Heat integration in reactive distillation: How far have we come and what is still missing?

Although several review papers have been published on reactive distillation (RD), none have provided a focused analysis and consolidated the full range of heat-integration (HI) strategies aimed at enhancing the energy efficiency of RD process. Recognizing RD as a promising process intensification technique, this review explores the various HI strategies that facilitate energy recovery and reuse within RD process. These include: (i) design-based modifications, which achieve internal HI without additional equipment while also recognizing an overlooked design variable, e.g., catalyst holdup, (ii) heat-pump-assisted approaches such as internally heat-integrated distillation column (HIDiC), mechanical vapor recompression (MVR), and bottom flash (BF), (iii) multi-effect configurations, and (iv) hybrid approaches combining multiple HI. While these strategies are considered mature and have been reviewed individually, existing reviews rarely explore how they may be refined or combined to achieve greater energy savings for RD. To address this gap, this review discusses the practical considerations and challenges, alongside identifying research gaps and future prospects for implementing HI strategies in RD. Of particular interest is the emerging double-effect HI, which leverages upon multiple columns operating at different pressures to significantly reduce external utility demands. While this method has demonstrated notable energy savings, its application in RD remains scattered across individual studies and has yet to be systematically reviewed. Given its promising nature, a comprehensive review to critically evaluate the role of double-effect HI in RD is highly valuable. Overall, this review aims to inspire new HI directions in RD to support the advancement of next-generation sustainable chemical manufacturing.