in the tail gas, the condensation behavior becomes more complex. The temperature level should be calculated based on the actual dew point of the mixed components, rather than applying it based on a single component. As usual, frost prevention in the low temperature section is managed according to the pressure difference trend; due to the high temperature of the dried tail gas, heat recovery pre-cooling is performed before entering the condensation section, saving both cold and heat energy.

How to prevent condensation and hydrolysis

The core issue of ester condensate is hydrolysis: once the condensate contains water, the ester slowly hydrolyzes to produce acetic acid, which increases acidity and corrodes carbon steel equipment, leading to a decline in reuse quality. Prevention and control measures can be taken from three aspects: rapid separation of condensate to shorten the contact time between ester and water; sealing of condensate tanks to avoid long-term exposure to moisture and long-term accumulation; regular testing of condensate acidity, timely reuse or concentration when acidity increases, and not storing condensate as long-term inventory. The materials of recovery pipelines and condensate tanks should be selected based on acid-containing conditions, as carbon steel's lifespan is reduced when in long-term contact with acidic condensate.

Configuration key points reference

How to implement operation management

1. High-concentration and low-concentration groups are collected separately, and the dried exhaust gas is first sent for heat recovery;
2. The condensation temperature level is calculated based on the dew point of the mixed components, rather than being directly applied from a single component;
3. Rapid water separation of condensate to shorten the contact time between ester and water;
4. Regularly detect the acidity of condensate, and promptly handle any increase in acidity;
5. The condensate tank should be stored in a sealed manner to avoid long-term accumulation;
6. The reconciliation between the amount of recycling and the amount of requisition is conducted on a monthly basis, and any anomalies are first investigated at the collection end.

Frequently Asked Questions

Can the ethyl acetate recovery solution be reused directly?

Depending on the purpose and acidity, ink mixing, cleaning, and other applications that are not sensitive to moisture can be directly reused after passing inspection; applications with high purity requirements undergo distillation and concentration. Moisture and acidity are tested batch by batch, and the reuse path is determined based on the test results, with records kept in a ledger to track the whereabouts.

How to deal with the sour condensate?

First, assess the acidity and equipment corrosion status: neutralize the condensate with mild acidification and then concentrate it for reuse, while dispose of the condensate with high acidity externally. Meanwhile, investigate the source of hydrolysis - whether the water diversion is timely and whether there is long-term water accumulation in the tank. Controlling the source is more important than neutralizing afterwards.

Is it okay to mix and collect with other solvents?

The composition of the condensate after the mixed collection of esters and alcohol ketones is complex, leading to increased costs for separation and purification and reduced reuse value. The initial investment for grouped collection is lower than post-separation, and indeed, low-concentration streams that cannot be grouped are then combined for treatment.

This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd., which provides design, manufacturing, and operation and maintenance services for condensation recovery, membrane separation recovery, and complete solvent recovery equipment to chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please feel free to contact us for discussion.