Disclosed is a cost-effective process for catalytic conversion of simple C6-based sugars (such as glucose and fructose) and industrial-grade sugar syrups derived from starch (such as different grades of High Fructose Corn Syrup) and cellulosic biomass to 5-HydroxyMethylFurfural (5-HMF) in a continuous-flow tubular reactor in bi-phasic media using inexpensive heterogeneous solid catalysts. Commercial and synthesized heterogeneous solid catalysts were used and their activities in terms of sugar conversion and HMF selectivity and yield were compared. Continuous dehydration of fructose, glucose and industrial-grade sugar syrups derived from corn and wood to HMF was achieved and the stability of selected catalysts and feasibility of catalyst recycling and regeneration were demonstrated. The performance of the catalysts and reactor system were examined under different operating conditions including reaction temperature, feeding flow rate, initial feedstock concentration, catalyst loading, presence of extracting organic solvent and phase transfer catalyst and aqueous to organic phase ratio. At the best operating conditions, HMF yield attained 60%, 45% and 53%, from dehydration of fructose, glucose and HFCS-90, respectively.