Sulfurized Isobutylene (T321) stands as a cornerstone additive in modern lubricants, constituting 50-70% of additive packages for automotive and industrial gear oils. Its vital role in providing extreme-pressure protection and anti-wear performance under severe operating conditions fuels consistent annual demand growth of approximately 10%, driven by the automotive and heavy machinery sectors.

Traditional manufacturing largely relied on a two-step process involving isobutylene, sulfur monochloride (S2Cl2), and sodium sulfide. This method, however, is plagued by severe drawbacks: high environmental impact and operational inefficiency. It generates nearly one ton of hazardous solid waste per ton of product, with disposal costs consuming up to one-third of production expenses. Wastewater output reaches 2.5 tons per ton of product, corrosion from S2Cl2 damages infrastructure, production cycles span ~40 hours, resource consumption is high (~2600kg raw materials/ton), and significant capital investment (~$30,000/ton capacity, est.) is required.

Emerging one-step processes using sulfur, sodium sulfide, and isobutylene offered environmental improvements, drastically reducing solid waste and wastewater. Yet, these struggled with critical issues: producing deeply colored, odorous final products and suffering from frequent maintenance of magnetically stirred reactors, hampering reliability and efficiency.

A newly patented synthesis overcomes these limitations with an innovative, integrated high-pressure approach. The streamlined process unfolds in three continuous stages: optimizing efficiency and eliminating waste streams.

The first stage involves preparing a molten sulfur mixture. Elemental sulfur and unrefined Sulfurized Isobutylene crude oil from previous batches (mass ratio 1:0.1-0.5) are combined in a melting tank. Under nitrogen atmosphere and slight pressure (0-0.05 MPa), heating to 140-170°C melts the sulfur. The mixture is stirred for 1-5 hours before being transferred via nitrogen pressure into a specialized loop reactor system, where an external pump initiates circulation.

Concurrently, the second stage enables rapid precursor formation. Gaseous hydrogen sulfide (H2S) and isobutylene are precisely metered into a static mixer – a key innovation enabling intense, immediate contact. Operated at 150-180°C and pressures ranging from 0.7 MPa to 6.5 MPa, with a molar ratio of isobutylene to H2S between 1.2-2.5:0.5-1.2 and a mass flow rate of 4-10 kg/min, the reaction completes in under two seconds. This generates a mixture containing Sulfurized Isobutylene precursor, unreacted H2S, and isobutylene.

In the crucial third stage, integration drives completion. The hot mixture from the static mixer is fed directly into the circulating molten sulfur stream within the loop reactor. Reacting at 130-190°C under elevated pressures of 1-6 MPa for 2-8 hours, this high-pressure loop environment ensures thorough reaction and minimizes unwanted byproducts like troublesome, odorous thiones. The overall molar feed ratio of isobutylene : H2S : sulfur is tightly controlled at 1 : 0.4-0.8 : 0.9-1.3. Upon reaction completion, pressure naturally decreases indicating termination, yielding high-quality Sulfurized Isobutylene crude product.

This process delivers profound advantages, significantly outperforming previous methods. A benchmark trial using the system produced 1280 kg of purified product from initial feeds (680 kg isobutylene, 221 kg H2S, 374.5 kg sulfur), showcasing exceptional raw material conversion exceeding 99.5% and product yields surpassing 95%. Crucially, the process generates zero solid or gaseous waste, with wastewater output reduced to minimal levels. The replacement of conventional stirred reactors with the static mixer and loop reactor combination has drastically cut equipment wear, leading to dramatically lower maintenance frequency and costs. Production cycles are notably shorter.

The quality leap is stark. Resultant Sulfurized Isobutylene exhibits remarkably lighter color, significantly reduced odor, exceptional performance metrics – achieving sulfur content of 44.5%, Flash Point of 103°C, copper corrosion ratings of 3B-4a (indicating very low corrosivity towards yellow metals), and a formidable maximum non-seizure load (PB/PD value) of 6500 N in Four-Ball testing. This performance directly translates to superior extreme-pressure protection in critical applications like gear oils.

This breakthrough synthesis presents a paradigm shift for the lubricant additives industry. By eliminating the environmental burden and corrosive hazards of traditional chlorine-based routes, surpassing the product quality limitations and maintenance woes of earlier one-step methods, this closed-loop, high-pressure process offers a truly cleaner, more economical, and sustainable route to produce vital extreme-pressure additives, paving the way for higher-performance lubricants essential for advanced machinery.